About Fit Testing

First, there are specific requirements that the firefighter be allowed to pick the most acceptable respirator make and size, so that the respirator correctly fits the firefighter. If your department has only one make of SCBA's, then you need to provide different sizes of facepieces, for fit testing and for use (not all round pegs will fit into the square hole). There are also specifics on how to judge what an "acceptable fit" is. User seal checks also need to be performed prior to the fit test. Be sure all firefighters are clean-shaven, as no hair growth is allowed between the face and facepiece during fit testing (and use). Any equipment normally worn that might interfere with the seal needs to be worn during the fit test as well. So, hoods and helmets should be on during fit testing. All of the specific details are found in Appendix A to Sec. 1910.134: Fit Testing Procedures (Mandatory). This appendix is found on pages 1276 through 1282 of 29 CFR 1910.134, which is chapter 12 of this manual.

Second, there are two types of fit testing procedures. The first is the Qualitative Fit Test (QLFT) and the second is the Quantitative Fit Test (QNFT). Let us compare fit testing procedures to pump testing procedures, to make the difference between these two fit tests clearer. Think of the QLFT (Qualitative) as being the test performed every time the pump is engaged. It either works, or it does not. It is a "yes" or "no" answer. Now think of the QNFT (Quantitative) as the annual service test (NFPA 1911) where you actually measure your pumps drafting and discharge GPM. You have a real number, a real measurement. No "ands ifs or buts" about the results. Keeping these distinctions in mind, let's get a bit more specific.

The QLFT is a subjective test. The firefighter makes the "yes" or "no" choice. "Yes I smell (or taste) the testing agent" or "No, I do not smell (or taste) the testing agent". This is the first source of error in the QLFT. There are several different testing agents that can be used for the QLFT. They are:

  1. Isoamyl Acetate (Banana Oil)
  2. Saccharin Solution
  3. Bitrex™ (Denatonium Benzoate) Solution
  4. Irritant Smoke (Stannic Chloride)

In general, these tests require mixing test agents to a specific concentration, determining if the firefighter can taste, smell or react to the test agent, then the actual testing is conducted in some sort of an enclosure - either a hood or a room. Then there is the requirement of an exact number of squeezes of the testing solution into the enclosure. Of these test agents, only the Stannic Chloride will elicit an involuntary response of the firefighter being tested. This smoke is a vapor of hydrochloric acid, and can be harmful to the firefighters tested, as well as the person conducting the tests. It does require extra precautions when chosen, in particular, proper room ventilation.

The QNFT is an objective test. The firefighter sits there. No response on their part is required. This eliminates the problem of (subjective) self-reporting. There are two different apparatus for QNFT testing, operating by two different methods. The first is the long used and most familiar, generated aerosol condensation nuclei counter (CNC), better known as the Portacount® manufactured by TSI, Inc. and their newer ambient aerosol CNC. The second, is state-of-the-art technology, using controlled negative pressure (CNP), the Occupational Health Dynamics (OHD) FitTester 3000®.

The original TSI, Inc. Portacount® also requires the use of sprayed particles in an enclosure, while the newer unit does not. It then "counts" the number of particles outside the facepiece and compares it to the count inside the facepiece. Obviously, this requires the placement of a sampling probe in the test chamber and in the facepiece. It also requires the placement of a HEPA filter onto the mask. Further, this method requires the mixing of solutions to precise concentrations and then the precise administration of that solution into the test chamber. After calculating the concentrations outside and inside the facepiece, an exact fit test value is generated. That value must be at least 100 for a half mask, and at least 500 for a full mask, like the SCBA. While the newer ambient aerosol unit does not require mixing solutions to count particles, it does require that the mask be worn for five minutes prior to beginning the test.

The Occupational Health Dynamics (OHD) FitTester 3000® applies a continuous negative pressure to the facepiece while the firefighter holds their breath. Once equilibrium is established, any additional leak is due to leak around the seal, or to the firefighter not holding their breath. The entire process takes only 8 seconds, and the machine readily detects if the firefighter did not hold their breath. This is reported as a "poor quality" test with "retest recommended". So, that test step is simply repeated. Another advantage to the Occupational Health Dynamics (OHD) FitTester 3000®, is that the unique work rate, mask, and gender of the firefighter can be entered into the machine for an even more accurate measurement. The only "modification" to the firefighter's facepiece is the removal of the low-pressure hose, and attachment of the FitTester valve. The valve is operated by the firefighter and seals off the "regulator end", so any leakage detected is through the face to facepiece seal. Again, the fit test values are a minimum of 100 for the half mask, or a minimum of 500 for the full mask.

There are specific protocols, which give the exact details of how to conduct the many steps in fit testing of either kind. These are also listed in Appendix A to Sec. 1910.134: Fit Testing Procedures (Mandatory).

In summary, with the QLFT, it must first be determined that the firefighter is able to react to the testing agent. Then, during the testing procedures, there are several maneuvers that simulate the motions a firefighter will be performing during normal use of the respirator. If the firefighter "senses" any of the test agent during any of the maneuvers, a score of "fail" results. If no reaction to the testing agent is acknowledged by the firefighter, then a score of "pass" results. In the QNFT protocols, similar maneuvers are performed. The end result of the QNFT is an actual numerical fit test value that determines a "pass" or "fail" result, with no subjective report by the firefighter.

There are several sources of error with the QLFT. The most concerning is the dependence upon the firefighter's subjective response. Other sources of errors are in mixing the concentrations of test agent and errors in administration of proper quantities of test agent.

In the QNFT, the generated aerosol Portacount® retains the mixing and administration errors while eliminating the error of subjective response. The newer ambient aerosol Portacount ® eliminates the mixing errors as well. The FitTester 3000® eliminates both sources of error while potentially introducing "breath holding" error. This latter is monitored and retesting recommended during the test itself, so this is not an issue.

The QNFT provides a greater confidence level with numerical fit factor values. The higher values equate to better face to facepiece seals. This means less air lost from a positive pressure mask, and fewer toxins inhaled in a demand mask. Less air loss should translate into extra service time for the firefighter within the IDLH atmosphere. Maybe only a minute or two, but that could make a difference in the safety of the firefighter.

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