Source / episode info

• **Episode:**657
• **Title:**DIP Ep 657: OMBRS 3-The OSHA Silica Standard
• **Published:**2026-05-29
• Source:Episode page

One-liner

This episode provides a comprehensive review of the OSHA Crystalline Silica Standard, covering exposure limits (PEL vs. Action Level), medical surveillance protocols (including 3-year exam intervals and TB screening), the differential diagnosis of silicosis types (Chronic, Accelerated, Acute/Proteinosis), and high-risk occupational exposures like engineered stone fabrication.

High-yield summary

• Exposure Limits: The OSHA PEL for respirable crystalline silica is 50 g/m^3 (8-hour TWA). The Action Level is half of that: 25 g/m^3.
• Key Comparison Trap: The ACGI TLV for silica (25 g/m^3) is numerically identical to the OSHA Action Level, but it is not the PEL.
• Medical Surveillance Trigger: Medical surveillance is required if an employee is exposed at or above the Action Level (25 g/m^3) for 30 or more days in a calendar year.
• Periodic Exams: Periodic medical exams are required every three years, not annually, and must include PFTs, CXR interpretation by a NIOSH-certified reader (ILO classification), and TB screening (TST or IGRA).
• Silicosis Types: Acute silicosis (silica proteinosis) is the most severe form, associated with very high intensity exposure over weeks to 5 years; radiographically presents with ground glass opacities and a "crazy paving pattern" on CT.
• High-Risk Industry Alert: Engineered stone countertops are a major emerging source of acute silica exposure due to their high crystalline silica content (90–95%).
• Systemic Associations: Silica is an IARC Group 1 carcinogen, strongly associated with increased risk of Tuberculosis (due to macrophage toxicity) and autoimmune diseases like scleroderma.

Learning objectives

• Differentiate between the OSHA PEL (50 \mu g/m^3) and the Action Level (25 \mu g/m^3) for respirable crystalline silica.
• Describe the components and frequency of medical surveillance required for silica exposure (initial exam, periodic exams).
• Classify silicosis based on latency period, exposure intensity, and characteristic radiographic findings (Chronic vs. Accelerated vs. Acute).
• Identify high-risk occupational settings, particularly engineered stone fabrication, as sources of acute silica exposure.