Noise
Under OSHA standards, employers must take action to protect workers from excess noise if the noise level is higher than 85 dBA.
Noise Monitoring
At 85 dBA and higher the employer must develop a Hearing Protection program and make hearing protection available. Workers are not permitted to be exposed to an 8-hour Time-Weighted-Average (TWA) equal to or greater than 90 dBA.
Nose levels are measured with either area noise dosimeters measuring during a walkaround or personal dosimeters placed on employees. Once noise measurements are completed, a Noise Sampling Plan can be developed for ongoing noise monitoring.
The following Noise Exposure Table below shows how long workers are permitted to be exposed to specific noise levels:
29 CFR 1910.95, Table G-16.
| Permissible Duration (Hours per Day) |
Sound Level (dBA, Slow Response) |
|---|---|
| 16 | 85 |
| 8 | 90 |
| 4 | 95 |
| 2 | 100 |
| 1½ | 102 |
| 1 | 105 |
| ½ | 110 |
| ¼ or less | 115 |
A worker's daily noise exposure typically comes from multiple sources, which have different noise levels for different durations. Typically local monitoring When adding different noise levels, only noise levels above 80 dBA should be considered.
The combined effect of these noise sources can be estimated using the following equation:
Where Cn is the total duration of exposure at a specific noise level, and Tn is the total duration of noise permitted at that decibel level. If the sum equals or exceeds "1," the combined noise level is greater than the allowable level. If the sum is less than "1," the combined noise level is less than the allowable level.
Example: Using the table below, calculate a worker's daily noise exposure. Does it exceed a time-weighted average at or above 90 dBA TWA?
| Example: Worker's Activity | Time | Measured Sound Level |
|---|---|---|
| Milling machine | 6:00 a.m. - 8:00 a.m. (2 hours) | 95 dBA |
| Parts department | 8:00 a.m. - 11:00 a.m. (3 hours) |
70 dBA |
| Milling assist | 11:00 noon - 2:00 p.m. (3 hours) |
90 dBA |
According to the table, the noise levels while working in the parts department is below 80 dBA, so we will not include it in the calculation. Therefore, the times and measured sound levels we will use is: 95 dBA for 2 hours and 90 dBA for 3 hours.
Calculate the ratio of actual exposure duration (Cn) to the permissible exposure duration (Tn)for each time segment and add them.
Use the formula: Sum = C1/T1 + C2/T2 = 2/4 + 3/8 = 7/8. The resulting value (7/8) is less than 1; therefore, this worker's exposure does not exceed the 90 dBA 8-Hour Time-Weighted-Average (TWA).
OSHA requires a hearing conservation program for workers who are exposed to an 8-hour TWA of 85 dBA or higher. A separate calculation would be required to determine if a hearing conservation program is required.
Knowledge Check Choose the best answer for the question.
5-4. The maximum legal permissible exposure limit (PEL) for noise is _____ for all workers during a 8-hour workday.
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