Breathing zone. The space around and in front of an employee's nose and mouth, forming a hemisphere with a six to nine inch radius.

Ceiling limit. See Permissible exposure limits (PELs).

Dust. Solid particles suspended in air. Dusts are generated by handling, drilling, crushing, grinding, rapid impact, detonation, or decrepitation of organic or inorganic materials such as rock, ore, metal, coal, wood, grain, etc.

Exposed or exposure. The contact an employee has with a toxic substance, harmful physical agent or oxygen deficient condition, whether or not protection is provided by respirators or other personal protective equipment (PPE). Exposure can occur through various routes of entry, such as inhalation, ingestion, skin contact, or skin absorption.

Fume. Solid particles suspended in air, generated by condensation from the gaseous state, generally after volatilization from molten metals, etc.

Gas. A normally formless fluid which can be changed to the liquid or solid state by the effect of increased pressure or decreased temperature or both.

General exhaust ventilation. The general movement of air out of an area or permit-required confined space by mechanical or natural means.

Immediately dangerous to life or health (IDLH). An atmospheric condition that would:

(a) Cause an immediate threat to life;

(b) Cause permanent or delayed adverse health effects; or

(c) Interfere with an employee's ability to escape.

Mist. Liquid droplets suspended in air, generated by condensation from the gaseous to the liquid state or by breaking up a liquid into a dispersed state, such as by splashing, foaming, spraying or atomizing.

Nuisance dust (or inert dust). Dusts that, when inhaled, have little adverse effect on the lungs and do not produce significant organic disease or toxic effect when exposures are kept under reasonable control.

The biological reaction to these dusts in lung tissue has the following characteristics:

(a) The architecture of the air spaces remains intact;

(b) Scar tissue (collagen) is not formed to a significant extent; and

(c) The tissue reaction is potentially reversible.

Oxygen deficient. An atmosphere with an oxygen content below 19.5% by volume.

Permissible exposure limits (PEL). The amount of an airborne chemical, toxic substance, or other harmful agent that must not be exceeded during any part of the workday.

An airborne chemical or toxic substance can have 3 PEL values:

(a) TWA8. This is an 8-hour, time-weighted average limit.

(b) Short-term exposure limit (STEL). This is typically a 15-minute, time-weighted average limit.

(c) Ceiling limit (C). This is an instantaneous limit.

Short-term exposure limit (STEL). See Permissible exposure limits (PELs).

Temper. To condition air for a specific work environment by changing its temperature or moisture content.

Time weighted average (TWA8). See Permissible exposure limits (PELs).

Toxic substance. Any chemical substance or biological agent, such as bacteria, virus, and fungus, which is any of the following:

(a) Listed in the latest edition of the National Institute for Occupational Safety and Health (NIOSH) Registry of Toxic Effects of Chemical Substances (RTECS).

(b) Shows positive evidence of an acute or chronic health hazard in testing conducted by, or known to, the employer.

(c) The subject of a safety data sheet kept by or known to the employer showing the material may pose a hazard to human health.

Vapor. The gaseous form of a substance that is normally in the solid or liquid state.

Ventilation. Providing, circulating or exhausting air into or out of an area or space.