Office of Research

VIII. Acronyms, Definitions, and Common Terms Used in Safety Data Sheets

Acid ‑ Any chemical which undergoes dissociation in water with the formation of hydrogen ions. Acids turn litmus paper red and have pH values of 0 to 6. They may cause severe skin burns.

Acute Effect ‑ Adverse effect on a human or animal which has severe symptoms developing rapidly and coming quickly to a crisis. Also see chronic effect.

Acute Toxicity ‑ Acute effects resulting from a single dose of or exposure to a substance. Ordinarily used to denote effects in experimental animals.

ACGIH ‑ American Conference of Governmental Industrial Hygienists is an organization of professional personnel in governmental agencies or educational institutions who are employed in occupational safety and health programs.

Aerosol - A fine aerial suspension of particles sufficiently small in size to confer some degree of stability from sedimentation (e.g., smoke or fog).

Air-purifying respirator - A respirator that uses chemicals to remove specific gases and vapors from the air or that uses a mechanical filter to remove particulate matter. An air-purifying respirator must only be used when there is sufficient oxygen to sustain life and the air contaminant level is below the concentration limits of the device.

Alkali ‑ The hydroxides and carbonates of the alkali metals and alkaline earth metals. They neutralize acids, impart a soapy feel to aqueous solutions and are the commonest cause of occupational dermatitis.

Allergic Reaction - An abnormal physiological response to chemical or physical stimuli 

Anesthetic - A chemical that causes a total or partial loss of sensation. Overexposure to anesthetics can cause impaired judgement, dizziness, drowsiness, headache, unconsciousness, and even death. Examples include alcohol, paint remover, and degreasers.

ANSI - American National Standards Institute is a privately funded, voluntary membership organization that identifies industrial and public needs for national consensus standards and coordinates development of such standards.

Asphyxiant - A vapor or gas that can cause unconsciousness or death by suffocation (lack of oxygen). Most simple asphyxiants are harmful to the body only when they become so concentrated that they reduce oxygen in the air (normally about 21 percent) to dangerous levels (18 percent or lower). Asphyxiation is one of the principal potential hazards of working in confined and enclosed spaces.

Auto-Ignition Temperature - The minimum temperature required to initiate or cause self-sustained combustion independent of the heat source. A steam line or a glowing light bulb may ignite carbon disulfide (ignition temperature 80C). Diethyl ether (ignition temperature 160C) can be ignited by the surface of a hot plate.

Base ‑ A water soluble compound capable of reacting with an acid to form a salt by releasing an unshared pair of electrons to the acid or by receiving a proton from the acid.

Benign ‑ Not recurrent or not tending to progress.

Biodegradable ‑ Capable of being broken down into individual components by the action of living things.

Boiling Point - (BP) - The temperature at which a liquid changes to a vapor state at a given pressure. The boiling point is usually expressed in degrees Fahrenheit at sea level pressure (760mmHg, or one atmosphere).

Bonding - The interconnecting of two objects by means of a clamp and bare wire. Its purpose is to equalize the electrical potential between the objects to prevent a static discharge when transferring a flammable liquid from one container to another. The conductive path is provided by clamps that make contact with the charged object and a low resistance flexible cable which allows the charge to equalize. See grounding.

Carcinogen ‑ A substance or agent capable of causing or producing cancer in mammals, including humans. A chemical is considered to be a carcinogen if:

a.         It has been evaluated by the International Agency for Research on Cancer (IARC) and found to be a carcinogen or potential carcinogen; or

b.         It is listed as a carcinogen or potential carcinogen in the Annual Report on Carcinogens published by the National Toxicology Program (NTP) (latest edition); or

c.         It is regulated by OSHA as a carcinogen.

Carcinogenicity ‑ The ability to produce cancer.

CAS ‑ Chemical Abstracts Service is an organization under the American Chemical Society. CAS abstracts and indexes chemical literature from all over the world in "Chemical Abstracts." "CAS Numbers" are used to identify specific chemicals or mixtures.

CERCLA ‑ Comprehensive Environmental Response, Compensation, and Liability Act of 1980. The Act requires that the Coast Guard National Response Center be notified in the event of a hazardous substance release. The Act also provides for a fund (the Superfund) to be used for the cleanup of abandoned hazardous waste disposal sites.

CFR ‑ Code of Federal Regulations. A collection of the regulations that have been promul­gated under United States law.

Chemical ‑ Any element, chemical compound or mixture of elements and/or compounds where chemical(s) are or distributed.

Chemical Cartridge Respirator ‑ A respirator that uses various chemical substances to purify inhaled air of certain gases and vapors. This type respirator is effective for concentrations no more than ten times the TLV of the contaminant, if the contaminant has warning properties (odor or irritation) below the TLV.

Chemical Name ‑ The name given to a chemical in the nomenclature system developed by the International Union of Pure and Applied Chemistry (IUPAC) or the Chemical Abstracts Service (CAS).

Chemical Family ‑ A group of single elements or compounds with a common general name. Example: acetone, methyl ethyl ketone (MEK), and methyl isobutyl ketone (MIBK) are of the "aldehyde" family.

Chemical Source ‑ The arrangement within the molecule of atoms and their chemical bonds.

Chronic Effect ‑ An adverse effect on a human or animal body, with symptoms which develop slowly over a long period of time or which recur frequently. Also see "acute."

Chronic Exposure ‑ Long term contact with a substance.

Chronic Toxicity ‑ Adverse (chronic) effects resulting from repeated doses of or exposures to a substance over a relatively prolonged period of time. Ordinarily used to denote effects in experimental animals.

Compressed Gas - (a) a gas or mixture of gases having, in a container, an absolute pressure exceeding 40 pounds per square inch (psi) at 70F (21.1C) or (b) a gas or mixture of gases having, in a container, an absolute pressure exceeding 104 psi at 130F (54.4C) regardless of the pressure at 70F or (c ) a liquid having a vapor pressure exceeding 40psi at 100F (37.8C) as determined by ASTM D-323-72.

Concentration ‑ The relative amount of a substance when combined or mixed with other sub­stances. Examples: 2 ppm hydrogen sulfide in air, or a 50 percent caustic solution.

Confined Space - Any area that has limited openings for entry and exit that would make escape difficult in an emergency, has a lack of ventilation, contains known an potential hazards, and is not intended nor designed for continuous human occupancy.

Container ‑ Any bag, barrel, bottle, box, can, cylinder, drum, reaction vessel, storage tank, or the like that contains a hazardous chemical. For purposes of Safety Data Sheets or the Hazard Communication Standard, pipes or piping systems are not considered to be containers.

Corrosive ‑ A chemical that causes visible destruction of, or irreversible alterations in, living tissue by chemical action at the site of contact. For example, a chemical is considered to be corrosive if, when tested on the intact skin of albino rabbits by the method described by the U.S. Department of Transportation in Appendix A to 49 CFR Part 173, it destroys or changes irreversibly the structure of the tissue at the site of contact following an exposure period of 4 hours. This term shall not refer to action on inanimate surfaces.

Decomposition - Breakdown of a material or substance (by heat, chemical reaction, electrolysis, decay, or other processes) into parts or elements or simpler compounds

Density - The mass (weight) per unit volume of a substance.

Dermal Toxicity ‑ Adverse effects resulting from skin exposure to a substance. Ordinarily used to denote effects in experimental animals.

Dike - A barrier constructed to control or confine hazardous substances and prevent them from entering sewers, ditches, streams, or other flowing waters.

DOL - Department of Labor. OSHA and MSHA are part of DOL.

DOT - Department of Transportation regulates transportation of chemicals and other substances.

Edema - An abnormal accumulation of clear watery fluid in the tissues.

Environmental Toxicity ‑ Information obtained as a result of conducting environmental testing designed to study the effects on aquatic and plant life.

EPA ‑ U.S. Environmental Protection Agency.

Epidemiology - Science concerned with the study of disease distribution in a general population. Determination of the incidence (rate of occurrence) and distribution of a particular disease (as by age, sex, or occupation) which may provide information about the cause of the disease.

Evaporation Rate - The rate at which a material will vaporize (evaporate) when compared to the known rate of vaporization of a standard material. The evaporation rate can be useful in evaluating the health and fire hazards of a material. The designated standard material is usually normal butyl acetate (NBUAC or n-BuAc), with a vaporization rate designated as 1.0. Vaporization rates of other solvents or materials are then classified as:

  • FAST evaporating if greater than 3.0. Examples: methyl ethyl ketone = 3.8; Acetone 5.6; Hexane = 8.3.
  • MEDIUM evaporating if 0.8 to 3.0. Examples: 190 proof (95%) Ethyl Alcohol = 1.4, VM&P Naphtha = 1.4.
  • SLOW evaporating if less than 0.8. Examples: Xylene = 0.6, Isobutyl Alcohol = 0.6, Normal Butyl Alcohol = 0.4, Water = 0.3, Mineral Spirits = 0.1.

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

Exposure or Exposed ‑ State of being open and vulnerable to a hazardous chemical in the course of employment by inhalation, ingestion, skin contact, absorption, or any other course; includes potential (accidental or possible) exposure.

Flammable ‑ A chemical that includes one of the following categories:

a.         "Aerosol, flammable". An aerosol that, when tested by the method described in 16 CFR 1500.45, yields a flame projection exceeding 18 inches at full valve opening, or a flashback (a flame extending back to the valve) at any degree of valve opening.

b.         "Gas, flammable". (1 ) A gas that, at ambient temperature and pressure, forms a flammable mixture with air at a concentration of 13 percent by volume or less; or (2) A gas that, at ambient temperature and pressure, forms a range of flammable mix­tures with air wider than 12 percent by volume, regardless of the lower limit.

c.         "Liquid, flammable". Any liquid having a flashpoint below 100°F (37.8°C),except any mixture having components with flashpoints of 100°F (37.8°C) or higher, the total of which make up 99 percent or more of the total volume of mixture.

d.         "Solid, flammable." A solid, other than a blasting agent or explosive as defined in 1910.109(a), that is liable to cause fire through friction, absorption of moisture, spontaneous chemical change, or retained heat from manufacturing or processing, or which can be ignited readily and when ignited burns so vigorously and persis­tently as to create a serious hazard. A is a flammable solid if, when tested by the method described in 16 CFR 1500.44, it ignites and burns with a self sustained flame at a rate greater than one tenth of an inch per second along its major axis.

FIFRA - Federal Insecticide, Fungicide, and Rodenticide Act.

Flashpoint ‑ The minimum temperature at which a liquid gives off a vapor in sufficient concen­tration to ignite when tested by the following methods:

a.         Tagliabue Closed Tester (see American National Standard Method of Test for Flash Point by Tag Closed Tester, Z11.24 ‑1979 [ASTM D56‑79]).

b.         Pensky‑Martens Closed Tester (see American National Standard Method of Test for Flash Point by Pensky‑Martens Closed Tester, Z11.7‑1979 [ASTM D93‑79l).

c.         Setaflash Closed Tester (see American National Standard Method of Test for Flash Point by Setaflash ClosedTester [ASTM D3278‑78]).

Foreseeable Emergency - Any potential occurrence such as, but not limited to, equipment failure, rupture or containers, or failure of control equipment which could result in an uncontrolled release of a hazardous chemical into the workplace.

Fume - A solid condensation particle of extremely small diameter, commonly generated from molten metal as metal fume.

Grounding - The procedure used to carry an electrical charge to ground through a conductive path. A typical ground may be connected directly to a conductive water pipe or to a grounding but and ground rod. See Bonding.

Hazard Warning ‑ Words, pictures, symbols, or combination thereof presented on a label or other appropriate form to inform of the presence of various materials.

Hazardous Chemical ‑ Any chemical whose presence or use is a physical hazard or a health hazard.

HCS ‑ Hazard Communication Standard is an OSHA regulation issued under 29 CFR Part 1910.1200.

Health Hazard ‑ A chemical for which there is significant evidence, based on at least one study conducted in accordance with established scientific principles, that acute or chronic health effects may occur in exposed employees. The term "health hazard" includes chemicals which are carcinogens, toxic or highly toxic agents, reproductive toxins, irritants, corrosives, sensitizers, hepatotoxins, nephrotoxins, neurotoxins, agents which act on the hematopoietic system, and agents which damage the lungs, skin, eyes, or mucous membranes.

Hematopoietic System ‑ The blood forming mechanism of the human body.

Hepatotoxin ‑ A substance that causes injury to the liver.

Highly Toxic ‑ A chemical falling within any of the following categories:

a.         A chemical with a median lethal dose (LD50) of 50 milligrams or less per kilogram of body weight when administered orally to albino rats weighing between 200 and 300 grams each.

b.         A chemical with a median lethal dose (LD50) of 200 milligrams or less per kilo­gram of body weight when administered by continuous contact for 24 hours (or less if death occurs within 24 hours) with the bare skin of albino rabbits weighing between 2 and 3 kilograms each.

c.         A chemical that has a median lethal concentration (LC50) in air of 200 parts per million by volume or less of gas or vapor, or 2 milligrams per liter or less of mist, fume, or dust, when administered by continuous inhalation for 1 hour (or less if death occurs within 1 hour) to albino rats weighing 200 and 300 grams each.

IARC - International Agency for Research on Cancer.

Incompatible - Materials that could cause dangerous reactions by direct contact with one another.

Inhibitor ‑ A chemical added to another substance to prevent an unwanted chemical change.

Irritant ‑ A chemical, which is not corrosive, but which causes a reversible inflammatory effect on living tissue by chemical action at the site of contact. A chemical is a skin irritant if, when tested on the intact skin of albino rabbits by the methods of 16 CFR 1500 .41 for 4 hours exposure or by other appropriate techniques, it results in an empirical score of 5 or more. A chemical is an eye irritant if so determined under the procedure listed in 16 CFR 1500.42 or other appropriate techniques.

Irritating ‑ An irritating material, as defined by DOT, is a liquid or solid substance which, upon contact with fire or when exposed to air, gives off dangerous or intensely irritating fumes (not including poisonous materials). See Poison, Class A and Poison, Class B.

Laboratory - A facility where the “laboratory use of hazardous chemicals” occurs. It is a workplace where relatively small quantities of hazardous chemicals are used on a non-production basis.

Laboratory Scale - Work with substances in which the containers used for reactions, transfers, and other handling of substances are designed to be easily and safely manipulated by one person. The laboratory use of hazardous chemicals means handling or use of such chemicals in which all of the following conditions are met:

  1. Chemical manipulations are carried out on a “laboratory scale”;
  2. Multiple chemical procedures or chemicals are used;
  3. The procedures involved are not part of a production process, nor in any way simulate a production process; and
  4. “Protective laboratory practices and equipment” are available and in common use to minimize the potential for employee exposure to hazardous chemicals.

LC ‑ Lethal concentration is the concentration of a substance being tested that will kill.

LCLO ‑ Lethal concentration low. Lowest concentration of a gas or vapor capable of killing a specified species over a specified time.

LC50‑ The concentration of a material in air that will kill 50 percent of a group of test animals with a single exposure (usually 1 to 4 hours). The LC50 is expressed as parts of material per million parts of air, by volume (ppm) for gases and vapors, or as micrograms of material per liter of air (g/l ) or milligrams of material per cubic meter of air (mg/m3) for dusts and mists, as well as for gases and vapors.

LD ‑ Lethal dose is the quantity of a substance being tested that will kill.

LDLO ‑ Lethal dose low. Lowest administered dose of a material capable of killing a specified test species.

LD50 ‑ A single dose of a material expected to kill 50 percent of a group of test animals. The LD50 dose is usually expressed as milligrams or grams of material per kilogram of animal body weight (mg/kg or g/kg). The material may be administered by mouth or applied to the skin.

LEL or LFL ‑ Lower explosive limit, or lower flammable limit, of a vapor or gas; the lowest concentration (lowest percentage of the substance in air) that will produce a flash of fire when an ignition source (heat, arc or flame) is present. At concentrations lower than the LEL, the mixture is too "lean" to burn. Also see "UEL."

Local exhaust ‑ A system for capturing and exhausting contaminants from the air at the point where the contaminants are produced (welding, grinding, sanding, other processes or opera­tions). Also see "general exhaust".

MSHA - Mine Safety and Health Administration, U.S. Department of Labor.

Mechanical exhaust ‑ A powered device, such as a motor driven fan or air stream venturi tube, for exhausting contaminants from a workplace, vessel, or enclosure.

Mechanical Filter Respirator ‑ A respirator used to protect against airborne particulate matter like dusts, mists, metal fume, and smoke. Mechanical filter respirators do not provide protection against gases, vapors, or oxygen deficient atmospheres.

Melting Point - The temperature at which a solid substance changes to a liquid state.

Mutagen ‑ A substance or agent capable of altering the genetic material in a living cell.

NCI ‑ National Cancer Institute is that part of the National Institutes of Health which studies cancer causes and prevention as well as diagnosis, treatment, and rehabilitation of cancer patients.

Narcosis - A state of stupor, unconsciousness, or arrested activity produced by the influence of narcotics or other chemicals.

NFPA - National Fire Protection Association is an international membership organization which promotes/improves fire protection and prevention and establishes safeguards against loss of life and property by fire.

Nephrotoxin ‑ A substance that causes injury to the kidneys.

Neurotoxin ‑ A material that affects the nerve cells and may produce emotional or behavioral abnormalities.

Neutralize ‑ To eliminate potential hazards by inactivating strong acids, caustics, and oxidizers. For example, acids can be neutralized by adding an appropriate amount of caustic substance to the spill.

NIOSH - National Institute of Occupational Safety and Health, U.S. Public Health Service, U.S. Department of Health and Human Services (DHHS), among other activities, tests and certifies respiratory protective devices and air sampling detector tubes, recommends occupational exposure limits for various substances, and assists OSHA and MSHA in occupational safety and health investigations and research.

Non-Sparking Tools - Tools made from beryllium-copper or aluminum-bronze greatly reduce the possibility of igniting dusts, gases, or flammable vapors. Although these tools may emit some sparks when striking metal, the sparks have a low heat content and are not likely to ignite most flammable liquids.

NRC - National Response Center is a notification center that must be called when a significant oil or chemical spill or other environmental-related accident occurs.

NTP - National Toxicology Program. The NTP publishes an Annual Report on Carcinogens.

OSHA - Occupational Safety and Health Administration, U.S. Department of Labor.

Odor Threshold - The lowest concentration of a substance’s vapor that can be smelled by most people.

Oral Toxicity ‑ Adverse effects resulting from taking a substance into the body by mouth. Ordinarily used to denote effects in experimental animals.

Organic Peroxide - An organic compound that contains the bivalent -O-O structure and may be considered a structural derivative of hydrogen peroxide where one or both of the hydrogen atoms has been replaced by an organic radical.

Oxidizer ‑ A chemical other than a blasting agent or explosive that initiates or promotes com­bustion in other materials, causing fire either by itself or through the release of oxygen or other gases.

Oxidizing Agent ‑ A chemical or substance that brings about an oxidation reaction. The agent may (1) provide the oxygen to the substance being oxidized (in which case the agent has to be oxygen or contain oxygen), or (2) it may receive electrons being transferred from the substance undergoing oxidation (chlorine is a good oxidizing agent for electron transfer purposes, even though it contains no oxygen).

PEL ‑ Permissible exposure limit is an exposure limit established by OSHA'S regulatory authority. It may be a time weighted average (TWA) limit or a maximum concentration exposure limit.

pH ‑ The symbol relating the hydrogen ion (H‑) concentration to that of a given standard solution. A pH of 7 is neutral. Numbers increasing from 7 to 14 indicate greater alkalinity. Numbers decreasing from 7 to 0 indicate greater acidity.

Physical Hazard ‑ Means a chemical for which there is scientifically valid evidence that it is a combustible liquid, a compressed gas, explosive, flammable, and organic peroxide, an oxidizer, pyrophoric, unstable (reactive) or water reactive.

Poison, Class A ‑ A DOT term for extremely dangerous poison; poisonous gases or liquids that, in very small amounts, either as gas or as vapor of the liquid, mixed with air, are dangerous to life. Examples: phosgene, cyanogen, hydrocyanic acid, nitrogen peroxide.

Poison, Class B ‑ A DOT term for liquid, solid, paste or semisolid substances other than Class A poisons or irritating materials that are known (or presumed on the basis of animal tests) to be so toxic to humans that they are a hazard to health during transportation.

ppm ‑ Parts per million is the concentration of a gas or vapor in air; parts (by volume) of the gas or vapor in a million parts of air; also the concentration of a particulate in a liquid or solid.

ppb ‑ Parts per billion is the concentration of a gas or vapor in air; parts (by volume) of the gas or vapor in a billion parts of air. Usually used to express extremely low concentrations of unusually toxic gases or vapors; also the concentration of a particular substance in a liquid or solid.

Pyrophoric - A chemical that will ignite spontaneously in air at a temperature or 130F (54.4C) or below.

RCRA ‑ Resource Conservation and Recovery Act is environmental legislation aimed at con­trolling the generation, treating, storage, transportation and disposal of hazardous wastes. It is administered by EPA.

Reactivity ‑ Chemical reaction with the release of energy. Undesirable effects--such as pressure buildup, temperature increase, formation of noxious, toxic or corrosive by‑products may occur because of the reactivity of a substance to heating burning, direct contact with other materials, or other conditions in use or in storage.

REL - Recommended Exposure Limit (NIOSH). The highest allowable airborne concentration which is not expected to injure the workers. It may be expressed as a ceiling limit or as a time-weighted average (TWA).

Reproductive toxin ‑ Substances that affect either male or female reproductive systems and may impair the ability to have children.

Respiratory protection ‑ Devices that will protect the wearer's respiratory system from overex­posure by inhalation to airborne contaminants. Respiratory protection is used when a worker must work in an area where he/she might be exposed to concentration in excess of the allowable exposure limit.

Routes of Entry - The means by which material may gain access to the body. These are: inhalation, ingestion, contact with the skin or eyes, and injection.

SDS - Safety Data Sheet

Self-Contained Breathing Apparatus - A respiratory protection device that consists of a supply or a means of respirable air, oxygen, or oxygen-generating material, carried by the wearer.

Sensitizer ‑ A chemical that causes a substantial proportion of exposed people or animals to develop an allergic reaction in normal tissue after repeated exposure to the chemical.

Solvent ‑ A substance, usually a liquid, in which other substances are dissolved. The most common solvent is water.

Specific gravity - The weight of a material compared to the weight of an equal volume of water is an expression of the density (or heaviness) of a material. The specific gravity of water is 1.0. Insoluble materials with specific gravity of less than 1.0 will float in (or on) water. In soluble materials with specific gravity greater than 1.0 will sink in water.

Splash-proof goggles - Eye protection made of a noncorrosive material that fits snugly against the face, and has indirect ventilation ports.

STEL - Short-Term Exposure Limit (ACGIH). See TLV

Systemic Poison - A poison that spreads throughout the body, affecting all body systems and organs. Its adverse effect is not localized in one spot or area.

Target Organ Effects ‑ The following is a listing of target organs, toxicants specific for these organs, and some of the toxic effects produced by these agents. These examples are presented to illustrate the diversity of hazards employers must consider in the workplace and are not intended as a complete listing of such agents and their target organs.


ORGAN         TOXICANT                                                   EFFECTS

Blood              Carbon monoxide; Cyanides                           Cyanosis; Loss of consciousness

Dermis            Ketones; Chlorinated compounds                  Rashes; De-fatting of skin

Eyes                Organic solvents; Acids                                  Conjunctivitis; Corneal damage

Kidney          Halogenated hydrocarbons; Uranium Edema; Proteinuria

Liver                Carbon tetrachloride; Nitrosamines                Jaundice; Liver enlargement

Lung                Silica; Asbestos                                         Cough; Shortness of breath

Gonads               Lead; DBCP                                        Birth defects; Sterility


Target Organ Toxin ‑ A toxic substance that attacks a specific organ of the body. For example, overexposure to carbon tetrachloride can cause liver damage.

Teratogen ‑ A substance or agent, exposure to which by a pregnant female can result in malformations in the fetus.

TLV ‑ Threshold Limit Value is a term used by ACGIH to express the airborne concentration of material to which nearly all persons can be exposed day after day without adverse effects. ACGIH expresses TLVs in three ways:

a.         TLV‑TWA: The allowable Time Weighted Average concentration for a normal 8- hour workday or 40‑hour work week.

b.         TLV‑STEL: The Short Term Exposure Limit, or maximum concentration for a continuous 15‑minute exposure period (maximum of four such periods per day, with at least 60 minutes between exposure periods, and provided the daily TLV/TWA is not exceeded).

c.         TLV‑C: The ceiling exposure limit; the concentration that should not be exceeded even instantaneously.


TOC ‑ TAG Open Cup. See flashpoint.

Torr ‑ A unit of pressure, equal to 1/760 atmosphere.

Toxic ‑ A chemical falling within any of the following categories:

a.         A chemical with a median lethal dose (LD50) of more than 50 milligrams per kilogram but not more than 500 milligrams per kilogram of body weight when administered orally to albino rats weighing between 200 and 300 grams each.

b.         A chemical that has a median lethal dose (LD50) of more than 200 milligrams per kilogram but not more than 1,000 milligrams per kilogram of body weight when administered by continuous contact for 24 hours (or less if death occurs within 24 hours) with the bare skin of albino rabbits weighing between two and three kilo­grams each.

c.         A chemical that has a median lethal concentration (LC50) in air of more than 200 parts per million but not more than 2,000 parts per million by volume of gas or vapor, or more than two milligrams per liter but not more than 20 milligrams per liter of mist, fume, or dust, when administered by continuous inhalation for one hour (or less if death occurs within 1 hour) to albino rats weighing between 200 and 300 grams each.


Toxic Substance ‑ Any substance which can cause acute or chronic injury to the human body, or which is suspected of being able to cause diseases or injury under some conditions.

Toxicant‑ Any substance producing a toxic effect.

Toxicity ‑ The sum of adverse effects resulting from exposure to a material, generally by the mouth, skin, or respiratory tract.

TSCA ‑ Toxic Substances Control Act (Federal Environmental Legislation administered by EPA) regulates the manufacture, handling, and use of materials classified as "toxic substances."

TWA - Time-weighted average - airborne concentration of a material to which a person is exposed, averaged over the total exposure time, generally the total workday (8 to 12 hours).

UEL or UFL - Upper explosive limit or upper flammable limit of a vapor or gal; the highest concentration (highest percentage of the substance in air) that will produce a flash of fire when an ignition source is present. At higher concentrations, the mixture is too “rich” to burn. Also see LEL.

Unstable Reactive ‑ A chemical that, in the pure state, or as produced or transported, will vigorously polymerize, decompose, condense, or become self‑reactive under conditions of shocks, pressure, or temperature.

Vapor Density - The weight of a vapor or gas compared to the weight of an equal volume of air, air density =1.0. Materials lighter than air have vapor densities less than 1.0 (e.g., acetylene, methane, hydrogen). Materials heavier than air (e.g., propane, hydrogen sulfide, ethane, butane, chlorine, sulfur dioxide) have vapor densities greater than 1.0. All vapors and gases will mix with air, but the lighter materials will tend to rise and dissipate (unless confined). Heavier vapors and gases are likely to concentrate in low places—along or under floors, in trenches and ditches—where they may create fire or health hazards.

Vapor Pressure - The pressure exerted by a saturated vapor above its own liquid in a closed container. When quality control tests are performed on products, the test temperature is usually 100F, and the vapor pressure is expressed as pounds per square inch (psig or psia), but vapor pressures reported as SDS information are in millimeters of mercury (mmHg) at 68F (20C), unless stated otherwise. Three facts are important to remember:

  1. Vapor pressure of a substance at 100F will always be higher than the vapor pressure of the substance at 68F (20C).
  2. Vapor pressure reported on SDS’s in mm Hg are usually very low pressures; 760mmHg if equivalent to 14.7 pounds per square inch.
  3. The lower the boiling point of a substance, the higher its vapor pressure.


Volatility ‑ A measure of how quickly a substance forms a vapor at ordinary temperature

Water-Reactive - A chemical that reacts with water to release a gas that is either flammable or presents a health hazard.

Work Area ‑ A room or defined space in a workplace where hazardous chemicals are produced or used, and where employees are present.

Workplace ‑ An establishment at one geographical location containing one or more work areas.