A review of available sources identified the following exposure limits: TWAs (PEL, REL, TLV), REL-C, and an IDLH. Data sources were evaluated according to the hierarchy listed in Table 3.1. The IDLH was selected as the TEEL-3; there are two reported 1990 IDLH values: a limit of 295 ppm and an “effective” limit of 250 ppm. The 295 ppm limit was developed from acute toxicity, while the 250 ppm limit was developed from an exposure limit; the lower value was selected due to conservativism. The REL-C was selected as the TEEL-2. The TLV-TWA was evaluated as a TEEL-1 basis, however this resulted in a value that is greater than the selected TEEL-2. Instead, the TEEL-1 was derived according to Table 3.1.
• TEEL-1 = TEEL-2/11
• TEEL-2 = REL-C (0.14 ppm/0.6 mg/m¬3)
• TEEL-3 = IDLH (1990, 250 ppm)
This review generated TEELs inconsistent with Rev. 29A. The Rev. 29A TEEL-3 was also the 1990 IDLH, however at that time the less conservative value was selected. The Rev. 29A TEEL-2 basis was a TDLo, which was not found during current review; instead, an available exposure limit was selected as the TEEL-2 (Table 3.1). The Rev. 29A TEEL-1 basis was the TLV-TWA, which was evaluated but not select during the current review due to it result in a TEEL-1 that is greater than the selected TEEL-2.