A review of available sources did not identify exposure limits or acute toxicity data for cyanic acid. Analysts evaluated exposure limits for cyanide (IDLH, ceiling limits; CASRN:57-12-5) for TEEL development. Data sources were selected according to the hierarchy listed in Table 3.1. Analysts evaluated the original (1990) and revised (1994) IDLH sources and determined that the inclusion of acute inhalation toxicity data is relevant to TEEL development; as such, the 1994 cyanide IDLH was selected as the TEEL-3 and a weight adjustment was applied (3.2.2). The cyanide TLV-C was selected as the TEEL-2 and a weight adjustment was applied (3.4.3.2). The TEEL-1 value was derived according to Table 3.5.
• PAC-1 = TEEL-1 = TEEL-2/11
• PAC-2 = TEEL-2 = MW-adjusted TLV-C (cyanides, as CN, CASRN: 57-12-5; 5 mg/m3)
• PAC-3 = TEEL-3 = MW-adjusted IDLH (1994; cyanides, as CN; CASRN: 57-12-5; 25 mg/m3)
This review generated PAC values that are inconsistent with Rev. 29A. The Rev. 29A TEEL-3 was a weight adjusted the 1990 cyanide IDLH, while the current TEEL-3 is a weight adjusted 1994 cyanide IDLH due to its inclusion of acute inhalation toxicity. The 1994 IDLH was used according to Handbook guidelines (Section 4.2-4.3). The Rev. 29A TEEL-2 was derived from the TEEL-3, while the current TEEL-2 is a weight adjusted cyanide TLV-C. The Rev. 29A TEEL-1 basis was a weight adjusted MAK-TWA for cyanides, while the current TEEL-1 was derived from the TEEL-2.