Assigned Protection Factor

An assigned protection factor is the level of protection a type of respirator is expected to give when it fits and is used correctly. A factor of 10 means the wearer should breathe no more than one-tenth of the contamination in the surrounding air. OSHA sets these factors, and employers use them to choose a respirator strong enough for the exposure.

Origin

Protection factors grew out of NIOSH and industrial hygiene testing of respirators in the 1970s and 1980s. OSHA published a single table of assigned protection factors in 2006, ranging from 10 for a half-mask air-purifying respirator to 10,000 for a pressure-demand self-contained breathing apparatus.

Significance in Asbestos Context

Assigned protection factors show that even a proper respirator lets some fibers through; a half-mask reduces exposure but does not stop it, and real-world protection is often lower than the assigned value because of poor fit, facial hair, talking, heavy work or worn parts. In a claim, defense experts may apply a protection factor to argue that a worker's inhaled dose was small, while plaintiffs' experts may show the respirator was the wrong type, not fit-tested, not worn throughout the task, or not provided at all. For much of the period when asbestos exposure was heaviest, workers had no respirator or only a single-use paper mask, which carries little or no assigned protection for asbestos. The numbers are a planning tool, not a measurement of what any one person actually breathed.

Example Sentence

The defense expert divided the air readings by an assigned protection factor of 10, but the worker testified he had worn his half-mask only part of the time and had never been fit-tested.

Related Terms

Respirator, Personal Breathing Zone Sample, Time-Weighted Average (TWA), Permissible Exposure Limit (PEL), Exposure Reconstruction, OSHA Asbestos Standard

Notes

• If an expert reduces your exposure estimate because you wore a respirator, ask what type it was assumed to be and whether it was fit-tested.
• Recall when you wore protection and when you did not, including breaks, cleanup and nearby work by others.