contaminant per million parts of air), while

particulate concentrations are expressed as

mg/m3 (milligrams of concentrations per cubic meter of air). For substances that can exist in more than one form (particulate or gaseous), concentrations are expressed in both values.

IDLH (Immediately Dangerous to Life or Health) characterizes an atmosphere that poses an immediate threat to life, would cause irreversible adverse health effects, or would impair an individual’s ability to escape from a dangerous atmosphere.

It is important to note that exposure limits and other exposure standards are constantly

changing as more data is gathered about specific chemicals and substances. As such, you must be certain that you are using the most recent data when determining allowable exposure levels for employees.

Hazard control should start at the process, equipment, and plant design levels where contaminants can be controlled effectively at the outset. With operating processes, the problem becomes more difficult. In all cases, however, attention should be given to the use of effective engineering controls to eliminate and/or reduce exposures to respiratory hazards. This includes consideration of process encapsulation or isolation; use of less toxic materials in the process’ and suitable exhaust ventilation, filters, and scrubbers to control the effluents.

Because it is sometimes not practical to maintain engineering controls that eliminate all airborne concentrations of contaminants, proper respiratory protective devices should be used whenever such protection is required.

All respirators in use must be NIOSH-approved

(NIOSH 42 CFR Part 84). Selecting respirators

entails knowing what level of respiratory

protection employees need, as well as which size respirator is right for any face and facial contours.

Respiratory protective devices vary in design,

application, and protective capability. Thus, the user must assess the inhalation hazard and understand the specific use limitations of

available equipment to assure proper selection.

If your calculation shows that exposure

concentrations exceed recommended limits and engineering/administrative controls do not reduce exposure below the permissible limit, tailor your respiratory protection program to your specific conditions based on:

• Maximum Expected Concentration

• Oxygen level

• IDLH concentration

• Warning properties (adequate or not)

• Sorbent limitations

• Facepiece fit

• Mobility requirements

• Type of use (routine, escape, or

emergency entry)

Respirators fall under two classifications:

respirators are used against particulates, gases, and vapors. These are categorized as negative pressure respirators that use chemical cartridges and/or filters; gas masks; and positive-pressure units such as powered air-purifying respirators (PAPRs). Air-supplied devices rely on a primary air source to deliver a steady flow of respirable

air to the user’s facepiece. These consist of

Self-Contained Breathing Apparatus (SCBA) and air-line devices.

simple disposable cup masks to low maintenance halfmask facepieces with cartridges and/or filters to the more complex PAPRs with full- facepieces, or hoods.

• APRs for particulates use filters to capture

dusts, mists, and fumes. Filters do not protect against gases or vapors, and generally become less effective as particles accumulate on the filter and plug spaces between the fibers.

Filtering APRs require filter replacement when

the user finds it difficult to breathe through

them.

• Gas and vapor APRs employ chemical

cartridges or canisters to remove hazardous

gases or vapors from the air. They do not

protect against airborne particles. Made to

protect against specific gases or vapors,

they provide protection only as long as the

cartridge’s absorbing capacity is not depleted.

The service life of a chemical cartridge depends upon many factors and can be estimated in various ways. Cartridges and canisters require

an end-of-service-life indicator (ESLI) or a change schedule, based on objective information or data that will ensure that canisters and cartridges are changed before the end of their useful life. In the respirator program, the employer must describe

the information and data relied upon and the basis for the canister and cartridge change schedule as well as the basis for reliance on the data.

• Combination APRs, fitted with both particulate filters and gas/vapor cartridges, are worn in atmospheres that contain hazards of both particulates and gases.

air-line respirators, SCBA, and combination

(supplied-air) respirators.

• Air-Line Respirators are used for extended

periods in non-IDLH atmospheres. They use an air-line hose to deliver clean breathing air from a stationary source of compressed air for prolonged periods of time. Although comparatively lightweight, air-line respirators can limit users’ mobility because of the air-line hose that must be attached.

• Self-Contained Breathing Apparatus (SCBA)

have an open-circuit design that provides air rated for 30 to 60 minutes. They consist of a wearable, clean-air supply and a tight-fitting facepiece, and are used for short duration entrance or escape from atmospheres thatare or may be IDLH. They offer relatively unrestricted movement.

• Combination SARs are air-line devices used for extended work periods in atmospheres that are or may be IDLH. They have an auxiliary self-contained air cylinder that can be used if the primary air supply fails. The air cylinder can also be used for entry into or escape from IDLH atmospheres, such as confined spaces.

Employers are required to provide employees using SARs with breathing gases of high purity, and ensure that compressed air, compressed oxygen, liquid air, and liquid oxygen used for respiration is in accordance with the specifications of OSHA Standard

For proper use of any respiratory protection device, it is essential that the user be properly instructed in its selection, use, and maintenance. Both supervisors and workers must be so instructed by competent persons.

• Methods of recognizing respiratory hazards

• Instruction in the hazards and an honest

appraisal of what could happen if the proper

respiratory protection device is not used

• Explanation of why more positive control is not immediately feasible. This must include recognition that every reasonable effort is first being made to reduce or eliminate the need for respiratory protection