OSHA Noise Dose and TWA Calculator
Calculate noise exposure dose and TWA using OSHA standards.
Returns permissible exposure time at any sound level and hearing protection requirements.
OSHA Noise Exposure Limits OSHA’s Permissible Exposure Limit (PEL): 90 dBA as an 8-hour TWA. OSHA Action Level: 85 dBA as an 8-hour TWA — hearing protection program required. NIOSH Recommended Exposure Limit (REL): 85 dBA for 8 hours. Impulse noise limit: 140 dB peak SPL.
The 5 dB Exchange Rate (OSHA) OSHA uses a 5 dB exchange rate (halving rate) for permissible durations. 90 dBA: 8 hours | 95 dBA: 4 hours | 100 dBA: 2 hours 105 dBA: 1 hour | 110 dBA: 30 min | 115 dBA: 15 min (maximum with protection) Formula: Permissible time (h) = 8 / 2^((L − 90) / 5)
Note: NIOSH Uses 3 dB Exchange Rate NIOSH (National Institute for Occupational Safety and Health) uses a 3 dB halving rate: 85 dBA: 8 hours | 88 dBA: 4 hours | 91 dBA: 2 hours | 94 dBA: 1 hour This is more protective — recommended by WHO and most international standards.
Noise Dose Calculation Dose (%) = Σ (C_i / T_i) × 100 Where C_i = actual time at level i, T_i = permissible time at level i. Dose ≥ 100%: exceeds PEL — engineering controls required. Dose 50–100%: action level range — hearing protection required. Dose < 50%: below action level.
Time-Weighted Average (TWA) TWA = 16.61 × log₁₀(D / 100) + 90 Where D = noise dose percentage. TWA represents the equivalent constant noise level over 8 hours.
Hearing Protection Devices (HPD) When controls are not sufficient, hearing protection must reduce exposure below PEL. NRR (Noise Reduction Rating) in dB: field derate by 50% for real-world use. Effective attenuation = (NRR − 7) / 2 Required attenuation = TWA − 90 (OSHA PEL) or TWA − 85 (NIOSH REL)