Noise - Maximum Daily Dose Level
When the daily noise exposure consists of periods of different noise levels, the daily dose can be calculated as:
D = ( te1 / td1 + te2 / td2 + ... + ten / tdn ) 100% (1)
where
D = daily noise exposure (%)
te = exposure time at a specified noise level (min)
According the National Institute for Occupational Safety - NIOSH - the daily dose level - D - should not equal or exceed 100%.
The daily dose can be converted to an 8-hr Time-Weighted Average -TWA by the formula
TWA = 10 log (D / 100) + 85 (2)
where
TWA = Time Weighted Average noise level (dB)
Daily noise dose as an 8-hr TWA for different daily noise doses:
| Daily Noise Dose (%) | 8-hr TWA (dB(A)) |
|---|---|
| 20 | 78.0 |
| 30 | 79.8 |
| 40 | 81.0 |
| 50 | 82.0 |
| 60 | 82.8 |
| 70 | 83.5 |
| 80 | 84.0 |
| 90 | 84.5 |
| 100 | 85.0 |
| 200 | 88.0 |
| 400 | 91.0 |
| 600 | 92.8 |
| 800 | 94.0 |
| 1,000 | 95.0 |
| 1,500 | 96.8 |
| 2,000 | 98.0 |
| 4,000 | 101.0 |
| 6,000 | 102.8 |
| 8,000 | 104.0 |
| 10,000 | 105.0 |
| 20,000 | 108.0 |
| 40,000 | 111.0 |
| 60,000 | 112.8 |
| 80,000 | 114.0 |
| 100,000 | 115.0 |
| 150,000 | 116.8 |
| 200,000 | 118.0 |
| 400,000 | 121.0 |
| 600,000 | 122.8 |
| 800,000 | 124.0 |
| 1,000,000 | 125.0 |
| 2,000,000 | 128.0 |
| 4,000,000 | 131.0 |
| 6,000,000 | 132.8 |
| 8,000,000 | 134.0 |
| 10,000,000 | 135.0 |
| 20,000,000 | 138.0 |
Example - Daily Noise Dose Level
During a working day a person is exposed to 100 dB in 5 minutes and 94 dB in 30 minutes.
The maximum noise exposure time for 100 dB is 15 minutes and for 94 dB 60 minutes.
The daily dose can be calculated as
D = ((5 min) / (15 min) + (30 min) / (60 min)) 100%
= 83 %
The Time-Weighted Average -TWA can be calculated as
TWA = 10 log (83 / 100) + 85
= 84 dB
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