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.
Short duration, rapidly changing conditions.
An intense exposure over a relatively short period of time.
The American National Standards Institute is a voluntary membership organization (run
with private funding) that develops consensus standards nationally for a wide variety
of devices and procedures.
A chemical (gas or vapor) that can cause death or unconsciousness by suffocation.
Simple asphyxiants, such as nitrogen, either remove or displace oxygen in the air.
They become especially dangerous in confined or enclosed spaces. Chemical asphyxiants,
such as carbon monoxide and hydrogen sulfide, interfere with the body's ability to
absorb or transport oxygen to the tissues.
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 Celsius. If a flammable material has a low boiling point, it indicates
a special fire hazard.
Degrees Celsius; the common metric laboratory temperature scale.
"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).
A substance or physical agent that may cause cancer in animals or humans.
Identifies a particular chemical by the Chemical Abstracts Service, a service of the
American Chemical Society that indexes and compiles abstracts of worldwide chemical
literature called Chemical Abstracts.
cc or CC
Cubic centimeter, a volumetric measurement that is also equal to one milliliter (ml).
As broadly applied to the chemical industry, an element or a compound produced by
chemical reactions on a large scale for either direct industrial and consumer use
or for reaction with other chemicals.
A change in the arrangement of atoms or molecules to yield substances of different
composition and properties. (see Reactivity)
Persistent, prolonged or repeated conditions.
A prolonged exposure occurring over a period of days, weeks, or years.
According to the DOT and NFPA, combustible liquids are those having a flash point
at or above 100°F (37.8°C), or liquids that will burn. They do not ignite as easily
as flammable liquids. However, combustible liquids can be ignited under certain circumstances,
and must be handled with caution. Substances such as wood, paper, etc., are termed
The relative amount of a material in combination with another material. For example,
5 parts of (acetone) per million (parts of air).
A substance that according to the DOT, causes visible destruction or permanent changes
in human skin tissue at the site of contact or is highly corrosive to steel or aluminum.
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.
The number assigned to chemicals regulated by the Environmental Protection Agency
The study of disease in human populations.
Reddening of the skin.
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.
Degrees Fahrenheit; the common temperature scale used in the U.S.
According to the DOT and NFPA a flammable liquid is one that has a flash point below
100°F. (See Flash Point)
Classes Of Flammable Liquids:
Flammable Solvent Class
Between 73°F and 100°F
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.
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).
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. However, the
system must be properly designed with correctly shaped and placed hoods, and correctly
sized fans and ductwork.
Lower Explosive Limit (LEL) (Also known as Lower Flammable Limit)
The lowest concentration of a substance that will produce a fire 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).
A unit of mass 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 or mL)
A metric unit used to measure volume. One milliliter equals one cubic centimeter.
One thousand milliliters equal one liter.
Stupor or unconsciousness caused by exposure to a chemical.
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.
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.
The minimum concentrations of a substance at which a majority of test subjects can
detect and identify the substance's characteristic odor.
Having to do with the mouth.
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.
The process of combining oxygen with some other substance or a chemical change in
which an atom loses electrons.
Is a substance that gives up oxygen easily to stimulate combustion of organic material.
An atmosphere having less than the normal percentage of oxygen found in normal air.
Normal air contains 21% oxygen.
An exposure limit that is published and enforced by OSHA as a legal standard. PEL
may be 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 device or clothing worn by the worker to protect against hazards in the environment.
Examples are respirators, gloves, and chemical splash goggles or other appropriate
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 a polymerization reaction with an uncontrolled release of energy.
Parts (of vapor or gas) per million (parts of air) by volume. May also pertain to
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 shock, will usually be specified as "Conditions to Avoid" when a chemical's reactivity
is discussed on a MSDS.
A device which is designed to protect the wearer from inhaling harmful contaminants
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.
A substance that may cause no reaction in a person during initial exposures, but afterwards,
further exposures of even small amounts 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
This designation sometimes appears alongside a TLV or PEL. It refers to the possibility
of absorption of the particular chemical though 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.
Short Term Exposure Limit.
Any chemical entity.
Another name by which the same chemical may be known.
Spread throughout the body; affecting many or all body systems or organs; not localized
in one spot or area.
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 workday), 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.
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.
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 12% and the UEL is 35%, then the explosive range
of the chemical is 12% to 35%. (See also LEL).
The gaseous form of substances which 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 readily.