Gas Turbine Handbook : Principles and Practices

386 Gas Turbine Handbook: Principles and Practices
sound level interval n, and Tn is the maximum allowable exposure
time at that sound interval level; and when the dose (D) computation
exceeds 50%, then an effective hearing conservation program is
required.
As an example, an employee will spend his day exposed to the
following sound levels: 4 hours at 80 dB, 1.5 hours at 95 dB and 2.5
hours at 92 dB. The dose computation is as follows:
D = 100 × (4/32 + 1.5/4 + 2.5/6) = 91.6%
The values in the calculation are all units of time. The first term.
4/32, is based on 4 hours at 80 dB where the maximum allowable
exposure time is 32 hours.
The eight-hour time weighted average (TWA) sound level exposure is
then computed by:
TWA = 16.61 log (D/100) + 90 dB
(C.13-3)
For D= 91.6, TWA = 89.4 dB which is greater than 85 dB; therefore,
a hearing conservation program is required to be implemented.