Assigned protection factor (APF) represents which of the following?

• A. Level of protection that a properly functioning respirator would be expected to provide to a population of properly fitted and trained users
• B. The maximum permissible exposure limit for a respirator's use
• C. The efficiency rating of a respirator's filter
• D. The duration of respirator wear required for protection

Answer: (A)

Assigned Protection Factor is about how much protection a respirator class is expected to provide to a properly fitted and trained user. It’s a standard numeric value assigned to respirator types that reflects the overall reduction in inhaled contaminants due to the respirator, accounting for fit, seal, leakage, and design.

In practice, this factor means the concentration outside the mask is divided by the APF to estimate what the wearer would inhale. For example, with an outside concentration of 50 units and an APF of 10, the wearer’s exposure inside the respirator would be about 5 units, assuming a proper fit and use. This helps determine whether workplace exposures meet regulatory limits: the outside concentration must be high enough to risk exceeding the limit, or the APF must be large enough, to keep the wearer's exposure at or below the permissible level.

This concept is different from a maximum permissible exposure limit, which is a workplace limit for exposure regardless of respiratory protection; it’s not a measure of how efficient a filter is in percent, and it doesn’t specify how long a wearer must use the respirator.