Reference duration for a sound level
Used on the ASP, CSP and CHST. The worked example below is computed by code and checked against the source.
T = 8 ÷ 2^((L − 90) ÷ 5)
L = A-weighted sound level in dBA. Each 5 dB above 90 halves the allowed time (OSHA's 5-dB exchange rate).
Worked example
L = 95 dBA.
8 ÷ 2^((95 − 90) ÷ 5) = 4.0 h
The source prints this result, and our code reproduces it.
Table G-16a lists 4 hours for 95 dBA. eCFR shows this formula as an image under the table.
Run your own numbers: noise dose calculator or decibel addition 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, Table G-16a(opens ecfr.gov in a new tab)“T is the reference duration corresponding to the measured sound level, L, as given in Table G-16a or by the formula shown as a footnote to that table.”
Questions
- What is the formula for reference duration for a sound level?
- T = 8 ÷ 2^((L − 90) ÷ 5). L = A-weighted sound level in dBA. Each 5 dB above 90 halves the allowed time (OSHA's 5-dB exchange rate).
- 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
- Noise dose
- Noise TWA from dose
- 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.