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Risk Management: Police Officers, Hearing Loss and Blast Overpressure

By Keith Mercer (ret)

Hearing is a powerful asset in situations in which an officer might need to communicate or localize sounds. However, officers are exposed to hazardous noise that can compromise their hearing every day. The primary source for this is noise and concussive force from firearm discharges, which damage hearing both in the short term and the long term. In the short term, firearm discharges cause flinch response and momentary disorientation, which can create vulnerabilities in the field. In the long term, firearm discharges will eventually cause tinnitus and hearing loss, even with standard double protection for the ears. In a 10-year study of 20 officers, more than 75 percent reported significant hearing loss as well as tinnitus even while using double protection.1 Further, according to a 2003 National Institute for Occupational Safety and Health report, noise levels and concussive force produced by firearms leads to a serious health risk for occupational hearing loss among officers.

WHAT IS BLAST OVERPRESSURE?
The concussive force from an explosion…

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travels on a wave called a shock wave. A shock wave is a front where the leading side is highly positive pressure, or blast overpressure (BOP), and the trailing side is the underpressure. The real danger lies in the instantaneous change of overpressure to underpressure, which doesn’t give the human body time to equalize pressure. To further clarify, blast overpressure and a shock wave are not the same as sound pressure. The damaging effects of a sound pressure wave are easily mitigated through commonly used ear protection devices. BOP and shock waves cannot be mitigated through ear protection as both travel right through the body, devastating any cavity organs filled with gas, such as the sinuses, ear canal, lungs and heart. Continued exposure to BOP events will cause a cumulative effect that, over time, will cause damage such as ruptured eardrums, tinnitus, hearing loss, pain, vertigo, stress and heart conditions. Chul-Hee Choi, author of “Mechanisms and Treatment of Blast Induced Hearing Loss,” states in the Korean Journal of Audiology, “The effects of blast on the human body are determined
by a variety of factors: distance…

IROC Tactical Muzzle Device Test Report

By Lt. Frank Borelli (ret)

A couple years ago, at SHOT Show, there was a booth showing off custom hearing protection and in that booth, to demonstrate the need for such, was an audiologist (hearing specialist).  I had my hearing tested and discovered that I have indeed lost some of my hearing.  The frequency range I’ve lost my hearing in is common to those who have been around gunfire over an extended period of time, even if they always wore ear protection.  “But,” you ask, “If you always wore hearing protection, how did you lose part of your hearing?”  An excellent question.  Here’s the answer as it was explained to me.

Hearing damage from exposure to loud noise is not only caused by sonic impact directly onto the ear drum but also is caused by sonic impact on the bone structure of the head.  Since all of the bones in the head are connected in some way, even if you have in ear plugs and are wearing quality muffs, there is still a sonic impact to your cranium that is passed to every other bone in your head, including the small ones in your auditory system.  The end result, over time, is unavoidable hearing loss.  The only solutions to such hearing loss are:

  • Either don’t ever shoot – and we all know that if you’re in the military or law enforcement that’s an impossibility; you have to train – or
  • Redirect the muzzle blast of the weapon so that it is more forward, away from the shooter so that the sonic impact itself is lessened as the shooter experiences it.

Enter the IROC Tactical Muzzle Device

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All over the shooting industry today you can find muzzle devices of every type. Each and every one of them claims to do something specific, although some of them are honest enough in their marketing to admit that they just look cooler than the standard M4/M16 “birdcage” flash “hider.” Let’s be honest: it does nothing to hide flash; it just focuses the blast into specific lanes of travel, if you will, in a 360° pattern around the end of the barrel after the bullet passes. Lots of the flash hiders, flash suppressors, etc. claim to reduce felt recoil (and some do); reduce muzzle flash; reduce flash signature, etc.

Once again I say, enter the IROC Tactical Muzzle Device (MD). When I was first introduced to the IROC Tactical MD I was more impressed with its adjustable pressure capability. The one thing I can clearly recall was the discussion about how the MD is adjustable to optimize the pressure dependent on barrel length. To me, that in and of itself was impressive. I remember the challenges some of our military forces faced when they were using short barreled M4s in Afghanistan with ammo that was designed and optimized for use in a 20” barrel. The difference in performance for a given round based on barrel length can present a challenge for the operator in the field. More often than not, the person behind the trigger doesn’t get to pick their ammo; the ammo gets issued to them when they need it. Very rarely is the ammo optimal for the weapon and the IROC Tactical MD allows you, to some extent, tune the MD to the barrel length, increasing the efficiency of the gas pressure use.

As if that isn’t impressive enough, I later came to learn that the MD also has a significant benefit in redirecting the concussive force of the sonic waves caused by gas over-pressure as the bullet leaves the barrel. In other words, the MD redirects the escaping gasses enough to decrease the impact we experience in our cranial vault (head).
Remember earlier when I talked about hearing loss and the inevitability of it in spite of wearing hearing protection? Remember that second option I listed as a partial solution to protecting the hearing? Redirecting the escaping gasses more forward away from the shooter? There ya’ go. That’s exactly what the IROC Tactical MD does: it focuses the gasses forward (see included image).

Now, one would think that if a muzzle device is projecting all those gasses forward then the felt recoil must be increased, right? I can’t say I understand the engineering of it all, but I can tell you from firsthand experience, the felt recoil is actually reduced. On my most recent range visit I had one AR style rifle with the IROC Tactical Muzzle Device mounted (the rifle was a Del-Ton AR-15 with a 16” barrel) and I had a different AR-15 rifle with a more standard “bird cage” style flash hider.

Shooting them side by side, admittedly without benefit of any laboratory equipment to measure pressure, etc., the Del-Ton’s felt recoil was noticeably reduced as compared to that of the other rifle. Further, virtually everyone on the range with me reported less “noise pressure” (best term we could come up with) from the shots fired with the Del-Ton – with the IROC Tactical MD mounted.

Two other shooters tried out the Del-Ton with IROC Tactical MD mounted versus the other AR rifle, and both of them reported feeling less recoil with the Del-Ton. Both also reported less audibly perceived “impact” from the shots fired.

I had performed previous accuracy tests with that particular Del-Ton and had documented ½ MOA accuracy at 100 yards. I wondered if the change from a “typical” flash hider to the IROC Tactical MD might result in a difference of accuracy; specifically, I wondered if the accuracy would be reduced due to the change in pressure behind the round. Testing showed no measurable reduction in accuracy. Several of my groups were as small as ¼ MOA but the average group still measured out to ½ MOA.
As a final noticed benefit, the IROC Tactical MDreduces your flash signature. What’s that, you ask? I remember one Fourth of July when another officer and I walked out of our Town Hall which was at one end of a big park. At the other end of the park, perhaps 200 yards away from where we were, was a roadway infamous for being a drug dealing hub. As we walked out that evening, someone fired some shots down on that roadway. The other officer and I both looked and saw elongated muzzle flashes from whomever was shooting. The mayor was busy trying to seek cover under the grass (I swear, he was burrowing). When the mayor asked us why we weren’t ducking we observed that the muzzle flashes were long and thin indicating that the weapons weren’t being fired our way. We told him that if the flashes were rounder and shorter, that would indicate that they were being fired more in our direction.

With the IROC Tactical MD, your muzzle flash may indeed by longer and skinnier, as viewed from the side or top, but the “out the end” flash would be smaller. Overall, as shown in the accompanying photo, the muzzle flash signature isn’t as significant as with a normal flash hider.

Now, one word of caution: If you’re not an armorer for the AR rifle platform, don’t try to mount the IROC Tactical MD yourself. In fact, you shouldn’t try to remove the mounted flash hider on your rifle. Here’s why: To safely remove the mounted flash hider, and to properly mount the IROC Tactical MD, you need to have the rifle barrel properly secured in a barrel vice or similar device. If you start torqueing pressure on the flash hider as you attempt to remove it without somehow properly securing the barrel, you stand the chance of twisting the barrel and ruining it beyond repair. I was lucky enough to have my IROC Tactical MDinstalled by the AR armorer from my local sheriff’s office.

Overall I think this is a pretty good piece of equipment. While many may not think the recoil and flash reduction benefits are enough to warrant purchasing one, I encourage you to consider the long term benefit to your hearing that this device will have. No other muzzle device on the market today, short of an actual sound suppressor, has been measured to reduce the blast impact on your head / bone structure as the IROC Tactical MD. Check it out. I think you’ll be pleased.

10 Hot New Products From SOFIC 2014

A plethora of great new gear was on display at the 2014 Special Operations Forces Industry Conference (SOFIC) in Tampa, Fla.

By Andre M. Dall’au | June 6th 2014

“Carbine shooting in enclosed structures is getting to be common for operators, multi-gun competitors and LE. The amplified concussive effect to nearby teammates causes involuntary reactions (flinching) as well as long-term hearing loss- conventional ear protection does not safeguard against concussive force. To counter the side blast from carbines, IROC Tactical now offers a muzzle device that sends the entire muzzle blast in a tight cone forward of the weapon. For entry teams, that means close supportive fire without disruptive and overlapping blast zones from typical muzzle brakes. The IROC Muzzle Device (IROC MD) is hand-adjustable to control the cyclic rate and regulate the gas fed back to the action.”

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travels on a wave called a shock wave. A shock wave is a front where the leading side is highly positive pressure, or blast overpressure (BOP), and the trailing side is the underpressure. The real danger lies in the instantaneous change of overpressure to underpressure, which doesn’t give the human body time to equalize pressure. To further clarify, blast overpressure and a shock wave are not the same as sound pressure. The damaging effects of a sound pressure wave are easily mitigated through commonly used ear protection devices. BOP and shock waves cannot be mitigated through ear protection as both travel right through the body, devastating any cavity organs filled with gas, such as the sinuses, ear canal, lungs and heart. Continued exposure to BOP events will cause a cumulative effect that, over time, will cause damage such as ruptured eardrums, tinnitus, hearing loss, pain, vertigo, stress and heart conditions. Chul-Hee Choi, author of “Mechanisms and Treatment of Blast Induced Hearing Loss,” states in the Korean Journal of Audiology, “The effects of blast on the human body are determined
by a variety of factors: distance…

Concussive Force: The Silent Variable in Hearing Loss

By Sergie Albino & Sean Bell | June 16th 2014

The U. S. Army Center for Health Promotion and Preventive Medicine lists hearing loss from gunfire as the most common injury for soldiers, and the Department of Veteran Affairs says hearing damage is the number one disability claimed by returning vets. In addition, a study from the Department of Otolaryngology, National Taiwan University Hospital, Taipei, Taiwan, found that even with double ear protection, hearing loss still occurred in about 75 percent of those studied. It’s not melodramatic or overblown to claim hearing loss is disabling some of our most brave men and women.

Why is this such a problem? Everyone who has ever taken a gun to a range, either as a professional or amateur, knows you need to wear ear protection. However, research shows there could be more to protecting your hearing than just wearing the ear muffs or inserting the plugs (or both). First, how is hearing loss defined, and how does it happen?

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The intensity or volume of sound is measured in decibels (dB). Without going into too much detail about decibels, understand that a whisper is about 30 dB, normal conversation would be 60 dB, an alarm clocks hit about 80 dB, and anything over 85 dB for an extended period of time can lead to permanent hearing damage. Over 140 dB for an impulse sound will do the same thing.Almost all firearms (pistols, rifles, shotguns, etc.) start at 140 dB and can increase dramatically from there. This is why protection is so important. From the first shot fired you are already at the threshold that causes permanent, irreparable hearing loss.

All standard hearing protective devices on the market have a noise reduction rating (NRR). This number is not a one-to-one ratio, meaning a set of ear muffs with an NRR of 30 does not actually lower sound by 30 dB. You have to subtract 7 from the NRR and divide by 2. So a device with NRR 30 is actually only about a 12 dB deduction (30-7/2=11.5). If you are doubling up on both ear plugs and ear muffs, add 5 to the protection with the highest rating.

Now go grab whatever hearing protection you’ve been using. Do the math; subtract that number from 140. Is it below 80? If not then you’re damaging your hearing.

But wait. You say, 140 dB is only for impact noises. I only shoot for a few minutes at a time, so my number is 80 dB. I say, nice try. If you’re in an environment where shooting is happening (shooting range, military situation, etc.) then you need to count all the time you’re there.

But here’s the kicker, this is something few people are aware of. Even if you get the best ear protection and then double up on both ear muffs and ear plugs, you still aren’t stopping the hidden danger of hearing loss through bone conduction. This is the area where traditional protection completely fails you.

Sound can be transmitted directly through the bones in your skull into your inner ear. Regular protection doesn’t stop this transmission of vibration and the skull only dampens between 40 dB to 60 dB of it. This type of damage is referred to as concussive damage, and it is the secret culprit causing so much damage to military personal and law enforcement officers. Unlike the average shooter, military and law enforcement personnel are far more likely to be involved in close-quarters combat. This means the concussive force from their firearms poses a much greater risk because of the close proximity.

To give you an idea of how prevalent hearing damage is, 60 percent of veterans returning from Iraq and Afghanistan are suffering from hearing loss. This amounted to $1.1 billion in disability payments in 2011. It’s not any better for police officers. In 2011 New York forced the retirement of police officers that wore hearing aids, many of whom needed hearing aids because of hearing loss received while working on the job.

How do we address this oversight in protection? Concussive damage is a little trickier to deal with than sound wave damage. One notable solution is a muzzle device. You want something specially designed to direct the concussive force of the shot away from the shooter and ideally force it parallel with the bullet. This means the sound and bullet are traveling in the same direction.

Understanding the different causes of hearing loss is the first step in keeping our military forces and police personnel safe. The second is making sure they are equipped with the proper education and tools to protect themselves.