Environmental Engineering Reference
In-Depth Information
begin the sound level survey. In doing so, the user is primarily interested in answer-
ing the following questions:
1. What is the noise level in each wind turbine and/or wind farm area?
2. What equipment or process is generating the highest/lowest level of noise?
3. Which local residents are exposed to the noise?
4. How long are nearby residents exposed to the noise?
When addressing these questions, the monitors record their findings as they move
from location to location, following a logical step-by-step procedure. The first step
involves using the sound level meter set in A-scale slow response mode to measure a
wind farm grid area. When making such measurements, restrict the size of the area
(grid) being measured to less than 1000 square feet. If the maximum sound level
does not exceed 80 dBA, it can be assumed that all residents or visitors in this grid
are in a relatively safe or satisfactory noise level.
The next step depends on the readings recorded when the entire work area was
measured. For example, if the measurements indicate sound levels greater than
80 dBA, then another set of measurements must be taken in each grid. The purpose
here, of course, is to determine two things: which wind turbine or group of turbines
is making noise above acceptable levels (i.e., >80 dBA) and which residents and visi-
tors are exposed to these levels.
If grid measurements indicate readings that exceed the 85-dBA level, another step
must be performed. This step involves determining the length of time of exposure for
residents and/or visitors (do not forget wind turbine service personnel). The easiest,
most practical way to make this determination is to have these persons wear a noise
dosimeter, which records the noise energy to which the person was exposed during
an 8-hour period (or longer).
What happens next? It is necessary to determine if anyone is or can be exposed to
noise levels that exceed the permissible noise exposure levels listed in
Table 2.2
. The
key point to remember is that the findings must be based on a time-weighted average
4 hours per day. Note that this parameter assumes that the exposed person has good
hearing acuity with no loss. If the exposed person has documented hearing loss,
exposure to 95 dBA or higher, without proper hearing protection, may be unaccept-
able under any circumstances.
Octave-Band Noise Analyzers
Several Type 1 sound level meters have built-in octave-band analysis capability.
These devices can be used to determine the feasibility of controls for individual
noise sources for abatement purposes and to evaluate hearing protectors. Octave-
band analyzers segment noise into its component parts. The octave-band filter sets
provide filters with the following center frequencies: 31.5, 63, 125, 250, 500, 1000,
2000, 4000, 8000, and 16,000 Hz. The special signature of a given noise can be
obtained by taking sound level meter readings at each of these settings (assuming
that the noise is fairly constant over time). The results may indicate those octave
bands that contain the majority of the total radiated sound power. Octave-band noise
