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.

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ACGIH

American Conference of Governmental Industrial Hygienist

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Acute Exposure

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

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Acute Toxicity

Any poisonous effect produced by a single short-term exposure. The LD₅₀ 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.

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Additive Effect

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

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Adsorption

The bonding of chemicals to soil particles or other surfaces.

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Aerosol

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

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Antagonism

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

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Aquifer

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

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Asphyxiants

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

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Biodegradable

Capable of decomposing quickly through the action of microorganisms.

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Biomagnification

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

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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.

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Carcinogen

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

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Central Nervous System Depressants

Toxicants that deaden the central nervous system (CNS), diminishing sensation.

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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.

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CHEMTREC

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

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Chronic Exposure

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

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Command Post

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

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Corrosive

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

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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.

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Dermal Exposure

Exposure to toxic substances by entry though the skin.

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Dose

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

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Epidemiology Studies

Investigation of factors contributing to disease or toxic effects in the general population.

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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.

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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.

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Explosive

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

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Extremely Hazardous Substance (EHS)

Any one of more than 300 hazardous chemicals on a list compiled by EPA to provide a focus for State and local emergency planning activities.

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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.

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Hazardous Materials Response Team (HMRT)

A team of specially trained personnel who respond to a hazardous materials incident. The team performs various response actions including assessment, firefighting, rescue, and containment; they are not responsible for cleanup operations following the incident.

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Incident Commander

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

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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.

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Irritant

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

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LD₅₀

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

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Leachate

Material that pollutes water as it seeps through solid waste.

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Leaching

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

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LEPC

Local Emergency Planning Committee.

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LOAEL

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

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Medium

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

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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.

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

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Mm³

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.

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MSDS (Material Safety Data Sheet)

A worksheet required by the U.S. Occupational Safety and Health 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.

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Mutagen

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

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NOAEL

No Observable Adverse Effect Level.

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NECP Suit

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

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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.

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OSHA

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

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Pathway

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

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PEL

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

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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.

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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.

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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.

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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.

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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:

Hazard Identification—Does the agent cause the effect?
Dose-Response Assessment—What is the relationship between the dose and its incidence in human beings?
Exposure Assessment—What exposures are experienced or anticipated, and under what conditions?
Risk Characterization—The total analysis producing an estimate of the incidence of the adverse effect in a given population.

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Runoff

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

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SARA

Superfund Amendments and Reauthorization Act of 1986.

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SERC

State Emergency Response Commission.

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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.

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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.

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Synergistic Effect

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

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Systemic Toxicants

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

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Teratogen

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

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Threshold

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

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Title III

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

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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.

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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.

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Toxicity

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

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Toxicology

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

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Transformation

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

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Transport

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

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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.

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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.

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Volatilization

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

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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.