Dust/Chemical Exposure Dose Calculator

TWA = Time-Weighted Average. Calculates 8-hour TWA exposure against an Occupational Exposure Limit (OEL/PEL/TLV), adjusts for extended work shifts, and checks combined exposure to multiple substances using the OSHA mixture rule.

TWA & Extended Shift

Mixture Exposure (Multiple Substances)

Exposure Segments

Exposure Limit & Shift Length

Occupational Exposure Limit (OEL) Enter the substance's 8-hour TWA PEL/TLV (same units as your concentration readings).

Actual Shift Length (hours) If longer than 8 hours, the OEL is adjusted using the Brief & Scala model.

8-Hour TWA

% of (Adjusted) OEL

Applies where two or more substances have similar toxicological effects (e.g., irritation of the same organ system) — per OSHA 29 CFR 1910.1000(d)(2)(i).

Substances

0.00

MIXTURE EXPOSURE INDEX (Em)

Formula Reference

8-Hour TWA = Σ (Concentration × Duration) ÷ 8 hours
Extended-Shift Adjustment (Brief & Scala model): Reduction Factor = (8 ÷ H) × [(24 − H) ÷ 16], where H = hours worked/day
Mixture Exposure Index: Em = Σ (Ci ÷ Li) — combined exposure exceeds acceptable limits if Em > 1.0

Notes on the Brief & Scala Model

This is a widely-referenced general-purpose model (cited by ACGIH as a "tentative" guideline), not an OSHA-mandated formula — OSHA has only formally mandated extended-shift PEL adjustment for two substances (lead, via a substance-specific formula in 29 CFR 1910.1025/1926.62, and the noise action level). Always check for a substance-specific OSHA/ACGIH extended-shift adjustment before defaulting to the general Brief & Scala model.

Based on OSHA 29 CFR 1910.1000 (TWA and mixture formula) and the Brief & Scala extended-shift model referenced by ACGIH. This tool supports interpretation of exposure monitoring data — it does not replace a calibrated sampling program, a certified industrial hygienist's assessment, or substance-specific OSHA standards (e.g., lead, silica, asbestos) which may impose additional requirements beyond a simple TWA comparison. For customized calculators tailored to your organization, please contact Impact Tech Solutions.