The following list of terms and abbreviations includes many of those that appear in technical documents on chemical safety, amateur radio, emergency management, Red Cross activities, and computing, as well as others used on this website. It is not intended to be a complete list of such terms. Nevertheless, if you find some term that is not listed here, but which you feel needs definition or a brief explanation, feel free to contact me. The same applies if you have suggestions for improving existing definitions. My e–mail addresses are to be found on my home web page.

Most of the links from within the glossary entries are cross–references to other entries in the glossary. This avoids multiple definitions of terms, and reduces the size of the glossary. If you need to see what a linked word in the definition means, just follow the link, then go back in your browser. When a link is to another website (outside my own), it is followed by a "external link" symbol.

The head entries in the glossary are in alphabetical order. The following index will take you to the entries that start with the indicated letter. Mouse click on the initial letter; this will work in any browser.

A B C D E F G H I J K L M N O P Q R S T U V W X Y Z

A (symbol)
A is the SI symbol for ampere, and a is the symbol for acceleration. A represents the set of algebraic numbers.
Abatement
Partial or complete reduction of a pollutant.
Abrasion
A scraping of the skin surface. Less severe than laceration. Categorized as:
  • First degree: involves only epidermal injury. Usually minimal bleeding.
  • Second degree: involves the epidermis and dermis. Slight bleeding.
  • Third degree: involves subcutaneous damage; often classed as an avulsion.
Absorption/absorb
Generally, incorporation of a gas or liquid into a solid by capillary action, osmosis or the like. For a person or an animal, absorption is the process of a gaseous or liquid substance getting into the body through the eyes, skin, stomach, intestines, or lungs. Compare to adsorption.
AC (electrical)
Alternating (electrical) Current. A flow of electrical current that flows alternately in one direction then the other through a conductor, as opposed to DC. The alternation of direction generally occurs at regular intervals; the frequency in which the cycle of direction of flow changes occurs is measured in hertz (Hz) or multiples thereof. The direction changes twice in each cycle, from (arbitrarily) forward to reverse, then back to forward. For household AC electricity in the US, this cycle happens 60 times a second; thus it is known as 60 Hz AC. Broadcast radio signals induce in a receiving antenna a low-voltage AC flow, whose base (carrier) frequency is measured in kilohertz or megahertz.
Acceleration
Rate of change in the velocity of a moving object with respect to time. Thus the second derivative of position with respect to time. Symbol is a; hence, a=d2x/dt2. See also jerk. Contrary to popular usage, a slowing of speed is also acceleration, but with a negative value. Also, since velocity is a vector quantity, so also is acceleration, and a change of direction even at a constant speed is acceleration in its physics sense. In SI units, acceleration is given as m/s2, though we often see "g" units used, referenced to the earth's normal surface gravity acceleration: 1 g = 9.80665 m/s2. Acceleration times mass is force.
Acclimatization
Physiological and behavioral adjustments of an organism to changes in its environment.
ACCP
Access Control Coordination Point. The location to which agency representatives are directed so that they can pass through the security perimeter at an incident.
Accuracy
The degree to which measurements are close to the actual value being measured. Contrast with precision and resolution.
ACGIH
American Conference of Governmental Industrial Hygienists external link. Organization that develops and publishes BEI® and TLV® values. Despite the name, their members may include "anyone engaged in the occupational hygiene, environmental health, occupational health, or safety professions even if their primary employment is not with a government agency."
Acrid
An irritating, bitter odor.
Action level
The exposure level, as a concentration in air at which OSHA regulations take effect to protect employees. Exposure at or above this level is termed "occupational exposure." It is generally set at one half the PEL concentration.
Active ingredient
A component of a product that directly contributes to the product's function, as opposed to an inert ingredient.
Acute
Of a medical condition, occurring quickly and for a short time, as opposed to a recurrent or chronic condition. Acute exposure to a substance is contact with the substance that occurs once or for only a short time (up to 14 days), as opposed to chronic exposure.
Additive
A biologic response to exposure to multiple substances that equals the sum of responses of all the individual substances added together [compare with antagonistic effect and synergistic effect].
Adenine
structure of the nucleobase adenineOne of the purine nucleobases in the nucleotides of RNA and DNA, whose structure is shown on the right. The corresponding nucleosides are adenosine and deoxyadenosine.
ADI
Acceptable Daily Intake. This is the dose of a substance which can be consumed every day for a lifetime in the practical certainty, on the basis of all known facts, that no harm will result. It is typically measured in mg (of substance)/kg (of body mass) units. See also ARfD.
ADP
Adenoside diphosphate. See ATP.
Adsorption/adsorb
Retention of gas or liquid molecules on the surface of a solid. "Activated charcoal/carbon," which is finely granulated to give it a large surface area, is commonly used to adsorb gases. Compare to absorption.
ADSL
See DSL.
AED
Automated External Defibrillator. A portable electronic device that automatically diagnoses the potentially life threatening cardiac arrhythmias, such as ventricular fibrillation and ventricular tachycardia. The AED treats these conditions through defibrillation: the application of electrical therapy which stops the arrhythmia. AEDs are designed to be easy for a layman to use, and the use of AEDs is taught in many first-aid classes. Contrary to the idea presented in many medical TV programs, a defibrillator cannot be used to establish a cardiac rhythm if the heart has stopped completely (asystole).
Aerosol
A suspension of fine solid particles (dust, smoke) or liquid drops (mist, fog) of a substance in air, small enough to remain suspended for an extended period of time.
ALA
structure of delta-aminolevulinic acidShort for δ-aminolevulinic acid, an organic chemical compound whose structure is shown on the right. When detected, it is an indicator of lead exposure.
ALARA
As Low As Reasonably Achievable
Alcohol
An organic chemical compound which has one or more hydroxyl (-OH) groups, each attached to a saturated carbon atom. IUPAC names of alcohols have suffix "-ol" or include "hydroxy". Hence the best known alcohol—part of alcoholic beverages—is formally designated "ethanol," or more loosely, "ethyl alcohol" (CH3-CH2OH).
Aldehyde
Also known as an "alkanal." An organic chemical compound containing a formyl (HC=O) group. See also ketone.
Algebraic (number)
A number that is the root of a finite polynomial in one variable, with integer coefficients. Symbol for the set of algebraic numbers is A. All rational numbers are trivially algebraic: a/b is the root of bx−a=0, where a and b are integers. An algebraic number may be complex. The complementary set to algebraic numbers among the complex numbers is called the "transcendental" numbers (such as π and e). Algebraic numbers are an infinitely countable set, but complex numbers are not, hence "almost all" complex numbers are transcendental. Algebraic numbers form a field over the arithmetic operations.
Aliphatic
Organic chemical compounds that are not aromatic. Aliphatic compounds may contain rings, but not those of the aromatic types. They are more often based on (possibly branching) chains of carbon atoms. Biological examples are (most) amino acids and all fatty acids.
Allergy/allergic/allergen
A condition in which initially asymptomatic exposure to a substance (called an "allergen") results in an adverse reaction to the substance at a later time. It is the result of an inappropriate immune response to an otherwise harmless substance, and generally results in inflammation. In extreme cases, an allergy can result in anaphylaxis. Contrast allergy with intolerance.
ALOHA
Areal Locations of Hazardous Atmospheres. Part of the CAMEO suite of programs that indicates how chemicals spread through the air depending on weather conditions. Developed jointly by the EPA and NOAA.
AM (Amplitude Modulation)
In radio terminology, a type of modulation in which the signal strength (amplitude) of the carrier varies directly with that of the signal it encodes, though never reaching zero. Thus there is always at least a bare carrier to which a receiver can tune and lock onto.
Amateur (radio)
Literally, amateur means done "for the love of" as opppsed to, for example, for remuneration. Anateur radio in the US at least is defined by the FCC as a "voluntary, non-commercial radio service [that] allows licensed operators to improve their communications and technical skills...." The FCC goes on to say how this provides the US with a pool of individuals who can provide emergency communication. Note that amateur radio operators (informally, "hams") must be licensed by the FCC, a process that involves examinations that cover the legal and technical aspects of amateur radio.
Ambient
Refers to existing or normal conditions of temperature, humidity, and the like.
Amino acid
An organic chemical compound that has both at least one carboxylic or acid group (COOH) and at least one amine group (usually NH2). Amino acids are the basic components of proteins, and otherwise occur naturally (see example ALA) and as artificially manufactured (see example EDTA). The amino acids in proteins have the amine group attached to the same carbon as the carboxyl group, and are referred to as α–amino acids, or as 2–amino acids. Also, except for the simplest one (glycine), the amino acid components of proteins occur in two mirrored forms and are chiral (that is, they are stereoisomers). As it happens, among those chiral amino acids, only the L–amino acids—those observing the CORN Law—are used in earthly life forms.
ampere
Symbol A, named for André-Marie Ampère. Often called "amp" informally. This is the SI base unit for the rate of electrical current flow. Its formal definition involves the force generated between infinitely long ideal conductors carrying current. In practice, other more easily realizable measures are used. A current of one ampere has one coulomb of charge carriers (e.g., electrons, holes, protons, ions) flowing past a given point every second.
Amylase
An enzyme that catalyses the hydrolysis of starch into sugars, particularly maltose. The form of amylase found in humans (α-amylase) is a protein containing calcium.
Anaphylaxis/anaphylactic shock
Anaphylaxis is a sudden, acute, multi-system, severe allergic reaction. It is a serious medical condition that can be fatal (approximately 1500 deaths per year in the US). Anaphylactic shock is a reaction that involves circulatory collapse or suffocation due to swelling of the trachea or bronchi.
Anesthetic
A drug which causes reversible loss of sensation, either to an organism as a whole: "general anesthetic"—which usually results in loss of consciousness—or to a limited part of the body: "local anesthetic." Contrasted with analgesics, which reduce pain without loss of sensation.
Anemia
A condition in which the blood is deficient in red blood cells (erythrocytes), hemoglobin or volume.
Anoxia
A condition in which there is relative lack of oxygen in the blood or tissues.
Antagonistic
A biologic response to exposure to multiple substances that is less than would be expected if the known effects of the individual substances were added together [compare with additive effect and synergistic effect].
Anterior
The front end of an organism. Usually also the head ("cephalic") and "oral" (mouth) end, and depending on the specific organism, the "cranial" (skull) or "rostral" (beak) end. Opposite of posterior.
Antidote
A remedy used to counteract a poison's toxic effects, by eliminating, absorbing, neutralizing, or chelating the poison.
AOR
Area[s] Of Responsibility.
Apnea
Temporary stoppage of breathing. See also dyspnea.
APRS
(Amateur Radio) Automatic Packet Reporting System. Sometimes rendered as "Automatic Position Reporting System," though it is a general packet radio system that is only in part used to report the geographic location of a transmitter. Another major use is reporting the readings from weather stations.
Aqueous
Having to do with water. An aqueous solution of a substance is one with water as the solvent.
ARES®
Amateur Radio Emergency Service, a Volunteer organization, administered by ARRL, consisting of amateur radio operators who are trained and equipped to assist with communications in emergencies, as well as for non-emergency public service events. See also RACES.
ARfD
Acute Reference Dose. This is the dose of a substance that can be consumed over a short period of time (usually during one meal or in one day), without an appreciable health risk to the consumer, based on all known facts at the time. See also RfD, and ADI.
Aromatic
A class of organic chemicals that, loosely speaking, contain flat ring structures with double bonds. Most aromatic rings have at least some carbon atoms, but "heterocyclic" aromatics have nitrogen, oxygen, sulphur, or the like as well. These in fact are the most common biological aromatics. For a more detailed explanation, see the Wikipedia article. Contrasted with aliphatic. Biological aromatic compounds include sugars, a handful of the amino acids, and the nucleobases of DNA and RNA.
ARRL
American Radio Relay League. external link A US national organization that provides information and services to amateur radio operators. ARRL also represents their interests to US government agencies—particularly Congress regarding legislation and the FCC regarding regulations and enforcement—and in international radio organizations, such as the IARU and the ITU.
Asphyxiant
A gas or vapor that can cause unconsciousness or death by suffocation (anoxia). Simple asphyxiants displace oxygen; chemical asphyxiants interfere with the body's ability to intake or use oxygen. Asphyxiation is the result of inhaling an asphyxiant or of choking, drowning, strangulation, apnea or the like.
Asthenia
Loss of strength or energy.
ASTM
The ASTM International. external link The organization formerly known as "American Society for Testing and Materials," (hence the initialism) that has developed over 12 000 industry technical standards for a variety of materials, products, systems and services.
Asystole
Cardiac arrest. Commonly called "flat line," this is a total lack of electrical activity in the heart, as seen on an electrocardiogram (EKG/ECG) as a straight ("flat") line.
ATP
structure of adenosine triphosphate Adenosine triphosphate. An organic chemical compound, universally used in biological cells on Earth as a medium of intracellular energy transport. The structure of ATP is shown on the right. The upper right-most block of atoms is the purine adenine, which is attached to a ribose sugar at the ribose 1' carbon. Phosphate groups are ester linked to the left off the hydroxyl (-OH) group on the ribose 5' carbon (refer to the diagram). So far, and with just one phosphate, this is one of the nucleotides of RNA (viz. adenosine monophosphate). In both RNA and DNA, the phosphate group on the ribose 5' carbon then ester links to the hydroxyl on the 3' carbon of the ribose in the next nucleotide in sequence.

Replacing the hydroxyl group on the 2' carbon of the ribose with a hydrogen (removing the oxygen) turns it into deoxyribose, giving the deoxyadenosine monophosphate nucleotide that is found in DNA. All other RNA and DNA nucleotides are constructed and linked similarly, with just one of the other nucleobases in place of adenine. Typically for the energy storage function of ATP, the left-most phosphate bond is broken (hydrolysed), yielding its binding energy to some cellular process, plus molecules of adenosine diphosphate (ADP) and phosphoric acid. Alternatively, ATP can be hydrolysed into adenosine monophosphate (AMP) and pyrophosphate.
Atrium
Plural atria, adjective atrial. The atria are the smaller, upper chambers of the heart that receive blood from body to be circulated through the lungs (right atrium), or from the lungs (left atrium) to be circulated through the body. The atria feed blood to ventricles, which deliver the blood.
ATSDR
(HHS) Agency for Toxic Substances and Disease Registry external link, created by CERCLA. Mission is to serve the public by using the best science, taking responsive public health actions, and providing trusted health information to prevent harmful exposures and disease related to toxic substances. Specific agency functions include public health assessments of waste sites, health consultations concerning specific hazardous substances, health surveillance and registries, and response to emergency releases of hazardous substances.
Avulsion
Injury in which part of the body is displaced from its normal location. An extreme case would be amputation by having the member pulled off. See also abrasion (third degree).

return to the glossary alphabetic index
BEI®
Biological Exposure Index. Guidance values developed by the ACGIH for assessing biological monitoring results. BEIs® represent the levels of determinants that are most likely to be observed in specimens collected from healthy workers who have been exposed to chemicals to the same extent as workers with exposure at the Threshold Limit Value (TLV® ). There are currently more than 50 of these. For more details on how this works, see the ACGIH's Introduction to BEI®.external link
Billion
Large number that is ambiguous, and therefore avoided as much as possible on this web site. In the US, and at least officially in the UK since 1974, "billion" is taken to mean a thousand million (109). In much of the rest of the world, including continental Europe and most French, Spanish and Portuguese speaking countries (Brazil excepted), "billion" (or a similar word) means a million million (1012). To me, the latter usage arguably is the more logical, but we live with the language we have. The same difficulty is to be found also with the larger such numbers: trillion, quadrillion, quintillion, etc.

There is an unambiguous word for 109, namely "milliard," but there are at least two reasons for me not to use it. First, relatively few English speakers, particularly in the US, will know what it means. Second, there is no ordinal/fractional number equivalent that I know of. I mean, "milliardth," really?
Biological agent
A general term for a pathogen. Examples are prions, viruses, bacteria, protists, fungi, and any of several multicellular parasitic animals. That doesn't leave much.
BIPM
Bureau international des poids et mesures (International Bureau for Weights and Measures). Paris-based standards and metrology agency that is both the French equivalent of the US NIST and the overseer of the definition of SI.
BLEVE
Boiling Liquid Evaporating Vapor Explosion [pronounced "blevy"]. The explosive release of expanding vapor and boiling liquid following the catastrophic failure of a pressure vessel holding a pressurized liquefied gas such as propane or LPG, especially when exposed to fire. Transportation BLEVE incidents involving hazardous substances may pose significant threats from explosions as well as contamination. A BLEVE does not require a flammable substance to occur, but in the case of flammable vapors, a fireball or fuel-air explosion is likely.
BMC, BMD, BMR, etc.
BMC and BMD are respectively the benchmark concentration and dose of an etiological agent that causes a predetermined change in the response rate of an adverse effect, called the benchmark rate or BMR. Specifically, BMCLx and BMDLx (e.g., BMDL50) combine these elements to mean the dose/concentration that produces the change x in the BMR. The US EPA has developed BMDS external link—BMD Software—that applies BMD methods to hazardous pollutant risk assessment.

This terminology provides a generalization to multiple possible adverse effects and effect levels of metrics such as LC50 and LD50. US EPA currently uses BMC and BMD techniques to establish RfC and RfD values, superseding the use of NOAEL.
Body burden
The total amount of a substance in the body. Some substances build up in the body because they are stored in fat or bone or because they leave the body very slowly.
BOINC
Berkeley Open Infrastructure for Network Computing external link. Operated by the University of California, Berkeley, this system makes idle computational power of numerous computers throughout the world available for projects in mathematics and the sciences that require massive amounts of computing.
Bradycardia
Slowed heart beat, generally meaning less than 60 pulses per minute. Compare to tachycardia.
Buffer
A substance that reduces the change in pH that might otherwise occur when there is an addition of an acid or alkali.
[n–]Butyl acetate
structure of n-butyl acetateAn organic chemical compound, a colorless, flammable liquid, whose molecular structure is shown at the right, and whose name is commonly abbreviated "BuAc." BuAc is used as the standard reference material for determining relative evaporation rate, using the ASTM Standard Test Method D3539–87 (2004). BuAc is the ester of n-butanol and acetic acid.

return to the glossary alphabetic index
C (symbol)
C is used as the symbol in electronics formulas representing electrical capacitance. C is also the symbol for the SI derived unit coulomb, and for chemical element carbon. C or ℂ represents the set of complex numbers. In physics, c (or c0) represents what is commonly called the "speed of light" with "in a vacuum" implied, but it is more fundamental than that.
CAA
The Clean Air Act of 1970, as amended. 40 CFR 50–80. The EPA has enforcement authority.
CAD
Computer Aided Design. A class of computer applications that allow the creation and manipulation of graphic images, usually in vector graphics format, but some also handle raster images.
Calibrate
Adjust a measuring device so that (ideally) it is accurate across its scale to within its indicated resolution. As a compromise, it may be adjusted so that it is most accurate within the range of measurement most commonly used or most critical to an application.
CAMEO
Computer–Aided Management of Emergency Operations. A suite of programs that assist planners for and responders to chemical release emergencies. CAMEO Chemicals refers to the database of over 6000 hazardous chemicals that comes with the programs. Other CAMEO components are ALOHA and MARPLOT. See also the CAMEO information external link on the EPA website. The program is compatible with LandView.
Capacitance/capacitor/capacitive
Electrical capacitance, symbol C, is the ability of a device known as a "capacitor" to store electrical energy by means of a static electrical field; measured in SI units of farads. An electrical circuit in which capacitance dominates over inductance is described as "capacitive," as is reactance due to capacitance.
Carbohydrate
Organic chemical compounds composed of carbon, hydrogen and oxygen, often with a hydrogen to oxygen ratio of 2:1 (as in water). Typically, they are polyhydroxy (many -OH groups) aldehydes and ketones in structure.
carbon dioxide
See CO2.
carbon monoxide
See CO.
Carcinogen
A substance that tends to cause cancers. Carcinogenicity is the degree to which the substance is capable of causing cancers.
Cardiac
Pertaining to the heart. For details, see the entries on the heart muscle and the heart chambers: atria and ventricles.
Carrier
In radio terminology, an unmodulated signal at a specific frequency, to which (or near which) a receiver is tuned to receive the information encoded by the modulation imposed on it.
CAS
Chemical Abstracts Service, a function of Chemical Abstracts, external link a scientific journal published by the American Chemical Society (ACS). They index papers published in the journal by the chemicals referenced in them, using a numeric coding system, called "Registry Numbers" (RN). RNs are commonly used to refer briefly and unambiguously to hazardous materials.
Catalyst
A chemical substance that facilitates or increases the rate of a chemical reaction without itself being consumed in the reaction.
Catenary
The curve followed by a rope, cable or chain (Latin catena) under its own, uniform weight in gravity. Mathemarically, the curve is y=a⋅cosh(x/a) = a/2(ex/a+e−x/a). Similar in shape to a parabola, with which it was initially confused.
CDRG
Catastrophic Disaster Response Group.
CEC
Community Emergency Coordinator. The individual or agency appointed by the LEPC who receives emergency notification of hazardous materials incidents under the provisions of EPCRA.
Ceiling value
The concentration of a substance that must never be exceeded at any time in the workplace, under OSHA regulations.
Cellulose
A complex carbohydrate polysaccharide, consisting of thousands of glucose subunits. Cellulose forms a large part of plant matter, especially of plant cell walls. It is indigestible by humans.
Celsius, degree
Common metric (but not SI) unit of temperature, symbol °C. Named after the Swedish astronomer Anders Celsius. Once, but not for the last 60 some years, known as the "degree centigrade." For further details, see entry kelvin.
CEOC
County Emergency Operations Center. See also EOC.
CEPPO
(EPA) Chemical Emergency Preparedness & Prevention Office external link. This site shows the section (CEPPS) responsible for management of the environmental Superfund for Region 5 (IL, IN, MI, MN, OH, & WI).
CERCLA
Comprehensive Environmental Response, Compensation, and Liability Act, 40 CFR 300. Also known as the "Superfund" Act, it provides funds to clean up hazardous materials releases into the environment The EPA has jurisdiction over its provisions.
Cerebral
(Somewhat loosely) pertaining to the brain; more precisely to the part of the brain responsible for the "higher" brain functions such as sensory processing, motor control, thought, learning, memory, and language.
CERP
Comprehensive Emergency Response Plan. Developed by the LEPC to provide detailed information that would be needed in a chemical release incident. A requirement of EPCRA.
CERT
Community Emergency Response Team. A group of private citizens who have trained and equipped themselves so as to be prepared to help themselves, their families, their neighbors and their communities in case of local emergencies and disasters.
CFR
Code of Federal Regulations. The set of 50 (as of 2005), typically multi–volume, documents that contain the text of all current US government regulations. Available from the National Archives and Records Administration.
Chelating agent
A chemical, such as EDTA, DMSA, or DTPAthat can form a chemical complex with a metal atom or ion, especially one that is toxic, and that is generally hydrophilic. Since the complex is also water soluble, it thus can be more easily eliminated from the body. A note of caution: chelating agents should only be used in known cases of heavy-metal poisoning, and only under proper medical supervision. These agents are not specific to any particular metal, and can cause loss of essential elements. "Chelate" is pronounced like "key-late."
CHEMTREC
CHEMical TRansportation Emergency Center external link. Established by the Chemical Manufacturers Association (CMA) to provide information on materials involved in transportation accidents.
Chiral[ity]
Literally "handed," chiral refers to objects, and specifically chemical molecules, that exist in two distinct forms that are mirror images of each other. Human hands are an excellent example, hence the name. In the case of the chemical molecules, the chirality is often significant in determining whether the molecule will take part in some reactions. A pair of chiral molecules are known as "enantiomers" of each other.
Chronic
Of a medical condition, persistent and lasting, and/or developing slowly over an extended time period, as opposed to recurrent or acute. Of exposure to a substance, occurring over an extended period (typically more than a year).
CIPM
Comité international des poids et mesures (International Committee for Weights and Measures). A group that meets annually at BIPM to ensure world-wide conformity in units of measure, based on SI.
CO (carbon monoxide)
A colorless, odorless, flammable gas slightly less dense than air, typically resulting from incomplete burning of carbon compounds. CO in concentrations above about 100 ppm (the OSHA limit for long term exposure is 50 ppm) is a chemical asphyxiant, which severely reduces the blood's ability to carry oxygen by binding strongly to hemoglobin. It also interferes with mitochondrial respiration by binding to cytochrome oxidase. Generally bad stuff. Interestingly though, very small concentrations of CO (< 1 ppm) are normal constituents of some living organisms, including humans.
CO2 (carbon dioxide)
A dense, colorless, odorless gas. Though relatively non-toxic and nonreactive, CO2 can displace oxygen and thus become a simple asphyxiant or a fire-extinguishing agent. In smaller atmospheric concentrations, CO2 is also a greenhouse gas.
Cobblestone
The Cobblestone is a unit of computing credit for validated work done on BOINC projects. The name is a (weak) pun on other, similarly named computing benchmark units: the Whetstone external link and of course then the Dhrystone, external link combined with a call-out to Jeff Cobb, a BOINC pioneer. The Cobblestone is defined such that a computer that operates at 1000 double-precision floating point MIPS for one day will accumulate 200 Cobblestones after validation of the work via duplication by another BOINC user. I know: TMI.
Commutative
The mathematical property of a binary operation in which the order of the operands is not relevant. Ordinary addition and multiplication are commutative, whereas subtraction and division are not: For a,b ∈ C, a+b=b+a, but a−b≠b−a (unless a=b).
Complex (number)
A number with both real and imaginary number components. Designated C. Typically means one in which both components are non-zero. Can be represented as a point on a plane. Used in electronics to represent impedance.
Concentration
The amount (mass or volume) of a substance in relation to the mass of, or in a specified volume of, the containing substance. For hazardous materials in the air, concentration is typically measured either in micrograms per cubic meter (µg/m3) or in parts per million (ppm) by mass (w/w). Chemical concentrations of substances dissolved in liquids are typically measured in moles of solute per liter of solvent.
Condensation
Physically, the transition from a vapor phase of a substance to the liquid phase: the reverse of evaporation. Chemically, refers to a reaction in which two or more molecules are combined with the release of one or more water molecules: the reverse of hydrolysis.
Contusion
Medical term roughly equivalent to eccthymosis or "bruise." A type of subdermal hematoma in which damaged capillaries seep or hemorrhage blood into subcutaneous tissues. Term also applies to similar deeper injuries to muscle or bone.
COOP
Continuity Of Operations Program/Plan. A set of plans designed to assure that essential operations of an agency of government, a company, or an NGO will continue in the face of natural or human-made or technological disasters.
CORN Law
An observation of and mnemonic for the spatial arrangement of elements of the naturally occurring chiral amino acids that occur in proteins. All such amino acids have four distinct elements attached to their alpha carbon atom. The acidic carboxyl (COOH) and amine (NH2) groups are obvious, since they are essential elements of an amino acid. There is also one hydrogen atom. Except for the simplest amino acid glycine, the last position is held by a molecular fragment known as a "radical" (symbol R). In space, the four elements are roughly at the corners of a tetrahedron (triangular pyramid). If you were to look down at the amino acid moleculefrom above the α–C hydrogen atom, the other elements, listed clockwise from the carboxyl, spell out CORN: (carboxyl=CO), radical R, amine N. Neat, huh?
Confined space
Spaces hazardous to an occupant due to limited means of escape combined with other possible hazards, including exposure to air contaminants or asphyxiants.
Contagious
A term applied to a disease which is spread by direct physical contact with a person infected with the disease or with secretions from or objects in contact with such a person. By contrast with inherited diseases, diseases transmitted through a biological vector, or caused by behavioral or environmental factors. Often defined in practice by the degree to which isolation or quarantine is effective in preventing spread of the disease.
Coordinate Time
In special relativity, a time interval as measured by an external observer, denoted by dt, as distinguished from proper time interval (dτ). The ratio of these intervals is given by the Lorentz factor (γ).
Corrosive
Causing visible destruction of or irreversible alterations to living tissue by chemical action at the site of contact.
coulomb
The SI derived unit of electrical charge, symbol C. Named for French physicist Charles-Augustin de Coulomb. The coulomb is equivalent to 6.241 509 629 152 65×1018 charge carriers, particularly electrons, and is defined as an ampere⋅second (A⋅s).
Countable (set)
A mathematically countable set is one whose elements can be matched one for one with the natural numbers (an "infinitely countable" set), or with a subset thereof. Proofs of the countability of a set range from trivial—the even numbers are an infinitely countable subset of the natural numbers—to quite sophisticated, as for the algebraic numbers. Not all sets are countable, most notably the set of real numbers. Such a set is called "uncountable" with "infinite" often implied. Also, clearly number types which are extensions of the real numbers such as complex numbers and quaternions are uncountable.
CP
Command Post. See also ICP.
CSS
Cascading Style Sheet. A language used to describe the "presentation semantics" (the look and formatting) of documents written in a markup language, such as web pages written in HTML and XHTML. A CSS file facilitates applying common global characteristics across an entire web site.
CTCSS
Continuous Tone-Coded Squelch System. Known for short as "tone squelch" or loosely as "PL," though the latter is strictly a Motorola trade name for their implementation of CTCSS. In CTCSS, a radio transmitter sends one of several distinct low frequency (<300 Hz) tones along with the normal voice signal. Radio voice transmissions only use the range of 300-3000 Hz, so they are sometimes called "sub-audible" tones, even though they are well within a normal human ear's audible range. A receiver set to use a CTCSS tone will only "hear" a radio signal that is sending that tone on its receive frequency. This can reduce interference between nearby systems that use distinct tones. By contrast, a receiver set only for carrier squelch will hear all sufficiently strong transmissions on its set frequency.
Current
In electronics and related physics, the rate of flow of charge carriers such as electrons, holes, or ions. In electronic circuits, this is measured in amperes; in formulas it is represented by the symbol "I".
CV
Comparison value. Calculated concentration of a substance in air, water, food, or soil that is unlikely to cause harmful (adverse) health effects in exposed people. The CV is used as a screening level during the public health assessment process. Substances found in concentrations greater than their CVs might be selected for further evaluation in the public health assessment process.
CW (Continuous Wave)
Sensu stricto, a radio signal of constant frequency and amplitude—that goes on forever. In amateur radio sensu latiore usage the last criterion is totally ignored. Well as they say, two out of three ain't bad. In fact, CW is used as the mode of modulation for transmitting Morse code. The signal is only on when the dots and dashes of the code are being sent. Also, "CW" is by synecdoche most often applied to Morse code itself in ham speak.
CWA
Clean Water Act of 1972 and as later amended, 40 CFR 100–140, 400–470. Regulates discharge of pollutants into surface waters. The EPA and Army Corps of Engineers have jurisdiction.
Cyanosis
Blue or purple coloration of the skin and mucous membranes due to anoxia. The color is caused by the presence of > 5g/dl deoxygenated hemoglobin in surface blood vessels. It is thus an indication or symptom of severe asphyxiation and must be treated immediately.
Cytosine
structure of the nucleobase cytosineOne of the pyrimidine nucleobases in the nucleotides of RNA and DNA, whose structure is shown on the right. The corresponding nucleosides are cytidine and deoxycytidine.

return to the glossary alphabetic index
DA
Disaster Assessment. A few years ago this was taken to mean "Damage Assessment" within the Red Cross, but the scope of the function has been expanded to view a disaster's effects as a whole. This would include the status of utilities and roadway access as well as the traditional look at damage to buildings. It is done initially as a wide area overview, then at progressively finer detail.
dalton
Convenience mass unit for individual atoms or (more commonly) molecules. The dalton, symbol Da—also referred to as the "unified atomic mass unit" (symbol u) for short—is defined as "one twelfth of the rest mass of an unbound atom of 12C in its nuclear and electronic ground state." Related to mole. You may know of the concept from school as "atomic weight" or "molecular weight" although those are of course not measures of weight, and were typically based on the mass of hydrogen atoms. As Mr Spock might say, the dalton has been experimentally determined to be approximately 1.660 538 782(83)×10-27 kg. It was named for John Dalton, who first proposed the idea.
DAT
Disaster Action Team. Red Cross team which responds quickly to incidents that directly affect people, such as home fires. The DAT provides immediate needed assistance to help those clients get through the first few days, to include food, clothing, medicine, and housing. A DAT may also respond to incidents in which only first responders are involved, such as industrial fires, providing the responders with food, liquid refreshment and the like ("canteening").
dB
Symbol for decibel; the bel, of which the decibel is a tenth, is mostly unused, but was named for Alexander Graham Bell—not for his work on the telephone but for his studies on auditory phenomena. The decibel is a dimensionless logarithmic magnitude of power or of power ratio, equal to 10⋅log10(P/P0), where P is the measured power, and P0 is the reference level. A change of 3 dB corresponds very nearly to a factor of 2 in power, since the common log of 2 is ~0.30103. Half power, used in determining bandwidth, is -3 dB. A change of 10 dB is a power factor of 10, 20 dB is a factor of 100, and so on. An advantage of defining gains and losses of power in decibels is that the values are additive, simplifying calculations.
DC (electrical)
Direct (electrical) current. A flow of electricity which consistently goes in one direction through a conductor, as opposed to AC. By convention, electric current flow is taken to be from a relatively positive voltage to a relatively negative one, and is nearly instantaneous—it actually occurs at a large fraction of the speed of light, depending on the conductor. This convention is used because "positive" and "negative" are historically arbitrary designations, and despite the fact that the primary electric charge carriers are electrons, which have a negative charge. The electrons are in fact moving in the direction contrary to current flow, though at a far slower speed. In fact, the typical ant can move faster than the average electron's flow through a solid conductor.
DC
DuPage County Illinois, my home county.
Decon
Decontamination.
Demulcent
A material used to soothe or protect inflamed, irritated mucous membranes.
Denature
With respect to an organic chemical compound, such as a protein, means to change its properties so as to reduce or eliminate its biological function. This can be done by heating, radiation, or by treatment with various chemicals. Also used to mean adding a substance to an otherwise edible or drinkable material—particularly ethyl alcohol—to make it poisonous or unpalatable.
Deposition
Change of state directly from gas to solid, without passing through a liquid phase. The reverse of sublimation.
Dermal
Referring to the skin. For example, dermal absorption means passing through the skin.
Dermatitis
Skin rash; inflammation of the skin.
Detection limit
The lowest concentration of a substance that can reliably be distinguished from a zero concentration.
DFO
(FEMA) Disaster Field Office.
DHCP
Dynamic Host Configuration Protocol. An OSI layer 7 (application layer) computer network protocol which provides network devices information such as their IP address, network mask, and addresses of important servers on the fly (i.e., "dynamically"), so that devices can be added and removed without having to administer them separately.
Dhrystone
See Cobblestone.
DHS
(US Federal) Department of Homeland Security external link.
Diaphoresis
Perspiration, especially when profuse.
Disease
An abnormal medical condition adversely affecting an organism's normal functions. There are several types, including pathogenic, deficiency, hereditary, degenerative, dysfunctional and mental, with substantial overlap between the categories. Generally, only a pathogenic disease will be communicable.
Distal
Located farthest (or farther) from the point of origin or attachment. Relatively distant from the mass of the body. The point of reference may have to be specified in particular cases. Synonym of "peripheral." Opposite of "central" or proximal.
DMSA
structure of dimercaptosuccinic acidmeso-2,3-dimercaptosuccinic acid. An organic chemical compound whose structure is shown at the right. Acts as a chelating agent for most heavy metals, and is thus used as an antidote for poisoning by lead and mercury, among others. See also the entries for DTPA and EDTA.
DNA
Deoxyribonucleic Acid. The genetic material of almost all living organisms. Some viruses use the closely related but less stable chemical RNA. DNA codes into RNA directly and into the amino acid sequences of proteins via RNA. DNA is an organic polymer of four different nucleotides; the sequence of those nucleotides provides the codes for the proteins. DNA is virtually unique to an individual sexually-reproducing organism, except in the case of identical twins or other clones. Unlike RNA, DNA normally appears as a pair of linked, complementary strands. These strands tend to be quite long: the largest human chromosome (#1) contains approximately 220 million nucleotides in each of its paired strands. See ATP for an example of the structure of an RNA nucleotide (adenosine monophosphate), and the change necessary to produce the DNA equivalent (deoxyadenosine monophosphate).
Dorsal
Towards or on the back or upper surface of an organism. Synonym is "superior." Opposite of ventral.
Dose
The mean mass of a substance incorporated into a living being as a ratio to the being's body mass. Usually measured in milligrams of substance per kilogram of body mass [mg/kg or parts per million (ppm)] or in micrograms of substance per kilogram of body mass [µg/kg or parts per billion—i.e., thousand million— (ppb)]. The concentration of the substance in specific body tissues may vary widely. An "exposure dose" is how much of a substance is encountered in the environment. An "absorbed dose" is the mass of a substance that was actually absorbed into the body.
Dose-response relationship
A mathematical model of the changes in body function or health [response] to the amount of exposure [dose] of a substance.
DOT
(US Federal) Department of Transportation external link. See some DOT functions relevant to materials safety under the headings PHMSA, the OET and RITA. They provide four-digit numbers used to identify materials for regulation or transportation, under 49 CFR 172.101, which numbers can be seen on diamond-shaped placards attached to vehicles that are transporting these materials.
DRO
(Red Cross) Disaster Relief Operation. An organized activity of the Red Cross, usually conducted in cooperation with other relief agencies, that provides essentials (such as shelter, food, medicines) to victims of a disaster, as well as performing other relief–related functions.
DSHR
(Red Cross) Disaster Services Human Resources. Like a corporate HR department, they see to the recruitment, training, and appropriate deployment in DROs of Red Cross personnel.
DSL
Digital Subscriber Line: techniques used to transfer data at high speeds over telephone lines, while preserving telephone service. Most often implemented as Asymmetric DSL (ADSL) in which download transfers (towards the customer) occur at higher speeds than uploads.
DST
(Red Cross) Disaster Services Technology. Four related functions, which provide computer, networking and voice communication for use by other Red Cross personnel, as well as customer service for those functions.
DTPA
structure of ethylenediaminetetraacetic acidDiethylenetriaminepentaacetic acid, (or pentetic acid), external link an organic chemical whose structure is shown on the right. DTPA is used as a chelating agent, particularly as an antidote for poisoning by actinide radioactive elements. DTPA also has industrial chelating uses (see the Wikipedia link). See also the entries for DMSA and EDTA.
Dyspnea
Difficulty in breathing; shortness of breath. See also apnea.

return to the glossary alphabetic index
E (symbol)
E is used as the symbol in electronics formulas representing EMF, also known as voltage. In physics, usually represents energy.
EAS
The Emergency Alert System. Radio and TV broadcasters and cable TV stations are required by the FCC to have the means to alert their audience when an emergency situation occurs in their area. Usually announced by a loud beep. Tests of the EAS end with the familiar message "If this had been an actual emergency …."
EC50
Median Effective Concentration. The concentration of a substance in the environment expected to cause a specified biological effect on 50% of exposed animals.
ECRV
(Red Cross) Emergency Communications Response Vehicle. Formerly used within the DST function to provide computers, networking and voice communication support to Red Cross operations centers such as DRO Headquarters and Service Centers where the resources available locally were limited. My introduction to DST was through my involvement with these vehicles.

There were 12 such vehicles in the continental US. They provided VSAT satellite access to the Red Cross facilities, and carried a variety of computing, networking, phone, and hand-held radio devices. The vehicles themselves, and much of the associated supplies, were donated by their respective manufacturers. Many hours of volunteer effort went into their construction. There were several reasons for their abandonment: the 2000 Ford Expeditions showed their age by needing occasional expensive and time-consuming repairs. This of course called into question their availability when needed to perform. Improvements in technology made many of their most significant advances obsolescent.

Nevertheless, I drove and operated ECRV 4711, based in Glenview IL, to numerous public events and Red Cross exercises, on occasion to repair facilities for as much as a week at a time, and most importantly to seven Red Cross DROs from MN and WI to NJ and NY.
ED50
Median Effective Dose. The dose of a substance expected to cause a specified biological effect on 50% of animals.
Edema
Accumulation of fluid in tissues, leading to swelling or obstruction. Pulmonary edema is associated with pneumonia.
EDTA
structure of ethylenediaminetetraacetic acidEthylenediaminetetraacetic acid (or ethylenediaminetetraacetate). A synthetic amino acid (or acid salt) that acts as a chelating agent for many divalent metal ions, particularly lead (Pb+2). A diagram of the acid's molecular structure is shown to the right. EDTA is used medically as an antidote for lead or other heavy metal poisoning in the form of the di-sodium salt, chelated with calcium: Na2Ca–EDTA; as a food preservative; and as an anticoagulant for stored blood (chelating Ca+2). See also the entries for DMSA and DTPA.
EEGL
Emergency Exposure Guidance Level. An acceptable concentration of a substance for unpredicted, single, short–term exposure of a defined occupational group (such as military personnel) to that substance. Developed by the National Academy of Sciences, NRC.
EFATG
Emergency First Aid Treatment Guide.
EHS
Extremely Hazardous Substance(s). A term for substances that must be reported if stored in sufficient quantity to be a potential threat. See TPQ for information on the term "sufficient quantity."
Electrolyte
A substance that in aqueous solution conducts electricity. In an animal, these are usually dissolved salts containing sodium or potassium ions. Electrolytes are also called ionic solutes. The concentration of electrolytes in blood affects bodily functions. For example, sodium and potassium ions are vital to the function of nerves, but too much of either is dangerous.
Electromagnetic Radiation
Energy radiated from a variety of physical processes that consists of coordinated variations in electrical and magnetic fields. Those fields are oriented perpendicular to each other, and vary in synchronization. Visible light is one of the more obvious manifestations of electromagnetic radiation (called EMR for short). Defining characteristics of an EMR wave are its frequency and amplitude (strength of the fields). Frequency ranges from a few hertz for ELF radio frequency signals to X-rays (30 PHz to 30 EHz) and gamma rays (>30 EHz). All EMR waves in a vacuum travel at the same speed relative to any observer, called for historical reasons the"speed of light." An EMR wave is embodied in a stream of photons. The energy of each photon in an EMR wave is proportional to its frequency: E=hν, where h is the Planck constant: 6.626 069×10−34 J⋅s, ν is the frequency in Hz, and E is in joules. The polarization of an EMR wave is determined by the orientation of its electrical field.
EMA
Emergency Management Agency. A generic term, often used for a local governmental agency responsible for dealing with emergencies of all kinds. Similar in meaning to ESDA.
Emesis / emetic
An emetic is a substance that can cause or induce vomiting (emesis).
EMF
Electro-Magnetic Force, the strength of the "push" of electrical flow through a circuit, or of the strength of a static field; measured in volts.
EMI
Emergency Management Institute. A training arm of FEMA.
EMS
Emergency Medical Services. This is a highly overloaded initialism, even within medical usage. Here, it means acute medical care out of hospital and transport of medical patients.
EMT
Emergency Medical Technician. Health–care providers trained to respond quickly to emergency medical situations. Examples are ambulance workers, and other paramedical providers of EMS as defined above.
Endemic
Adjective, indicating the occurrence of an infectious disease in a limited geographic region for an extended period of time. Compare to pandemic and epidemic. Endemic diseases are often widespread in the affected region and chronic in the affected population. Occasionally used as a noun, equivalent to "endemic disease."
Energy
In its sense in physics (which is all this entry deals with), energy is the work actually or potentially done when a force is exerted through a distance. The SI derived unit for energy is the joule. Energy can appear in different forms, such as kinetic and potential, and have different sources such as chemical, electrical, thermal, nuclear and gravitational, but all forms of energy can be converted from one to another. Symbol is E. Einstein famously equated energy and mass, with a unit conversion factor of c2.
Entropy
Too complicated a topic to be covered here adequately. I refer you to the Wikipedia external link article on the subject for a start. Entropy has a complex history, and different interpretations in thermodynamics, statistical mechanics, and quantum mechanics. Symbol is usually S. S is considered to be non–decreasing in closed systems (this is the 2nd law of thermodynamics), though this behavior is just a statistical likelihood, albeit a virtual certainty in non-trivial systems.
Enzyme
Organic chemicals that act as catalysts for chemical reactions in biological systems. Most enzymes are proteins, although some are molecules of RNA, or complexes of protein and RNA (ribosomes).
EOC/EOF
Emergency Operations Center/Facility. In an emergency, agencies responsible for dealing with the situation meet in this area of an ESDA or EMA office to share information and coordinate their activities. See also CEOC and SEOC.
EPA
(US Federal) Environmental Protection Agency external link. Administers among others, the CAA, CWA, CERCLA, RCRA and TSCA.
EPCRA
US Emergency Planning & Community Right–to–know Act. This is Title III of SARA, under the provisions of which all LEPCs are organized.
Epidemic
Noun and adjective, referring to an occurrence of an infectious disease in a limited geographic region for a limited period of time. Compare to pandemic and endemic.
Epidemiology
The study of the distribution and determinants of disease or health status in a population; the study of the occurrence and causes of health effects in humans.
ERG2012
Emergency Response Guidebook, 2012 edition. Latest issue of the book issued by DOT, which contains descriptions of the hazardous materials that may be transported on North American roads, and of the placards that identify the materials.
ESDA
Emergency Services & Disaster Agency. A generic term, often used for a local governmental agency responsible for dealing with emergencies of all kinds. Similar in meaning to EMA. DeKalb County external link has an ESDA.
Ester
An organic chemical compound typically formed by the reaction of an organic (carboxylic) acid with an alcohol. The hydroxyl (-OH) groups of both components are reduced to a single -O- (oxygen) link, with release of a water molecule. The IUPAC name of an ester is formed from the alcohol name with suffix "-yl" replacing "-ol" and the acid name with suffix "-oate" replacing "-oic". So as an example, the ester of ethanol and propanoic acid is formally ethyl propanoate. For another example, see BuAc, noting that "acetate" is a common (and IUPAC approved) synonym for the systematic name "ethanoate." Inorganic acids which have -OH groups, such as phosphoric and sulfuric acids, can also form esters. See entry phosphate as an example.
Ether
Generally, an organic chemical compound in which an oxygen atom joins two organic groups. "Ether" as a specific designation is the common name for diethyl ether, CH3CH2-O-CH2CH3, formerly at least used widely as an anesthetic.
Etiologic agent
Anything that can cause illness. Since it may be a chemical or even psychological or physical cause as well as a biological one, it is more general term than pathogen.
Evaporation Rate
In the terms used for MSDS, it is the ratio of the rate at which the substance described in the MSDS evaporates (changes state from a liquid to a gas) to the rate of evaporation of a standard chemical: n-butyl acetate, under standard conditions, as specified by the ASTM as Standard Test Method D3539–87 (2004). Evaporation rate information can be useful in evaluating the health and fire hazards of a material. For example, a substance with a high evaporation rate will readily form a vapor that can be inhaled or that can explode. Since evaporation rate is a ratio of like terms, it has no units. Substances with an evaporation rate greater than 3 are considered "fast" evaporators; those with a rate less than 0.8 are considered "slow." N-butyl acetate itself, whose evaporation rate is by definition 1, is considered "medium."
EVC
Equilibrium Vapor Concentration. The limiting atmospheric concentration of the vapor phase of a substance in contact with the liquid (or solid) phase of the same substance, at a specified temperature (typically "room temperature"—25 ℃).
exaFLOP
A quantity of 1018 (a million million million) basic floating point computer operations, such as addition, multiplication and comparison.

return to the glossary alphabetic index
F (symbol)
F is the SI symbol for farad. In physics, F represents force.
FAA
US Federal Aviation Authority. Among other things, regulates and controls quantity and packaging of substances sent by air.
farad
Named for Michael Faraday, this is the SI derived unit of electrical capacitance, symbol F. It is equal to a coulomb per volt, to a second per ohm, or in SI base units: kg-1⋅m-2⋅s2⋅A2. A one farad capacitor is quite large. Most capacitors used in electronic circuits are measured in fractions of microfarads (µF) or in picofarads (pF).
Fat, fatty acid
A fat is an organic chemical compound that is an ester of aliphatic (carboxylic) acids with glycerol. Glycerol is an alcohol with three active hydroxyl (-OH) groups, hence a "triol." Each hydroxyl binds to a fatty acid: that is an organic acid with a chain of carbon atoms. There are usually an even number of carbon atoms from 4 (butyric acid) to 28. The fatty acids are either saturated or unsaturated. The structure of glycerol (also known as "glycerine") is CH2OH-CH2-CHOH-CH2-CH2OH.

Some fatty acids are described as "essential." These are ones that humans cannot produce for themselves, at least in sufficient quantities. Those fatty acids must therefore be obtained from the diet. Examples of essential fatty acids are linoleic and alpha-linolenic acids; both are readily available from plants.
FCC
US Federal Communications Commission external link. The government agency responsible for regulating the cable, phone, satellite, radio and other communications media within the US and its possessions and between those and other countries. The Commission's regulations are contained in Title 47 of the CFR.
FEMA
US Federal Emergency Management Agency external link. FEMA is part of the Department of Homeland Security's Emergency Preparedness and Response Directorate. FEMA works in partnership with other organizations that are part of the nation's emergency management system including state and local emergency management agencies, 27 federal agencies and the American Red Cross. FEMA's mission is to lead the effort to prepare the nation for all hazards and effectively manage federal response and recovery efforts following any national incident. FEMA also initiates proactive mitigation activities, trains first responders, and manages the National Flood Insurance Program and the U.S. Fire Administration.
Fibrillation
Generally, uncontrolled and usually rapid twitching of muscle fibers, with little or no overall muscle movement. In paritcular, as in ventricular or atrial fibrillation (aka V-fib and A-fib), the uncoordinated contraction of the heart muscles, making them quiver rather than contract properly. By contrast with tachycardia, which can be a consequence of A-fib, ventricular fibrillation is a serious medical emergency, both because blood is not being circulated, and the condition can easily and quickly degenerate to asystole.
Fibrosis
Scarring. Pulmonary fibrosis can produce anoxia.
Field
A mathematical (algebraic) structure that is one step up from a ring, in that it has all the properties of the commutative ring, plus one more: the second (multiplication-like) operator must also have an inverse within the set, except for the zero (additive identity) element. That is to say that for any set element a (≠0), there is an element b, such that a⋅b=1 (the multiplicative identity element). This is obviously not true for the set of integers, but it is for rationals (ℚ) and higher (real, complex) number types. This means that both operators must have the closure, associative, commutative, identity and inverse properties, and the second operator must be distributive over the first. For details on those properties, refer to the glossary entry for ring.

As with groups and rings, the set for a field may be finite. Fields with finite sets are known as Galois fields.

As you may have noticed, I tend to think as a mathematician. So I must acknowledge at least two other meanings for "field." In physics, a field is the assignment of a value to every point in a space. That's pretty general, but so are fields. A weather map showing precipitaton (scalar value) or wind speed (vector value) on a two dimensional map is a field. So is the gravitational field (tensor value) at each point in spacetime (four dimensions). Lots of options. Another important use of "field" is the computer sense of a location within a data record that holds a specific value, say last name or cell phone number.
Floating point / FLOP
A number, usually as stored in a computer, that approximates a mathematical real number, as opposed to an integer. Such numbers are often called "real" in computer programming languages, though they are strictly only a subset of rational numbers, even within their limited range. A FLOP (floating point operation) refers to a basic computation performed by a computer using these numbers, such as addition, subtraction, multiplication or comparison. (Division is usually done by multiplying the numerator by the computed reciprocal of the denominator.)
FM (Frequency Modulation)
A mode of radio signal modulation in which the the frequency of the continuously transmitted carrier signal varies in response to changes in the amplitude of the signal it is encoding. Compare to AM.
FOIA
Freedom Of Information Act external link — 5 U.S.C. §552, under which citizens can request certain kinds of information from public agencies. For security reasons, information on Tier II sites in DeKalb County must be requested under FOIA.
Force
In physics, an influence that causes a massive object to undergo a change of velocity (i.e., to accelerate), or to undergo a strain. The SI derived unit of force is the newton. Symbol is F, hence F=m⋅a.
FPD
Fire Protection District.
FRP
Federal Response Plan.
Frequency
The rate, in number of full cycles per second, at which an electrical signal changes. Units are in inverse seconds (s-1), hertz, or particularly for radio–frequency signals, in multiples thereof (kilohertz, megahertz, etc.)
FTP
File Transfer Protocol, an OSI level 7 computer network protocol used to copy a file over a TCP/IP-based network, such as the Internet.

return to the glossary alphabetic index
Gamma (γ)
Gets lots of uses. Among there are:
  • Symbol for a photon.
  • Gamma radiation, otherwise generally known as electromagnetic radiation (light), and particularly to the highest frequency such radiation (>30 EHz).
  • The Lorentz factor, the ratio of coordinate time to proper time intervals dt/dτ in special relativity: γ = (1−v²/c²)−½. A factor in many relativistic equations, such as that for momentum.
GHz
SI symbol for gigahertz. An electronic signal of 1 gigahertz varies in cycles which recur one thousand million (109, US: one billion) times per second.
GIMP
GNU Image Manipulation Program. A free, open-source digital image creation and editing tool, available on most computer platforms. It comes standard on Linux distributions, and can be downloaded in versions for Windows and Mac.
GIS
Geographic Information System. A computerized mapping system that divides geographic and statistical data into viewable layers that can be removed or included depending on the user's needs.
[D-]Glucose
structure of simple sugar D-glucoseThe most common simple sugar in nature. See its chemical structure on the right. It is a hexose (formula C6H12O6) It appears not only as a component of "sugars" sensu lato, but also in widely distributed polysaccharides such as cellulose and starch. The D- stereoisomer of glucose is the only one common in nature; consequently, glucose is also known as "dextrose".
GPS
Global Positioning System. The complex of satellites, ground stations and receivers used to tell people where and when they are, with potential accuracy for ordinary users of a few meters horizontally and vertically, and fractions of a microsecond. GPS receivers used by people on the ground are often loosely called "GPSes." The US military runs the satellites and ground stations, and has an encrypted higher-accuracy system as well. WAAS has made the civilian system nearly as good, such that it can be used to land aircraft within the region it covers.
Group
A mathematical (algebraic) structure that has two elements: a set, and a binary operator that acts on pairs of members of the set. An example is the set of integers and the addition operator. There are four properties that a group must have. (1) Closure: the result of applying the operator to any two set elements must be in the set also. (2) Associativity: when there are two or more uses of the operator in a row, the order in which the operators are applied is irrelevant; in general the order of the set elements is relevant unless (like the example integer/addition group) the group is commutative (aka abelian). (3) Identity: there is an "identity" element such that any element is unchanged if combined with it via the operator. For the example group the identity element is the number zero. (4) Inverse: for any element a of the set there is an inverse element b such that applying the operator to a and b gives the identity element. For the example group the negative integers are the inverses of the corresponding positive integers (and vice versa).

Note that the group's set may be finite. In particular, the set of integers {0, 1, ... n} with n>1, designated Zn, together with addition modulo n forms an abelian group, known as a cyclical group. As with the example above, the identity element is zero. The inverse of element a is n−a, and is unique.
Guanine
structure of nucleobase guanineOne of the purine nucleobases in the nucleotides of RNA and DNA, whose structure is shown on the right. The corresponding nucleosides are guanosine and deoxyguanosine.
GUI
Graphical User Interface. Arguably by far the most common way for people these days to interact with computers. Smart phones and GPS receivers to tablet computers and laptops to desktop computers use graphical displays to get user input and display their results. Systems like X Window System and internet web browsers provide graphical remote access over networks to other computers' applications and resources. Gone are the days of DOS command lines and text only output on 80–column by 25–line displays (much less punched cards and line printers), all of which I most definitely do not miss.

return to the glossary alphabetic index
H (symbol)
H is the SI symbol for the henry. H is also the symbol for the chemical element hydrogen. In mathematics, H or ℍ represents the Hamiltonian (quaternion) numbers. Forms of H are used, since Q is already assigned to the rational numbers. In physics, ℎ represents the Planck constant, and ℏ represents the Planck constant divided by 2π.
Half–life
The period of time required to reduce the concentration of a substance by one half. In the environment, the half–life is the time it takes for half the original amount of a substance to disappear when it is eliminated, or changed to another form by radioactivity, bacteria, fungi, sunlight, or other chemical or physical processes. In the human body, the half–life is the time it takes for half the original amount of the substance to disappear, either by being changed to another substance or by leaving the body.
Ham
Informal designation of an amateur radio operator. The etymology of the term is disputed.
Hamiltonian (number)
A form of number named for William Rowan Hamilton, the mathematician who described it. See quaternions.
HazCom
Hazard Communication. Required by the OSH Act.
HazMat
Short form for "Hazardous Materials." See details under the heading HM.
HAZWOPER
HAZardous Waste OPerations and Emergency Response. OSHA standard 29CFR1910.120 regulates safety and health of people involved in the clean-up and decontamination response to hazardous materials releases.
Hematoma
A mass of blood collected outside of blood vessels within tissues.
Hemoglobin
A protein containing iron in the blood of most vertebrate animals, contained within red blood cells (erythrocytes). Hemoglobin is responsible for transporting oxygen from lungs or gills to all the body's tissues to support aerobic metabolism. This is far more efficient than transport by dissolving oxygen in the blood fluid itself. A shortage of hemoglobin, often due to iron deficiency, is a common cause of anemia.
henry
Plural "henries," and named for Joseph Henry, this is the SI derived unit of electrical inductance, symbol H. It is equal to an ohm⋅second, or in SI base units: kg⋅m2⋅s-2⋅A-2.
HF
High Frequency radio waves, specifically those with frequencies of 3-30 MHz, or wavelengths of 10-100 m. In informal usage among hams, the amateur radio 160 m band is lumped into HF (strictly, it's MF—Medium Frequency).
HHS
(US Federal) Department of Health and Human Services external link.
HM
Hazardous Materials. See also "HazMat." A hazardous material includes any substance that is a health or physical hazard as defined by OSHA. OSHA Regulations require that an MSDS be kept on hand for all hazardous materials. Such a substance may harm or injure humans, animals, agriculture, structures, waterways, highways, the environment, or other public or private property.
HMEP
Hazardous Materials Emergency Preparedness.
Homogeneous
Uniform in composition throughout a mass of material, at all relevant measurement scales. Not "lumpy."
HTML
HyperText Markup Language. Versions of html (latest is 5) are the most widely used computer languages for developing web pages. I prefer to use the closely related XHTML for its more rigorous syntax. For both, elements of the web page are created using tags . One such tag, which starts "<img", allows inserting of a graphics image. Amother, <em> (emphasis), on an English language web site, typically causes the following text to be in italics. Most html tags have a matching close tag. For the em tag that is </em>, which indicates return to normal type. Exceptions are like the self-contained img tag, which ends in " />". The overall format of a web page can be specified using CSS.
HTTP
HyperText Transfer Protocol. An OSI layer 7 (application layer) network protocol for distributed, collaborative, hypermedia information systems. It is the basic Internet text data communication protocol. Related is https, which provides secure, encrypted communications via the [layer 7] secure socket layer or later transport layer [layer 4] security (SSL/TLS) protocols.
Hydrolysis
The splitting of a chemical compound into two parts by the addition of a water molecule. Examples from this glossary are the reduction of ATP to ADP, and the separation of disaccharides (such as sucrose and lactose) and polysaccharides (such as cellulose and starch) into their simple sugar components. Such hydrolysis of organic molecules often requires a catalyst, whereas inorganic ionic molecules will typically hydrolyse when they dissolve in water. The inverse reaction, forming a single molecule from two or more with the release of one or more water molecules is known as condensation.
Hydrophilic
Generally, "compatible with water." Can mean that a substance easily absorbs, is wetted by, or dissolves in water. As opposed to "hydrophobic."
Hypertext
Text, such as is typically found on web sites, that contains links to other information; thus a kind of multi-level text. Look right around here for numerous examples. The links are known as "hyperlinks."
Hz
Symbol for hertz, named for Heinrich Hertz. Plural of hertz is also hertz. The hertz is the SI derived unit of frequency, equivalent to an inverse second of time (s-1). An electrical signal with frequency 1 Hz varies in a cycle that lasts one second; the cycle of a 10 Hz signal lasts a tenth of a second. Only audible frequencies (roughly 20-20 000 Hz for humans) are usually given in Hz. Nearly all radio frequencies use the multiples of kilohertz (kHz), megahertz (MHz), and gigahertz (GHz).

return to the glossary alphabetic index
I (symbol)
I is used as the symbol in electronics formulas representing electrical current. For that reason, electronics type people tend to use j instead of i to represent the unit imaginary number, the square root of -1. I or ⅈ represents the set of all imaginary numbers: a⋅i, where a is any real number.
IARU
International Amateur Radio Union. A confederation of national amateur radio organizations, such as ARRL in the US. It provides a forum for discussion of common issues.
ICP
Incident Command Post. Location from which an Incident Commander operates under the ICS.
ICS
Incident Command System. The mechanism used to coordinate the activities of multiple agencies responding to a disaster, led by an Incident Commander (IC). For more details on ICS, see this web site: What is an Incident Command System? external link ICS is widely used today on a local level, but is supplemented by the UCS, and is being replaced on a national level by NIMS.
IDLH
Designates the concentration of a hazardous material that is Immediately Dangerous to Life or Health. Values were determined by NIOSH.
IDNS
Illinois Division of Nuclear Safety. A part of IEMA, IDNS external link is responsible for protecting Illinois residents from the potentially harmful effects of ionizing radiation.
IEMA
Illinois Emergency Management Agency. IEMA external link is the SERC for Illinois.
IF
Intermediate Frequency. A frequency different from the native frequency of a radio signal, to which the signal is converted for ease in processing. Very high frequency signals, as from satellites, require specialized and expensive means to carry the signal to where it will be used. Conversion to lower–frequency IF allows it to be carried by coaxial cable. Also, signal processing is improved if all possible external frequencies are first converted to a single IF (via mixing with a local oscillator).
Imaginary (number)
A number which when multiplied by itself ("squared") yields a negative number. Designated I. All real numbers—positive or negative—by contrast always give a positive number in this case.
Impedance
(Electrical) impedance, measured in ohms and phase angle, with symbol Z∠θ, is a complex number equal to the vector sum of real (number) resistance and imaginary (number) reactance in an AC electrical circuit. Since the value of reactance is frequency dependent, so is the value of impedance.
Incidence
The number of new cases of disease in a defined at-risk population over a specific time period or more usually as the fraction or percentage of that population getting the disease (incidence rate). A measure of morbidity. [Contrast with prevalence].
Incision
A wound, often deep, caused by a sharp object like a knife, razor, or fragment of broken glass. Usually linear, unlike a laceration.
Incompatible
A combination of two or more chemicals that gives an undesired reaction when mixed. This usually refers to a mixture that will react to cause an imminent threat to health and safety through an explosion, fire, and/or formation of toxic materials. The MSDS for a substance is supposed to list its incompatibilities. But be aware that even ordinary household chemicals—notably bleach and ammonia—can be incompatible.
Incubation period
The interval between the time of infection by a biological agent and the time of first appearance of indications or symptoms of infection. Depending on the agent, this can be hours to decades. For longer incubation periods, a mean and variance provide a more useful description. Compare to the related term is latency period.
Inductance/inductor/inductive
Electrical inductance, symbol L, is the ability of a device known as an "inductor" to store electrical energy by means of a magnetic field; measured in SI derived units of henries. An electrical circuit in which inductance dominates over capacitance is described as "inductive," as is reactance due to inductance.
Infarction
Death of biological tissue caused by lack of oxygen due to a blood flow blockage (in turn due to a clot, constriction of blood vessels, hernia, tumor or the like). The mass of dead tissue resulting from this trauma is called an "infarct." Can affect any tissue or organ, but commonly known examples affect the brain (cerebral infarction or "stroke") or heart (myocardial infarction or "heart attack").
Infection, infectious
Infection is the colonization of a host organism by an invasive biological agent which causes detriment to the host, typically a (pathogenic) disease. Also typically, the invasive agent uses the host to reproduce and propagate itself. A disease caused by an infection is called "infectious."
Infectivity, infective
The ability of a pathogen to establish an infection by horizontal transmission, viz. not parent to child. A pathogenic disease with a short latency period and a high virulence must generally also be highly infective to maintain itself. Contrast infectivity with transmissibility.
Infrared
"IR". The part of the electromagnetic radiation spectrum that is longer wavelength than that of visible light, that is, longer than about 750 nm and shorter than radio frequencies. This latter limit is somewhat fuzzy: infrared is often taken down to a wavelength of 1 mm, but there is a sub-millimeter band in the radio spectrum. Both are extremes. "Near" infrared radiation—that is, near to visible light—is sensed as heat. Human body temperature radiates infrared at around 10 µm (as long-wavelength infrared). About half of sunlight power is in the infrared; most of the rest is visible.
Integer (number)
A number—positive, negative or zero— that has no fractional part. Designated Z or ℤ. The integers form an abelian (i.e., commutative) group with addition as the operator element. It also forms a ring with second operator element multiplication. It is the smallest non–cyclical group and ring based on the natural numbers.
Intolerance
Also known as non-allergic food hypersensitivity. A negative physiological reaction, immediate or delayed, to a food or food component, that does not involve an immunological response. Examples are lactose and fructose intolerance, and sensitivity to peanuts. Intolerance can be due to a metabolic error in processing normally tolerated nutrients, such as diabetes, phenylketonuria, or lack of lactase (the last of which may be perfectly normal in adults from some regions).
IOMA
Illinois Open Meetings Act external link. Requires government agency transparency in their activities, in most cases allowing public access to their deliberations. All DeKalb County LEPC meetings are conducted in accordance with this law.
Ionization
Change of state from gas to plasma. The reverse of recombination. or deionization.
Ionosphere
The earth's upper atmosphere, from about 50 km up. So called because solar radiation—especially UV (ultraviolet) and shorter wavelengths of light—causes air molecules to lose some of their electrons, thus becoming ionized. Among other things, the resulting layers of ionized gas can reflect (strictly speaking, "refract") radio waves, as long as the waves do not exceed the MUF, thus allowing them potentially to travel around the world—or at least beyond the line of sight.
IPC
The Illinois Poison Center. Serves all of Illinois 24 hours a day, 365 days a year. Staffed by nurses, physicians, pharmacists and other poison specialists, the IPC offers free, confidential poison prevention advice and treatment recommendations via a toll–free hot line, 1–800–222–1222. The IPC also has informative and preventative information at their website external link.
ISFI
Illinois State Fire Institute. Provides training for fire fighters.
Isolation
The segregation from the general population of an individual infected with a contagious disease, to prevent further spread of the disease. The one infected can be a human, or possibly another animal. Distinguished in strict usage from quarantine, in that an isolated individual is usually known to be infectious. An exception to this is "reverse isolation" in which a person who is susceptible to disease is kept isolated from potential carriers. Isolation of humans is most often to be found in health-care facilities such as hospitals.
ITU
International Telecommunications Union. A UN agency responsible for coordinating the global use of the radio spectrum, the development of technical standards, and similar technical functions.
IUPAC
The International Union of Pure and Applied Chemistry. An international group representing national organizations of chemists. Perhaps best known—and in this document, exclusively so—for its standardized system of chemical nomenclature, particularly for organic compounds.

return to the glossary alphabetic index
J (symbol)
J is the SI symbol for joule. In physics, j represents Jerk. Electronics types often use j instead of i as the imaginary number unit.
JCAHO
Joint Commission on Accreditation of Health–care Organizations external link. Evaluates and accredits nearly 17 000 health–care organizations and programs in the United States. Focused on improving the quality and safety of care.
Jerk
The time rate of change of acceleration. Symbol j. Thus the third derivative of position with respect to time: j=d3x/dt3. Jerk times mass is known as Yank, symbol Y. Further time derivatives of position are known as snap: s (4), crackle: c (5) and pop: po (6). The last has to have a two-letter symbol since "p" is already used by momentum. Not kidding. Not much, anyway.
JIC
Joint Information Center. Common source for several organizations and agencies to provide coordinated and verified information to the public in the case of an emergency.
joule
Symbol J; named for James Prescott Joule. The SI derived unit of energy or work. By Newton's formula equating work with force (in units of newtons) times distance, this works out to SI base units of kg⋅m2⋅s-2.

return to the glossary alphabetic index
K (symbol)
K is the SI symbol for kelvin. K is also the chemical symbol for potassium.
kelvin
Symbol K; named after William Thomson, Lord Kelvin. This is the SI base unit for temperature. It is defined such that the thermodynamic temperature of the triple point of pure, standard (VSMOW) water is 273.16 K—0 K is absolute zero, so all values on the kelvin scale are positive. Note first that the unit is called the "kelvin," not the "degree kelvin" and the symbol has no degree (°) mark. Secondly, the everyday metric unit for temperature, the degree Celsius (symbol ℃), is defined such that an interval of one ℃ is one kelvin; the zero point for ℃ is 273.15 K, not the freezing point of water. This in effect defines the triple point of water as 0.01 ℃.
Ketone
An organic chemical compound in which two carbon-containing groups are joined by a carbonyl (C double-bonded to O, in print usually designated C=O). If the carbonyl group is at the end of a group instead of joining two groups, the result is an aldehyde.
kHz
SI symbol for kilohertz. An electronic signal of 1 kilohertz varies in cycles which recur one thousand times per second.
kilogram
The SI base unit for mass, symbol kg. This is in at least two respects unusual among SI units. For one, its name and symbol include a multiplicative prefix (kilo, k). For another, it is the only SI unit still defined by a physical prototype. This latter means that it uniquely cannot be duplicated by instruments in a metrology laboratory other than at BIPM, where the international kilogram prototype is kept. Others must rely on carefully replicated and maintained secondary standard kilograms. This is awkward to say the least; I understand that talks are underway to see how we can get away from this mode of definition (as was done earlier with the meter), so stay tuned.
Kinetic rate coefficient
A number that describes the rate at which, for example, an air pollutant reacts.
KSA
Knowledge, Skills, and Abilities.

return to the glossary alphabetic index
L (symbol)
L is used as the symbol in electronics formulas representing electrical inductance.
Laceration
An irregular tear-like wound, often caused by blunt trauma, such as scraping more severe than an abrasion. Not to be confused with an incision.
LAN
Local Area Network. A network that provides data links for computers that are located within a limited geographical area, typically a single building or a campus. Today, typically implemented in Ethernet and/or Wi-Fi. Contrast with WAN.
LandView
A GIS from the US Census Bureau that can be used with MARPLOT to estimate the number of people affected by a hazardous materials release. See also CAMEO.
Latency period
The time interval between exposure to an infectious biological agent or a toxic substance and the first manifestation of illness caused by that agent or substance. May range from a few seconds for toxic substances or hours for biological agents to decades for either. In the case of an infection, the latency period is often taken to be the interval between the time of infection and the time the infected host becomes itself infective. Compare the related term incubation period.
Lateral
Towards the side of an organism on the left-right axis. Opposite of medial.
LC50
Median Lethal Concentration. The concentration value of a hazardous material at which 50% of animals would be expected to die from its effects; a calculated value.
LCLO
Lethal Concentration LOw. The lowest concentration of a hazardous material at which death occurred.
LD50
Median Lethal Dose. The dose of a hazardous material at which 50% of animals would be expected to die from its effects; a calculated value.
LDLO
Lethal Dose LOw. The lowest dose of a hazardous material at which death occurred.
LEL
Lower Explosive Limit. The atmospheric concentration of a flammable hazardous material below which it lacks sufficient fuel to be subject to explosion. Also known as the Lower Flammable Limit (LFL). See also UEL.
LEPC
Local Emergency Planning Committee. A group responsible for developing plans to deal with release of hazardous materials. In Illinois, there is an LEPC for every county, established by IEMA, the SERC for Illinois. The legal provisions for LEPC organization are part of EPCRA.
Lesion
An abnormal change, injury or damage to an animal or plant tissue. Lesions are typically caused by trauma or disease, but may be induced deliberately in surgery.
Light
Usually refers to the part of the EMR spectrum that is visible to humans, a wavelength range of roughly 380 nm (violet) to 750 nm (red). Light slightly shorter than this range is known as ultraviolet; many longer wavelengths are designated infrared. The boundaries are a bit loose, since some animals can see well into the infrared and ultraviolet ranges, and there is even some variation within humans.
liter (or litre)
Common metric (but not SI) unit of volume, equal to a cubic decimeter. There are thus 1000 liters in a cubic meter (m3). There is no standard symbol for liter, but L is often used, as well as a script lower-case l.
LOAFL
Lowest Observed Adverse Effect Level. The lowest tested dose of a substance that has been reported to cause harmful (adverse) health effects in people or animals.
LOC [plume]
Level Of Concern. In the context of hazardous materials releases, the maximum TWA atmospheric concentration of a substance to which members of the general public can be exposed, for a specified period of time (typically 15 minutes). For smoke, for example, the LOC concentration is 150 µg/m3 for up to 1 hour. For hazardous materials, the LOC is usually set at 0.1 times the IDLH value.

An "LOC plume" is the volume of dispersed substance in the air that exceeds the LOC concentration.

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M (symbol)
Symbol for the meter, the SI unit of length is m; m is also the symbol in physics for mass.
MAA
Mutual Aid Agreement.
MABAS
Illinois Mutual Aid Box Alarm System external link. An organization of more than 1000 fire-fighting departments in Illinois, southern Wisconsin, and parts of Indiana, Iowa and Missouri. MABAS provides a mechanism for fire fighters, EMS personnel (EMTs) and specialized teams (such as Search and Rescue and HazMat) to get assistance from other FPDs as required. MABAS also serves IEMA as an Illinois statewide emergency resource, since the state has no fire department of its own.
Maltose
A disachharide sugar made by chemical condensation of two glucose units. It is commonly formed in the hydrolysis of starch by the enzyme amylase. Amylase also produces some of the trisaccharide (or oligosaccharide) maltotriose, condensed from three glucose unita. Both maltose and maltotriose are in turn hydrolysed to glucose by the enzyme maltase.
MARPLOT
Mapping Applications for Response, Planning and Local Operational Tasks. Part of CAMEO, jointly developed by the EPA, NOAA, and the US Census Bureau. A GIS that shows areas affected by a HazMat incident on street–level maps. See also LandView.
Mass
IMO one of the most slippery of physical concepts (time takes the cake). Primarily mass is a measure of an object's inertia—that is, as how much force it takes to change the object's state of motion. Fine, but force is then defined in terms of mass and change of motion. Circular? Blame Newton. "Gravitational mass" would appear to be an obsolete concept, given general relativity, wherein any object in the same inertial frame of reference will follow the same geodesic in spacetime, regardless of mass. In any case, the SI base unit of mass is the kilogram, though other units are used for specific applications. See the entry on the dalton for example. Distinguish mass from weight. The symbol for mass in physics formulas is m.
Matrix
Mathematically, a rank 2 tensor: ai j, but more usually notated am,n. Simply described, that is a table with m rows and n columns. If m=n, it is a square matrix; otherwise it is rectangular. If m=1 it is a row vector; if n=1 it is a column vector.
Medial
Towards the center of an organism on the left-right axis. Opposite of lateral.
Mercaptan
See thiol.
MERS
Mobile Emergency Response System.
METAR
Routine aviation weather report (the term "METAR" is an acronym for the French equivalent phrase). A compact, internationally recognized format for routine—usually hourly and automated—weather reports, typically from airport locations. The report shows a location code, day of month and (UTC) time, dry bulb and dew point temperatures (°C), precipitation, cloud cover code(s) and height(s), wind compass direction and speed (m/s or knots), visibility (km or statute miles), and the like. Geared towards aircraft pilots, but obviously also of general interest.
meter (metre)
The SI base unit of length. Symbol is m. Defined as the length of the path traveled by light in a vacuum during a time interval of 1/299 792 458 of a second (symbol s). Note that this in effect defines the speed of light in a vacuum as exactly 299 792 458 m/s. The definition has been through changes over the years. Originally (and still very nearly) it was the fraction 1/10 000 000 of the distance on the longitude of Paris between the earth's north pole and equator. Thus the circumpolar circumference of the earth is very nearly 40 000 000 m. For a while, it was defined by marks on a bar kept at BIPM, then in terms of wavelengths of atomic radiation—but a different one than used for the second.
MHI
Material Hazard Index. A number used to rank chemical materials to determine the level of controls necessary for regulation. MHI is determined by dividing the EVC of a material at 25 ℃ by the LOC value for that material in the same units.
MHz
SI symbol for megahertz. An electronic signal of 1 megahertz varies in cycles which recur one million times per second.
micrometer/Micrometer
[1] Spelled micrometer/micrometre, and pronounced "MIKE ro me ter", the length of one millionth (10-6) of a meter, symbol μm. [2] Spelled with unspecified initial capitalization, and pronounced "my KROM eh ter" it is a generic, relatively high resolution length measuring deviceexternal link occurring in various forms. Micrometers (second meaning) which incorporate a vernier scale, can measure to 10-4 inches or 10-6 meter (i.e., to a micrometer, first meaning); though to achieve those levels of accuracy requires very careful manufacture and calibration. Without a vernier scale, the resolution of either type of micrometer [2] is one digit less.
MIPS
Million [computer] Instructions Per Second, a measure of a computer's processing speed.
Modulation
In radio and electronics terminology, the process by which information is embedded in a signal. Without radio modulation there would only be a bare carrier, or (as with modulation techniques such as SSB and CW), no signal at all.
mole
The SI base unit of quantity of a substance. Symbol is mol. Defined as the amount of substance of a system which contains as many elementary entities as there are atoms in 0.012 kilogram [i.e., 12 g] of 12C. Note that "mole" by itself is meaningless; one must specify the elementary entities being measured, which may be specific atoms, molecules, or ions; electrons or other particles; or specified groups of such particles.
Momentum
Ignoring relativity, Mass times velocity: p=mv. Since velocity is a vector quantity, so also is momentum. Total momentum is a conserved property in any closed system. Symbol is p. There is no named SI unit for momentum; its units are kg⋅m/s. For objects at relativistic speeds, momentum is given as mvγ. See entry gamma for details.
Morbidity
The incidence rate or prevalence rate of a disease or other medical condition. Contrast with the mortality specific to that disease.
Mortality
The number of deaths, in general or due to a specific cause, in a population per unit time. Usually represented as a percentage of the population size. Contrast with morbidity.
MSDS
Material Safety Data Sheet. One of around 500,000 documents that details the characteristics of a substance sold or used in the US. Both the OSHA Hazard Communication (HazCom) Standard and EPRCA §311 require employers to have an MSDS for each hazardous chemical in their facility. Many of the MSDS can be looked up at this web site: Vermont Safety Information Resources, Inc. MSDS external link.
MUF
Maximum Usable Frequency. The highest radio frequency that can, under specified conditions, be reliably used for communication via refraction of the wave by layers of ionized gas in the ionosphere. MUF depends on solar activity, especially sunspots: the more activity, usually the more ionization and the higher the MUF; and on the time of day: especially at night, absent the sunlight, some of the ionized layers disappear. On a given day, radio communications may or may not succeed at the MUF—the optimal operating frequency for a given path is usually estimated to be around 80% to 90% of the MUF.
Myocardial
Pertaining to the muscle of the heart (the myocardium).

return to the glossary alphabetic index
N (symbol)
N is the SI symbol for the derived unit of force, the newton. N is also the symbol for the chemical element nitrogen. N or ℕ represents the set of all natural numbers.
Na
Na is the chemical symbol for sodium.
Narcosis
A state of drowsiness, stupor, or greatly reduced activity caused by a chemical or physical agent. Thus sleep deprivation does not count. Often associated with drugs, it can be caused by a number of substances.
Natural number
One of the "counting numbers," designated N: the positive integers. If zero is included, may be designated N0.
NBS
(US) National Bureau of Standards. Obsolete name. See NIST.
NECC
National Emergency Coordination Center of FEMA.
Net
In radio usage, a net is a controlled meetup of several individuals, using a common frequency or set of frequencies. There is a net control operator who is responsible for being the "traffic cop"; most net communication is through or with the net control operator.
Neurotoxin
A substance whose primary toxic effect is on the central nervous system (CNS).
Neutralize
To make a substance less chemically reactive, or to change the ambient pH to approximately 7.
newton
The SI derived unit of force. Symbol is N; named of course for Isaac Newton. By Newton's formula F=m⋅a (force equals mass times acceleration), this works out to SI base units of kg⋅m⋅s-2.
NFA
National Fire Academy. Run by FEMA's US Fire Administration in Emmitsburg MD.
NFPA
National Fire Protection Association external link. An international voluntary organization formed to promote and improve fire protection and prevention. Publishes the National Fire Codes, a multi-volume set of standards, recommended practices and manuals.
NGO
Non-Governmental Organization. Somewhat loosely defined category of agencies that at least are not associated directly with a govenment (though may be chartered or partially supported by one). An NGO is also nearly always a not-for-profit organization. Term was created by the United Nations (which is a prime example of an NGO) in 1945.
NIMS
National Incident Management System. Developed and managed by DHS, this is a version of ICS and UCS for use at a national level. As a central part of the NRP, NIMS provides a consistent nationwide template to enable all government, private–sector, and nongovernmental organizations to work together during domestic incidents. For further information, see the NIMS website external link from FEMA, and the on–line courses external link on NIMS offered by the EMI.
NIOSH
National Institute for Occupational Safety and Health external link. An organization under the US Department of Health and Human Services' Centers for Disease Control & Prevention (CDC). Publishes the RTECS.
NIPSTA
Northeastern Illinois Public Service Training Academy. (From their web pages: external link) "An intergovernmental agency comprised of municipalities, fire protection districts, and other organizations located in the Chicago metropolitan area that have combined energies and resources to create a regional, state-of-the-art public safety training facility." NIPSTA occupies a 20 acre campus, part of the former Glenview Naval Air Station. Of personal interest because it was in the NIPSTA Field Training Facility where ECRV 4711 resided when it was not in service, and in the NIPSTA Education Center where many elements of Red Cross training are provided for the Chicago area.
NIST
(US) National Institute of Standards and Technology. Formerly known as the National Bureau of Standards (NBS, 1901-1988), the successor to the Office of Standard Weights and Measures, part of the US Treasury Department (1830-1901). An agency of the US Department of Commerce that sets standards for US usage of weights and measures, and provides metrology expertise to the country. A time standard is provided via radio stations WWV, WWVB and WWVH on various carrier frequencies, as well as via phone (1-303-499-7111 in the US) and the internet (using NTP).
NOAA
US National Oceanic & Atmospheric Administration. Runs the National Weather Service (NWS), which provides weather forecasts nationwide, especially through its network of NOAA Weather Radio external link stations for Illinois counties. Co–developer of ALOHA, since weather conditions strongly affect the distribution of hazardous materials in the air.
NOAEL
No Observed Adverse Effect Level. The highest experimental dose for which no adverse health effects have been documented. Formerly used by the US EPA to set RfC and RfD values. Has been superseded by BMC/BMD methods.
Noxious
Capable of causing injury, or harmful effects on health. See also "toxic."
NRC
National Research Council of the National Academy of Sciences.
NRC
National Response Center of the EPA. Receives reports of hazardous materials releases.
NRP
National Response Plan. Establishes a comprehensive all-hazards approach to enhance the ability of the United States to manage domestic incidents. The plan incorporates best practices and procedures from incident management disciplines—homeland security, emergency management, law enforcement, firefighting, public works, public health, responder and recovery worker health and safety, emergency medical services, and the private sector—and integrates them into a unified structure. The NRP is predicated on NIMS. Together the NRP and the NIMS provide a nationwide template for various agencies to work together in preventing or responding to threats and incidents regardless of cause, size, or complexity.
NRT
US National Response Team. A cooperative effort of the EPA, NOAA, and the Coast Guard. It does not respond directly to incidents, but (1) distributes information, (2) plans for emergencies, and (3) trains for emergencies.
NTP
Network Time Protocol. An OSI layer 7 (application layer) network protocol Used to synchronize clocks across a computer network, especially the internet. Somewhat limited in ultimate accuracy by network latency, it still is capable of maintaining time within 10 ms, even over the internet. On a local network, it is much more accurate.
Nucleotide
Basic chemical components of all living organisms. They form the polymers of DNA and of RNA, and perform other biochemical functions such as energy storage and as components of enzymes. DNA uses four nucleotide bases ("nucleobases"): adenine (symbolized: A), cytosine (C), guanine (G), and thymine (T); RNA substitutes uracil (U) for thymine. The sequence of these nucleobases forms the genetic code; triplets of the nucleobases code for amino acids in proteins. For DNA, A pairs with T and C with G in its double, helical strands.

A nucleobase linked to a ribose or deoxyribose sugar on the sugar's 1' carbon is known as a nucleoside. The four ribose–based nucleosides corresponding to the above listed nucleobases are adenosine, cytidine, guanosine and uridine. For DNA, which uses deoxyribose sugar, prepend "deoxy" to the above names: deoxyadenosine, deoxycytidine, etc. Also add [deoxy]thymidine in place of uridine. A nucleotide (note subtle spelling difference) consists of one of the above nucleosides ester–linked to at least one phosphate group through the 5' carbon of the sugar. The RNA and DNA chains of nucleotides use a single phosphate group to ester link the 3' carbon of one [deoxy]ribose to the 5' carbon of the next. This leaves an unpaired carbon at each end of the chain. The RNA and DNA ends are thus called the 3' end and the 5' end. For an example of the structure of a representative RNA nucleotide (adenosine monophosphate), see entry ATP.
NVOAD
National Voluntary Organizations Active in Disaster. external link Organization of American national disaster relief agencies with the goal of fostering more effective service to people affected by disaster. The key NVOAD principles are cooperation, coordination, communication, education, mitigation, convening mechanisms, and outreach. There are national members, and also state VOADs.
NWS
National Weather Service. See NOAA.

return to the glossary alphabetic index
O (symbol)
O is the symbol for the chemical element oxygen.
Oboe
A WMD cleverly disguised as a musical instrument. See my occasionally whimsical comments about it on this web site.
OEM
Office of Emergency Management.
OET
The Office of Emergency Transportation external link of DOT performs coordinated crisis management functions for multimodal transportation emergencies, including natural disasters and technological incidents or accidents.
ohm
Symbol Ω (Greek capital omega); named for Georg Simon Ohm. Measure of the opposition to current flow in an electrical circuit. The ohm is an SI derived unit, equal to a volt per ampere, a watt per squared ampere, or in SI basic units: kg⋅m2⋅s-3⋅A-2. For details, see resistance, reactance, and impedance, all of which are measured in ohms.
Oligosaccharide
A polymer of a few simple sugars, typically three to nine, formed by chemical condensation.
Order of Magnitude
As used here, and in common usage, an approximate factor of 10 difference between two numbers. If two numbers differ by one order of magnitude, one number is about ten times larger than the other. If they differ by two orders of magnitude, they differ by a factor of about 100 (102), and so on for higher integer powers of 10.
Organic chemicals/compounds
Naturally occurring (animal– or plant–produced) or synthetic substances containing carbon, plus some combination of hydrogen, oxygen, and nitrogen. Phosphorus and sulfur are also often part of an organic compound. More than 10 million have been identified. The opposite is "inorganic." For examples, see the entries for ALA, n–butyl acetate, DMSA, DTPA and EDTA. Since both DNA and RNA are organic compounds, the number of distinct organic compounds in nature must be in the trillions. The term "organic food" is little more than a marketing gimmick. The only non-organic food type substance I can think of is table salt (NaCl), and I've even seen examples of that called "organic."
ORM
Other Regulated Material. A DOT classification of some hazardous materials for labeling during transportation.
OSH Act
US Occupational Safety and Health Act of 1970, 29 CFR 1910 et seq. Administered by OSHA for firms with ten or more employees. The act established the Hazard Communication (HazCom) Rule.
OSHA
US Occupational Safety & Health Administration external link. Federal agency, part of the Department of Labor, responsible for worker safety and health.
OSI model
The Open Systems Interconnection model is the model that is most often used to describe the elements of a communications system such as (in particular) a computer network. It partitions the functions of such a system into seven layers. Here are brief, and necessarily incomplete, descriptions of each of these layers:
  • Level 1, Physical Layer: defines the electrical and physical characteristics of the transmission medium and low-level flow control.
  • Level 2, Data Link Layer: allows for transfer of data between directly–connected devices. Sometimes loosely called the MAC (media access control) layer, from one of its sublayers. MAC addresses are built into devices and are unique.
  • Level 3, Network Layer: allows data transfer between devices on the same network. It translates logical (such as IP) addresses into physical MAC addresses.
  • Level 4, Transport Layer: controls the reliability of a network connection via flow control, security and error correction. Example is TCP used with IP.
  • Level 5, Session Layer: establishes, maintains, terminates and restarts connections between applications on different devices.
  • Level 6, Presentation Layer: called the "syntax" layer, it translates data into the form recognized by an application.
  • Level 7, Application Layer: basically, the user interface to the network to provide a requested function.
Osmosis
Passage of a fluid through a membrane to equalize a concentration on both sides.
OSWER
Office of Solid Waste & Emergency Response. Part of EPA.
Oxidizer
Abbreviated "OX". The DOT narrowly defines an oxidizer or oxidizing material as a substance that readily yields oxygen to cause or enhance the combustion [burning] of other materials. Some oxidizers, such as chlorine, act only when exposed to other substances. The definition of oxidizer in chemistry is broader.
Ozone
structure of the ozone moleculeA form of oxygen molecule, O3, that is relatively unstable, particularly at higher pressures and temperatures. See the diagram on the right. It is formed when a free oxygen atom reacts with an ordinary oxygen molecule, O2. The free oxygen atom is formed by high energy electromagnetic radiation from sunlight, such as ultraviolet light of wavelength <240 nm or x-rays, splitting O2. In the low–density upper atmosphere ozone can persist for several hours to a day. Often naturally destroyed by the same oxygen atoms that formed it, ozone is also vulnerable to atmospheric pollutants, notably chlorofluorocarbons. Ozone is much more reactive, even explosively so, than molecular oxygen, and has a sharp odor. Ozone is valuable to us, since it effectively blocks some of the shorter, more dangerous wavelengths of ultraviolet light longer than about 200 nm that are not blocked by atmospheric oxygen and nitrogen.

return to the glossary alphabetic index
P (symbol)
P is used as the symbol in electronics formulas representing electrical power. P is also the symbol for the chemical element phosphorus. Lower-case bold p is the symbol in physics for momentum.
Pandemic
Noun and adjective, referring to an occurrence of an infectious disease in a large geographic region, possibly worldwide, for a limited period of time. Compare to epidemic and endemic.
pascal
Symbol Pa; named for Blaise Pascal. The SI derived unit of pressure, equal to one newton of force per square meter. In SI base units this works out to kg⋅m-1⋅s-2. Standard earth atmospheric pressure is taken to be 101 325 Pa .
Pathogen, pathogenic
An infectious biological agent that can cause a disease. Such a disease is classified as "pathogenic." See also the more general term, etiologic agent.
PDF
Portable Document Format. Developed by Adobe® Systems, Incorporated, it is a widely used and supported form for distributing documents electronically. Some of the information available from this website is in PDF files. For more information, see the Adobe PDF external link webpage.
PEL
Permissible Exposure Limit. The maximum or TWA amount or concentration of a substance to which a worker may be exposed, under OSHA regulations. About 470 substances have OSHA PEL's. Exposure can be by inhalation, or by absorbtion through the skin or eyes.
Percutaneous
Through the skin, referring to the absorption of a chemical.
petaFLOPS
Quantity of 1015 FLoating-point (computer) Operations Per Second. A measure of massive computing power.
pH
Roughly, a measure of the acidity or alkalinity of a substance. Pure water at 25 ℃ is considered neutral, with a pH close to 7.0. Substances with pH much below 7 are acid; the lower the value, the more acid. Those much above 7 are alkaline; the higher the value, the more alkaline. A commonly used formal chemical definition is −log10[H+], where the brackets indicate concentration of hydrogen ions (H+) in moles per liter. But even this is an approximation in some cases to what would be measured.
Phase (of matter)
A physically distinctive form of a substance. Examples are solid, liquid, gas, and plasma.
Phase angle
In an alternating current electrical circuit, represents the difference in angular degrees between the peaks of voltage and current (in a direct current circuit these would be the same). The value ranges ±90°. In a primarily inductive circuit, voltage peaks lead the current peaks; this is considered a positive phase angle. A primarily capacitive circuit has voltage peaks lagging the current ones and a negative phase angle. See headings reactance and impedance for more information.
PHC
Principal Hazardous Constituent. In a mixture, the component that has the greatest potential risk.
PHMSA
The Pipeline and Hazardous Materials Safety Administration external link of DOT has public responsibilities for safe and secure movement of hazardous materials to industry and consumers by all transportation modes, including the nation's pipelines.
Phosphate
Inorganic phosphates are just salts of phosphoric acid: (HO)3P=O. Organic phosphates, which largely are the ones referenced in this glossary, are esters of that acid. See the entry for ATP for an example of how organic phosphates link up. An organic monophosphate group looks like (OH)2O=P-, where the right-most bond of the phosphorus is to the ester link oxygen.
Photophobia
Intolerance to light. Discomfort or pain on exposure to light. Not a "phobia" in the usual sense of "fear." Many possible causes, including eye defects, drug reactions, and diseases.
PIO
Public Information Officer. The individual primarily responsible for distributing factual information about an incident, generally via media interviews and press releases.
PL
Private Line. A Motorola trade name, often used for the proper term: CTCSS.
Plasma
A state of matter in which molecular bonds become dissociated, and atoms become ionized. Electrons from the atoms are independently part of the plasma. Plasma is the most common form for matter in the universe.
Plume
A volume of a substance that moves from its source to places farther away from the source. Plumes can be described by the volume of air or water they occupy and the direction they move. For example, a plume can be a column of smoke from a chimney or a substance moving with groundwater.
Pneumonia
A disease characterized by inflammation of and accumulation of fluids in the lungs. Although usually thought of as an infectious disease, pneumonia can also be caused by physical and chemical irritants, or by inhaled fluids.
PNG
Portable Network Graphics, a file format for the lossless, portable, well-compressed storage of raster images. PNG provides a patent-free replacement for GIF and can also replace many common uses of TIFF. Graphic images on this web site are largely PNG format.
POHC
Principal Organic Hazardous Constituent.
Poison
A toxin that is ingested, inhaled, or otherwise absorbed. Contrasted with venom.
Posterior
Towards the rear end of an organism. For many vertebrates, also known as "caudal" (tail). Opposite of anterior.
Pound
One of the many reasons for avoiding use of units outside of SI ones. For historical reasons, in common use "pound" refers to a unit of force (weight). In this case, the unit of mass is typically the "slug." "Pound" can also be used as a unit of mass in another system of units. Engineers stuck with this (mostly in the US), clumsily distinguishing pounds–force, symbol lbf from pounds–mass, symbol lbm. The latter, in the form of the "international avoirdupois pound" is by definition 0.453 592 37 kg. So it all ties back to SI in any case. I'll stick with N and kg.
Power
In physics, power is the rate of performing work or using energy per unit time. The SI derived unit of power is the watt.
PPE
Personal Protective Equipment. Devices or clothing used to help isolate a person from direct exposure to hazardous materials.
ppm / ppb
Designates a concentration expressed in Parts Per Million or in Parts Per Billion (thousand million). Usually this is the ratio by mass (loosely speaking, "weight"), often designated by the suffix "w/w," but it is occasionally by volume, designated "v/v".
Precision
The degree to which repeated measurements of a quantity show the same value. Also known as repeatability. Contrast with accuracy and resolution.
Prevalence
The number of existing disease cases in a defined at-risk population during a specific time period or more usually as the fraction or the percentage of that population with the disease (prevalence rate). A measure of morbidity. [Contrast with incidence].
Prime (number)
A prime number is a natural number greater than one which is not exactly divisible by any natural number other than itself and one. The only even prime is 2, since all other even numbers are divisible by 2. Non-prime natural numbers are known as "composite." The count of prime numbers less than or equal to n is designated by the function π(n); no exact formula exists for this function, but the prime number theorem gives it as approximately n/ln(n). Euclid (book IX, proposition 20) gave a proof that there is no largest prime; hence there is a (countably) infinite number of them.
Proper Time
In special relativity, the time interval local to a moving entity, denoted dτ, as distinguished from coordinate time, dt. The ratio of these intervals (dt/dτ) is given by the Lorentz factor (γ). Proper time interval Δτ is given as (Δ²t−[Δ²x+Δ²y+Δ²z]/c²)½.
Protein
Also known as polypeptides, proteins are complex organic molecules, composed of amino acid residues, joined at a carboxyl group of one amino acid to an amino group of another by chemical condensation. Proteins form in straight or branching chains of the amino acids. In organisms, proteins are ubiquitous. They form structural elements, and as enzymes, catalyze most biochemical reactions. Also in organisms, proteins are formed via templates of RNA derived from DNA sequences.
Protocol
In computer networking terms, a protocol is set of rules which is used by computers to connect, communicate, and transfer data with each other across a network. These include lower level protocols such as DSL and ISDN [OSI layer 2], TCP/IP [OSI layers 4/3], and higher level [usually OSI layer 7] ones such as DHCP, SNMP, NTP, HTTP, and FTP.
Proximal
Located closest (or closer) to the point of origin or attachment. Relatively close to the mass of the body. The point of reference may have to be specified in particular cases. Synonym of "central." Opposite of "peripheral" or distal.
PRP
Potentially Responsible Party. A company, government, or person legally responsible for cleaning up the pollution at a hazardous waste site under Superfund. There may be more than one PRP for a particular site.
PSAP
Public Safety Answering/Access Point external link. Often known in the US as a "9-1-1 Center." The location and associated real phone number that is called to report emergency (e.g., police, fire, weather) situations, when a phone company customer "dials" the number 911. The local telephone company's telephony switch is responsible for translating "911" into the actual number of the PSAP.
PSTN
Public Switched Telephone Network external link: all the electronic, fiber optic, RF, satellite, electromechanical, etc. components that together allow voice and data connections between publicly accessible telephones around the world. Details of PSTN operation differ from place to place.
Public health advisory
A statement made by ATSDR to EPA or a state regulatory agency that a release of hazardous substances poses an immediate threat to human health. The advisory includes recommended measures to reduce exposure and reduce the threat to human health.
Pulmonary
Pertaining to the lungs, as in pulmonary fibrosis or pulmonary edema.
Purine
A class of aromatic organic chemical compounds with a double ring: a pyrimidine ring with a second, 5-atom ring sharing the carbon atoms of pyrimidine at locations 4 and 5, and with -NH-CH=N- connecting those. Purines are very common in nature. In particular, DNA nucleobases adenine and guanine are purines. Other well–known purines are caffeine and uric acid.
Pyrimidine
A class of aromatic organic chemical compounds containing a single 6–atom ring, with nitrogen in positions 1 and 3. DNA bases cytosine, thymine, and uracil are pyrimidines.
Pyrolysis
Chemical decomposition produced by heating, as in a fire.
Pyrophoric
A substance that can spontaneously burn when exposed to air. It is not only atmospheric oxygen that ignites them: they may also burn more intensely if a CO2 fire extinguisher is used on them, or if they are exposed to water (liquid or vapor). Not a household item, but this type of material is often used in chemical manufacturing.

return to the glossary alphabetic index
Q (symbol)
Q or ℚ represents the set of all rational numbers. In physics, Q represents heat energy.
Q (factor)
Originally indicating the "quality" of a resonant circuit, or in general any oscillator, it is today nearly always just referred to as "Q" or the "Q factor." Q is a strictly positive dimensionless quantity. In amateur radio usage, Q most commonly refers to how "sharp" or "tight" an electrical circuit's frequency response is: a high Q circuit has narrow bandwidth and high selectivity. One definition for Q is the ratio of the resonant (peak) frequency to the half–peak–power (-3 dB) bandwidth (in the same units). Q can also be computed as the ratio of the circuit's reactance to its resistance.

High Q is not always desirable (or "high quality"). For example, one might well wish a general–use antenna to have low Q, and a correspondingly wide bandwidth. For further details on this subject, including applications of Q in acoustics, mechanics and other non-electronic fields, see the Wikipedia external link article on the subject.
Q signals
Q signals are a standardized set of three-letter codes; "Q" is the first letter of each code. Originally developed for telegraphy, as shortcuts in Morse code, they are often used for brevity in informal and casual amateur radio voice transmissions. They are, however, deprecated when used outside that scope, such as in emergency communications, since they are in effect "jargon" and likely not to be understood by a general population. For a list of Q signals commonly used in amateur radio, see this Wikipedia external link table.
Quaternion (number)
 ×   1  i j k
1 1 i j k
i i −1 k j
j j k −1 i
k k j i −1
An extension of complex numbers, also known as Hamiltonian numbers, whence the symbols H amd ℍ for them. Whereas complex numbers extend real numbers to represent 2-dimensional concepts effectively (see in particular the entry for impedance), the quaternions are especially useful in describing rotations in 3-dimensional space. Unlike reals and complex numbers, quaternions are not commutative. In addition to i as found in complex numbers, there are multipliers j and k. The relationships between these are as shown in the table on the right. Note that i⋅j⋅k = i² = j² = k² = −1. Note also how multiplication of quaternions is not commutative: i⋅j=k, but j⋅i=−k. Just as a complex number can be expressed as a+bi, a and b real, so a quaternion can be written as a+bi+cj+dk, with a, b, c and d real. The first element is known as its pure real scalar part, and the remainder as its pure imaginary (3-)vector part.
Quarantine
The temporary segregation from the general population, whether voluntary or compulsory, of persons, other animals, or physical objects who or which may have been exposed to a contagious disease, to prevent further spread of the disease. The term originated from Venetian Italian, indicating a 40-day period for the separation, but in practice the period of separation can be quite variable. In strict usage, "quarantine" is distinguished from "isolation," in that the ones quarantined may or may not be or become ill from the disease.

return to the glossary alphabetic index
R (symbol)
R is used as the symbol in electronics formulas representing electrical resistance. R or ℝ represents the set of all real numbers.
RACES
Radio Amateur Civil Emergency Service. Volunteer organization of amateur radio operators organized under a sponsoring government agency, typically an ESDA or an EMA. RACES members are prepared, trained and equipped to assist with communications in an emergency, when activated by the sponsoring agency. See also ARES.
Radio
As used in this glossary, the adjective "radio" refers generally to any electromagnetic radiation of frequency less than that of light that is deliberately used to transmit information. As a noun, it thus includes (broadcast) radio and television receivers, RFID tags, satellite communications, radar, cell phones, garage door openers, Wi-Fi, GPS receivers, remote car starters, and so on. The upper radio frequency limit is around 300 GHz, at the extreme lower edge of infrared light. The lower limit is in the ELF range. See the entry for Radio Frequency.
Rational (number)
A number that can be expressed as a fraction; that is as a ratio of two integers. Designated Q. Rational numbers constitute an infinitely countable set of numbers. Real numbers that are not rational are called "irrational," and since real numbers are uncountable, "almost all" of them are irrational.
Raster
A raster image is one that is stored as a dot matrix, a generally rectangular grid of colored points. Distinguished from a vector graphic image. Raster images are generally only usable within a limited range of sizes. They are, however, best suited to easy image display; thus html with its "img" tag assumes a raster image file format such as png, jpeg, gif or the like.
RCRA
The Resource Conservation and Recovery Act of 1976. Authorized the EPA to control hazardous waste from "cradle to grave," including its generation, transportation, treatment, storage, and disposal. The corresponding EPA regulations are in 40 CFR 240–299. RCRA also created a framework for management of non–hazardous wastes. In 1984, the Hazardous and Solid Waste Amendments (HSWA) were added to RCRA. This requires phasing out of landfill disposal of hazardous waste.
Reactance
(Electrical) reactance, measured in ohms, with symbol X, is the imaginary number component of impedance in an electrical circuit. It appears in two complementary forms: inductive, symbol XL=2πfL, and capacitive, symbol XC=1/(2πfC), where f is frequncy in hertz, L is inductance in henries and C is capacitance in farads. These reactances are due to presence in the circuit of inductance and capacitance, respectively. XL is taken to have values of multiples of +i (or +j if\ you're an EE), and XC has values of multiples of -i; thus for a given AC frequency, it is possible for inductive and capacitive impedance to cancel each other out. The frequency at which this occurs is known as the "resonant" frequency of the circuit. In general, X is frequency dependent.
Real (number)
A number that represents any point on a number line, including for example one represented by any arbitrary string of decimal digits. Designated R. If distinguished from a rational number, it is called "irrational," designated I, and is represented by an unending, non-repeating string of digits. Real numbers constitute an (infinitely) uncountable set. Compare the computer use of the term.
Recombination
Change of state from plasma to unionized gas. The reverse of ionization.
Recurrent
Of a medical condition, one that occurs or appears repeatedly or periodically, as opposed to acute or chronic conditions.
Resistance
(Electrical) resistance, measured in ohms, with symbol R, is the real number component of impedance. It is the only effective component in a DC circuit; or in an AC circuit without inductors or capacitors, real or effective.
Resolution
The smallest change in a physical quantity that results in a measurable change. Particularly noticeable on a measuring device with a digital readout that does not allow for interpolation. For that, the resolution is limited by the last displayed digit. Contrast with accuracy and precision.
RF
Radio Frequency. This is a rate of oscillation, typically of electromagnetic radiation signals or their associated alternating currents, that can range from a few hertz (so-called "ELF": Extremely Low Frequency signals) to hundreds of gigahertz (short of frequencies that would be otherwise called "infrared light"). The ITU has definitions for each radio frequency band; each band is an order of magnitude higher in frequency and shorter in wavelength. Here is the ITU list, showing the band code and designation, followed by the frequency range, the wavelength range, and my notes on any other identifying information:
  • ELF Extremely Low Frequency; 3-30 Hz; 10-100 Mm
  • SLF Super Low Frequency; 30-300 Hz; 1-10 Mm; submarine communications
  • ULF Ultra Low Frequency; 300 Hz-3 kHz; 100 km-1 Mm
  • VLF Very Low Frequency; 3-30 kHz; 10-100 km
  • LF Low Frequency; 30-300 kHz; 1-10 km; navigation, weather, time
  • MF Medium Frequency; 300 kHz-3 MHz; 100 m-1 km; AM radio broadcast
  • HF High Frequency; 3-30 MHz; 100-10 m; "shortwave" broadcasts, CB
  • VHF Very High Frequency; 30-300 MHz; 1-10 m; FM broadcast, few TV
  • UHF Ultra High Frequency; 300 MHz-3 GHz; 10 cm-1 m; most TV broadcast
  • SHF Super High Frequency; 3-30 GHz; 10-100 mm; microwave, cell phone
  • EHF Extremely High Frequency; 30-300 GHz; 1-10 mm; millimeter wave
  • THF Tremendously High Frequency; 300 GHz-3 THz; 0.1-1 mm; sub-millimeter
RfC, RfD
Reference Concentration and Reference Dose. US EPA estimates, with uncertainty or safety factors built in, of the daily lifetime environmental concentration or dose of a substance that is unlikely to cause harm in humans. The US EPA uses BMD techniques to determine these values. See also ARfD, and ADI.
RFID
Radio Frequency IDentification. Term applies to a variety of passive or active devices that contain electronically coded identification information, and which respond to radio signals that request that identification information. RFID tags are used to track packages, identify pets, and for automated toll collection on the road, among many such applications.
Ribose
structures of sugars ribose and deoxyribose Pentose (formula C5H10O5) sugar that inter alia is a central component of RNA and DNA. Structures of the RNA and DNA (deoxyribose) versions are shown at the right. Note that the difference is on the 2' carbon: deoxyribose has a hydrogen in place of a hydroxyl (-OH) group (hence one fewer oxygen: "deoxy"). In an RNA or DNA molecule, the ribose is ester linked to one of the nucleobases at the ribose's 1' carbon; the ribose groups are themselves connected into the long RNA and DNA chains via ester links at their 3' and 5' carbons to a phosphate group.
Riemann hypothesis
Has nothing much to do with anything else in this glossary, but is fascinating as one of the few unsolved mathematical ideas. It says that the non-trivial roots of ζ(s) all have real part ½. Widely assumed to be true in proving other mathematical hypotheses, particularly with regard to prime number distribution, it has resisted proof itself for a century and a half.
Ring
A mathematical (algebraic) structure. It consists of a commutative (aka abelian) group plus a second binary operator that may be applied to any pair of elements of the set. An example ring is (as with the group) the set of integers (ℤ) and addition operator, plus also the multiplication operator. The second operator must have four properties. (1) Closure: the result of applying the second operator to any two set elements must also be in the set. (2) Associative: as with the group this means that when there are two or more operators in a row, the order in which the operators are applied is irrelevant. The order of the elements themselves is relevant unless like the example, the ring is also commutative. (3) Distributive: readily represented by the example ring: ∀ x,y,z ∈ ℤ, x⋅(y+z) = (y+z)⋅x = x⋅y+x⋅z. Note that it is the second (new) operator that is distributive over the group operator: x+(y⋅z) ≠ (x+y)⋅(x+z). (4) Identity: the second operator, like the first, has an "identity" element, such that applying that element to any element of the set via that operator leaves that set element unchanged. In the example ring, the multiplicative identity element is the number one.
RITA
The Research and Innovative Technology Administration external link of DOT was created in 2005 to coordinate and manage the department's research, and to expedite implementation of new technology.
RN
The Registry Number used by CAS to identify chemicals.
RNA
Ribonucleic Acid. Used in all living organisms as templates for making proteins in cells, in regulating gene expression, as catalysts for cellular reactions and as components with protein of other catalysts, among many functions. Its structure is a (usually) single-stranded polymer of nucleotides. In organisms, RNA is transcribed from sequences of the nucleotides in DNA molecules. See ATP for an example of the structure of an RNA nucleotide (adenosine monophosphate). Other RNA nucleotides commonly use—instead of adenine— cytosine, guanine or uracil.
RQ
Reportable Quantity. Any release of one or more of the roughly 800 CERCLA or 360 EPCRA hazardous substances that equals or exceeds this quantity (RQ) in any 24–hour period must be reported to the NRC at the EPA. The RQs are adjusted to one of five levels: 1, 10, 100, 1000, or 5000 pounds. EPA bases adjustments to the RQs on the intrinsic characteristics of each hazardous substance, such as the aquatic toxicity, acute and chronic toxicity, ignitability, reactivity, and potential carcinogenicity. An RQ value is established for each of these characteristics of a hazardous substance, with the most stringent RQ value (i.e., the lowest quantity) becoming the final RQ or reporting trigger for that hazardous substance.
RSPA
The research functions of the Research and Special Programs Administration of DOT were replaced in 2005 by RITA. The pipeline safety function was moved to PHMSA. The OET became part of the office of the Secretary.
RTECS
Registry of Toxic Effects of Chemical Substances, published by NIOSH. Has toxicity data on numerous materials, with references to the studies that generated the data.

return to the glossary alphabetic index
S (symbol)
S is the symbol for the SI unit of conductance (the inverse of resistance) known as the siemens, named for Ernst Werner von Siemens. Units of the Siemens are Ω-1, or A/V. In physics, S represents entropy. S is also the symbol for chemical element sulfur.
SARA
Superfund Amendments & Reauthorization Act of 1986. Title III of SARA is EPCRA, under the provisions of which the LEPC was organized.
Saturated
Of an organic chemical compound, means that the carbon atoms are all linked to each other by single bonds. If there are any double or triple bonds between carbon atoms, the compound is described as "unsaturated." A fat is saturated or unsaturated depending on the links within the constituent fatty acids.
Scalar
A "simple" numeric value, invariant under coordinate system rotation. Also (rather whimsically) decribable as a zero-rank tensor.
second [time]
The SI base unit of time interval. Symbol is s. Defined as the duration of 9 192 631 770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the Cs 133 atom at 0 K, located at a fixed position on the gravitational equipotential of the earth's geoid at mean sea level. Which I'll admit is as clear as mud to non geeks. Sorry folks, but that's the way it is. The bits about "fixed position" and "sea level" are there to allow for effects of relativity. Given that the earth's orbit around the sun and the moon's about the earth are elliptical, and thus the sun's and moon's gravitational fields at the earth vary, I'm surprised the definition doesn't also specify the time of month and year. Also, what happens if sea level rises? Just asking.
Selectivity
This definition applies to the term's use in radio receiver technology. Selectivity measures how well a radio receiver responds only to the frequency to which it is tuned, rejecting nearby ("adjacent channel") radio signals. Tuned circuits with a high Q factor will tend to be more selective, though there are other means of increasing selectivity.
Sensitivity
Sensitivity of a test, also known as the recall rate, measures the proportion of actual positives which are correctly identified as such by the test. Corresponds to a type II or β probability statistical error (false negative: the test incorrectly retains a null hypothesis), a significantly large value of which would indicate poor sensitivity. Contrast with specificity. Consider a drug-testing model: a highly sensitive test will detect nearly all who have used the drug being tested for; it will have a low β error rate.
Sensu
Latin ablative singular of sensus [4]: "in the sense [meaning] of." Used with an adjective indicating the intended breadth of meaning. For example, "sensu stricto" = "in the limited/restricted sense" means what "literally" is often thought to mean literally (though the Oxford English Dictionary also recognizes an emphatic sense of that word). "Sensu lato" means "in the broad sense" or perhaps "loosely speaking." "Sensu latiore," "in the broader sense" means roughly "whatever you care to make of it."
SEOC
State Emergency Operations Center. See also EOC.
SERC
State Emergency Response Commission. A general term used to designate the state agency responsible under EPCRA for organizing the LEPC and collecting hazardous materials information. In Illinois, the SERC is IEMA.
SHF
Super High Frequency radio waves, specifically those with frequencies of 3-30 GHz, or wavelengths of 10-100 mm (around an inch).
SI
le Système international d'unités (the International System of units). The formal name for the modern metric system, adopted in 1960 by the 11th CGPM (General Conference on Weights and Measures). SI is founded on base units including the second (symbol: s), meter (m), kilogram (kg), kelvin (K), ampere (A), mole (mol), and candela (cd). Wherever possible, values listed on this web site are given in SI base or derived units, or multiples or sub-multiples thereof, usually by factors of integer powers of 1000.

The SI symbols listed in this glossary are just that: symbols, not abbreviations. Capitalization of the symbols is significant, they are not pluralized, and they are never followed by a period (hardly ever; unless, of course, they occur at the end of a sentence). If you should write, say, "Ms" for "meters," you would have actually written the symbol for megasecond. I often see "Kgs" (instead of kg) for kilograms; this actually represents a kelvin⋅gram⋅second, whatever that might be. Whatever … it's simply wrong.
SIP
Shelter In Place. Remaining in a location where hazardous materials are in the environment, while taking precautions to minimize exposure to those materials.
SIRT
[IL] State Interagency Response Team.
SNMP
Simple Network Management Protocol. An OSI level 7 (application layer) computer network protocol that provides monitoring and management of IP network devices, especially routers, switches, servers, printers and the like. Can also be used at the workstation level, but those are more commonly handled by DHCP.
Solvent / solute / solution / soluble
A solvent is a substance that dissolves another substance or substances to form a solution (a homogeneous mixture). The solvent is the component in the solution that is present in the largest amount, or is the one that determines the state of matter of the solution. Solvents are often, but not always, liquids. They can also be gases or solids. The material dissolved in the solvent is called the "solute." Together, the solvent and solute comprise the "solution." A solute substance that readily dissolves in a particular solvent is said to be "soluble" in that solvent. For example, a substance that dissolves in water is said to be "soluble in water," or more simply "water soluble."
Specificity
Specificity of a test measures the proportion of negatives which are correctly identified by the test. Corresponds to a type I or α probability statistical error (false positive: the test incorrectly rejects a null hypothesis), a significantly large value of which would indicate poor specificity. Contrast with sensitivity. Consider a drug-testing model: a highly specific test will rarely give a positive result for a non-user; it will have a low α error rate.
SPEGL
Short–term Public Emergency Guidance Level. An acceptable concentration of a substance for unpredicted, single, short–term exposure of the general public to that substance in emergencies. Developed by National Academy of Sciences, NRC.
SSB
Single Side Band radio signal modulation. A pared-down form of AM, which for efficiency and minimal bandwidth, transmits only one "side" (either upper or lower) of the full AM signal, and which usually—always in amateur radio technique—suppresses the carrier as well. Downside of SSB is that lacking a carrier reference, receiving the signal is bit more fussy. Also one has to be aware which of the sides is being used. Common practice conventions denote this last factor.
SSID
As used here, means "sub-station Identifier"; the same acronym is also used in networking. A sub-station ID for an amateur radio call sign is a number from 1 to 15 appended after a hyphen to the base call sign. It indicates a separate transmitter used concurrently with another under the base call sign to distinguish it. For example, I may be operating a voice or Morse code transmission on one frequency as NE9ET while sending APRS packets reporting my status and location on another (typically 144.390 MHz in the US) as NE9ET-9.
Staging area
The location designated by the ICS Liaison Officer or Incident Commander where personnel and equipment not immediately needed for an emergency response are organized and kept ready for use.
Starch
A mostly insoluble polysaccharide (many sugar unit) organic chemical compound made up of glucose subunits bonded by chemical condensation. There are two, related components of starch, both deriving from glucose: amylose (helical) and amylopectin (branched). Both are hydrolysed by amylase. Starch serves as a compact food reserve in plants, but is also usable as food by most animals. Humans have also found uses for starch in cooking and in manufacturing—particularly of paper and textiles.
State of matter
For our purposes, one of solid, liquid, gas or plasma. Most substances can exist, depending on temperature and pressure, in any one or a combination of these states.
STEL
Short–Term Exposure Limit. The concentration of a substance to which people can be exposed continuously for a "short" period of time without suffering from (a) irritation, (b) chronic or irreversible tissue damage, or (c) narcosis of sufficient degree to increase the likelihood of accidental injury or to impair self–rescue.
Stereoisomer
Stereoisomers are chemicals with the same molecular formula (isomers) and sequence of atoms, differing only in the 3-dimensional orientation of the atoms. Contrasted with structural isomers, such as butane and isobutane (2-methylpropane). Biological stereoisomers are usually enantiomers, that is mirror images of each other. In nature, usually only one of these forms is biologically active.
STP
No, not the automotive petroleum products manufacturer or any of several other possible interpretations. Here, it has the meaning as in chemistry and physics of "Standard Temperature and Pressure"—the conditions under which physical properties are commonly measured. Defined as 0 °C temperature and 101 325 Pa atmospheric pressure.
Strain
A deformation of a solid object due to an applied force. The force is usually referred to technically as a "stress," although in common usage these two terms are often equated.
Sublime
To change state directly from a solid to gas, without passing through a liquid phase. The opposite of deposition.
Sugar
Generally, a short-chain, water soluble, sweet carbohydrate, often found in foods. Also used to mean specifically "table sugar" or sucrose. Sucrose is made up of two simple sugars, fructose and glucose, and so is called a disaccharide. Lactose (milk sugar, which many adults cannot digest) is another disaccharide, made up of galactose and glucose. The sugar ribose is a component of the backbone of RNA; and the similar deoxyribose (less one oxygen atom, as its name implies) is similarly a component of DNA. See also starch and cellulose.
Superfund
Set up by the US Congress to fund remediation of hazardous waste conditions. For connections to LEPC, see under headings CERCLA and SARA.
SWR
Standing Wave Ratio. Also known as Voltage Standing Wave Ratio (VSWR). It is the ratio of the amplitude (in volts, for an electronic system) of the maximum in a standing wave to an adjacent minimum within an electrical conductor. For the case where there is no standing wave, the maximum equals the minimum, and SWR=1. In any other case, SWR>1. For the best impedance match and effective transfer of electrical power in a system, one wants the SWR to be as close as possible to 1. The standing wave itself is created by the interference of the original (forward) signal in the conductor with a reflected one from an impedance mismatch. Since impedance is frequency dependent, so is SWR.
Symptom
A departure from normal body function observed by a patient, which is a sign of disease or abnormality. Note that results of medical tests (e.g., a blood test for diabetes) are not considered symptoms but signs or indications of these conditions, since the test result would not be directly noted by the patient. A medical condition which results in symptoms is called symptomatic, otherwise it is asymptomatic (the patient is not aware of the condition until it is diagnosed through medical tests).
Synergistic
A biologic response to multiple substances where one substance increases the effect of another substance. The combined net effect of the substances acting together is greater than the sum of the effects of the substances acting by themselves [compare additive effect and antagonistic effect].

return to the glossary alphabetic index
T (symbol)
In physics, t is the symbol for time.
Tachycardia
Increased heart beat, generally meaning more than 100 pulses per minute. Compare to bradycardia.
TCP/IP
Internet Protocol Suite (commonly known as TCP/IP) is the set of communications protocols used by the Internet and similar networks. It is named from the two most important protocols in it: the [OSI layer 4 = transport layer Transmission Control Protocol (TCP) and the OSI layer 3 = network layer Internet Protocol (IP). The address used by IP is known as an "IP address," which corresponds for example to an Internet domain name. The TCP address is known as a "port," which corresponds to an OSI application layer protocol such as http or ftp. The combination of an IP address and a port is known as a "socket."
TDLO
Toxic Dose LOw; the lowest dose at which toxicity occurred.
Tensor
A mathematical object that extends the concept of a vector. A tensor in an m-dimensional space can have an arbitrary integer number of indices (n≥0); it then has mn conponents, and is known as an n-th rank tensor. If n=0 (one component), it is a zeroth-rank tensor, also known as a scalar value. For n=1, it is an ordinary vector. If n=2, it us usually called a matrix. So the term tensor is typically reserved for those with n≥3. Notation of a tensor A looks like Aijk ... λμν .... The lower indices (i,j,k etc.) are known as "covariant" indices, and the upper (here Greek) ones as "contravariant" indices.
Teratogen
A substance that causes defects in development between conception and birth. A teratogen is a substance that causes a structural or functional birth defect.
Thiol
An organic chemical compound which contains one or more sulfhydryl (aka thiol) groups. A sulfhydryl group is -SH, which is analogous to the hydroxyl -OH group of an alcohol. For an example, see entry DMSA. Thiols are often referred to by an older designation as "mercaptans" from a Latin phrase meaning "capturing mercury." As with DMSA, binding to heavy metals such as mercury is a common use for thiols. As to the odor of thiols, suffice it to say that skunk spray consists mostly of low molecular weight thiols.
Thymine
structure of nucleobase thymineOne of the pyrimidine nucleobases in the nucleotides of DNA, whose structure is shown on the right. In RNA, uracil is used instead. The corresponding nucleoside to thymine is [deoxy]thymidine, for which the RNA equivalent is uridine.
Tier II Report
The Emergency and Hazardous Chemical Inventory form that must be submitted annually under EPCRA regulations (§312) by any facility that has on hand substantial quantities—as defined by the EPA — of hazardous substances. The form lists the substances and quantities, and provides employee contact information. Copies of this form go to the LEPC, the SERC and the local fire department. A Windows program, tier2submit.exe, allows this report to be created easily.
TIH
Toxic by inhalation. Describes a gaseous material that is toxic when breathed. Some water-reactive materials (WRM) that are TIH produce additional TIH substances when exposed to water (e.g. BrFl3, SOCl2).
Time
Where (when) do I start? Many large books have been written to explain time; this is no place for an epitome of them. So to start, I observe that SI measures time intervals in seconds. Humans use a variety of other units also: minutes, hours, days, weeks, months, centuries, etc. [But not light years or parsecs]. There is no standard clock, however (see below). Even on Earth we have dozens of time zones, though UTC has pride of place among them.

Newton (wrongly) supposed that time was a universal constant. Einstein's special relativity showed us that elapsed time depends on one's path in spacetime. Fortunately and in practice, we and most of our artifacts do take much the same path. But not all. GPS satellites, with their high precision atomic clocks, go somewhat faster than normal, and also travel in a weaker gravitational field. So their clocks differ from ours in small but significant amounts.

In special relativity, time is just another coordinate in spacetime, making time interchangeable with space coordinates. Two observers will likely not agree on what events (as defined by all four coordinates) are simultaneous. For events that are not causally connected—that is ones far enough distant from each other that information at the speed of light could not pass between them—the observers may even differ on their order of occurrence.

The only constant in special relativity is the spacetime interval (Δs) between the events, defined as Δ2s = Δ2x + Δ2y + Δ2z − c2⋅Δ2t, with dimensions of length. This formula, by the way, with positive values for spatial and negative for time values is known as the "space-like convention" with a (−+++) metric, in which the first sign is for time. The reverse convention, with positive time and metric (+−−−) is equivalent, but not discussed here. (Note that in the space-like convention, ordinary causally connected events—in which the time component is larger than the spatial distance—have Δ2s<0, and thus imaginary number interval lengths.)

I'll conclude this grossly oversimplified explanation—for one thing, I've assumed flat (Euclidean) space unaffected by general relativity—by quoting someone, maybe J A Wheeler and maybe Woody Allen, as "Time is nature's way of keeping everything from happening at once." Hard to beat that.
Tissue
In biology, a collection of cells, not necessarily identical, that together perform a specific function in an organism. Tissues are intermediate in level of organization between cells and organs.
TLV®
Threshold Limit Value. The ACGIH guideline for the atmospheric concentration of a substance to which nearly all U.S. workers can be exposed day after day without adverse effect. There are more than 700 of these.
TMDL
Total Maximum Daily Load. The largest amount of a substance that may be added to a waterway in one day under the provisions of the National Clean Water Act. This value is determined by the state, with oversight by the EPA.
ton (tonne)
Apart from metaphorical use to mean "a lot" this is a unit of measure that is seriously ambiguous. The simplest case is that of the "metric ton" (often spelled "tonne" to disambiguate it) which is a mass of 1000 kg = 1 Mg. Note that this ton is "metric" but is not SI. The first problem is that, in addition to mass, the term "ton" can be a measure of weight, volume, even energy (as in atomic bombs) or power (as in refrigeration). We stick to mass (and related weight) here.

Next, in the US and Canada a ton of weight is taken to be 2000 pounds (also known as a "short ton"). In the UK it is 2240 pounds (a "long ton" = 160 stone). Then there was once the "ton longweight" at 2400 pounds. Note that the metric ton can be taken to be approximately 2205 pounds; but it is not strictly comparable, since "pound" is a unit of weight, and thus in principle varies with gravity; and the metric ton is an invariant unit of mass. The ton ambiguity problem is one of the many reasons I stick to SI units whenever possible.
Toxic[ity]/Toxin
Toxic means capable of causing harmful effects to living organisms under certain circumstances of exposure. Roughly equivalent to "poisonous" or "venomous." Toxicity is the degree to which a substance is toxic. A toxic substance is often called a "toxin" (poison or venom). A substance is considered to be a toxin if there is evidence that it is a health hazard at specified doses, especially if it is listed in the RTECS. Note that the term "toxin" in some contexts is restricted to poisons of biological origin. "Toxic" is not so restricted. Nor is "toxicology," the scientific study of poisons.
TPQ
Threshold Planning Quantity (of an EHS.) The maximum amount, in pounds, of an EHS present at any one time at a facility during the year. Depending on the substance, this amount can range from a lower quantity of 1 to 1 000 pounds to an upper quantity of 10 000 pounds. If a facility has any EHS present in an amount greater than the established TPQ, the facility must comply with reporting provisions of EPCRA §301, §302, and §303
Transcendental (number)
See algebraic numbers.
Transitive
A relationship between members of a set (mathematical or otherwise) such that if the relationship holds between set members a and b, and also between members b and c, then it also holds between a and c. Less wordy examples are: a=b, b=c, ∴ [therefore] a=c; a<b, b<c ∴ a<c; a implies b, b implies c, ∴ a implies c. Holds for many similar types of relationship, such as "is an ancestor of." But not all. An example of an intransitive relationship might be "is a parent of." Another interesting example of intransitivity is the relationship "is the same biological species as." Since the ability to interbreed is often used as the criterion of species membership, then so-called ring species external link are intransitive with respect to interbreeding.
Transmissibility
The transmissibility of a pathogen is its capacity for "vertical" transmission, viz. perinatally from mother to child. Contrast with infectivity.
TRI
Toxics Release Inventory. EPCRA §313. Requires certain facilities to submit a form annually to the EPA and SERC covering releases and waste management of toxic chemicals. The information is available to the public external link, although it is not up to date: there is around a two year delay in posting of results.
TSCA
Toxic Substances Control Act, 40 CFR 700–799. Gives the EPA jurisdiction to control the use of and exposure to industrial chemicals not subject to other laws.
TWA
Time–Weighted Average. An arithmetic mean value taken over a time period. Multiply each value by the number of time units in which that value occurred, sum the products, and divide the sum by the total number of time units.

return to the glossary alphabetic index
UCS
Unified Command Structure. An expanded version of the concept of ICS. It is a system for managing a multi–jurisdictional emergency response situation, made up of key officials from each affected jurisdiction plus the ICS functional departments. A UCS is led by a Unified Commander (UC).
UEL
Upper Explosive Limit. The atmospheric concentration of a flammable hazardous material above which it is too rich in fuel (deficient in oxygen) to be subject to explosion. See also LEL. Note that ventilation of an area which contains a flammable substance above this concentration can bring the concentration into the explosive range, and result in a sudden fire or explosion. Known also as Upper Flammable Limit (UFL).
UHF
Ultra High Frequency radio waves, specifically those with frequencies of 300-3000 MHz (0.3-3 GHz), or wavelengths of 0.1-1 m (10-100 cm).
Ultraviolet (light)
"UV". The part of the electromagnetic radiation spectrum that is shorter in wavelength than that of visible light, and longer than X-rays, that is, between about 380 and 10 nm. We distinguish several sub-bands of UV:
  • UVA: 380-315 nm; "black light", not absorbed by ozone (O3) layer, visible to birds and insects
  • UVB: 315-280 nm; mostly absorbed by O3 layer
  • UVC: 280-100 nm; completely absorbed by O3 and atmospheric oxygen (O2) and nitrogen
  • Extreme UV: 100-10 nm; only seen in space, absorbed by O2

As indicated in the chart, most UV radiation is absorbed efficiently by O3, and most of the shorter wavelengths (<200 nm) also by ordinary molecular oxygen (O2). UVC wavelengths around 250 nm are effective in killing bacteria. Sunlight in space is about 10% UV, but absorption by the atmosphere, and particularly the ozone layer, reduces this to 3%—mostly UVA—at the earth's surface, even at mid-day.
Unicode
For most of my computer–using life, the 7–bit ASCII character coding was more than adequate, since I rarely had to print or display much more than the upper– and lower–case Roman alphabet, digits and common punctuation. The 8–bit extended version added Greek characters and some European accented variants of Roman characters, but not for example, Cyrillic. This webpage shows that further extensions become desirable for many technical texts.

The solution that the computer community, partiularly the Unicode Consortium external link, arrived at is intended to fix all such problems; in fact as many as the developers of Unicode could imagine. Unicode characters are up to 32 bits wide. This allows for an incredibly large set of distinct characters, of which some 110 000 are currently in use. As an example of what this allows, the entire set of Chinese ideographs (some 70 000 of them) fits comfortably into a corner of Unicode, as well as all the alphabets and syllabaries of the Indian languages, of Russian and related Slavic languages, plus the writing systems of Thai, Japanese, Korean, Hebrew, Arabic, Egyptian hieroglyphs, Braille and well, the writing systems of some languages you may have never heard of. Sorry, but Klingon is not yet officially included. Plus there is every mathematical symbol I've ever seen in print and some I haven't. To save space, the traditional ASCII character set still uses just one byte per character, but two or four bytes (16 or 32 bits) can be employed for more remote areas of the character set.
Uracil
structure of nucleobase uracilOne of the pyrimidine nucleobases in the nucleotides of RNA, whose structure is shown on the right. The corresponding nucleoside is uridine; note that the DNA equivalent is thymidine.
URL
Uniform Resource Locator. A Uniform Resource Identifier (URI) that specifies where an identified resource is available and the mechanism for retrieving it. A common example is a website page address; for my site the home page URL is "http://ne9et.net/index.html". The "http" part says to use the HyperText Transfer Protocol to retrieve a file called "index.html" from the root level of website "ne9et.net," and to interpret the file as written in a variety of HyperText Markup Language—in this case, as xhtml.
UTC
Coordinated Universal Time. What used to be called Greenwich Mean Time (GMT) about 50 years ago. The British continue to call it GMT, even though it no longer has anything much to do with the Royal Observatory at Greenwich, England. It is a consensus time between a number of atomic clocks located worldwide. It is thus no longer dependent on the slightly erratic (and gradually slowing) rotation of the earth, and the annual variations due to the earth's slightly elliptical orbit. The former is accommodated by the infamous "leap seconds." As to why it's called "UTC" rather than (say) "CUT," that's an international linguistic compromise. FYI, revision dates and times for my web pages are given in UTC.

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V (symbol)
V is the SI symbol for volt, and v is the symbol in physics for velocity.
v/v
A label attached to the concentration value of a substance in percent, ppm, ppb or the like, that indicates the value is concentration "by volume": so many volume units of the substance as a fraction of the total volume of the mixture.
Vector
In physics, a vector quantity is one that has both a magnitude (amount) and a direction (vs. a scalar quantity with only magnitude). This is similar to the more general mathematical vector, othewise known as a rank 1 tensor.

In biology, a vector can inter alia be an organism that transmits a pathogen to a host organism.

Vector graphics define an image in terms of geometric primitives such as lines, points, and shapes. Have an advantage over raster graphics in being scalable without loss of resolution. CAD packages use this form of image representation.
Velocity
The instantaneous rate of change (first derivative) of the position of a moving object with respect to time. Symbol is v. Since position is usually represented in physics formulas as "x," we have v=dx/dt. "Velocity" differs from "speed" in that the direction of motion is also significant—it is a vector quantity. Velocity times mass is momentum. See also acceleration.
venom
A toxin of animal origin that is injected into another animal's blood stream through a bite or sting ("envenomation"). Contrasted with poison.
Ventilation
Replacement of contaminated air with air from the surrounding area. Typically, the replacement air will be cleaner and/or contain more oxygen.
Ventral
Towards or on the front or lower ("belly") surface of an organism. Synonym is "inferior." Opposite of dorsal.
Ventricle
Adjective ventricular. The lower, larger chambers of the heart. Blood is fed from the smaller atria above them, which the ventricles then pump to the lungs (right ventricle), and to the body (left ventricle).
Vernier (scale)
A measuring tool that allows higher resolution measurements than can be read directly and otherwise unaided from a measuring device's native scale. Works when the native scale is linear. Named for its developer, Pierre Vernier, though pronounced "VER nee er." It uses a supplementary scale adjacent to the main one, with slightly different spacing, such that n divisions of the vernier scale cover n+1 divisions of the main scale. N is typically 10. The vernier scale line that precisely aligns with a main scale line indicates the interpolated final digit of resolution more accurately than could normally be estimated by eye.
VHF
Very High Frequency radio waves, specifically those with frequencies of 30-300 MHz, or wavelengths of 1-10 m.
Virulence, virulent
The ability of a pathogenic biological agent to cause disease harmful to its host, often severe enough to incapacitate or kill the host. Virulence is measured by the mortality rates associated with the disease, and/or by the ability of the biological agent to invade its host's tissues.
VOAD
Voluntary Organizations Active in Disaster. Generally refers to the state affiliates of NVOAD.
VOC
Volatile Organic Compounds. Organic compounds with a "fast" evaporation rate into the air. VOCs include substances such as benzene, toluene, methylene chloride, and methyl chloroform.
Volatilization
A general term for the state change of a substance into a gas. It covers both evaporation (from liquid to gas), and sublimation. A substance is "volatile" if it readily undergoes volatilization at ordinary temperatures.
volt
Symbol V; named for Alessandro Volta. This is the SI derived unit of electromagnetic force (EMF). Equal to a watt per ampere, or in SI base units, kg⋅m2⋅s-3⋅A-1.
VSAT
Very Small Aperture Terminal. It is a two-way satellite ground station with a dish antenna smaller than 3 m diameter.
VSMOW
Vienna Standard Mean Ocean Water. This is the standard for water used in defining the kelvin (and by extension Celsius) thermodynamic temperature scale. It specifies the isotopic composition of hydrogen (1H, 2H and 3H) and oxygen (16O, 17O and 18O). Despite the name, VSMOW is unlike ocean water in that it has no dissolved salts.
VSWR
See SWR.

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W (symbol)
W is the SI symbol for watt. In physics, W is the symbol for work.
w/w
A label attached to the concentration value of a substance in percent, ppm, ppb or the like, that indicates the value is concentration "by weight" (loosely speaking): so many mass units of the substance as a fraction of the total mass of the mixture.
W3C
World Wide Web Consortium. external link An international community that develops standards to ensure the long-term growth of the Web.
WAAS
Wide Area Augmentation System. Primarily an air navigation aid developed by the US Federal Aviation Administration (FAA) to augment the Global Positioning System (GPS), with the goal of improving its accuracy, integrity, and availability. Most commercial GPS receivers these days include the possibility of reception of the WAAS correction signals, making them correspondingly accurate.
WAI
Web Accessibility Initiative. external link An organization whose object is to develop strategies, guidelines, and resources to help make the Web accessible to people with disabilities. These web pages were designed and executed with WAI guidelines in mind.
WAN
Wide Area Network. A network that provides data links for computers that are located within a broad geographical area. Subspecies of WANs include MANs (Metropolitan Area Networks). Contrast with LAN.
WAP
Wireless Access Point. A device that provides access to a wireless network for devices such as computers, using standards such as Wi-Fi.
watt
Symbol W; named for James Watt. The SI derived unit of power. Although popularly primarily associated with electrical power, the watt is not defined in electrical terms, and can be used for any kind of power: automotive engines can be (and are) rated in watts (or kilowatts) as well as in, say, horsepower. Since the SI unit for work/energy is the joule, the watt is a joule per second, or in SI base units: kg⋅m2⋅s-3.

Apart from the ampere, which is an SI base unit, most SI electrical units include the watt directly or indirectly as part of their definition. (Notable exception: the coulomb, equal to an ampere⋅second).
WEEL
Workplace Environmental Exposure Level. Guidelines of the American Industrial Hygiene Association for substances that do not currently have a TLV established.
Weight
The force exerted on an object that has mass under the influence of gravity, or of an equivalent acceleration. Thus gravitational weight Wg = m⋅g, where m is mass, and g is the (local) value of the acceleration of gravity. On the earth's surface, g is a vector of magnitude 9.80665 m/s2, directed towards the earth's center of gravity. A key point is that weight is properly measured in force units, not mass ones (for example in pounds, but not in kilograms). Also, an object in orbit or freefall is (nearly) weightless, but not massless. Opinions differ on whether weight should be defined as a vector quantity (since force is a vector), or as just the scalar magnitude of the vector. If the latter, the formula becomes Wg = m⋅|g| . Take your pick.
WGS84
World Geodetic System, 1984 revision. This is the model of the earth's shape used by GPS. WGS84 also includes definition of a gravitational equipotential surface used to define nominal sea level. A marginally interesting factoid: under WGS84, the prime meridian no longer goes exactly through the Royal Observatory at Greenwich, England, but about 100 m east of it.
Whetstone
See Cobblestone.
Wi-Fi
A trademark of the Wi-Fi Alliance for a type of wireless Local Area Network based on the IEEE 802.11 standards. The Wi-Fi Alliance provides certification that a wireless device is compatible with the relevant standards.
WMD
Water Management District.
WMD
Weapon(s) of Mass Destruction.
Work
In physics, equivalent to energy, and like energy has SI units of joules. Symbol is W. Often taken to be the energy not dissipated as heat, thus dE=δQ − δW. See entry on energy for further details.
WRM
Water-Reactive Material.
WWV[B]
Radio stations operated by NIST on frequencies of 2.5, 5, 10, 15 and 20 MHz (WWV) and 60 kHz (WWVB). The WWV stations, located near Fort Collins CO, plus the related Kekaha HI station WWVH, broadcast a variety of information, particularly UTC time signals. The carrier frequencies are used to calibrate radio transceivers, and the audio tones used are also standards (including A=440 Hz). Along with the beeps each second, there are regular voice broadcasts that provide a variety of technical information. The WWVB signals are used to synchronize a variety of commercially available clocks and clock radios; these are often loosely called "atomic" clocks. See NIST's WWV external link and WWVB external link web pages for details.

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X (symbol)
X is used as the symbol in electronics formulas representing electrical reactance. In physics fomulas, x is often the symbol for spatial position.
X Window System
Based on the X11 protocols developed originally at MIT, this is a suite of tools for developing cross-platform GUI applications. Personal note: I wrote a great deal of code in my last years of employment for PC users to access UNIX-based systems, using X (as it is known for short). The PC runs an application called an X Server that takes input from clients on the remote system over a network and renders it graphically.
XHTML
eXtensible HyperText Markup Language. An XML-based markup language that extends Hypertext Markup Language (HTML). By basing the web site markup language on XML, it becomes possible to incorporate the existing variety of XML formatting tools. The structure of XHTML is also more strictly defined and interoperable than the rather loose HTML standards. My web site pages are written in conformance with XHTML level 1.1.
XML
eXtensible Markup Language. A family of languages for "text markup," that is, for encoding the structure of a text document in computer-readable form. Commonly used XML-based languages include XHTML, RSS, SOAP, and the native Open Office document file storage formats.

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Y (symbol), Yank
Yank is the name given to the instantaneous rate of change of force. Thus the second derivative of momentum. Equal to jerk times mass: Y=j⋅m. Further derivatives of momentum have been named Tug (3), Snatch (4) and Shake (5).
Z (symbol)
Z is used as the symbol in electronics formulas representing electrical impedance. Z or ℤ represents the set of all integers. In chemistry, the atomic number (number of protons in the atom) of an element.
Z list
OSHA's Toxic and Hazardous Substances Tables Z-1, Z-2 and Z-3 of air contaminants. These tables give the TWA, STEL and Ceiling values for the listed materials.
Zero air
Air purified to a concentration of less than 0.1 ppm total hydrocarbons.

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