A review of available sources identified a TLV-TWA, REL-TWA, PEL-TWA, IDLH (1990), and rat LCLo toxicity data. 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. A rat 4-hour LCLo and IDLH (1990) for silica, crystalline (quartz, tripoli) were evaluated for the TEEL-3 basis, with the IDLH being selected due to data source preference (Table 3.1). The TEEL-2 value was derived according to Table 3.5, and the TLV-TWA remains the TEEL-1 basis as it yields the most conservative value amongst the other data found.
• TEEL-1 = TLV-TWA x 3 (0.025 mg/m3)
• TEEL-2 = TEEL-3/6
• TEEL-3 = IDLH (1990) (50 mg/m3)
This review generated TEEL-2 and TEEL-3 values that are more conservative and therefore inconsistent with those of Rev. 29A, while the TEEL-1 remains unchanged. In Rev. 29A the TEEL-3 basis was a rat intravenous LD50, however that data was not found during current research, and a more preferred data type, an IDLH (1990) was chosen.