Lab Safety Manual: Glossary


rev 8/2007

ACGIH: The American Conference of Governmental Industrial Hygienists is a voluntary membership organization of professional industrial hygiene personnel in governmental or educational institutions. The ACGIH develops and publishes recommended occupational exposure limits each year called Threshold Limit Values (TLV's) for hundreds of chemicals, physical agents, and biological exposure indices.

BOILING POINT: The temperature at which the vapor pressure of a liquid equals atmospheric pressure or at which the liquid changes to a vapor. The boiling point is usually expressed in degrees Fahrenheit. If a flammable material has a low boiling point, it indicates a special fire hazard.

"C" OR CEILING: A description usually seen in connection with ACGIH exposure limits. It refers to the concentration that should not be exceeded, even for an instant. It may be written as TLV-C or Threshold Limit Value-Ceiling. (See also THRESHOLD LIMIT VALUE).

CARCINOGEN: A substance or physical agent that may cause cancer in animals or humans.

DERMAL: Pertaining to or affecting the skin.

DERMATITIS: An inflammation of the skin.


DOT: The United States Department of Transportation is the federal agency that regulates the labeling and transportation of hazardous materials.

DYSPNEA: Shortness of breath; difficult or labored breathing.

EPA: The Environmental Protection Agency is the governmental agency responsible for administration of laws to control and/or reduce pollution of air, water, and land systems.

EPA NUMBER: The number assigned to chemicals regulated by the Environmental Protection Agency (EPA).

EPIDEMIOLOGY: The study of disease in human populations.

ERYTHEMA: A reddening of the skin.

EVAPORATION RATE: The rate at which a material is converted to vapor (evaporates) at a given temperature and pressure when compared to the evaporation rate of a given substance. Health and fire hazard evaluations of materials involve consideration of evaporation rates as one aspect of the evaluation.

oF: Degrees, Fahrenheit; a temperature scale.

FLAMMABLE LIQUID: According to the DOT and NFPA, a flammable liquid is one that has a flash point below 100oF. (See FLASH POINT)

Classes Of Flammable Liquids

Flammable Solvent Class

Boiling Point

Flash Point

Class 1A



Class 1B

>= 100oF


Class 1C

>= 100oF

Between 73 and 100oF


FLASH POINT: The lowest temperature at which a liquid gives off enough vapor to form an ignitable mixture with air and burn when a source of ignition (sparks, open flames, cigarettes, etc.) is present. Two tests are used to determine the flash point: open cup and closed cup. The test method is indicated on the MSDS after the flash point.

g: See GRAM.

GENERAL VENTILATION: Also known as general exhaust ventilation, this is a system of ventilation consisting of either natural or mechanically induced fresh air movements to mix with and dilute contaminants in the workroom air. This is not the recommended type of ventilation to control contaminants that are highly toxic, when there may be corrosion problems from the contaminant, when the worker is close to where the contaminant is being generated, and where fire or explosion hazards are generated close to sources of ignition (See LOCAL EXHAUST VENTILATION).


GRAM (g): A metric unit of weight. One ounce equals 28.4 grams.

GRAMS PER KILOGRAM (g/Kg): This indicates the dose of a substance given to test animals in toxicity studies. For example, a dose may be 2 grams (of substance) per kilogram of body weight (of the experimental animal).

HAZARDOUS MATERIAL: Any substance or compound that has the capability of producing adverse effects on the health and safety of humans.

IGNITABLE: A solid, liquid, or compressed gas that has a flash point of less than 140oF. Ignitable material may be regulated by the EPA as a hazardous waste, as well.

INCOMPATIBLE: The term applied to two substances to indicate that one material cannot be mixed with the other without the possibility of a dangerous reaction.

INGESTION: Taking a substance into the body through the mouth, such as food, drink, medicine, or unknowingly as in contaminated hands or cigarettes, etc.

INHALATION: Breathing in of an airborne substance that may be in the form of gases, fumes, mists, vapors, dusts, or aerosols.

INHIBITOR: A substance that is added to another to prevent or slow down an unwanted reaction or change.

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


KILOGRAM (Kg): A unit of weight in the metric system equal to 2.2 pounds.





LETHAL CONCENTRATION50: The concentration of an air contaminant (LC50) that will kill 50 percent of the test animals in a group during a single exposure.

LETHAL DOSE50: The dose of a substance (LD50) or chemical that will  kill 50 percent of the test animals in a group within the first 30 days following exposure.


LITER (L): A measure of capacity. One quart equals .9 liters.

LOCAL EXHAUST VENTILATION: (Also known as exhaust ventilation.) A ventilation system that captures and removes the contaminants at the point where they are being produced before they escape into the workroom air. The system consists of hoods, ducts, a fan and possibly an air cleaning device. Advantages of local exhaust ventilation over general ventilation include: it removes the contaminant rather than dilutes it; it requires less air flow and thus is more economical over the long term; and the system can be used to conserve or reclaim valuable materials. The system, however, must be properly designed with the correctly shaped and placed hoods, and correctly sized fans and duct work.

LOWER EXPLOSIVE LIMIT (LEL): (Also known as Lower Flammable Limit). The lowest concentration of a substance that will produce a fire or flash when an ignition source (flame, spark, etc.) is present. It is expressed in percent of vapor or gas in the air by volume. Below the LEL or LFL, the air/contaminant mixture is theoretically too "lean" to burn. (See also UEL).


MELTING POINT: The temperature at which a solid changes to a liquid. A melting range may be given for mixtures.




MILLIGRAM (mg): A unit of weight in the metric system. One thousand milligrams equal one gram.

MILLIGRAMS PER CUBIC METER: Units used to measure air (mg/m3) concentrations of dusts, gases, mists, and fumes.

MILLIGRAMS PER KILOGRAM: This indicates the dose of a substance (mg/kg) given to test animals in toxicity studies. For example, a dose may be 2 milligrams (of substance) per kilogram of body weight (of the experimental animal).

MILLILITER (ml): A metric unit used to measure capacity. One milliliter equals one cubic centimeter. One thousand milliliters equal one liter.


MSHA: The Mine Safety and Health Administration, a federal agency that regulates the mining industry in the safety and health area.

MUTAGEN: Anything that can cause a change (or mutation) in the genetic material of a living cell.

NARCOSIS: Stupor or unconsciousness caused by exposure to a chemical.

NFPA: The National Fire Protection Association is a voluntary membership organization whose aims are to promote and improve fire protection and prevention. NFPA has published 16 volumes of codes known as the National Fire Codes. Within these codes is Standard No. 704, Identification of the Fire Hazards of Materials. This is a system that rates the hazard of a material during a fire. These hazards are divided into health, flammability, and reactivity hazards and appear in a well-known diamond system using from zero through four to indicate severity of the hazard. Zero indicates no special hazard and four indicates severe hazard.

NIOSH: The National Institute of Occupational Safety and Health is a federal agency that among its various responsibilities trains occupational health and safety professionals, conducts research on health and safety concerns, and tests and certifies respirators for workplace use.

ODOR THRESHOLD: The minimum concentration of a substance at which a majority of test subjects can detect and identify the substance's characteristic odor.

ORAL: Having to do with the mouth.

OSHA: The Occupational Safety and Health Administration, a federal agency under the Department of Labor that publishes and enforces safety and health regulations for most businesses and industries in the United States.

OXIDATION: The process of combining oxygen with some other substance to cause a chemical change in which an atom loses electrons.

OXIDIZER: A substance that gives up oxygen easily to stimulate combustion of organic material.

OXYGEN DEFICIENCY: An atmosphere having less than the normal percentage of oxygen found in normal air. Normal air contains 21% oxygen at sea level.


PERMISSIBLE EXPOSURE LIMIT (PEL): An exposure limit that is published and enforced by OSHA as a legal standard. PEL may be either a time-weighted-average (TWA) exposure limit (8 hour), a 15-minute short term exposure limit (STEL), or a ceiling (C). The PEL's are found in Tables Z-1, Z-2, or Z-3 of OSHA regulations 1910.1000. (See also TLV).

PERSONAL PROTECTIVE EQUIPMENT: Any devices or clothing worn by the worker to protect against hazards in the environment. Examples are respirators, gloves, and chemical splash goggles.

POLYMERIZATION: A chemical reaction in which two or more small molecules combine to form larger molecules that contain repeating structural units of the original molecules. A hazardous polymerization is the above reaction with an uncontrolled release of energy.

ppm: Parts (of vapor or gas) per million (parts of air) by volume.

REACTIVITY: A substance's susceptibility to undergoing a chemical reaction or change that may result in dangerous side effects, such as explosions, burning, and corrosive or toxic emissions. The conditions that cause the reaction, such as heat, other chemicals, and dropping, will usually be specified as "Conditions to Avoid" when a chemical's reactivity is discussed on a MSDS.

RESPIRATOR: A device designed to protect the wearer from inhaling harmful contaminants.

RESPIRATORY HAZARD: A particular concentration of an airborne contaminant that, when it enters the body by way of the respiratory system or by being breathed into the lungs, results in some bodily function impairment.

SENSITIZER: A substance that may cause no reaction in a person during initial exposures. Afterwards, further exposures will cause an allergic response to the substance.

SHORT TERM EXPOSURE LIMIT: Represented as STEL or TLV-STEL, this is the maximum concentration to which workers can be exposed for a short period of time (15 minutes) for only four times throughout the day with at least one hour between exposures. Also the daily TLV-TWA must not be exceeded.

"SKIN": This designation sometimes appears alongside a TLV or PEL. It refers to the possibility of absorption of the particular chemical through the skin and eyes. Thus, protection of large surface areas of skin should be considered to prevent skin absorption so that the TLV is not invalidated.

STEL: Short Term Exposure Limit.

SUBSTANCE: Any chemical entity.

SYNONYM: Another name by which the same chemical may be known.

SYSTEMIC: Spread throughout the body; affecting many or all body systems or organs; not localized in one spot or area.

TERATOGEN: An agent or substance that may cause physical defects in the developing embryo or fetus when a pregnant female is exposed to that substance.

THRESHOLD LIMIT VALUE: Airborne concentrations of substances devised by the ACGIH that represent conditions under which it is believed that nearly all workers may be exposed day after day with no adverse effect. TLV's are advisory exposure guidelines, not legal standards, that are based on evidence from industrial experience, animal studies, or human studies when they exist. There are three different types of TLV's: Time Weighted Average (TLV-TWA), Short Term Exposure Limit (TLV-STEL) and Ceiling (TLV-C). (See also PEL.)

TIME WEIGHTED AVERAGE: The average time, over a given work period (e.g. 8-hour work day), of a person's exposure to a chemical or an agent. The average is determined by sampling for the contaminant throughout the time period. Represented as TLV-TWA.


TOXICITY: The potential for a substance to exert a harmful effect on humans or animals and a description of the effect and the conditions or concentrations under which the effect takes place.

TRADE NAME: The commercial name or trademark by which a chemical is known. One chemical may have a variety of trade names depending on the manufacturers or distributors involved.




UNSTABLE LIQUID: A liquid that, in its pure state or as commercially produced, will react vigorously in some hazardous way under shock conditions (i.e., dropping), certain temperatures, or pressures.

UPPER EXPLOSIVE LIMIT: Also known as Upper Flammable Limit. Is the highest concentration (expressed in percent of vapor or gas in the air by volume) of a substance that will burn or explode when an ignition source is present. Theoretically, above this limit the mixture is said to be too "rich" to support combustion. The difference between the LEL and the UEL constitutes the flammable range or explosive range of a substance. That is, if the LEL is 1ppm and the UEL is 5ppm, then the explosive range of the chemical is 1ppm to 5ppm. (see also LEL).

VAPOR: The gaseous form of substances that are normally in the liquid or solid state (at normal room temperature and pressure). Vapors evaporate into the air from liquids such as solvents. Solvents with low boiling points will evaporate.