**GLOSSARY**

**Absorption** The passing of a substance into the circulatory system of
the body. Also used specifically to refer to entry of toxicants through
the skin.

**ACGIH** American Conference of Governmental Industrial Hygienist

**Acute Exposure** An exposure to a toxic substance which occurs in a
short or single time period.

**Acute Toxicity** Any poisonous effect produced by a single short-term
exposure. The LD~50~ of a substance (the lethal dose at which 50 percent
of test animals succumb to the toxicity of the chemicals) is typically
used as a measure of its acute toxicity.

**Additive Effect** A biological response to exposure to multiple
chemicals which is equal to the ***sum*** of the effects of the
individual agents.

**Adsorption** The bonding of chemicals to soil particles or other
surfaces.

**Aerosol** A solid particle or liquid droplet suspended in air. An
aerosol is larger than a molecule and can be filtered from the air.

**Antagonism** The situation in which two chemicals interfere with each
other's actions, or one chemical interferes with the action of the
other.

**Aquifer** An underground bed, or layer, of earth, gravel, or porous
storage that contains water.

**Asphyxiants** Chemicals that starve the cells of an individual from
the life-giving oxygen needed to sustain metabolism.

**Biodegradable** Capable of decomposing quickly through the action of
microorganisms.

**Biomagnification** The tendency of certain chemicals to become
concentrated as they move into and up the food chain.

**Boiling Point** The temperature at which a liquid will start to become
a gas, and boil. A chemical with a low boiling point can boil and
evaporate quickly. If a material that is flammable also has a low
boiling point, a special fire hazard exists.

**Carcinogen** A chemical or physical agent that encourages cells to
develop cancer.

**Central Nervous** Toxicants that deaden the central nervous system
(CNS),

**System Depressants** diminishing sensation.

**CERCLA** The Comprehensive Environmental Response, Compensation, and
Liability Act of 1980---the Federal statute that authorized "Superfund."
Administered by EPA, the law provides funding for cleanups and emergency
response actions for hazardous substances at the worst hazardous waste
sites in the United States. CERCLA is also significant because it set
the first criteria for notification of emergencies involving hazardous
substances. Superfund regulates abandoned waste disposal sites; for
***active*** disposal site regulation, see RCRA.

**CHEMTREC** Chemical Transportation Emergency Center, a service
operated by the Chemical Manufacturers Association to provide
information and other assistance to emergency responders.

**Chronic Exposure** Process by which small amounts of toxic substances
are taken into the body over an extended period.

**Command Post** A centralized base of operations established near the
site of a hazardous materials incident.

**Corrosive** A chemical that destroys or irreversibly alters living
tissue by direct chemical action at the site of contact.

**Decontamination** The process of removing or neutralizing contaminants
that have accumulated on personnel and equipment. This process is
critical to health and safety at hazardous waste incidents.

**Dermal Exposure** Exposure to toxic substances by entry though the
skin.

**Dose** The quantity of a chemical absorbed and available for
interaction with metabolic processes.

**Epidemiology** Investigation of factors contributing to disease or
toxic effects in

**Studies** the general population.

**Evaporation Rate** The rate at which a chemical changes into a vapor.
A chemical that evaporates quickly can be a more dangerous fire or
health hazard.

**Exercise** A simulated emergency condition carried out for the purpose
of testing and evaluating the readiness of a community or organization
to handle a particular type of emergency.

**Explosive** A chemical that causes a sudden, almost instantaneous
release of pressure, gas, and heat when subjected to sudden shock,
pressure, or high temperatures.

**Extremely Hazardous** Any one of more than 300 hazardous chemicals on
a list compiled **Substance (EHS)** by EPA to provide a focus for State
and local emergency planning

activities.

**Hazard Class** A group of materials, as designated by the Department
of Transportation, that share a common major hazardous property such as
radioactivity or flammability.

**Hazardous Materials** A team of specially trained personnel who
respond to a hazardous

**Response Team (HMRT)** materials incident. The team performs various
response actions including assessment, firefighting, rescue, and
containment; they are ***not*** responsible for cleanup operations
following the incident.

**Incident Commander** The person in charge of on-scene coordination of
a response to an incident, usually a senior officer in a fire
department.

**Inversion** An atmospheric condition caused by a layer of warm air
preventing cool air trapped beneath it from rising, thus holding down
pollutants that could otherwise be dispersed.

**Irritant** Chemicals which inflame living tissue by chemical action at
the site of contact, causing pain or swelling.

**LD~50~** The calculated dosage of a material that would be fatal to
50% of an exposed population (Lethal Dose 50%).

**Leachate** Material that pollutes water as it seeps through solid
waste.

**Leaching** The process by which water dissolves nutrient chemicals or
contaminants and carries them away, or moves them to a lower layer.

**LEPC** Local Emergency Planning Committee.

**LOAEL** The Lowest Observed Adverse Effect Level, i.e., the lowest
dose which produces an observable adverse effect.

**Medium** The environmental vehicle by which a pollutant is carried to
the receptor (e.g., air, surface water, soil, or groundwater).

**Melting Point** The temperature at which a solid material changes to a
liquid. Solid materials with low melting points should not be stored in
hot areas.

**Mg** Milligram, a metric unit of mass, one thousandth of a gram: 1 mg
= 0.001 g = 1000 μg.

**Mm^3^** Milligrams per cubic meter. The mass in micrograms of a
substance contained within a cubic meter of another substance or vacuum.
This is the standard unit of measure for the mass density
(concentration) of particles suspended in air; also sometimes used for
the concentration of gases in air.

**MSDS (Material** A worksheet required by the U.S. Occupational Safety
and Health

**Safety Data Sheet)** Administration (OSHA) containing information
about hazardous chemicals in the workplace. MSDSs are used to fulfill
part of the hazardous chemical inventory reporting requirements under
the Emergency Planning and Community Right-to-Know Act.

**Mutagen** A chemical or physical agent that induces a permanent change
in the genetic material.

**NOAEL** No Observable Adverse Effect Level.

**NECP Suit** Non-encapsulating chemical protective suit. Not gas or
vapor tight.

**Organic Compound** Chemicals that contain carbon. Volatile organic
compounds vaporize at room temperature and pressure. They are found in
many indoor sources, including many common household products and
building materials.

**OSHA** The Occupational Safety and Health Administration, part of the
Department of Labor.

**Pathway** A history of the flow of a pollutant from source to
receptor, including qualitative descriptions of emission type,
transport, medium, and exposure route.

**PEL** Permissible Exposure Limits set by OSHA as a guide to acceptable
levels of chemical exposure.

**Percent Volatile** The percentage of a chemical that will evaporate at
ordinary temperatures. A high volatile percentage may mean there is more
risk of explosion, or that dangerous fumes can be released. Evaporation
rates are a better measure of the danger than the percent volatile
measure.

**PH** The pH is a measure of how acidic or caustic a chemical is, based
on a scale of 1 to 14. A pH of 1 means the chemical is very acidic. Pure
water has a pH of 7. A pH of 14 means the chemical is very caustic. Both
acidic and caustic substances are dangerous to skin and other valuable
surfaces.

**Poison** A chemical that, in relatively small amounts, is able to
produce injury by chemical action when it comes in contact with a
susceptible tissue.

**RCRA** The Resource Conservation and Recovery Act (of 1976). A Federal
statute which establishes a framework for proper management and disposal
of all wastes. Generation, transportation, storage, treatment, and
disposal of hazardous wastes are all regulated under this Act.

**Risk Assessment** Broadly defined as the scientific activity of
evaluating the toxic properties of a chemical and the conditions of
human exposure to it, with the objective of determining the probability
that exposed humans will be adversely affected. Its four main components
are:

1.  ***Hazard Identification***---Does the agent cause the effect?

2.  ***Dose-Response Assessment***---What is the relationship between
    the dose and its incidence in human beings?

3.  ***Exposure Assessment***---What exposures are experienced or
    anticipated, and under what conditions?

4.  ***Risk Characterization***---The total analysis producing an
    estimate of the incidence of the adverse effect in a given
    population.

**Runoff** Water from rain, snow melt, or irrigation that flows over the
ground surface and returns to streams.

**SARA** Superfund Amendments and Reauthorization Act of 1986.

**SERC** State Emergency Response Commission.

**Solubility in Water** An indicator of the amount of a chemical that
can be dissolved in water, shown as a percentage or as a description. A
low percent of solubility (or a description of "slight" solubility or
"low" solubility) means that only a small amount will dissolve in water.
Knowing this may help firefighters or personnel cleaning a spill.

**Specific Gravity** A comparison of the weight of the chemical to the
weight of an equal volume of water. Chemicals with a specific gravity of
less than 1 are lighter than water, while a specific gravity of more
than 1 means the chemical is heavier than water. Most flammable liquids
are lighter than water.

**Synergistic Effect** A biological response to exposure to multiple
chemicals which is greater than the sum of the effects of the individual
agents.

**Systemic Toxicants** Chemical compounds that affect entire organ
systems, often operating far from the original site of entry.

**Teratogen** A material that produces a physical defect in a developing
embryo.

**Threshold** The lowest dose of a chemical at which a specific
measurable effect is observed. Below this dose, the effect is not
observed.

**Title III** The third part of SARA, also known as the Emergency
Planning and Community Right-to-Know Act of 1986.

**TLV** Threshold Limit Values, which are the calculated airborne
concentrations of a substance to which all workers could be repeatedly
exposed 8 hours a day without adverse effects.

**TECP Suit** Totally encapsulating chemical protective suit. Special
protective suits made of material that prevents toxic or corrosive
substances or vapors from coming in contact with the body. Gas and vapor
tight suit.

**Toxicity** The degree of danger posed by a substance to animal or
plant life.

**Toxicology** The study of the adverse effects of chemicals on
biological systems, and the assessment of the probability of their
occurrence.

**Transformation** The chemical alteration of a compound by processes
such as reaction with other compounds or breakdown into component
elements.

**Transport** Hydrological, atmospheric, or other physical processes
that convey pollutants through and across media from source to receptor.

**Vapor Density** The measure of the heaviness of a chemical's vapor as
compared to the weight of a similar amount of air. A vapor density of
1.0 is equal to air. Vapors that are heavier than air may build up in
low-lying areas, such as along floors, in sewers, or in elevator shafts.
Vapors that are lighter than air rise and may collect near the ceiling.

**Vapor Pressure** The measure of how quickly a chemical liquid will
evaporate. Chemicals with low boiling points have high vapor pressures.
If a chemical with a high vapor pressure spills, there is an increased
risk of explosion and a greater risk that workers will inhale toxic
fumes.

**Volatilization** Entry of contaminants into the atmosphere by
evaporation from soil or water.

**Workers Right-to-Know** Legislation mandating communicating of
chemical information to employees. A regulatory initiative by OSHA, and
an antecedent to Community Right-to-Know.