both concentration and time of exposure are noted. For purposes of this report, the more modern notation is used and cumulative exposures are expressed in Ct (equivalent to mg min/m³) to avoid repetition, because the vast majority of chamber tests were conducted in 60-minute trials. To place the concentrations that follow into additional context, Table 3-4 summarizes the concentrations required to produce specific physiological effects.

For further comparison, it may be useful to consider two additional calculations. First, according to the International Agency for Research on Cancer (IARC, 1975), the average and maximum atmospheric concentrations of sulfur mustard in combat zones were estimated to be approximately 20 and 33 mg/m³. To determine exposure levels, however, one must consider the duration of exposure to a given atmospheric concentration. The exposure threshold for death from respiratory damage has been estimated to be between 1,000 and 1,500 mg·min/m³ (Ct, see Table 3-4). Thus, fatal exposures on the battlefield in WWI must have lasted between 50 and 75 minutes (the product of 50 minutes and 20 mg/m³ would equal a Ct of 1,000), if the estimated atmospheric concentrations were sustained, or longer if the concentrations dropped substantially.

Recent Centers for Disease Control (CDC) recommendations for safe levels of exposure to mustard agents and Lewisite provide a second useful frame of reference. Responding to the mandated destruction of all unitary lethal and chemical munitions, CDC published chemical agent control limits for atmospheric exposures to chemical munitions in the Federal Register in 1988. For general population exposures, the limits are 0.0001 and 0.003 mg/m³ for sulfur mustard and Lewisite, respectively. For workers directly involved in munitions removal and destruction, the limits (averaged over 8 hours) are 0.003 mg/m ³ for both agents (CDC, 1988).

It is important to remember, when considering these comparisons, that the battlefield and estimated safe occupational levels of sulfur mustard and Lewisite refer to atmospheric concentrations, rather than "dose" level. However, it is the concentration and cumulative exposure to an unprotected target tissue (e.g., the eye, skin, or breathing passages) that determines the dose received and thus the damage to tissues from these agents. The presence of protective clothing and/or a gas mask reduces considerably the amount of agent reaching such a target tissue. Sections of this chapter to follow contain estimates and analysis of the probable cumulative exposures achieved in the chamber and field tests, as well as occupational situations.

Information on the specific protocols used in patch tests was obtained from a variety of sources, including archived materials from the NRC