A worker is exposed to noise levels of 95 dBA for 4 hours and 85 dBA for 4 hours during an 8-hour shift. What is the calculated noise dose?
Correct Answer
B) 125%
Using OSHA's noise dose formula: (4 hours at 95 dBA ÷ 4 hours allowable) + (4 hours at 85 dBA ÷ 16 hours allowable) = 1.0 + 0.25 = 1.25 or 125%. This exceeds the 100% allowable dose.
Why This Is the Correct Answer
The correct answer is C (125%) because OSHA's noise dose formula requires calculating the fraction of allowable exposure time for each noise level and adding them together. At 95 dBA, workers can be exposed for 4 hours maximum, so 4÷4 = 1.0. At 85 dBA, workers can be exposed for 16 hours maximum, so 4÷16 = 0.25. The total dose is 1.0 + 0.25 = 1.25 or 125%, which exceeds the 100% allowable limit.
Why the Other Options Are Wrong
Option C: 150%
150% is incorrect because it overestimates the noise dose. While this would still indicate unsafe exposure levels, the precise calculation yields 125%, not 150%.
Option D: 75%
75% is incorrect because it underestimates the noise exposure. This would suggest the worker is within safe limits, but the calculation shows they exceed the allowable dose.
Memory Technique
Remember 'OSHA's Noise Ladder': 90 dBA = 8 hours, 95 dBA = 4 hours, 100 dBA = 2 hours, 105 dBA = 1 hour. Each 5 dBA increase cuts allowable time in half. 85 dBA = 16 hours (double the 8-hour baseline).
Reference Hint
OSHA 29 CFR 1926.95 - Personal Protective Equipment, or safety management chapter covering noise exposure standards and permissible exposure limits
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