Noise TWA from dose
Used on the ASP, CSP and CHST. The worked example below is computed by code and checked against the source.
TWA = 16.61 × log10(D ÷ 100) + 90
D = dose in percent. A 100% dose is a 90 dBA TWA; a 50% dose is 85 dBA, the hearing conservation action level.
Worked example
A 150% dose (the example above).
16.61 × log10(1.5) + 90 = 92.9 dBA
The source prints this result, and our code reproduces it.
1910.95 Table A-1 lists 92.9 dBA for a 150% dose.
Run your own numbers: noise dose calculator or hearing protection NRR calculator.
Where it appears on the exam
ASP: ASP11 Domain 1, Mathematical Calculations
Blueprint: ASP11 Domain 1, task 5: noise hazards (TWA)
Practice: Occupational Noise and Hearing Conservation, Safety Math: Incident Rates, Noise Dose, Slopes, Lifting
CSP: CSP11 Domain 6, Occupational Health and Applied Science
Blueprint: CSP11 Domain 6, task 1: occupational exposures (noise)
Practice: Exposure, Noise, Containment and Lifting Calculations, Occupational Noise
CHST: CHST5 Domain 1, Hazard and Risk Identification and Control
Blueprint: CHST5 Domain 1, knowledge 18: noise exposure
Practice: Construction Safety Math: Noise and Excavation Slopes, Noise, Hearing Protection, Radiation and Lasers
Source
The formula comes from
29 CFR 1910.95, Appendix A(opens ecfr.gov in a new tab)“The eight-hour time-weighted average sound level (TWA), in decibels, may be computed from the dose, in percent, by means of the formula: TWA = 16.61 log10 (D/100) + 90.”
Questions
- What is the formula for noise TWA from dose?
- TWA = 16.61 × log10(D ÷ 100) + 90. D = dose in percent. A 100% dose is a 90 dBA TWA; a 50% dose is 85 dBA, the hearing conservation action level.
- 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.
BCSP on formulas at the exam
BCSP, What to Expect When Sitting for a BCSP Exam (item 7)(opens bcsp.org in a new tab)“For any question requiring a mathematical formula, the formula will be included within the exam question (unless the question is specifically testing your knowledge of a formula). You will not be provided or permitted to bring a formula sheet.”
Related
- Time-weighted average (TWA)
- Action level
- Noise reduction rating (NRR)
- Noise dose
- Reference duration for a sound level
- Adding decibels
- Sound level at a distance
- Hearing protector NRR (estimated exposure)
- ASP formula sheet
- CSP formula sheet
- CHST formula sheet
Checked 2026-10-16. Spot a problem? Email hello@passcited.com.