Permissible Noise Exposures
- PEL: The permissible exposure limit (PEL) for noise is 90 dBA, as an eight hour
time-weighted average (TWA). The PEL is also referred to as a 100 percent "dose" noise exposure.
[Table G-16]
- Exchange Rate: The standard utilizes a 5 decibel (dB) exchange rate.
- Maximum Continuous Noise: As interpreted from the table, exposure to continuous steady-state noise is limited
to a maximum of 115 dBA.
- If the variations in noise level involve maxima at intervals of one second or less, it is to be considered continuous.
[1910.95(b)(2)]
- Impulse Noise: The standard states that exposure to impulsive or impact noise should not exceed
140 dB peak sound pressure level. [Table G-16]
|
|
| Comparison of Duration Per Day in Hours to Allowable Sound Level
in dBA (Slow-Response SPL) |
Duration per day
(hours)
|
Sound level
(dBA, slow response)
|
PEL = 90 dBA (TWA),
or
100% Dose
|
| 8 |
90 |
| 6 |
92 |
| 4 |
95 |
| 2 |
100 |
| 1 |
105 |
| ½ |
110 |
| 0.25 |
115 |
|
| Conversion from Percent Noise Exposure or Dose to 8 Hour
Time-Weighted Average Sound Level |
Dose or percent
|
TWA (dBA)
|
| 50 |
85.0 |
| 55 |
85.7 |
| 60 |
86.3 |
| 65 |
86.9 |
| 70 |
87.4 |
| 75 |
87.9 |
| 80 |
88.4 |
| 85 |
88.8 |
| 90 |
89.2 |
| 95 |
89.6 |
| 100 |
90.0 |
| 105 |
90.4 |
| 110 |
90.7 |
| 115 |
91.1 |
| 120 |
91.3 |
| 125 |
91.6 |
Assumes 5 dB exchange rate
and 90 dBA PEL. |
|
- Since the standard utilizes a 5 dB exchange rate, a TWA exposure of 95 dBA is equivalent to a dose of 200 percent, while a TWA exposure
of 85 dBA is equivalent to a dose of 50 percent.
- Most modern noise measuring instruments provide readouts in both noise dose and TWA.
- Refer to
1910.95 Appendix A: Noise Exposure Computation for instructions and additional information for computing employee noise exposures.
Engineering and Administrative Controls
- Feasible engineering or administrative controls must be utilized when employees are subjected to sound exceeding the PEL. If such
controls fail to reduce sound levels below the PEL, personal protective equipment (PPE) must be provided and used to reduce sound levels
below the PEL. [1910.95(b)(1)]
- In determining the need for engineering or administrative controls, only exposures to sound levels greater than or equal to
90 dBA are considered in the exposure calculation.
- Noise control should minimize sources of noise; prevent the propagation, amplification, and reverberation of noise; and protect workers
from excessive noise. Engineering controls may include antivibration machine mountings, acoustical enclosures, and component replacement.
Administrative practices may include shift rotation or exposure limitation.
|
Hearing Conservation Program
- The employer must administer a continuing, effective hearing conservation program whenever employee noise exposures are at or above an
eight hour time-weighted average (TWA) of 85 dBA or, equivalently, a dose of 50 percent.
[1910.95(c)(1)]
- In determining whether a hearing conservation program is required, all sounds at or above 80 dBA are used in
the exposure calculation.
- Refer to the Hearing Conservation Program section for additional
information.
|
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