To determine an atmosphere's oxygen content or concentration levels of particulate and/or gaseous contaminants, air samples must be taken with proper sampling instruments during all conditions of operation. The sampling device and the type and frequency of sampling (spot testing or continuous monitoring) will be dictated by the exposure and operating conditions.  Breathing zone samples are recommended and sampling frequency should be sufficient to assess the average exposure under the variable operating and exposure conditions.

Should contaminant concentrations exceed exposure limits recommended by the American Conference of Governmental Industrial Hygienists (ACGIH), OSHA or NIOSH, hazard control procedures must be implemented promptly.

Exposure monitoring plays a critical role in the respirator selection process. The results from such tests will help you determine whether respiratory protection is needed and, if it is, the type of respirator required. Generally, respirator selection is based on three factors: 1. the results of your atmospheric monitoring or sampling program; 2. the accepted ACGIH, OSHA or NIOSH exposure limits for the substance(s) present; 3. and the maximum use concentration (of a substance) for which a respirator can be used.

Exposure limits listed in the Response Respirator Selector include ACGIH Threshold Limit Values (TLVs), OSHA Permissible Exposure Limits (PELs), NIOSH Recommended Exposure Limits (RELs) and AIHA Workplace Environmental Exposure Levels (WEELs). These values are guides for exposure concentrations that healthy individuals can normally tolerate for eight hours a day, five days a week without harmful effects. Unless otherwise noted, exposure limits are eight-hour, time-weighted-average (TWA) concentrations.

In general, gas and vapor exposure limits are expressed in ppm by volume (parts of contaminant per million parts of air), while particulate concentrations are expressed as mg/m3 (milligrams of contaminant per cubic meter of air).  For substances that can exist in more than one form (particulate or gaseous), concentrations are expressed in both values. In the Response Respirator Selector, the exposure limits for a substance's secondary form are indicated by parenthesis.

An additional part of Hazard Assessment is the determination of whether the contaminant has adequate warning properties. This affects respirator selection in that chemical cartridge respirators and gas masks can only be used for routine use against gases and vapors with adequate warning properties unless: (1) it is equipped with an end of service life indicator, or (2) a documented cartridge/canister change-out schedule is developed based on objective information or data (including MSA service-life performance data against the specific material) that will ensure that cartridges and canisters are changed before the end of their service life. Note: Since the requirement regarding a change-out schedule is based on OSHA Regulation 29 CFR 1910.134 issued January 8, 1998, check with MSA regarding the availablility of service life data.

The Response Respirator Selector classifies the warning properties of gases and vapors and limits the respirator selection accordingly if the warning properties are poor or the odor threshold is unknown.The odor thresholds listed in the Response Respirator Selector were obtained from the following references:

1.Documentation of TLVs and BEIs, American Conference of Governmental Industrial Hygienists, 6th edition (1991).

2.Odor Thresholds for Chemicals with Established Occupational Health Standards, American Industrial Hygiene Association (1989).

3.J. E. Amoore and E. Hautula, Odor as an Aid to Chemical Safety, Journal of Applied Toxicology 3(6):272-290 (1983).

4.L. J. Van Gemert, Compilation of Odor Threshold Values in Air, Supplement IV, CIVO-TNO Zeist, Netherlands (1982)

5.F. A. Fazzuluri, Compilation Odor and Taste Threshold Values Data, American Society for Testing and Materials (1978).

6.K. Verchueren, Handbook of Environmental Data on Organic Chemicals, pp. 12-21, Van Nostrand Reinhold, NY (1977).

7.L. J. Van Gemert and A. H. Nettenbreijer, Compilation of Odor Threshold Values in Air and Water, CIVO-TNO, Netherlands (1977).

8.Warning Properties of Industrial Chemicals, Occupational Health Resource Center, Oregon Lung Association.

In accordance with the OSHA Regulation, should the applicable information and data be available regarding cartridge/canister change-out, the appropriate cartridge/canister (based on the data) may be used for routine use applications.

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 Response Respirator Selector when determining allowable exposure levels for employees.

The following are types of ACGIH, OSHA, NIOSH and AIHA exposure limits listed in the RESPONSE guidebook.

ACGIH:

ACGIH exposure limits include three categories of Threshold Limit Values (TLVs). They are as follows:

Time-Weighted Average (TWA) - This exposure limit is based on acceptable contaminant concentrations for a normal, 8-hour workday and a 40-hour workweek.

Short-Term Exposure Limit (STEL) - This is a 15-minute TWA exposure that should not be exceeded at any time during a workday. Exposures above the TWA up to the STEL should not be longer than 15 minutes and should not occur more than four times per day. Additionally, there should be at least 60 minutes between successive exposures in this range.

Ceiling (CEIL) - This refers to concentrations that must not be exceeded during any part of the working exposure. As such, Ceiling TLVs take precedent over all TWAs and STELs.

OSHA:

Permissible Exposure Limit (PEL) - Based on an 8-hour TWA, PELs are exposure levels below which OSHA does not require respiratory protection.  When exposures surpass this level, certain respiratory protection requirements must be met.

Short-Term Exposure Limit (STEL) - This is a 15-minute TWA exposure that should not be exceeded at any time during a workday.

Ceiling (CEIL) - Same as ACGIH definition.

NIOSH:

Recommended Exposure Limit (REL) - A TWA concentration for up to a 10-hour workday during a 40-hour workweek.

Short-Term Exposure Limit (STEL) - Same as OSHA definition.

Ceiling (CEIL) - Same as ACGIH definition.

Immediately Dangerous to Life or Health (IDLH) - As its name implies, the IDLH level refers to acute respiratory exposures that pose an immediate threat of loss of life. Exposures at this level may result in irreversible or severe health effects, eye damage, irritation or other conditions that could impair an employee's escape from the hazardous atmosphere.

AIHA: