OSHA Noise Dose and TWA Calculator
Calculate occupational noise exposure dose and time-weighted average (TWA) using OSHA standards.
Determine permissible exposure time at any sound level and check 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)