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This document may not reflect OSHA's respirable silica rule published on March 25, 2016.
For more information on the new rule, see OSHA's Final Rule on Respirable Crystalline Silica Page.

Silica, Crystalline Tridymite, Respirable Dust

General Description

  • Synonyms: Tridymite prior to 9/1/89
  • OSHA IMIS Code Number: 9017
  • Chemical Abstracts Service (CAS) Registry Number: 15468-32-3

Exposure Limits

  • OSHA Permissible Exposure Limit (PEL):
  • American Conference of Governmental Industrial Hygienists (ACGIH) Threshold Limit Value (TLV): 0.05 mg/m3 TWA; (Respirable fraction)
  • National Institute for Occupational Safety and Health (NIOSH) Recommended Exposure Limit (REL): 0.05 mg/m3 TWA; Potential carcinogen

Health Factors

  • Carcinogenic Classification:
    • International Agency for Research on Cancer (IARC): Silica - Group 2A, probably carcinogenic to humans (Crystalline + Silica)

Monitoring Methods used by OSHA

Primary Laboratory Sampling/Analytical Method (SLC1):
  • See Silica, Crystalline Quartz, Respirable Dust (IMIS 9010)
  • note: Recognized reference material not available, analysis not performed at the Salt Lake Technical Center. Occurrence of Tridymite extremely rare. Submit respirable sample to the Salt Lake Technical Center for quartz &/or cristobalite analysis.

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