Noise-Induced Hearing Loss

Wednesday, December 24th, 2014

As early as the 16th century, French barber-surgeon Ambroise Paré noted that firearms caused noise-induced hearing loss. Today, shooters wear hearing protection, even when shooting relatively low-power guns, like pistols, alone, outdoors, but it wasn’t that long ago that a machine-gunner was supposed to tough it out. The military didn’t address the problem until a new technology made it impossible to ignore:

Even though World War II was a major contributing factor in the evolution of hearing conservation, it was not until after the war that the most significant event occurred. The Army Air Corps became a separate branch of service from the US Army and was renamed the US Air Force. Concurrently, this new branch of service introduced the jet engine aircraft to the military. No sound of that volume and duration had ever before been experienced. It was immediately noted that exposure to jet engine noise caused permanent hearing loss in a brief time. It also made verbal communication impossible and caused a series of physical manifestations described as “ultrasonic sickness.” Symptoms included earache, headache, excessive fatigue, irritability, and feelings of fear. Initially, it was believed that these symptoms were caused by inaudible, ultra-high-frequency sounds being generated by the jet engines. These symptoms, widely reported by air force maintenance crews, triggered a medical study that revealed that the illness was real; however, research attributed it to high levels of audible frequencies.

As a result, the US Air Force published the first military regulation on hearing conservation in 1948. AFR 160-3, “Precautionary Measures Against Noise Hazards,” is significant not only because it was the first enforceable regulation in the history of hearing conservation, but it also placed responsibility for the new program on the medical leadership at air force installations. Some of the preventive measures described in AFR 160-3 include limiting noise exposures in terms of overall sound levels and using cotton wads moistened with paraffin as hearing protection for exposures to hazardous noise.

In 1952, the Office of Naval Research reported the results of extensive interviews with hundreds of returning frontline soldiers who indicated that in combat, “sound was more important than all other means of equipment identification.” Combat-relevant sound sources included aircraft, mortar and artillery rounds, rifle and machine gunfire, and various other weapons. According to the report, “The men regarded the sound of enemy weapons as such an important means of identification that they rarely made use of captured equipment because it resulted in their being fired upon by friendly troops.”

Ordinary riflemen have only been issued hearing protection recently:

The combat arms earplug was introduced into the military at the start of the war in Afghanistan (Operation Enduring Freedom). However, as with most hearing protection, it was shunned for operational use and, at approximately $6.00 per pair, was considered prohibitively expensive by individual army units. The device allows soft sounds to flow unimpeded through a filter but blocks loud impulse sounds, such as an explosion or a rifle discharging. This allows effective communication, enables situational awareness, and provides protection from hazardous weapons firing and explosions. With units’ strength decreasing because of hearing loss, commanders began to recognize that hearing readiness is an extremely important factor of a unit’s performance in combat. All deploying soldiers were therefore issued the earplugs in 2004. In fact, the US Marine Corps was so convinced of the effectiveness of the combat arms earplug that it ordered over 20 000 pairs, thereby temporarily depleting the entire national stock in 2003.

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The problem of protecting hearing while enhancing soldiers’ communication ability and situational awareness was solved with a new generation of hearing protection. This new category of equipment was called tactical communications and protective systems (TCAPS). In 2007, TCAPS were introduced into the army as a possible solution to an age-old problem. TCAPS compose a new category of electronic hearing protection that uses active noise reduction to soften noise and enhance speech discrimination while at the same time reducing noise by up to 40 dB. In addition to being light and rugged, TCAPS provide protection and let soldiers monitor environmental sounds, communicate, accurately gauge auditory distance, and localize sound sources without hindrance. Further, the devices allow radio connections specifically used by the military to be processed without interrupting the signal when the TCAPS are actively blocking environmental sounds. Although this category of device is still being studied and protocols for use are being created, it represents a new era in the history of hearing protection.

Comments

  1. JC says:

    After reading the self-licking ice cream cone article, it stands to reason that maybe the $6 per soldier for those ear plugs just wasnt going to the “right” contractor.

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