Silica TWA
Respirable crystalline silica exposure is usually assessed as an 8-hour time-weighted average:
TWA = Σ (Ci × ti) ÷ 8, then compare to your limit (e.g. UK WEL 0.1 mg/m³, or OSHA PEL as adopted).
Silica / RCS Exposure Calculator
Silica · 8-hour TWA
Estimate respirable crystalline silica TWA from task concentrations and hours, then compare to a WEL/PEL.
Formula: TWA = Σ (Ci × ti) ÷ 8 · Ratio = TWA ÷ Limit
- Use respirable crystalline silica results — not total dust.
- Water, LEV, and isolation beat RPE alone.
- UK WEL is often 0.1 mg/m³; OSHA PEL may be lower — set limit deliberately.
Frequently asked questions
Is task dust “RCS”?
Only the respirable crystalline silica fraction counts. Use lab results or validated estimates — not total dust alone.
Controls first?
Yes. Water suppression, LEV, and isolation beat relying on RPE.
Multiple tasks?
Add each Ci×ti pair for the shift, then divide by 8.
Medical surveillance?
Follow local rules when exposures approach action levels — this tool does not decide health surveillance.
