What is the additive mixture formula?
When several chemicals have similar toxicological effects on the same organ system, ACGIH and many OSHA programmes treat combined exposure with:
Em = C₁/L₁ + C₂/L₂ + … + Cn/Ln
where Ci is the measured concentration of each substance and Li is its limit (TLV, PEL, WEL, etc.) in the same units. If Em > 1, the mixture is considered to exceed the combined limit.
Do not use this formula for independent effects, carcinogens with non-additive rules, or substances with ceiling/STELs that need separate assessment.
Chemical Mixture TLV Calculator
Mixture · Additive Em = Σ (C ÷ L)
For similarly acting substances: if Em > 1, the combined exposure exceeds the additive criterion. Same units for every C and L.
Formula: Em = C₁/L₁ + C₂/L₂ + … + Cn/Ln
- Only for similarly acting substances per your IH procedure.
- Keep every concentration and limit in the same unit.
- Evaluate STEL and ceiling limits separately.
Frequently asked questions
When is additivity appropriate?
When your IH procedure or ACGIH guidance says the substances act on the same organ system in a similar way. Independent-effect mixtures are assessed differently.
Can I mix ppm and mg/m³?
No. Convert every Ci and Li pair to the same unit before dividing.
What about STEL or ceiling limits?
This tool is for an 8-hour TWA-style additive check. Evaluate STEL and ceiling limits separately for each substance.
Does Em replace sampling statistics?
No. You still need valid exposure measurements, SEGs, and professional judgment for compliance decisions.
