Time-Weighted Average (TWA)

Time-Weighted Average (TWA)

CH-05
ASPCSPFoundational

Formula
TWA = (C₁T₁ + C₂T₂ + ... CₙTₙ) ÷ (T₁+T₂+...Tₙ)
When to Use

Calculate the 8-hour TWA exposure for a worker exposed to different concentrations at different times during a shift.

Symbol Legend
SymbolMeaningUnitNote
TWATime-Weighted Average exposureppm or mg/m³Compare to TLV-TWA
C₁...nConcentration during each exposure periodppm or mg/m³
T₁...nDuration of each exposure periodhoursTotal must equal shift length (usually 8 hrs)

🔒

Worked Example for Blueprint Members

Blueprint members get full exam-style worked problems, step-by-step solutions, solution videos, common exam traps, and linked practice questions — for every equation.

Join Be Safe ASP | CSP Blueprint™ →