Glossary of MSDS Terms and Acronyms 

Action Level, AL:  Certain OSHA regulations take effect if this exposure level is reached. These regulations include workplace air analysis, employee training, medical monitoring, and record keeping. This level is about half of the permissible exposure limit.

Acute:  A short term period of action measured in seconds, minutes, hours, or days.

Acute Effects of Overexposure:  Refers to the adverse effects that normally are evident immediately or shortly after exposure to a hazardous material without implying a degree of severity.

American Conference of Governmental Industrial Hygienists, ACGIH:  This organization includes professionals in government and education involved in occupational safety and health programs. One important function of this group is the determination and publication of recommended occupational exposure limits for chemical substances.

American National Standards Institute, ANSI:  This private organization identifies industrial and public national consensus standards. These standards relate to safe design and performance of equipment, and practices.

Burnback:  The distance a flame will travel from the ignition source back to the aerosol container.

C.A.S. Number:  Chemical Abstracts Service , a service of the American Chemical Society, identifies particular chemicals with a number.

Ceiling, C:  See Threshold Limit Values.

Chronic:  A long time period of action in weeks, months, or years.

Chronic Effects of Overexposure:  The adverse effects that develop slowly over a long period of time or upon repeated prolonged exposure to a hazardous material without implying a degree of severity.

Cutaneous Hazards:  Chemicals which affect the skin. Signs and symptoms are defatting of the skin, rashes, irritation.

Defatting:  The removal of natural oils from the skin by a fat-dissolving solvent.

Density:  The mass of a substance per unit volume. The density of a substance is usually compared to water, which has a density of 1. Substances which float on water have densities less than 1; substances which sink have densities greater than 1.

Dermatitis:  An inflamation of the skin.

Evaporation Rate:  The rate at which a product will vaporize when compared to the rate of vaporization of a known material (usually Butyl Acetate with rate designated as 1.0). Evaporation rate can be useful in evaluating the health and fire hazards of a material. Rates are classified as fast (greater than 3.0), medium (0.8 to 3.0), and slow (less than 0.8). The evaporation rate of water is 0.3.

Extinguishing Media:  Specifies the fire-fighting agents that should be used to extinguish fires.

Flame Extension:  The distance a flame will travel from the aerosol container when exposed to an ignition source.

Flash Point:  The minimum temperature at which a liquid will give off enough flammable vapor to ignite in the presence of an ignition source.

Hazardous Chemical:  Any chemical that is a physical (i.e.-flammable, reactive) or health (i.e. irritant, carcinogen) hazard.

Health Hazard:  A chemical for which there is statistically significant evidence that acute or chronic health effects may occur in exposed employees.

Immediately Dangerous to Life and Health, IDLH:  These values are used to determine the appropriate respirators for hazardous chemicals. These values stand for the maximum concentration from which a worker could escape within 30 minutes without any escape-impairing symptoms or irreversible health effects in the event of a respirator failure.

Irritant:  A substance that produces an irritating effect when it contacts the skin, eyes, nose, or respiratory system.

Lethal Concentration, LC:  A concentration of a substance being tested which will kill a test animal.

Lethal Concentration 50, LC-50:  This concentration of a hazardous material in air is expected to kill 50% of a group of test animals when given as a single respiratory exposure in a specific time period.

Lethal Concentration Low, LC-LO:  This value indicates the lowest concentration of a substance in the air that caused death in humans or laboratory animals. The value may represent periods of exposure that are less than 24 hours (acute) or greater that 24 hours (subacute and chronic).

Lethal Dose, LD:  The dose of a substance being tested which will kill a test animal.

Lethal Dose 50, LD-50:  The single dose, other than inhalation, that causes death in 50% of an animal population from exposure to a hazardous substance.

Lethal Dose Low, LD-LO:  The lowest dose, other than inhalation, that caused death in humans or animals.

Lower Explosive Limit, LEL:  The lowest concentration of gas or vapor (% by volume in air) which will burn or explode if an ignition source is present.

Material Safety Data Sheet:  A document that contains information and instructions on the chemical and physical characteristics of a substance, its hazards and risks, the safe handling requirements, and actions to be taken in the event of fire, spill, or overexposure, etc.

Milligrams per Cubic Meter of Air, mg/m³:  This unit of measuring concentrations of particulate (minute dust-like particles).

Mutagen:  An agent that causes biological mutation.

N/A:  An abbreviation for not applicable or not available.

National Fire Protection Association, NFPA:  This group of fire protection personnel established a rating system used on many labels of hazardous materials. The label consists of a diamond divided into four sections representing health, flammability, reactivity, and special precautions.

National Institute of Occupational Safety and Health, NIOSH:  This agency of the public Health Service tests and certifies respiratory and air-sampling devices. It recommends to OSHA exposure limits for hazardous substances. It also investigates incidents and researches occupational safety.

Odor Threshold, OT:  This is required on Canadian MSDSs and is sometimes shown on U.S. MSDSs. It represents the concentration in the air at which most people can smell the chemical. If the OT is smaller than the TLV, the chemical provides a sensory warning before health effects are expected. If the OT is larger than the TLV, you are already at risk by the time you smell it.

Parts Per Million, ppm:  This is a common unit of concentration for gas or vapor in air. It is defined as parts of gas or vapor per million parts of air by volume at 25 degrees C and 1 atm of pressure.

Permissible Exposure Limit, PEL:  This is one of the most important OSHA limits used. It is defined as the allowable limit for air containment in which workers may be exposed day after day without adverse health effects.

pH:  A measure of the acidity or alkalinity of a solution, equal to 7 for neutral solutions, increasing with increasing alkalinity and decreasing with increasing acidity.

Physical Hazard:  A chemical for which there is evidence that it is a combustible liquid, compressed gas, explosive, flammable, an organic peroxide, an oxidizer, pyrophoric (ignites spontaneously in air), unstable (reactive) or water reactive.

Reactivity:  A description of the tendency of a substance to undergo chemical reaction with the release of energy. Undesirable effects such as pressure build-up, temperature increase, formation of noxious, toxic, or corrosive byproducts may occur because of the reactivity of a substance by heating, burning, direct contact with other materials, or other conditions in use or in storage.

Recommended Exposure Limit, REL:  The highest allowable air concentration that will not injure a person.

Sensitizer:  A substance which may cause no reaction in a person during initial exposure, but to which further exposure will cause an allergic response.

Short-Term Exposure Limit, STEL:  See Threshold Limit Value.

Solubility:  The extent to which a substance mixes with a liquid to produce a solution.

Solvent:  Usually a liquid in which other substances are dissolved. The most common solvent is water.

Synergy:  The combined effects of more than one hazardous material resulting in more damage than the additive effects of each material.

Teratogen:  Causes physical defects in the developing embryo.

Threshold Limit Value, TLV:  The air concentration levels of hazardous substances to which workers may be repeatedly exposed day after day without adverse health effects. There are three categories of TLVs.


Time Weighted Average:  See Threshold Limit Value.

Toxic Concentration Low, TC-LO:  This is the lowest concentration of an airborne substance to which humans or animals have been exposed that resulted in any toxic effects in humans or produced any tumors or adverse reproductive effects in animals or humans.

Toxic Dose Low, TD-LO:  The lowest dose of a hazardous substance introduced by means other than inhalation over a given time period that has been reported to produce toxic effects in humans or produced any tumors or adverse reproductive effects in animals or humans.

Vapor Density:  The density of a materials vapor, compared to the density of air. If a vapor density is greater than 1, it is more dense than air and will drop to the floor or the lowest point available. If the density is less than 1, it is lighter than air and will float upwards.

Vapor Pressure:  The higher the vapor pressure, the more easily a liquid will evaporate. Liquid materials that evaporate easily are termed volatile, and this means that air concentrations can build up quickly when working with the material in liquid form. Materials with high vapor pressures may be particularly hazardous when working in confined or enclosed areas, or if air circulation is poor.

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

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