Why formulas matter
Calculation questions appear across several domains. They are reliable points if you know the setup and units well.
Exam details change; always confirm the current blueprint, eligibility and policies on the official BCSP website before you book.
Incident rates
OSHA-style incident rates normalise cases to 100 full-time workers using 200,000 hours (100 workers × 40 hours × 50 weeks). TRIR = recordable cases × 200,000 ÷ total hours worked. DART uses days-away, restricted or transferred cases in the same formula. Example: 6 recordables in 480,000 hours gives 6 × 200,000 ÷ 480,000 = 2.5.
Noise dose and TWA
Noise dose D = 100 × Σ(C ÷ T), where C is time at a level and T is the allowed time at that level. Under the OSHA criterion (90 dBA, 5 dB exchange rate), TWA = 16.61 × log10(D ÷ 100) + 90. A dose of 100% equals 90 dBA TWA; 200% equals about 95 dBA. NIOSH uses 85 dBA and a 3 dB exchange rate.
NIOSH lifting equation
The recommended weight limit is RWL = LC × HM × VM × DM × AM × FM × CM, with load constant LC = 23 kg (51 lb). Each multiplier reduces the limit for horizontal distance, vertical height, travel distance, asymmetry, frequency and coupling. The lifting index LI = load ÷ RWL; above 1 indicates elevated risk.
Worked noise example
A worker spends 4 hours at 90 dBA and 2 hours at 95 dBA. Under the OSHA criterion, the allowed time is 8 hours at 90 dBA and 4 hours at 95 dBA. The dose is 100 × (4/8 + 2/4) = 100 × (0.5 + 0.5) = 100%, which corresponds to a TWA of 90 dBA. If the same worker added 1 hour at 100 dBA, where the allowed time is 2 hours, the dose would rise to 150% and the TWA to about 92.9 dBA.
Other formulas worth knowing
Beyond these, many candidates review severity rates, basic probability for risk assessment, ventilation and airflow relationships such as Q = V × A, simple statistics like mean and standard deviation, and engineering economics such as present value. The exact list depends on the current blueprint and the reference sheet provided, so check what BCSP supplies before memorising everything.
Common calculation mistakes
Mixing units, such as feet and metres or minutes and hours, is the most frequent error. Another is using the wrong exchange rate in noise problems, or forgetting that the NIOSH equation multipliers must each be calculated from the task geometry. Write the formula first, list each value with units, then calculate. This habit saves marks.
Incident rate practice
Try this: a site logs 3 DART cases in 150,000 hours. DART = 3 × 200,000 ÷ 150,000 = 4.0. If the same site has 5 recordable cases in that period, TRIR = 5 × 200,000 ÷ 150,000 ≈ 6.67. Practising quick setups like these builds speed.
Building a formula sheet
Write each formula once on a single page with units and a worked example. Review it daily.
Practice tips
Write units at each step, estimate before calculating, and practise with a calculator like the one you will be allowed. Work many short problems rather than a few long ones.
Frequently asked questions
What is the 200,000 in incident rates?
Hours worked by 100 full-time employees in a year.
What is the NIOSH load constant?
23 kg (51 lb).
What TWA is a 200% dose under OSHA?
About 95 dBA.
What is DART?
Days away, restricted or transferred cases, calculated like TRIR.
Which noise criterion does the exam use?
Questions specify it; know both OSHA and NIOSH criteria.