A review of available sources identified exposure limits (REL-C, PEL-STEL, and IDLH) and acute toxicity data (LD50, LC50, TCLo) 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. Inhalation exposures were scaled to 60-minute equivalents using the ten Berge equation (Section 3.3.4). The 1990 and 1994 IDLH were evaluated; the additional human inhalation toxicity evaluated for the revised IDLH (1994) could not be verified, therefore it’s unclear what these values were and if they’re consistent with TEEL development. As such, analysts selected the 1990 IDLH as the TEEL-3. The REL-C (0.5 ppm) was selected as the TEEL-2 basis. A ratio of available acute toxicity data (TCLo) indicates it is appropriate to scale this exposure limit by a factor of 100 (Section 3.4.7.1). See ratio calculation below:
TEEL-2 (Rat TCLo, 1114 ppm/6H) = 160 ppm
TEEL-2/Exposure limit = 160 ppm/0.50 ppm = 320>100 (adjust x100)
The lowest 15-minute OEL-STEL (Finland) was selected as the TEEL-1.
• TEEL-1 = OEL-STEL (Finland, 1.5 ppm)
• TEEL-2 = REL-C (0.5 ppm) x 100
• TEEL-3 = IDLH (1990, 2500 ppm)
This review generated TEEL-3 and TEEL-2 values consistent with Rev. 29A. Use of the toxicity derived TEEL-2 to exposure limit ratio was used in accordance with handbook guidelines (Section 3.4.7.1 and Section 4.2). The Rev. 29A TEEL-1 was derived from the TEEL-2, while the current TEEL-1 is an OEL-STEL, a more preferred source (see note, Table 3.5).