A review of available sources identified the following federal exposure guidelines: TWA, IDLH. 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 1990 basis was a PEL x 500, while the 1994 basis was a REL x 500. Considering that PEL > REL in TEEL source priority (Section 3.2.1, Table 3.1), analysts selected the 1990 IDLH as the TEEL-3. The TEEL-2 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 mg/m3)
• PAC-2 = TEEL-2 = TEEL-3/6
• PAC-3 = TEEL-3 = IDLH (1990, 500 mg/m3)
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 was derived from the TEEL-2, while the current TEEL-3 is a 1990 IDLH (Section 3.1). 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.