You’ll need to select equipment based on whether your work environment contains a particulate hazard (particles such as hazardous dusts or fibers), a gas or vapor hazard (such as solvent vapors or chlorine gas), or both types of hazards.

Generally, you protect against particulate hazards with a filter and against gas and vapors with a cartridge. If both types of hazards are present, combination cartridges are an option that can filter out both particles and gas or vapors.

The exposure assessment should yield employee exposure levels for the substances you tested for. The results are typically measured in parts per million (ppm) or milligrams per cubic meter of air (mg/m3), commonly averaged over an eight-hour work shift.

Compare your exposure levels to the occupational exposure limit (OEL) or permissible exposure limit (PEL) set by the Occupational Safety and Health Administration (OSHA) to determine if action is required by law. You can often use values set by other groups, such as the American Conference of Governmental Industrial Hygienists (ACGIH) – if those values are lower than the OEL. In any event, make sure both your measured concentrations and the levels to which you are comparing them (such as the OEL) use the same units of measure. For instance, both could be expressed in ppm for an eight-hour time-weighted average (TWA). Measurements may also be in the form of 15-minute short-term exposure limits (STEL) or a ceiling limit (C), which is the absolute limit that should never be exceeded at any time by a worker.

If your employee exposure levels are below the OEL, then respirators aren’t legally required, though you may still want to offer respirators for voluntary use. If your levels are above the limit, look to reduce exposures through engineering, or administrative controls. If putting those controls into place is not feasible, choose respiratory protection that help bring exposures down to an acceptable level for workers.

The only respirators OSHA allows for use in the workplace are those approved by the National Institute for Occupational Safety and Health (NIOSH). All NIOSH-approved respirators have an assigned protection factor (APF), which can range from 10 to 10,000.

The APF is the workplace level of respiratory protection that a respirator or class of respirators is expected to provide to employees when the employer implements a continuing, effective respiratory protection program as specified by 29 CFR 1910.134. For instance, an APF of 10 means the respirator can protect against exposure levels that are up to 10 times the PEL for that hazard.

To see what level of APF your workplace needs, divide your exposure levels by the exposure limit. (This is called the “hazard ratio.”) For instance:

Exposure level: 500 ppm
÷
OEL or PEL: 50 ppm
—
APF: 10

Once you know your required APF, you can narrow down your choices to those respirators that can reduce exposure to below the OEL. OSHA lists APFs for different types of respirators. For example, half-mask respirators with cartridges and filters have an APF of 10.

Besides choosing equipment appropriate for your workplace’s types and levels of hazards, you must also consider compatibility with other required protective equipment, such as safety glasses and hard hats. Glasses and half face respirators, for example, may compete for space on the same part of the face — the bridge of the nose — so it’s vital to find equipment that fits together without causing either leakage around the respirator edges or loss of eye protection.

Comfort and ability to do the job are also important considerations; if the work is particularly strenuous, try to select respirators that are as lightweight and streamlined as possible. And keep in mind that people’s faces come in all shapes and sizes; you may need to select from a variety of models and sizes to find properly fitting respirators for all workers who need one.