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Appendix II:A. General Industry Standard
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]


  • 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.
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
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.

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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