Assigned Protection Factor & Maximum Use Concentration

The effectiveness of a respirator is determined by its assigned protection factor (APF). A respirator's APF can be used to determine the maximum use concentration (MUC), which is the highest concentration of a particular hazard at which the respirator is still effective. Maximum use concentrations can be determined by multiplying a respirator's APF by that substance's permissible exposure limit (or PEL, which is the maximum concentration of a hazard before it becomes unsafe to breathe without protection). For instance, the PEL of lead is 50 micrograms of lead per cubic meter of air. An air-purifying respirator with a half-mask attachment has an APF of 10. So the MUC for lead when using that respirator is 500 micrograms per cubic meter of air. If lead concentration levels are below 500 micrograms per cubic meter of air, this respirator should provide enough protection. If lead levels are above 500 micrograms per cubic meter of air, employers must provide a respirator with a higher APF.

Assigned protection factors and maximum use concentrations cannot be used in IDLH atmospheres. Instead, there are specific respirators that must be used.

To learn more about Respiratory Protection visit our Cal/OSHA Respiratory Protection Online Training web page.