Correspondence

Respiratory Protection

N Engl J Med 2003; 348:175-176January 9, 2003

Article

To the Editor:

Martyny et al. (Sept. 12 issue)1 provide a very useful review of respiratory protection; however, a few points should be noted. Some self-contained breathing apparatuses, such as rebreathers, can last several hours. The note that air-purifying respirators should be used only when the hazardous substance has warning properties is applicable only in the case of gases and vapors, since the cartridges for these substances can become saturated and allow “breakthrough.” (It is generally assumed that particulate filters become more efficient with use.) In fact, the current regulations of the Occupational Safety and Health Administration (OSHA)2 do not rely primarily on this detection, but instead require either a data-based cartridge-change schedule or an end-of-service-life indicator. The current classification for the former high-efficiency particulate air filter is the 100 series, not a 99 (which also exists), as stated in the article.

There is great variability in the fit quality of some types of respirators currently approved by the National Institute for Occupational Safety and Health, including the filtering face-piece half-masks commonly used for protection against tuberculosis.3,4 Fit tests, particularly qualitative fit tests, are not that good at accurately determining the protection provided5; false pass rates and false failure rates on the order of 10 percent and 50 percent, respectively, have been noted. The former lead to potentially overexposed workers, and the latter to inefficiency in respirator programs. Future regulations may once again require minimal respirator fit-test characteristics, but in any case, programs and users should consider their respirator selections carefully.

Thomas K. Hodous, M.D.
National Institute for Occupational Safety and Health, Morgantown, WV 26505
thh1@cdc.gov

5 References

1. 1

   Martyny J, Glazer CS, Newman LS. Respiratory protection. N Engl J Med 2002;347:824-830
   Full Text | Web of Science | Medline

2. 2

   Respiratory protection, 29 C.F.R., part 1910, §134 (d) (3) (iii) (2002).
   

3. 3

   Campbell D, Coffey CC, Lenhart SW. Respiratory protection as a function of respirator fitting characteristics and fit-test accuracy. AIHAJ 2001;62:36-44
   CrossRef | Medline

4. 4

   Cohen HJ, Hecker LH, Mattheis DK, Johnson JS, Biermann AH, Foote KL. Simulated workplace protection factor study of powered air-purifying and supplied air respirators. AIHAJ 2001;62:595-604
   CrossRef | Medline

5. 5

   Coffey CC, Zhuang Z, Campbell DL. Evaluation of the Bitrex qualitative fit test method using N95 filtering facepiece respirators. J Int Soc Respir Protect1998;48-55
   

Author/Editor Response

We appreciate Dr. Hodous's helpful comments. All respirator users must be reminded that respirators are one of the least effective forms of exposure control. Respirators add a margin of safety but are no guarantee. In practice, awareness of environmental conditions and the actions of the wearer are probably the two most important factors in determining the success or failure of a respirator. Qualitative fit testing of disposable respirators is imperfect yet still improves the chances of protection.

We agree that it is not necessary to attend to warning properties when an air-purifying respirator is worn for protection against particulates, if no other protection is required. As a practical matter, respirator wearers should be taught to recognize the warning properties of gases and vapors. Air-purifying respirators should be used only for those gases and vapors that have warning properties, except under very controlled conditions. Although end-of-service-life indicators and data-based cartridge-change schedules are appealing in concept, we do not rely on them. Even though they are allowed by OSHA, cartridges with end-of-service-life indicators are not commonly available. Information on cartridge longevity provided by suppliers may not take into account poor storage practices or unusual exposure conditions.

Rebreathers can extend the time that a person can remain in a contained suit. However, rebreathers are not in common use by emergency personnel in the United States.

John Martyny, Ph.D.
Craig Glazer, M.D.
Lee S. Newman, M.D.
National Jewish Medical and Research Center, Denver, CO 80206
deohs@njc.org