Maximum Noise Exposure Time
Calculate the maximum daily allowed noise exposure time, T = 8 ÷ 2^((SPL − 85) ÷ 5), from the sound pressure level SPL (dB(A)). The result, in hours, is the maximum exposure duration before reaching a 100% dose under the Brazilian NR-15 (85 dB(A) limit for 8 h, with a 5 dB dose-doubling rate). Every 5 dB above 85 halves the allowed time: 90 dB(A) allows 4 h, 95 dB(A) only 2 h. It is the basis for dose calculation and the planning of rotation and breaks. Enter the sound pressure level.
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Maximum noise exposure time
NR-15 (the Brazilian occupational health standard on unhealthy working conditions) sets how long a worker may stay exposed to each noise level before reaching the maximum daily dose. The relationship is T = 8 ÷ 2^((SPL − 85) ÷ 5), where SPL is the sound pressure level (dB(A)) and the result is the maximum time allowed, in hours. The anchor point is the tolerance limit: 85 dB(A) for 8 hours. From there the Brazilian dose doubling factor (or exchange rate) applies, q=5 dB: for every 5 dB increase in level, the permitted time drops by half, since sound energy (and the damage potential) grows exponentially. So 85 dB(A) → 8 h; 90 dB(A) → 4 h; 95 dB(A) → 2 h; 100 dB(A) → 1 h; 105 dB(A) → 30 min, and so on. (Note that other countries, such as the United States under ACGIH, use q=3 dB, based on the equal-energy criterion, which is more conservative.) This maximum time is the denominator in the dose calculation (D = C/T × 100%) and the basis for organizing job rotation, breaks and occupancy limits in noisy areas. Above 115 dB(A), no exposure at all is permitted without protection, however brief. Enter the sound pressure level.
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Calculate the occupational noise dose, D = (C ÷ T) × 100%, dividing the effective exposure time C by the maximum allowed time T for the measured noise level and multiplying by 100. The result, in %, shows how much of the maximum daily exposure the worker accumulated: 100% is the tolerance limit (85 dB(A) for 8 hours, with a 5 dB exchange rate in Brazil). Doses above 100% require controls and indicate risk of noise-induced hearing loss. For several levels, the C/T terms are summed. Enter the exposure time and the maximum allowed time.
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The results provided by this tool are for general informational and educational purposes only and do not constitute professional, financial, medical, legal, tax or accounting advice. Always confirm important decisions with a qualified professional and official sources.