There is significant science behind evaluating the fit of respiratory protection. Have you ever heard of qualitative fit testing and quantitative fit testing? No? Let’s learn more.
U.S. OSHA specifies approved procedures for both qualitative fit testing (QLFT) and quantitative fit testing (QNFT). There are several methods of QNFT – some involve measuring the concentration of an aerosol challenge agent both inshttps://www.3m.com/blog/en_US/safety-now/science-of-safety/3m-and-the-science-of-fit-testing/ide and outside the facepiece; others involve measuring the seal of the respirator by creating a vacuum inside the facepiece. All six OSHA-approved QNFT methods yield a numerical value called a Fit Factor, which is meant to represent the ratio of the concentration outside the facepiece to the concentration inside the facepiece – i.e., the reduction in the airborne concentration of the relevant contaminant. QLFT, on the other hand, yields either a pass or fail result, depending on whether the subject reports detecting the challenge agent during the fit test.
Regulatorily, either QNFT or QLFT can be used for most classes of respiratory protection including filtering facepiece respirators (FFRs), also known as disposable respirators. However, quantitative fit testing is required for full facepieces used in negative-pressure configurations if the assigned protection factor (APF) of 50 is required (i.e., if airborne concentrations of contaminants exceed 50 times the occupational exposure limit).
Table 1 summarizes some of the differences between QLFT and QNFT.
When is qualitative fit testing an acceptable fit test method? When is quantitative fit testing required?
According to 29 CFR 1910.134, qualitative fit testing is an acceptable method for tight-fitting facepieces used in negative-pressure and positive-pressure configurations, with a few exceptions:
- The assigned protection factor of 50 is needed while using a full facepiece in negative-pressure air-purifying mode.
- A supplied-air respirator (SAR) or self-contained breathing apparatus (SCBA) is used in demand mode (currently very uncommon and distinct from pressure-demand mode).
- Facepieces used in SCBAs for structural firefighting must be quantitatively fit tested, per the National Fire Protection Association.
Achieving a proper fit and seal is a crucial part of getting the most protection out of your respirator. For more information about fit testing, please review this technical bulletin, and do not hesitate to contact our respiratory protection specialists for assistance.