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apparatus and this could result in leakage of contaminated air into the facepiece of the apparatus during the peak inhalation portion of the breathing cycle.

In 1992, Johnson et al. used five work classifications to evaluate workplace-performance degradations caused by respirator usage. The following is an abridged version of Table II from Johnson et al.: Work Classification Representative Activities Physical Respiratory Peak Work Rate Ventilation Flow (Watts) (U/min) (L/min) Very light Lying, sitting, reading, answering phone, intermittent typing 0 8 31 Light Washing clothes, polishing, light gymnas- tics, walking at 2 mph 10 15 59 Moderate Climbing hills, shoveling fast 140 50 125 Heavy Running at 9-10 mph unencumbered, ski- ing, playing squash 240 80 192 Very heavy Sprinting 430 110 284

  For most filter-mask users, peak inhalation flow rates are probably not the best indicator of filter leakage risk, since peak flow rates occur for such short periods of time. For filter masks, a more relevant indicator of leakage risk is the time-averaged inhalation flow rate (i.e., minute volume, the volume of air inhaled per minute or respiratory ventilation).
  Silverman's results indicate that for typical periods defined as medium work, one can expect that filter-mask users will inhale at average volumetric rates of about 35 to 55 L/min/mask through their filter(s) with peak volumetric rates of 100 to almost 150 L/min/mask. Correspondingly, Johnson et al. defined moderate work as that with an average respiratory ventilation of 50 L/min/mask with a peak flow of 125 L/min/mask. For typical periods defined by Silverman as heavy work, one can expect that filter-mask users will inhale at average volumetric rates of 75 to about 228 Revoir, W. H.: Comments on OSHA's Proposal to Modify Existing Provisions for Controlling Employ ee Exposure to Toxic Substances Found in 29 CFR 1910.1000(3) and 29 CFR 1910.134(a)(1). Comments submitted to OSHA (May 30, 1990), p. 10. 22 Johnson, A. T., R. A. Weiss, and C. Grove: Respirator Performance Rating Table for Mask Design, Am. Ind. Hyg. Assoc. J., 53(3):193–202 (1992).