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Silica, amorphous																				Related Pages
										May 1994
Immediately Dangerous to Life or Health Concentrations (IDLH)
**CAS number:** 7631–86–9
**NIOSH REL:** 6 mg/m3 TWA
**Current OSHA PEL:** 20 mppcf TWA; 80 mg/m3/%SiO2 TWA
**1989 OSHA PEL:** 6 mg/m3 TWA
**1993-1994 ACGIH TLV:** 10 mg/m3 TWA
**Description of substance:** Transparent to gray, odorless powder.
**LEL:** . . Noncombustible Solid
**Original (SCP) IDLH*:** No Evidence [*Note: “Effective” IDLH = 500 times the OSHA PEL — see discussion below.]
**Basis for original (SCP) IDLH:** The available toxicological data contain no evidence that an acute exposure to a high concentration of amorphous silica would impede escape or cause any irreversible health effects within 30 minutes. For this draft technical standard, therefore, respirators have been selected on the basis of the assigned protection factor afforded by each device. However, for some particulate substances for which no evidence of an IDLH exists, the determination of allowable respiratory protection based on protection factors may result in the assignment of respirators for concentrations that are not likely to be encountered in the occupational environment. Therefore, for all such particulate substances it has been arbitrarily determined that only the “most protective” respirators are permitted for use in concentrations exceeding 500  ́ the OSHA PEL.
**Short-term exposure guidelines:** None developed
**ACUTE TOXICITY DATA:**
**Animal or human data:** None relevant for use in determining the revised IDLH.

**Revised IDLH:** 3,000 mg/m3**Basis for revised IDLH:** The available toxicological data contain no evidence that an acute exposure to a high concentration of amorphous silica would impede escape or cause any irreversible health effects within 30 minutes. However, the revised IDLH for amorphous silica is 3,000 mg/m3 based on being 500 times the NIOSH REL of 6 mg/m3 (500 is an assigned protection factor for respirators and was used arbitrarily during the Standards Completion Program for deciding when the "most protective" respirators should be used for particulates).

			
							
								Page last reviewed:  December 4, 2014						Content
							source: 	National Institute for Occupational Safety and Health NIOSH Publications & Products
Immediately Dangerous To Life or Health (IDLH) Values
Table of IDLH Values
Criteria for Determining IDLH Values
Historical Documentation
Original (SCP) Values
Abbreviations for IDLH Documentation
Abbreviations for Journal Titles Follow NIOSH Facebook
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