Fit testing and fit factors for N95 respirators

March 4, 1996
Dr. John F. McCarthy, ScD, CIH
Ms. Nanette Moss
Environmental Health and
Engineering
[Recipient address omitted]
Dear Dr. McCarthy and Ms. Moss:
This letter is in response to your request for written information regarding fit testing and fit factors for the N-95 respirators recently certified by the National Institute of Occupational Safety and Health (NIOSH). The Occupational Safety and Health Administration's (OSHA) [Respiratory Protection Standard], [29 CFR 1910.134], requires that fit tests be conducted for those workers required to wear respiratory protection. Under this standard either a quantitative (QNFT) fit test or a qualitative (QLFT) fit test is acceptable. Your use of a Portacount to conduct quantitative fit testing is acceptable provided the tests are conducted according to the recommendations of the manufacturer of the respirator.
You are correct in your letter when you state that a fit factor of 100 should be used when conducting a quantitative fit test. In your earlier discussion with Mr. Richard Fairfax of my staff, Mr. Fairfax was discussing the generally accepted assigned protection factor (APF) of 10 for disposable respirators. As you are aware, when a quantitative fit test is conducted, the wearer of the mask is assigned a fit factor that is based upon the APF plus a safety factor of 10. The combination of the APF and the safety factor is the derivation of the fit factor (100). The agency has not taken a formal position on the APF for these respirators. OSHA is engaged in rulemaking on a final respiratory protection standard, and until a final standard is issued OSHA will not be assigning protection factors to respirators. Nevertheless OSHA continues to require that, for a quantitative fit test, the wearer of the respirator must achieve a fit factor of at least 100.
The agency also requires, as addressed in [29 CFR 1910.134], that wearers of respirators conduct a fit check each and every time they don a respirator. The fit check may be conducted according to the manufacturer's instructions. If you have any additional questions or comments please do not hesitate to contact the [Office of Health Enforcement at (202) 693-2190].
Sincerely,
John B. Miles, Jr.
Director
[Directorate of Enforcement Programs]
[Corrected 12/31/2003]

[Requester letter reproduced on OSHA page; omitted here.]