Gas Turbine Handbook : Principles and Practices

Appendix C 385
Appendix C-13
Occupational Noise Exposure
Occupational Safety and Health Act of 1970 (OSHA) regulates
employee exposure to noise as described in the U.S. code of federal
regulations. The code states, “The employer shall administer a continuing,
effective hearing conservation program, as described whenever
employee noise exposures equal or exceed an 8-hour time-weighted
average sound level (TWA) of 85 decibels…or equivalently, a dose of
fifty percent.” This is termed the action level when an employer must
institute a hearing conservation program and provide hearing protection
to employees. The following table lists selected maximum allowable
noise level exposure times (see the CFR for a full listing). When
an employee is exposed to levels and/or times that exceed those listed
then the employer is mandated to reduce employee noise exposure.
Table C.13-1 Permissible Noise Exposure Limits (without hearing
protection)
Decibel Level, n 80 85 90 92 95 97 100 102 105 110 115
Exposure Time, Tn 32 16 8 6 4 3 2 1.5 1 0.5 0.25
Tn is in hours. For other sound levels, the maximum allowable
exposure time (T) based on a particular (measured) sound level (L) is
calculated by:
T= 8/2 (L-90)/5 hours (C.13-1)
When employees are exposed to variable levels of noise then the total
noise dose is calculated by,
D= 100Σ(Cn/Tn) (C.13-2)
This summation is done to measure the employee’s total noise exposure
where Cn is the actual exposure time, in hours, at a maximum