Glossary of Terms: A

Absorption
Diffusion process in which molecules are transferred from the gas phase to a liquid
AC/DC Output
Outputs the AC or DC signal to a data acquisition system or chart recorder.
ACGIH
American Conference of Governmental Industrial Hygienists, which develops and publishes recommended occupational exposure limits for hundreds of chemical substances and physical agents.
Acid
Any chemical with a low pH that in water solution can burn the skin or eyes. Acids turn litmus paper red and have pH values of 0 to 6.
Action level
Term used by OSHA and NIOSH to express the level of toxicant which requires medical surveillance, usually one half of the PEL.
Activated alumina
A highly porous chemisorbent media - usually impregnated with KMnO4
Activated charcoal
Charcoal is an amorphous form of carbon formed by burning wood, nutshells, animal bones, and other carbonaceous materials. Charcoal becomes activated by heating it with steam to 800-900°C. During this treatment, a porous, submicroscopic internal structure is formed which gives it an extensive internal surface area. Commonly used as a gas or vapor adsorbent in air-purifying respirators and as a solid sorbent in air-sampling.
Acute effect
A change that occurs in the body within a relatively short time (minutes, hours, days) following exposure to a substance. Adverse effect on a human or animal which has severe symptoms developing rapidly and coming quickly to a crisis. Also see "chronic effect."
Acute exposure
A single exposure to a hazardous agent.
Administrative controls
Methods used to control employee exposure to airborne contaminants, e.g., by job rotation or work re-assignment
Adsorbents
Gas scrubbing, porous materials with a very high ratio of interior surface area to external surface area, e.g. (a) activated carbon: the most common adsorbent material due to inherently high surface area and relatively low cost, (b) blended media: mixture of chemically impregnated activated carbon and activated alumina
Adsorption
a physical process in which a gas or vapor adheres to the surface of a solid (usually a highly porous material, e.g., activated carbon. The condensation of gases, liquids, or dissolved substances on the surfaces of solids.
Aerosols
A suspension of solid or liquid particles in air; typical aerosols: (a) Dusts: Solid aerosols generated from the reduction of larger materials; airborne dust range, 0.1 to 30µ, (b) Fumes: Solid aerosols formed by the condensation of solid materials, e.g., welding fumes, range, 0.001 to 1.0µ (c) Smoke: Aerosol mixture formed from incomplete combustion of organic matter, size range, 0.01 to 1.0, (d) Vapors: Gases formed by the evaporation of materials which are normally liquid or solid, size 0.005µ, (e) Gas: materials with the tendency to expand indefinitely and which completely and uniformly fills the container it occupies.
Agent
Any substance, force, organism or influence that affects the body, a part of the body, or any of its functions. The effects may be beneficial or harmful.
AIHA
American Industrial Hygiene Association.
Air purifier
A device to capture and contain industrial process air contaminants
Air
The mixture of gases that surrounds the earth; its major components are as follows: 78.08% nitrogen, 20.95% oxygen, 0.03% carbon dioxide, and 0.93% argon. Water vapor (humidity) varies.
Air-line respirator
A respirator that is connected to a compressed breathing air source by a hose of small inside diameter. The air is delivered continuously or intermittently in a sufficient volume to meet the wearer's breathing requirements.
Air-purifying respirator
A respirator that uses chemicals to remove specific gases and vapors form 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.
AIT
Auto Ignition Temperature.
Alkali
Any chemical with a high pH that in water solution is irritating or caustic to the skin. Strong alkalies in solution are corrosive to the skin and mucous membranes. Alkalis turn litmus paper blue and have pH values from 8 to 14. Also called base.
Allergy
An abnormal response of a hypersensitive person to chemical and physical stimuli. Allergic manifestations of major importance occur in about 10 percent of the population.
American Conference of Governmental Industrial Hygienists (ACGIH)
An organization of industrial hygiene professionals that develops occupational health and safety programs. ACGIH develops and publishes recommended occupational exposure limits for hundreds of chemical substances and physical agents (see Threshold Limit Value).
Analog output
Standard mA output from a sensor or transmitter. Normally described as 4-20mA. The alternative is a mV bridge output from a catalytic type sensor or a digital output.
ANSI
American National Standards Institute, a voluntary membership organization that develops consensus standards nationally for a wide variety of devices and procedures.
Apparatus group
The classification of flammable gases into groups that are associated with required apparatus design standards.
Area sampling
Collection and analysis of representative samples of air in general work areas in order to determine the concentrations of any contaminants that are present.
Asphyxiant
A vapor or gas that can either reduce the oxygen content in the air or interfere with the body’s ability to use oxygen. Exposure to an asphyxiant can result in unconsciousness or death due to being unable to breathe. One of the principal potential hazards of working in confined spaces.
Asphyxiation
Death resulting from lack of Oxygen.
ASTM
American Society for Testing and Materials.
ATEX
European Explosive Atmospheres Directives (ATmospheres EXplosibles).
Atmosphere-supplying respirator
A respirator that provides breathing air from a source independent of the surrounding atmosphere. There are two types: air-line and self-contained breathing apparatus.
Atmospheric pressure
The pressure exerted in all directions by the atmosphere. At sea level, mean atmospheric pressure is 29.92 inches Hg, 14.7 psi, or 407 inches w.g.
Attenuation
A decrease in signal magnitude from one point to another, or the process causing this decrease. .
Audiometric Testing
Tests that are conducted to determine the hearing ability of a person. These tests may be used to establish an employee’s baseline hearing, to identify any subsequent hearing loss, and to monitor the effectiveness of noise controls.