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I watched as the next IDPA
shooter stepped up to the firing line. You
could tell he had done this before. He
carefully but purposefully loaded a magazine into his handgun and chambered a
round. On cue, he drew and shot a
perfect score in amazing time. His handgun seemed like an extension of his arm.
The bullets landed exactly where he willed them to on the cardboard
target. After safely holstering he
stepped back, turned around and flashed a smile, which told you he was pleased
with his results and all that training and endless hours of practice had finally
paid off. As he made it back to the
observer area I walked over and congratulated him for a job well done.
Curious as to what type of handgun he was using I asked him, “What kind
is it?” He replied, “It's 2:30pm.” It never ceases to amaze me
the high number of shooters that I come in contact with that do not wear any
type of hearing protection while shooting.
Granted, some things in our lives we cannot control.
However, noise induced hearing loss (NIHL) and Acoustic Trauma are
phenomenon that we most certainly do have control over and yet many shooters
ignore the very basic principle of wearing hearing protection. When is firearm noise is too
much? When do we cross that line
between loud and damagingly loud? Table
1 [1]
displays some of the decibel (dB) levels of various sounds found in our daily
lives. A decibel is a unit of
measurement and for our purposes here it is measured on a logarithmic scale and
there is a 10-fold increase in noise energy for each 10 dB increase.
Said another way, an increase of 10 dB doubles the loudness level. dB dB Sounds over 140dB can cause
pain, and prolonged exposure to noise over 85-90dB can result in permanent
hearing loss. Gunfire may be
categorized as an impulse noise, which has the characteristic of an
explosive burst. Impulse noise of sufficient intensity and pressure is often a
cause of acoustic trauma. Generally,
studies have shown that such impulse sounds may result in the shifting, skewing,
bending, swelling, bursting, tearing, fusing &/or severe mechanical
damage to the inner ear cells, structures, and auditory pathways. That is,
short-duration sounds of sufficient intensity (e.g., a gunshot or explosion) may
result in an immediate, severe, and permanent hearing loss, which is termed
acoustic trauma. The degree of hearing impairment seen after acoustic trauma
varies and may range from a mild to profound hearing loss.
Figure 1 (Pickles &
Heumen; 2001) compares electron microscopy of normal, healthy outer hair cells
(specialized hearing cells in our inner ear) to damaged ones. Once such damage occurs, it is permanent.
There is no method of regenerating these cells or “curing the
damage.” Bear in mind that this
is only one site where such damage can occur from noise exposure along our
auditory pathway. There is evidence to suggest
that once deterioration of certain specialized hearing cells (spiral ganglion
cells) has begun, there is a corresponding deterioration within the central
nervous system at areas higher up in the auditory system (Kim et al., 1997;
Morest et al., 1998). Thus, once
damage has occurred at lower levels it is not isolated there but rather may
progress upwards through the auditory pathway.
This is very characteristic of impulse noise such as gunfire that causes
acoustic trauma. The inner ear,
then, is not the only structure at risk from such exposure. Figure 1.
Normal, healthy outer hair cells (L) vs. damaged outer hair cells (R). Virtually all of the
structures of the ear and hearing system can be damaged from gunfire noise (NIH
Consensus Statement; 1990). Generally,
for sound levels below 140 dB, different types of sounds produce the same
hearing loss. This does not appear to be the case at levels above 140 dB, where
impulse noise creates more damage than would be predicted. This may imply that
impulse noise above a certain critical level results in acoustic trauma
from which the ear cannot recover (NIH Consensus Statement; 1990). Exposure to noise between 90
and 140 dBA (dBA denotes a decibel measure made with a filter that adjusts for
human auditory sensitivity) damages the inner ear metabolically
rather than mechanically and causes injury depending on the level and duration
of exposure. Noise-induced hearing loss, in contrast to acoustic trauma,
develops slowly over years, and is caused by any regular and consistent exposure
exceeding a daily average of 85-90 dBA (Clark & Bohne; 1999).
Acoustic trauma may occur from just one unprotected exposure to gunfire
noise. For
sounds between 75 - 90 dBA, the ear has a natural protective mechanism to reduce
its sensitivity to low frequency impact sounds through what is termed the middle
ear reflex. Generally speaking,
muscles in our middle ear contract and stiffen three tiny bones (the smallest
bones in the human body called ossicles; see Figure 2) that relay sound to the
inner ear. However, a delay of 300
to 500 milliseconds is required to set this protection fully in operation. Most
naturally occurring impact sounds can easily be dealt with by the middle ear,
but many man-made sounds, such as explosions from guns, as well as certain
industrial noises, occur so quickly that our middle ear protective mechanism
cannot respond quickly enough. The hearing
loss caused by such sounds is permanent
acoustic trauma
(Truax; 1999). Peak sound levels from rifles
and shotguns can range from 132 dB SPL (sound pressure level is another unit of
measurement) for small-caliber rifles to more than 172 dB SPL for high-powered
firearms. Americans collectively own more than 230 million guns, and more than
half of men in the American industrial workforce occasionally use guns. The
National Rifle Association estimates that 60 to 65 million Americans
collectively own more than 230 million guns. Because guns are so prevalent in
our culture, shooting firearms is the most important source of excessive noise
outside the workplace. The severity
of injury produced by impulsive noise exposure and the prevalence of shooting by
Americans makes gun noise America's most serious non-occupational noise hazard.
The acoustic energy in a single report from a high-powered rifle or shotgun is
equivalent to almost 40 hours of continuous exposure at 90 dBA. In other
words, 1 bullet equals 1 week of hazardous occupational noise exposure. An avid
target shooter can be exposed to an entire year's worth of hazardous
occupational noise in just a few minutes (Clark & Bohne, 1999; NRA,
1999). What about firearms
themselves? Is a .22LR any better on your ears than a .45ACP?
Table 2 [2]
compares the dB levels of various cartridges. Table 2. SHOTGUN
NOISE DATA (DECIBEL AVERAGES) CENTERFIRE
RIFLE DATA CENTERFIRE
PISTOL DATA Recall that sounds over 85-90
dB can lead to permanent hearing damage without hearing protection.
As can be seen from Table 2, even firing a .22LR (134 dB) has the
potential of causing permanent, irreversible, inner ear damage. There are various kind of
hearing loss. Conductive
hearing loss refers to physical damage, infection or fluid build up in the
middle ear cavity (Figure 2). If
the gunblast is of sufficient intensity a conductive loss may be seen and
accompanied by such symptoms as eardrum rupture or middle ear bone damage. Figure 2.
Anatomy of the ear [3] Conductive losses are
typically open to medical treatment from a physician who specializes in diseases
of the ear (Otologist or Otolaryngologist).
Sensorineural hearing loss refers to damage within the inner ear. This is usually, incorrectly, referred to as “nerve type
deafness” which really only occurs in about 1% of the American population
(Mueller and Hall, 1998). Sensorineural
hearing loss is the most common type of hearing loss in America, and noise
induced hearing loss or acoustic trauma from firearms is typically sensorineural.
It is permanent, irreversible and with proper hearing protection, can
be avoided or minimized. Probably the most common
excuse I have heard from shooters is that “my ears have toughened up from
shooting and I don’t have to wear hearing protection.”
Well, I’m sorry to say that this is not possible.
What is more likely is that you have sustained sensorineural hearing loss
and some sounds just don’t seem as loud any longer (along with speech).
However, it is still critical to wear hearing protection as the hearing
you do have left can still be harmed from unprotected firearm exposure.
As researchers and educators have noted, “Ears don’t get tough,
they get deaf.” (Mueller & Hall, 1998). Typically, noise induced
hearing loss and acoustic trauma affect the high frequencies first. Our ears
respond to sounds across a wide range of frequencies, from about 20 to 20 000
Hertz (Hz). Speech frequencies are
roughly located between 250-8000 Hz. Low
frequencies are used to “hear people” while the highs are what we use to
understand what they say. To put it
another way, the power of speech (vowels) is located in the low frequency range
while the clarity of speech (consonants such as s, k, th, sh, f, th) is located
in the highs. High frequency
consonants are necessary to maximize speech intelligibility.
Noise damage from firearms affects these high frequencies first due to,
some believe, anatomical reasons (Mueller & Hall, 1999).
Figure 3 [4] depicts an audiogram
(record of one’s hearing) of a sensorineural hearing loss typical of shooters. As such, many people complain
that “I hear people, but sometimes I don’t understand what they said.”
Women’s and children’s voices, typically in the high frequency range,
are usually the most difficult to understand when one has such a high frequency
hearing loss. Add to all this that
our hearing gets worse just from the normal aging process and you quickly
realize just how important hearing protection really is. Other factors also determine
how susceptible one is to firearm noise exposure.
For examples, blue-eyed individuals may be more susceptible than people
with greater melanin content in their eyes.
Some studies have shown that males are more susceptible to noise induced
hearing loss (NIHL) than females. Newborns
and older individuals also seem to be more likely to develop hearing loss from
NIHL. Finally, some studies have
also shown that smoking increases one’s chances of acquiring hearing loss from
noise. This may be due to the
carbon monoxide in the smoke (Henderson, Subromaniam, & Boettcher; 1993). I’ve also noticed that some
shooters will wear their hearing protection, but only while shooting.
When observing from just a few yards away, they do not wear their hearing
protection. This is simply not good
hearing conservation practice and is against competition rule #7 of your IDPA
manual. In fact, if one was to
comply with this rule, anyone within 50 yards of the firing line must
wear not only hearing protection, but eye protection also.
Some handguns at IDPA produce a very discernible boom that can still
damage your ears (see Table 2), even if you are not shooting and are only a few
feet to yards away. Of course, this will vary with the type of firearm,
cartridge, and distance from the shooter, but Table 2 clearly shows that even a
report from a .22 can damage your ears. Though
not relevant to IDPA purposes, the use of muzzle brakes and ports dramatically
increases the level of noise exposure from firearms. In the consideration of
sounds that can damage hearing, one point is clear: it is the acoustic energy of
the sound reaching the ear, not its source, which is important. That is, it does
not matter if the hazardous sound is generated by a machine in the workplace, by
a loudspeaker at a rock concert, by a lawnmower or a firearm during an IDPA
event. Significant amounts of acoustic energy reaching the ear may
create damage--at work, at school, at home, or during leisure activities.
Although there has been a tendency to concentrate on the more significant
occupational and transportation noise, the same rules apply to all potential
noise hazards, including and especially firearms (Clark and Bohne; 1999). Sound advice dictates that
when at the gun range, by all possible means, take appropriate measures to
practice safe gun handling. Wearing
hearing protection (along with eye protection) falls into this category, whether
you are the shooter or an observer. Think
of it this way: hearing aids could
cost you anywhere from $600 to $8000 per pair!
Wouldn’t you rather spend that on more important things…like
firearms, ammunition, training & IDPA? References Dr.
Amin Musani is a Clinical Audiologist practicing in Denison, TX.
Any comments or questions may be directed to DrAminMusani@cableone.net
or The Hearing Clinic 119 W. Main St. Denison, Texas, USA 75021,
Phone: (903) 463-9900, FAX: (903) 463-9911. |
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