OSHA requirements are set by statute, standards and regulations. Our interpretation letters explain these requirements and how they apply to particular circumstances, but they cannot create additional employer obligations. This letter constitutes OSHA's interpretation of the requirements discussed. Note that our enforcement guidance may be affected by changes to OSHA rules. Also, from time to time we update our guidance in response to new information. To keep apprised of such developments, you can consult OSHA's website at https://www.osha.gov.

March 4, 1996

Dr. John F. McCarthy, ScD, CIH
Ms. Nanette Moss
Environmental Health and
255 Washington Street
Newton, Massachusetts 02158-1634

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].


John B. Miles, Jr.
[Directorate of Enforcement Programs]

[Corrected 12/31/2003]

November 13, 1995

Mr. John B. Miles, Jr., Director
Directorate of Compliance Programs
The Occupational Safety and Health
Room N 3468
200 Constitution Avenue NW
Washington, DC 20210

RE: OSHA Enforcement Policy for Preventing Exposure to TB

Dear Mr Miles:

The purpose of this letter is to confirm information discussed during a conversation on November 7, 1995 between myself and Mr. Richard Fairfax regarding respiratory protection using N95 respirators in preventing occupational exposure to tuberculosis (TB).

Due to health concerns among employees and labor unions regarding the use of saccharin for qualitative fit testing of respirators we have explored alternate methods to conduct respirator fit testing. Through discussions with technical representatives from companies that manufacture N95 respirators, we were advised that it is possible to equip N95 respirators with probes to conduct quantitative fit tests. After confirming the feasibility of this practice with PortaCount(R) technical information specialists, we began to trial this method.

Success during our quantitative fit testing trial period prompted me to contact Mr. Fairfax to inquire whether quantitative fit testing with a PortaCount for N95 respirators is an appropriate practice in accordance with the OSHA Respiratory Protection Standard. He indicated that quantitative fit testing would be acceptable under the TB Standard if a fit factor pass level of ten is used. However, in recognition of preferred industrial hygiene practice with respect to respiratory protection in preventing occupational exposure to TB, it will be our policy to attempt to achieve a fit factor level of 100 for optimum protection.

Please provide us with written confirmation regarding quantitative fit testing for the N95 respirators for compliance with the TB Standard. Please do not hesitate to contact either of us if you have any questions.


John F. McCarthy, ScD, CIH

Nanette Moss
Senior Associate