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IV Navy diaphragm gas masks. These masks were probably equipped with M9A1 (prior to July 1943) or M9A2 canisters that contained Whetlerite, a copper-, chromium-, and silver-impregnated activated charcoal as the sorbent (Brophy et al., 1959). The PF afforded by these masks for sulfur mustard or Lewisite was not available to the committee. However, an individual involved in this testing reported that the WWII British and U.S. masks were very effective in removing sulfur mustard (Howard Skipper, personal communication; see Appendix A). Yet some chamber tests were conducted at high concentrations. For example, a test conducted at chamber concentration of 100 mg/m3 for 60 minutes would have resulted in a cumulative, unprotected, exposure of 30,000 Ct over five trials. Even an assumed PF of 1,000 for the gas mask (10 times greater than that estimated for modern full-face respirators) would have resulted in concentrations as high as 0.1 mg/m3 in each trial, corresponding to a cumulative exposure of 6 Ct just from the inspired air in each trial. This would have been below the odor threshold for sulfur mustard and, over five trials, would have resulted in a cumulative inhalation exposure of 30 Ct, enough to cause signs and symptoms in the eyes and respiratory tract (see Table 3-4). If a more realistic estimate is used, such as a mask with a PF of 100, the per trial exposure would have been 60 Ct. Over five trials then, a subject could have had an inhalation exposure of 300 Ct, more than sufficient to cause an incapacitating injury (see Table 3-4). It is important to remember that any such inhalation exposure would have been in addition to any skin exposure through breakdown of the protective clothing.

It is important to note also that the gas masks and clothing used in the NRL tests were worn repeatedly by the subjects. In at least one series of studies, it was reported that the rubber of the gas mask facepieces and connecting tubes absorbed enough sulfur mustard after 12 to 15 exposures to cause conjunctivitis, laryngitis, and erythema of the face (Taylor et al., 1943). Therefore it is clear that some exposure to the respiratory tract occurred from absorption of sulfur mustard on masks. Finally, as mentioned previously, the special diaphragm element in the types of gas masks used in the NRL chamber tests was eventually shown to provide an additional route of mask leakage, independent of the filter capacity (Brophy et al., 1959).

The presence of erythema of the face, conjunctivitis, laryngitis, or bronchitis within 24 to 72 hours following an exposure to sulfur mustard or Lewisite would be clear evidence that a significant inhalation and eye exposure had occurred, even if the subject was wearing a mask during the exposure. Conversely, it would appear that a lack of such symptoms following even a low-level exposure of 5 to 6 days to sulfur mustard would indicate a cumulative exposure (Ct) of less than about 12 Ct (see Table 3-4). However, in terms of the Centers for Disease Control's

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