# Respirable crystalline silica — OSHA medical surveillance trigger thresholds by substance For Respirable crystalline silica, cfr section is 1910.1053; action level is 25 µg/m3, calculated as an 8-hour TWA; pel is 50 µg/m3, calculated as an 8-hour TWA; surveillance trigger is each employee who will be occupationally exposed to respirable crystalline silica at or above the action level for 30 or more days per year; exam frequency is Initial (baseline) examination within 30 days after initial assignment; periodic examinations at least every three years, recorded from its source on 2026-08-12. - **Substance:** Respirable crystalline silica _(verified: appears in the quote below)_ - **CFR section:** 1910.1053 _(verified: appears in the quote below)_ - **Action level:** 25 µg/m3, calculated as an 8-hour TWA - **PEL:** 50 µg/m3, calculated as an 8-hour TWA - **Surveillance trigger:** each employee who will be occupationally exposed to respirable crystalline silica at or above the action level for 30 or more days per year _(verified: appears in the quote below)_ - **Exam frequency:** Initial (baseline) examination within 30 days after initial assignment; periodic examinations at least every three years - **Record retention:** maintained and made available in accordance with 29 CFR 1910.1020 ## What the source says > Medical surveillance —(1) General. (i) The employer shall make medical surveillance available at no cost to the employee , and at a reasonable time and place, for each employee who will be occupationally exposed to respirable crystalline silica at or above the action level for 30 or more days per year. ## Source - https://www.law.cornell.edu/cfr/text/29/1910.1053 Last verified: 2026-08-12. Review by: 2027-02-08. Part of [OSHA medical surveillance trigger thresholds by substance](https://referencesource.org/osha-medical-surveillance-triggers/).