A review of available sources identified exposure limits (IDLH, TWAs) and acute toxicity studies (LDLO, LD50, LCLo) for several species and routes. Data sources were selected according to the hierarchy listed in Table 3.1. Toxicity data were selected according to type of exposure, species, and route according to the hierarchies stated in Sections 3.3.1, 3.3.2, and evaluated using factors in Tables 3.2, 3.3, and 3.4. The 1990 and 1994 IDLH were evaluated; the 1994 IDLH incorporated acute inhalation toxicity in animals, while the 1990 IDLH was developed from an analogy to chloroform and protective factors. Considering this, analysts selected the 1994 IDLH as the TEEL-3 basis. The TEEL-2 value was derived according to Table 3.5. The TLV-TWA was selected as the TEEL-1 basis.
• PAC-1 = TEEL-1 = TLV-TWA (0.5 ppm) x 3
• PAC-2 = TEEL-2 = TEEL-3/6
• PAC-3 = TEEL-3 = IDLH (1994, 850 ppm)
This review generated PAC-3 and PAC-2 values inconsistent with Rev. 29A and a PAC-1 value consistent with Rev. 29A. The Rev. 29A TEEL-3 basis was mouse LC50 toxicity, while the current TEEL-3 is an IDLH (Table 3.1). The 1994 IDLH was used according to handbook guidelines (Section 4.2-4.3). The Rev. 29A and current TEEL-2 use the same methodology, with differences due to the change in TEEL-3. The Rev. 29A and current TEEL-1 values, source, and methodology are consistent.