Exposure Assessment

When? What? How Much?

Employers must characterize the nature and magnitude of employee exposures to respiratory hazards before selecting respiratory protection equipment. Paragraph 29 CFR 1910.134(d)(1)(iii) requires the employer to identify and evaluate the respiratory hazard(s) in the workplace. Employers must make a "reasonable estimate" of the employee exposures anticipated to occur as a result of those hazards, including those likely to be encountered in reasonably foreseeable emergency situations, and must also identify the physical state and chemical form of such contaminant(s). The final rule does not specify how the employer is to make reasonable estimates of employee exposures for the purposes of selecting respirators.

When must an employer conduct an exposure assessment?

When you expose your employees to a respiratory hazard and/or require them to wear respirators. Examples of when you should consider assessments may include but are not limited to:

• When OSHA has a substance specific standard (e.g., lead, methylene chloride).
• When employees notice symptoms (e.g., irritation, odor) or complain of respiratory health effects.
• When the workplace contains visible emissions (e.g., fumes, dust, aerosols).

What is the identity and nature of the airborne contaminant?

Specific characteristics of the airborne hazard must be established in order to select an appropriate respirator.

• Is the airborne contaminant a particulate (dust, fumes, mist, aerosol) or a gas/vapor?
• Is the airborne contaminant a chemical and are material safety data sheets available?
• Is the airborne contaminant a biological (bacteria, mold, spores, fungi, virus)?
• Are there any mandatory or recommended occupational exposure levels for the contaminant?

How much employee exposure is there in the workplace?

The final rule permits employers to use many approaches for estimating worker exposures to respiratory hazards.

• Sampling - Personal exposure monitoring is the "gold standard" for determining employee exposures because it is the most reliable approach for assessing how much and what type of respiratory protection is required in a given circumstance.
  • Sampling should utilize methods appropriate for contaminants(s).
  • Sampling should present the worst case exposures; or
  • Sampling should represent enough shifts and operations to determine the range of exposure.
• Objective Information - You may rely on information and data that indicate that use or handling of a product or material cannot, under worst-case conditions, release concentrations of a respiratory hazard above a level that would trigger the need for respirator use or require use of a more protective respirator.
  • You can use data on the physical and chemical properties of air contaminants, combined with information on room dimensions, air exchange rates, contaminant release rates, and other pertinent data, including exposure patterns and work practices, to estimate the maximum exposure that could be anticipated in the workplace.
  • Data from industry-wide surveys by trade associations for use by their members, as well as from stewardship programs operated by manufacturers for their customers, are often useful in assisting employers, particularly small-business owners, to obtain information on employee exposures in their workplaces.

• Variation - You should account for potential variation in exposure by using exposure data collected with a strategy that recognizes exposure variability, or by using worst-case assumptions and estimation techniques to evaluate the highest foreseeable employee exposure levels. The use of safety factors may be necessary to account for uneven dispersion of the contaminant in the air and the proximity of the worker to the emission source.

The Physical Configuration of the Jobsite

Tightly constrained areas may not permit the use of self-contained breathing apparatuses even though they might be an acceptable choice otherwise. Likewise, working around obstructions or moving machinery that can snag hoses may limit the use of airline respirators.

Worker Medical Condition

Wearing respiratory protection poses a physical burden on the wearer. When a worker's medical condition would prohibit restrictive breathing conditions, negative pressure respirators would not be an appropriate choice.

Worker Comfort

Worker preferences should be a consideration during the respirator selection process. Among air purifying respirators, powered air purifying helmets have been subjectively rated the best for breathing ease, skin comfort, and in-mask temperature and humidity while filtering facepieces rated high for lightness and convenience. Each, however, has its own drawbacks, and all these factors should be taken into account during selection.

Assigned Protection Factors

The assigned protection factor (APF) of a respirator reflects the level of protection that a properly functioning respirator would be expected to provide to a population of properly fitted and trained users. For example, an APF of 10 for a respirator means that a user could expect to inhale no more than one tenth of the airborne contaminant present.

See: Table 1. Assigned Protection Factors. [29 CFR 1910.134(d)(3)(i)(A)]