Page 38 - OHS, July/August 2021

PPE: RESPIRATORY PROTECTION
wanted to use a half-mask APR with appropriate cartridges for an atmosphere containing hydrogen sulfide. The OSHA PEL for hydrogen sulfide is 20 ppm as a ceiling concentration. With the proper cartridges, the MUC would be 10 X 20 ppm = 200 ppm. However, the published IDLH concentration is 100 ppm, so you would have to reduce the MUC to 100 ppm.
How does this relate to when you can use QLFT methods and when you have to use QNFT methods? OSHA has stated that QLFT methods can only be used for negative pressure APRs when they will be used in concentrations less than 10 times the PEL. This is because current studies do not validate the protocols higher than that level. So, if you are going to use a negative pressure APF (half- or full-mask) in an atmosphere that is less than 10 times the PEL, you can use one of the QLFT protocols. If you want to use a negative pressure APR in an atmosphere greater than 10 times, the PEL you must use one of the QNFT methods.
OSHA allows the use of any of the QLFT or QNFT methods for all positive-pressure ASRs because they are almost always used in the positive pressure mode in the workplace. The ASRs are tested in the negative pressure mode so the facepiece must be modified for the fit testing. Once the positive pressure ASR passes any QNFT or QLFT test, OSHA allows the use of the higher APF for that respirator.
Greg Boothe, Ph.D., CIH, CSP is the faculty lead for occupational safety and health at Columbia Southern University.
NOTES
1. Employers may select respirators assigned for use in higher workplace con- centrations of a hazardous substance for use at lower concentrations of that substance, or when required respirator use is independent of concentration.
2. The assigned protection factors in Table 1 are only effective when the em- ployer implements a continuing, effective respirator program as required by this section (29 CFR 1910.134), including training, fit testing, maintenance, and use requirements.
3. This APF category includes filtering facepieces, and half masks with elastomeric facepieces.
4. The employer must have evidence provided by the respirator manufacturer that testing of these respirators demonstrates performance at a level of protec- tion of 1,000 or greater to receive an APF of 1,000. This level of performance can best be demonstrated by performing a WPF or SWPF study or equivalent testing. Absent such testing, all other PAPRs and SARs with helmets/hoods are to be treated as loose-fitting facepiece respirators and receive an APF of 25.
5. These APFs do not apply to respirators used solely for escape. For escape respirators used in association with specific substances covered by 29 CFR 1910 subpart Z, employers must refer to the appropriate substance-specific standards in that subpart. Escape respirators for other IDLH atmospheres are specified by 29 CFR 1910.134 (d)(2)(ii).
REFERENCE
1. https://www.osha.gov/laws-regs/regulations/ standardnumber/1910/1910.134
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