| AIHA |
American Industrial Hygiene Association |
| ACGIH |
American Conference of Industrial Hygienists |
| Ceiling |
Concentration limit for airborne substances that should never be exceeded for any time period. |
| EPA |
Environmental Protection Agency (USA) |
| ERPG |
Emergency Response Planning Guideline (AIHA) |
| ERPG-1 |
The maximum airborne concentration below which it is believed that nearly all individuals could be exposed for up to 1 hour without experiencing other than mild transient adverse health effects or perceiving a clearly defined, objectionable odour (AIHA). |
| ERPG-2 |
The maximum airborne concentration below which it is believed that nearly all individuals could be exposed for up to 1 hour without experiencing or developing irreversible or other serious health effects or symptoms which could impair an individual's ability to take protective action (AIHA). |
| ERPG-3 |
The maximum airborne concentration below which it is believed that nearly all individuals could be exposed for up to 1 hour without experiencing or developing life-threatening health effects (AIHA). |
| MEL |
Maximum exposure limit |
| NAAQS |
National Ambient Air Quality Standards (USA) |
| NIOSH |
National Institute for Occupational Safety and Health at the Centers for Disease Control and Prevention (USA) |
| OEL |
Occupational exposure limit |
| OSHA |
US Department of Labor Occupational Safety and Health Administration |
| Primary |
Primary standards set limits to protect public health, including the health of "sensitive" populations such as asthmatics, children, and the elderly. |
| PM |
Particulate matter. Generally designated by size, with particles with a mean aerodynamic diameter 2.5-10 microns referred to as coarse particles, and those < 2.5 (PM2.5) microns in diameter referred to as fine particles. |
| PEL |
Permissible exposure limit |
| REL |
Recommended exposure limit |
| Secondary |
Secondary standards set limits to protect public welfare, including protection against decreased visibility, damage to animals, crops, vegetation, and buildings. |
| STEL |
Short term exposure limit, generally 15 minute time-weighted average that should not be exceeded at any time during a workday. |
| TWA |
Time weighted average |
