Mica

CAS number: 12001–26–2

NIOSH REL: 3 mg/m³ (respirable dust) TWA

Current OSHA PEL: 20 mppcf TWA

1989 OSHA PEL: 3 mg/m³ (respirable dust) TWA

1993-1994 ACGIH TLV: 3 mg/m³ (respirable dust) TWA

Description of substance: Colorless, odorless flakes or sheets of hydrous silicates.

LEL:. . . Noncombustible Solid

Original (SCP) IDLH*: No Evidence [*Note: "Effective" IDLH = 10,000 mppcf -- see discussion below.]

Basis for original (SCP) IDLH: The available toxicological data show no evidence that an acute exposure to a high concentration of mica 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 (500 ´ 20 mppcf is 10,000 mppcf).

Short-term exposure guidelines: None developed

ACUTE TOXICITY DATA:

Animal or human data: None relevant for use in determining the revised IDLH.

Revised IDLH: 1,500 mg/m3 Basis for revised IDLH: The available toxicological data contain no evidence that an acute exposure to a high concentration of mica would impede escape or cause any irreversible health effects within 30 minutes. However, the revised IDLH for mica is 1,500 mg/m3 based on being 500 times the NIOSH REL of 3 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).