8-hour TWA exposure (air contaminants)

Worked example

OSHA example: 2 h at 150 ppm, 2 h at 75 ppm, 4 h at 50 ppm; limit 100 ppm.

(2 × 150 + 2 × 75 + 4 × 50) ÷ 8 = 81.25 ppm, under 100 ppm

The source prints this result, and our code reproduces it.

Where it appears on the exam

• ASP: ASP11 Domain 1, Mathematical Calculations

  Blueprint: ASP11 Domain 1, task 14: exposure assessments (TWA)

  Practice: Exposure Assessment and Storage Capacity Calculations

• CSP: CSP11 Domain 6, Occupational Health and Applied Science

  Blueprint: CSP11 Domain 6, task 1: occupational exposures (hazardous chemicals)

  Practice: Exposure, Noise, Containment and Lifting Calculations, Air Contaminants and Silica (General Industry)

• CHST: CHST5 Domain 1, Hazard and Risk Identification and Control

  Blueprint: CHST5 Domain 1, knowledge 21: chemical exposure

  Practice: Respirable Crystalline Silica in Construction

Source

Questions

What is the formula for 8-hour TWA exposure (air contaminants)?

E = (Ca × Ta + Cb × Tb + … + Cn × Tn) ÷ 8. C = concentration during a period; T = hours at that concentration. E may not exceed the substance's 8-hour TWA in Subpart Z.

Will this formula be given on the BCSP exam?

BCSP says the formula is included in the question whenever one is needed, unless the question is testing whether you know the formula. You can't bring a formula sheet into the exam, so learn what each formula does and when to use it.