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 With
the Troy System™:• Save Time and
Money
• Fast and Easy Installation
• Superior Acoustical Ratings
• Exceed Fire Protection Requirments
• Increase the Quality of Your Building |
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The following are commonly asked questions of
Troy Acoustics Corporation regarding the Troy System™ for indoor
shooting range facilities:
Q. If shooters are exposed
to gunfire noise for a very short duration, then why is the
noise level so critical?
A. Shooting outdoors is not
as critical due to the absence of reflective surfaces for
gunfire impulse noise levels. When the shooters are exposed to
the same impulse noise levels in an indoor facility the
untreated reflective surfaces increase the impulse noise levels.
Impulse noise is a sharp sound level peak occurring in a short
time interval. OSHA & NIOSH regulations state the impulse noise
exposure limit is 140dB peak or 100 impulses for an 8-hour
period. The OSHA & NIOSH noise regulations state that the 140 dB
should not be exceeded; OSHA does not enforce this limit. The
limit is based upon the assumption that there is a “critical
level”, a level above which there is high risk, no matter how
short the duration might be. John Franks, NIOSH noise expert,
has defined “regular” exposure to 85dBA as one day or more a
month unless a worker is exposed to over 110dBA for any length
of time in which case the dose does not matter. According to
Franks, workers such as firefighters, medical emergency
responders, and policemen who fire weapons, need to be enrolled
in a hearing conservation program. Based upon anecdotal data,
these workers may experience abrupt changes in hearing. OSHA
developed the following table in determining exposure limits of
workers to noise levels.
OSHA'S TABLE G-16 PERMISSIBLE DAILY NOISE EXPOSURE
| Length of Time, Hours/Day |
Noise Level, dBA |
| 8 |
90 |
| 6 |
92 |
| 4 |
95 |
| 2 |
100 |
| 1.5 |
102 |
| 1 |
105 |
| 0.5 |
110 |
| .25 or less |
115 |
The impulse levels of gunfire indoors often
exceed 165dB. Typically, shooters training at a range facility
undergo one to two hours of indoor range use per day. This far
exceeds the OSHA established limits.
Q. What is the risk shooting in
an indoor facility?
A. If the indoor facility is not
acoustically treated properly, the risk is hearing loss, even
with ear protection. Impulse noise (gunfire) at 140dB may
cause significant hearing loss with one exposure. With
peak gunfire exceeding 165dB, and wearing the best hearing
protection of 25dB attenuation, the shooter is still exposed to
levels above 140dB, very dangerous levels. In an
acoustically untreated facility, noise levels, due to
reflection, build up exposing shooters to a
higher cumulative noise level.
Hearing loss caused by exposure to high noise levels may be
permanent and irreversible. According to the American
Academy of Otolaryngology, there is no treatment, no medicine,
and no surgery, not even a hearing aid that completely restores
hearing once it is damaged by noise. When sound levels are
too high, they begin to kill nerve endings in the inner ear.
As the exposure time to high sound levels increases more and
more nerve endings are destroyed resulting in greater hearing
loss. Noise exposure is cumulative; exposure levels at
work are only part of the total exposure during any one-day.
With nearly 30 million workers exposed to
potentially hazardous noise levels on the job, occupational
hearing loss is a common and expensive problem in the work place
today. According to the World Health Organization,
excessive noise is the biggest compensable occupational hazard
in many countries. The consequences of work related
hearing loss go beyond an annoying bi-product of employment.
Associated with the problems are:
- Compromised quality of life- hearing loss
can lead to isolation, impacting the
personal and professional life.
- Tinnitus- this condition is characterized
by a constant ringing, hissing or other sound in the head when
no external sound is present.
- Loss of productivity- impaired
communication can result in a difficult working environment,
compromising productivity on a variety of levels.
- Work related accidents- a lack of
communication between coworkers can
increase the risk of accidents in the work place. According to
data from the
National Health Interview survey, workers with hearing
impairment show
55% greater risk of accident than those without.
Economic impact of work related hearing
loss results are estimated to be over one hundred millions
dollars a year in worker compensation payouts and hearing aid
purchases. A Navy report released in 2003 shows that
veteran disability benefits paid for hearing loss as primary
disability, for all services for the year 2003 exceeded
$680,000,000. The report states that hearing loss occurs
primarily during training, not in combat. The Bureau of
justice estimates there are 738,000 law enforcement officers in
the Unites States. These officers are required to train
constantly in the accurate and proficient use of firearms.
Q. What about increased hearing
protection?
A. The most sophisticated
hearing protection will attenuate, at best, 20-25dB.
 | Per a recent study conducted by G. Richard
Price of the US Army Research
Laboratory, Aberdeen Proving Grounds- Even when Hear
Protection Devices (HPD)
are properly designed and used, there is still an inherent
variability in the attenuation they provide. The study
finds that the standard deviation for ear protection fit
ranges from 8-10db. |
| Per the National Institute for Occupational
Safety & Health (NIOSH) a new study
published in October 2003 by William Murphy and John Franks
show standard
deviations of plugs and muff protection for ears range on
average from 3dB to 10dB. This study used HPD with Noise
Reduction Rating (NRR) of 12 to 33. |
| Per OSHA’s Hearing Conservation Amendment
(HCA)- To estimate the noise level
under the protector, the employer subtracts the NRR from the
workers C-weighted exposure level. If the C-weighted
levels are not available, 7dB must be subtracted from the NRR
to obtain the A-weighted sound level at the ear. OSHA
acknowledges that hearing protector attenuation in the field
is not nearly as good as in the laboratory. The 7dB
adjustment is for the uncertainty in the spectrum of the noise
environment. Because of the importance of low frequency
noise in the assessment of hearing protector attenuation, the
NRR is designed to be used with C-weighted environmental noise
level. |
Q. How is a shooting range
properly acoustically treated?
A. Hard reflective surfaces
and gunfire do not mix; the surfaces should be absorptive to
reduce reflection, thus maintaining very low reverberation
times. There is no general standard for areas of
acoustical treatment for shooters, or degree of acoustical
treatment per exposure limits. The key is to have the
greatest absorption on the most exposed surfaces. The
differences between absorption and reflection are simple. A ball
striking the wall in a racquetball court produces and echo, the
noise of the ball striking the wall is not absorbed, thus
travels to another wall and is reflected off that wall and so
on. In an open field covered with snow, the environment is
quiet. Yelling in the open field the sound
level quickly dissipates. There are no surfaces for
reflection to occur. The openness and the snow absorb the
acoustical energy.
Sound absorption is an energy conversion
process. The kinetic energy of the sound is converted to
heat energy as the sound comes in contact with an absorptive
surface. Thus the sound level disappears after coming into
contact with an absorptive surface. Because sound passes through
materials differently, as different frequencies, the sound
absorption will typically change with frequencies. Sound
absorption is measured in terms of the NRC (Noise Reduction
Coefficient), which is simply the average absorption for the
material tested, primarily over the speech frequencies (250,
500, 1000, 2000). NRC is a single-number index for rating
how absorptive a particular material is. The NRC gives no
information as to how absorptive a material is in the low and
high frequencies. Because the rating is an average, two
materials with the same rating might not perform the same.
A study completed in 2003 by C.A. Kardous for
the Applied Occupational and Environmental Hygiene states
“Impulse noise behaves differently in indoor shooting ranges
because of the reverberation effect when it reflects off hard
surfaces.” The hard reflective surfaces of an indoor
shooting range results in high reverberation times, generally
exceeding 9 seconds. The high reverberation time will cause a
build up of the noise level in the space. This build up of
noise increases the noise exposure of the shooters in the
untreated shooting facility.
Reverberation can be reduced or eliminated,
depending on the degree of absorption on the surfaces in the
shooting range. Since NRC ratings are deceptive for
absorption values of materials for shooting ranges, actual test
results from independent laboratories of the materials or
designs must be reviewed. Gunfire peak levels in excess of
165dB cannot be absorbed with materials rating an NRC .85 to
have a noticeable effect in an indoor shooting range. Only
materials or designs with a minimum NRC .95 should be considered
for shooting range applications. This ensures that the
intense sound level of gunfire will be absorbed without
deficiencies. Covering, as many of the hard reflective surfaces
of the shooting range will reduce the reverberation time.
The reduction of reverberation times will eliminate the build up
of noise level thus reducing the noise levels of the shooting
range while in operation. The exposed hard surfaces would
include all wall surfaces and overhead baffles or safety
ceilings. The concrete floors and bullet trap areas will
be the only surface areas not acoustically treated. Once
treated, the reverberation time in the range should not exceed
1.5 seconds.
Troy Acoustics Corporation has patented
proven materials designed
specifically for indoor shooting ranges.
Acoustical performance is guaranteed.
Do not place your shooters or your agency
at risk with inferior
designs and products!
 
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