U.S. Occupational Safety & Health Administration - OSHA - Standards

As of August 1981, OSHA noise exposure standards consist of a two-stage program where hearing conservation measures become mandatory at 85 dBA for an 8-hour day but feasible engineering or administrative noise controls are required when exposures exceed 90 dBA.

Hearing Conservation Programs - include annual audiometric testing and provision of hearing protectors.

Engineering Controls - include reducing machinery noise through redesign, replacement with quieter equipment or by reducing the transmission of noise along the path from source to receiver.

Administrative Controls - include reducing noise exposure by limiting the time an employee is exposed to given noise levels.

1. Criteria for Engineering or Administrative Controls

Feasible administrative or engineering controls shall be utilized if noise dose D is greater than 1.0 in accordance with the following equation:

D = C1/T1 + C2/T2 + CN/TN

where:
D = Daily noise dose (must not exceed unity)
C = Actual exposure time at given noise level.
T = Permissible exposure time at that level in accordance with the table below.

Duration Per Day, Hr
Permissible Exposure
"Slow" Response, dBA
8
90
6
92
4
95
3
97
2
100
1.5
102
1
105
0.5
110
0.25 or less
115


Exposure to impulsive or impact noise should not exceed 140 dB peak sound pressure level.

Examples:

1. For an 8 hour day at constant noise levels, 90 dBA is the maximum allowable level.
2. Assure exposure of:

100 dBA for 2 hours, 90 dBA for 6 hours

D = 2/2 + 6/8 = 1.75

Engineering or administrative controls are necessary to reduce noise dose to unity.

3. Assume exposure of:

100 dBA for 1 hour
90 dBA for 4 hours
85 dBA for 3 hours

Exposure below 90 dBA does not contribute of OSHA noise "dose" for administrative or engineering controls to be employed. Therefore:

D = ½ + 4/8 = 1.00
(Acceptable)

2. OSHA Criteria for Hearing Conservation Programs

Employers shall administer continuing, effective hearing conservation programs wherever employee noise exposures equal or exceed an 8-hour time weighted average of 85 dBA or, equivalently, a dose or 50% measured according to the following equation:

D = 100 (C1/T1 + C2/T2 + C3/T3 + CN/TN)

where:

D = Workday dose in percent
1,2,3 = Period of exposure to different dBA levels
C = Actual exposure time at different levels
T = Permissible exposure time at that level in accordance with the following table.

A-weighted Sound
Level, L (dB)
Reference Duration, T
(hr)
80
32.0
81
27.9
82
24.3
83
21.1
84
18.4
85
16.0
86
13.9
87
12.1
88
10.6
89
9.2
90
8.0
91
7.0
92
6.2
93
5.3
94
4.6
95
4.0
96
3.5
97
3.0
98
2.6
99
2.3
100
2.0
101
1.7
102
1.5
103
1.4

Examples:

1. Assume exposure of:

85 dBA for 5 hours
87 dBA for 2 hours
80 dBA for ½ hour

D = 100 (5/16 + 2/12.1 + 0.5/32) = 49.34%
(Acceptable, since D is less than 50%)

2. Assume exposure of:

100 dBA for 1 hour
90 dBA for 4 hours
85 dBA for 3 hours

D = 100 (1/2 + 4/8 + 3/16) = 118.75%
(Unacceptable, since D exceeds 50%)


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