We must become more aware or our "sound" environment, determine acceptable exposure limits, and take any steps necessary to avoid overexposure and potentially adverse psychological and physiological effects. OSHA standards require businesses compute the employee noise exposure. Noise exposure can be measured with an audiodosimeter or with a decibel meter. The following section will explain the recommended method using a decibel meter. This is accomplished using two rules.
1. When the sound level, L ,1 is constant over the entire work shift, the noise dose, D, in percent, is given by:
where D = Dose level (%); C = the total length of the work day (hr); T = the reference duration level corresponding to the measured sound level (L). (L can be determined by table or by equation).
2. When the work shift noise exposure is composed of two or more periods of noise at different levels, the total noise dose over the workday is given by:
C1 C2 Cn
T1 T2 Tn where C (n) = the total time of exposure at a specific noise level, and T (n) = the reference duration for that level as given by Table 11.2 or equation.
The first equation determines the dose (%) for the employee. A dose of 100% is the maximum allowed.
The reference duration level (T) is computed using the following equation:
where T = reference duration; L = dBA exposure.
Problem: Determine the sound dose for an individual who was subject to a sound of 55 dBA for 1.25 hr and a level of 105 dBA for 5.0 min.
Solution: The dose equation requires a different reference duration (T) for each sound level and duration. The first step is to determine the value of T for each sound level and duration.
8 8 8 8 T1 = „ „„„ = ,„ „n„ = —- =-= 1,024 or 1,000
the next step is to determine the value for each exposure using the dose equation:
= 100 x (0.00125 + 0.0833...) = 8.458 ... or 8.4% The worker dose was 8%, well within the range of the maximum allowed of 100%.
1 OSHA 1910.95 App A, Noise exposure computation.
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