Respirators must be fit-tested

By Ingemar Olsson, Dalloz Safety

If you are going to wear a respirator, you want it to do its job. That’s why OSHA 29 CFR 1910.134(f) requires fit testing.

Appendix A of that standard outlines the requirements and procedures for fit testing. It applies to any employee using a negative- or positive-pressure respirator.

Fit tests now required annually
With the latest revision of 1910.134, fit testing must be performed annually. The test determines the quality of the respirator-to-face seal and is the only way to screen out poorly fitting facepieces. It verifies the assigned protection factor (APF) for any respirator.

Appendix A of the standard requires that test subjects be allowed to pick the most acceptable respirator from a sufficient number of respirator models and sizes so that the respirator is acceptable to, and correctly fits, the user.

The fit test must be completed with an identical model the user selects.

Two types of fit tests
Employers can choose one of two types of fit tests: quantitative fit test (QNFT) or qualitative fit test (QLFT).

During a fit test, the test subject must perform exercises that include:
1. Normal breathing;
2. Deep breathing;
3. Turning the head side to side;
4. Moving the head up and down;
5. Talking;
6. Grimacing (applies only to QNFT);
7. Bending over or jogging in place; and
8. Normal breathing.

The test subject performs the exercises in this order for one minute, except for the grimace exercise, which is performed for 15 seconds.

Quantitative fit tests
Quantitative fit testing provides a numerical measurement of the respirator’s fit.

Its “fit factor” is the ratio of a test agent (oil mist, salt particles, ambient dust particles or sulfur hexafluoride gas) concentration outside the facepiece divided by the concentration of the test agent inside the facepiece. 

It requires a probed respirator with P100 (HEPA) filters and an aerosol easily detected by the fit test instruments.

Manufacturers offer probed respirators, which have been modified to provide a sampling port so internal air can be monitored. A probed respirator can only be used for fit testing and never for respiratory protection. Fit test adapters are also available so respirators can be put into service after fit testing.

The ambient aerosol condensation nuclei counter (CNC), such as the Portacount manufactured by TSI, Inc., is one of the more familiar quantitative fit testing instruments. It can accurately verify assigned protection factors while generating consistent fit factors.

Another type of QNFT is the controlled negative pressure (CNP) fit test. This method is based on exhausting air from a temporarily sealed respirator to generate and maintain a constant negative pressure inside the facepiece. However, studies show this QNFT consistently produces lower fit factors than other tests.

A fit factor represents the actual fit of the respirator in a test environment, while the assigned protection factor (APF) is a limit set by the applicable regulatory agency. To be deemed adequate, the fit factor must be at least 10 times the assigned protection factor. The respiratory program administrator may set the safety factor even higher.

Qualitative fit tests
QLFTs provide a pass/fail result. The respirator’s facepiece-to-face seal is challenged by a substance detectable by the senses. The test subject must provide an unbiased and honest response.

Because the test subject is the detector, he or she must be tested to demonstrate his or her ability to detect the test agent. Commonly used substances include OSHA-approved isoamyl acetate (IAA), irritant smoke, Bitrex and saccharin. If the person’s senses detect the substance inside the facepiece, the respirator fails the fit test.

Although passing a QLFT only verifies a protection factor of 10, this type of fit test can be used to comply with OSHA’s fit-testing requirements for all tight-fitting facepieces in its 29 CFR 1910.134 standard. It requires negative pressure testing, whether or not the respirator operates on negative or positive pressure.

Negative-pressure testing can be accomplished by temporarily converting the respirator facepiece to a negative-pressure mode. For instance, a Willson 6670ALB continuous-flow respirator can be converted to a 6400 dual-cartridge facepiece by removing the cartridge plugs and threaded connector and replacing them with cartridge connectors and an end plug. The facepiece can now accept the appropriate filter or cartridge to match the QLFT method.

For example, with the Bitrex test protocol, the test subject is put inside a test enclosure. A dilute solution of Bitrex (denatonium benzoate), an extremely bitter compound, is aspirated inside the enclosure. If the test subject can sense the compound, the test can proceed.

In the next step, the subject dons a respirator approved for dust/mist or any filter certified to meet the 42 CFR part 84 NIOSH standard. Once the test subject dons the respirator, the test solution is sprayed into the enclosure. The test subject must keep his or her mouth open during the entire test, and if he or she tastes the Bitrex solution, the respirator fails the fit test.

Which test method is best?
Each fit test has advantages and disadvantages. All QLFT protocols are subjective and do not identify the magnitude of respirator leakage. Plus, test subjects must be able to sense the test compound. The only way to overcome these limitations is to perform QNFTs.

However, QNFTs are not any more accurate than QLFTs and are more expensive. Test instruments cost about $7,000 plus the cost of probed respirators and adapters. A highly trained operator must calibrate, operate and maintain the equipment.

The equipment to conduct QLFTs costs about $200, and protocols are much more convenient and easier to perform. That’s why qualitative testing is more prevalent.

Fit test help
Consult 29 CFR 1910.134 and its Appendix A for proper procedures, or contact your nearest OSHA office.

Respirator manufacturers offer guidance on fit testing procedures. Dalloz Safety, for example, offers qualitative fit test kits, probed facepieces, and quantitative fit test adapters. Factory probed respirators are available in both half mask and full facepiece configurations. The fit test kits contain the instructions and items necessary to perform an OSHA-acceptable qualitative fit test.

Published in the January/February 2001 issue of Contractor Tools and Supplies magazine.

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