Environmental Engineering Reference
In-Depth Information
When implementing a hearing conservation program, the plant
safety person usually asks the same standard question: “Where do
I start?” The first step is to conduct a noise survey of the plant site,
including pumping stations and maintenance centers. This noise sur-
vey should be conducted using a calibrated sound meter. Each building
at each facility should be surveyed for sound. Keep in mind that even
administrative office areas, at times, can contain high noise levels.
When conducting the plant sound level survey it is important to
remember that various machines might not be online and in operation at
the particular moment the survey is conducted. It is impossible to con-
duct a sound level survey that will provide a true picture of actual noise
levels unless all machinery is running.
While conducting the plant sound level survey, it is wise to draw a
rough map of the layout of each building. On this map, include pictorial
representations of each noise-making machine or device. When testing
for sound level, start at the machine and work around the machine; it is
important to survey the entire area around the machine. Moreover, the
sound level survey should be conducted at varying distances from each
machine. Sound measured at a certain distance from the source in open
air is reduced by about 6 dB for each doubling of that distance. Sound is
reduced less when it spreads inside a room. The point is that by moving
away from the sound source the sound level is reduced.
When measuring for noise level, measure the sound level close to
the pump, motor, or blower (within 2 feet) and then move outward from
the device by doubling the distance from the machine (e.g., 4 feet, 8 feet,
and 16 feet). On the rough sketch, at the particular machine being mea-
sured, draw concentric circles at each distance and record the meter
readings on each circle.
The concentric circle approach aids in two significant ways. First,
by knowing the sound level for varying distances from the noise source
it is possible to label or mark off high noise areas and direct routine
traffic away from the noise. Second, the noise level mapping system also
provides a reference for future comparisons. In some cases, where it has
been noted that an appreciable increase in decibel level occurs (as mea-
sured by the sound level meter), you will be able to point this out to the
plant superintendent. This can be important information. The increase
in decibel level might indicate, for example, that the motor bearings or
perhaps a drive belt is about to fail. Maintenance personnel may later
determine that failure of some machine component was indeed immi-
nent. Thus, a sound level survey can pay off in more ways than one.
After conducting the plantwide noise survey and entering the find-
ings on the map, the plant safety person should then compare the mea-
sured readings with the 85-dB rule. If any of the measured readings are
equal to or exceed 85 decibels and workers could be exposed to these
levels for 8 hours (or less if the noise level is higher), then a written hear-
ing conservation program is required. The written hearing conservation
program should include several parts. To begin with, it should include
