Reducing Noise
Levels
Through Engineering Controls
Article Written By:
By Henry P. Shotwell, Ph.D., CIH
Vice President, Atlantic Environmental, Inc.
Atlantic Environmental, Inc.
Dover, NJ
http://www.atlenv.com/
It’s fairly easy to control personal exposure to noise
by limiting exposure time or using hearing protectors
like ear plugs or ear muffs. Engineering controls
are usually applied to the machinery that produces noise.
Imagine a 200 foot x 175 foot manufacturing facility
with a 30 foot high ceiling. In this building are
a variety of cut-off saws, grinders, millers and other
metal-working machines. There is also a small foundry
shake-out station. When normally operating, the
overall noise level is 89 decibels (A-scale). Individual
machines can produce up to 106 decibels at the point of
operation. The HVAC system has long runs of rectangular
duct which vibrates visibly. Management would like
the overall noise level to be below 85 decibels.
One of the options management has under consideration
is to hang sound-absorbing panels from the ceiling.
This approach, while effective, would be prohibitively
expensive. We feel a more effective approach is
to identify each machine that produces noise over 85dB,
and then control the noise at the source. This allows
for much greater flexibility in designing controls and
selecting noise absorbing materials.
Almost every sound-producing device generates a mix of
frequencies and intensities (decibels). What we
perceive with our ears or measure with a sound level meter
is a composite of all these frequencies and intensities.
Usually, an Octave Band Analysis (OBA) is needed to fully
analyze the sound produced by a machine. The OBA
will allow you to measure the intensity (in decibels)
at 31, 62, 125, 250, 500, 1,000, 2,000, 4,000 (and sometimes
8,000 depending on the OBA model used) Hertz (Hz).
This is important. Low frequency noise (up to about
125 Hz) is more difficult to control but has less potential
for impairing hearing. The higher the frequency,
the easier it is to control. This is fortunate,
because noise intensity at higher frequency is more damaging
to hearing than the same intensity at lower frequency.
The most effective noise control method is to leave the
noise producing machine off; but, that defeats the purpose
of having the machine. Other, similar approaches would
be to put the offending machine outside the work area.
In some cases, that will work. An HVAC blower fan
could be mounted outside the building it serves, for example.
But, in most cases, the noisy device has to be inside the
workplace, usually near work stations. For the remaining
situations, noise can be controlled (i.e. absorbed or deflected)
at the source, usually in the form of barriers or small
enclosures. The choice of material to construct these
controls depends on their sound absorbing capacity.
Engineering tables, showing this capability for a variety
of materials, are available. Controlling noise at
the source is generally more effective and more economical
to install and maintain than other approaches.
Atlantic Environmental Inc
2 East Blackwell Street
Dover, NJ 07801
(800) 344-4414
(973) 366-4660
(973) 366-3116 Fax
info@atlenv.com
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