Start with the four essentials. OSHA says that in order to select appropriate respirators for employees, you must:

• Conduct an exposure assessment to determine the type and amount of hazardous exposure.
• Take into account factors that can influence respirator selection such as jobsite and worker characteristics.
• Understand the assigned protection factors (APFs).
• Know the various kinds of respirators and their characteristics.

Determine the risks. An exposure assessment will answer essential questions such as:

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

Once you've determined the nature of the respiratory hazard, you have to find out how much employee exposure there is in your workplace. This is generally accomplished by personal exposure monitoring,

which OSHA calls the "gold standard" for determining employee exposures. But you can also use data on the physical and chemical properties of air contaminants as well as data from industrywide surveys by trade associations for use by their members or information from stewardship programs operated by manufacturers for their customers.

Take into account other factors that influence respirator selection. There are at least three key factors to consider:

• Physical configuration of the work area. For example, tightly constrained areas might 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. Workers with certain medical conditions, such as heart conditions, may not be able to use respirators safely.
• Worker comfort. It's important for workers to feel comfortable when wearing any PPE, including respirators. If PPE isn't comfortable, employees might not use it.

Make sure you pick a respirator with the right APF. The APF of a respirator reflects the level of protection that a properly functioning respirator would be expected to provide to a properly fitted and trained employees. For example, an APF of 10 for a respirator means that an employee could expect to inhale no more than one-tenth of the airborne contaminant present. Last year OSHA revised the respiratory protection standard to add definitions and requirements for APFs.

Kinds of respirators. Basically, there are two kinds of respirators--air-purifying respirators to filter out airborne contaminants and atmosphere-supplying respirators to supply oxygen in oxygen-deficient environments. But within those two broad categories, there are three types of each. The three types of air-purifying respirators are:

• Particulate respirators, which capture such particles in the air as dust, mists, and fumes, but do not protect against gases or vapors
• Combination respirators, which are normally used in atmospheres that contain both particulate and gas hazards and have both particulate filters and gas/vapor filters
• Gas and vapor respirators, which are normally used when there are only hazardous gases and vapors in the air and have chemical filters (called cartridges or canisters) to remove the dangerous gases or vapors

The three kinds of atmosphere-supplying respirators are:

• Air-supplied respirators (also called "airline respirators"), which use a hose to deliver clean, safe air from a stationary source of compressed air
• Combination respirators, which have an auxiliary self-contained air supply that can be used if the primary supply fails and are often used for entry into confined spaces
• Self-contained breathing apparatus (SCBA), which consists of a wearable, clean-air supply pack that does not restrict movement with a hose connection and is normally used when atmospheres are, or may be, immediately dangerous to life and health (IDLH)