Basic Calculations for Occupational Safety and Environmental Health Professionals - Mathematics and Statistics for the Environment - page 427

15.7.4 e ngineering C ontrol For i industrial n oise
When environmental professionals engineers investigate the possibility of using engineering con-
trols to control noise, the first thing they recognize is that reducing and/or eliminating all noise is
virtually impossible. And this should not be the focus in the first place, eliminating or reducing the
“hazard” is the goal. While the primary hazard may be the possibility of hearing loss, the distrac-
tive effect (or its interference with communication) must also be considered. The distractive effect
of excessive noise can certainly be classified as hazardous whenever the distraction might affect the
attention of the worker. The obvious implication of noise levels that interfere with communications
is emergency response. If ambient noise is at such a high level that workers can't hear fire or other
emergency alarms, this is obviously an unacceptable situation.
So what does all this mean? Environmental professionals must determine the “acceptable” level
of noise. Then he or she can look into applying the appropriate noise control measures. These
include making alterations in engineering design (obviously this can only be accomplished in the
design phase) or making modifications after installation. Unfortunately, this latter method is the one
the environmental professional is usually forced to apply—and also the most difficult, depending
upon circumstances.
Let's assume that the environmental professional is trying to reduce noise levels generated by
an installed air compressor to a safe level. Obviously, the first place to start is at the source : the air
compressor. Several options are available to employ at the source. First, the safety engineer would
look at the possibility of modifying the air compressor to reduce its noise output. One option might
be to install resilient vibration mounting devices. Another might be to change the coupling between
the motor and the compressor—install an insulator-cushioning-device between the couplings to
dampen noise and vibration.
If the options described for use at the source of the noise are not feasible or are only partially
effective, the next component the environmental professional would look at is the path along which
the sound energy travels. Increasing the distance between the air compressor and the workers could
be a possibility. (Sound levels decrease with distance.) Another option might be to install acousti-
cal treatments on ceilings, floors, and walls. The best option available (in this case) probably is to
enclose the air compressor, so that the dangerous noise levels are contained within the enclosure,
and the sound leaving the space is attenuated to a lower, safer level. If total enclosure of the air
compressor is not practicable, then erecting a barrier or baffle system between the compressor and
the open work area might be an option.
The final engineering control component the environmental professional might incorporate to
reduce the air compressor's noise problem is to consider the receiver (the worker/operator). An
attempt should be made to isolate the operator by providing a noise reduction or soundproof enclo-
sure or booth for the operator.
15.7.5 n oise u nits , r elationships , and e quations
A number of noise units, relationships, and equations that are important to safety engineers involved
with controlling noise hazards in the workplace are discussed below.
15.7.5.1 Sound Power
Sound power of a source is the total sound energy radiated by the source per unit time. It is expressed
in terms of the sound power level ( L w ) in decibels referenced to 10 -12 watts ( w 0 ). The relationship to
decibels is shown below:
L w = 10 log 10 w / w 0