In the 1988 movie "Good Morning, Vietnam," character Adrian Cronauer, a Saigon- based military disc jockey, performs an on-air skit in which he contacts an artilleryman in the field and offers to play a song for him. "Anything," the artilleryman screams into the phone, "Just play it loud!"
It was a funny line in a popular movie, but for many military veterans— and consequently, for US taxpayers— the noise-induced hearing loss incurred by substantial numbers of US military personnel is no laughing matter. The statistics are staggering. According to a recent Department of Defense (DoD) briefing, "Noise and Military Service: Implications for Hearing Loss and Tinnitus," 75,316 new recipients received Department of Veterans Affairs (VA) compensation for auditory impairments in 2003. Furthermore, the briefing indicates that disabilities of the auditory system (hearing loss and tinnitus, otherwise known as ringing in the ears) were the third most common service-incurred disability, representing 10% of the military's total disabilities in 2003. In 2004, VA costs were $660 million for hearing loss and $190 million for tinnitus, with total expenditures since 1977 topping $6.7 billion in the treatment of injuries related to hearing loss.
Aircraft maintainers routinely remove their hearing protection to communicate with others on the flight line or otherwise complete their tasks in a safe manner. While they may be solving their immediate hearing problem, in doing so they are creating a hazardous situation that ultimately contributes to increasing the number of hearing loss victims and the amount of money spent on their treatment. It is a costly, cruel irony that maintainers need to remove their protective headsets in order to hear each other clearly, and therefore function safely, on the flight line. Currently, maintainers wear foam earplugs under their communication headsets—a practice which effectively muffles all external noise, including important communications. Clear ground communications in the highnoise flight line environment are critical both to ensuring the safety of the ground crew and the aircraft pilot and to preventing costly ground-based accidents involving the aircraft.
The DoD briefing concludes that "further investigation of mechanisms, natural history, epidemiology, meas urement, and treatment of noiseinduced hearing loss and tinnitus" is warranted. Dedicated to the prevention of hearing loss, AFRL audiologists offer pragmatic advice for those working in high-noise environments: put on the appropriate ear protection and leave it on while performing duties. In a written response to the DoD study, AFRL researchers assert that "consistency in the use of hearing protection by military personnel continues to be an issue of concern. It parallels inconsistency experienced in industrial hearing conservation programs."
The researchers' documented response also illuminates a major difference between the noises found in military settings and those common to an industrial setting. Military noise levels— propagated by sources such as aircraft, artillery, and explosives and encountered during both training and combat—are orders of magnitude more intense than the noise levels found in most industrial environments. Sound pressure levels above 85 dB can cause hearing damage, and the noise from a jet engine, to name one common military noise source, can approach 150 dB.
AFRL researchers recommend that the DoD Hearing Conservation Working Group add an operational need to its goals: to develop, mature, and procure improved hearing protection technologies for use by military members in high-level/highdose noise environments. The recommendation recognizes that AFRL hearing protection technology offers near-, mid-, and long-term solutions to the hearing loss problem.
The near-term solution is AFRL's Attenuating Custom Communications Earpiece System (ACCES®), a custommolded, deep-insert earpiece that is easy to install and provides better protection than traditional headsets and foam plugs offer. Having completed a unique cycle of technology transfer and transition, this state-of-the-art hearing protection technology is now being marketed and sold directly to commercial and military customers alike. The General Services Agency contracted with Westone Laboratories, Inc., a commercial designer and manufacturer of custom ear molds, and AFRL in the development and production of ACCES for the federal supply schedule. Westone can integrate specialized electronics and a voice communications cable into these earpieces to provide clear communications in even the highnoise environments endured by pilots and maintainers (see Figures 1 and 2).
The midterm solution is to integrate the ACCES custom plugs with active noise reduction technology. Researchers have successfully demonstrated prototypes, and Westone has begun production of units to be delivered for the F-35 Joint Strike Fighter, which was the first program to require active noise reduction/hearing protection technology.
The long-term solution to the hearing loss problem is for researchers to gain a better understanding of how bone and tissue conduct sound energy to the cochlea, the spiral tube of the inner ear that contains nerve endings critical to hearing. By acquiring this knowledge, researchers hope to develop applicable strategies for reducing the amount of sound energy that reaches the head via air circulation.
Meanwhile, AFRL research audiologists would like pilots and ground crew to take advantage of the available ACCES technology. According to a "safe to fly" memorandum issued by the F-22 System Program Office, "Use of ACCES has proven to be a vast improvement over current earplugs in the area of noise attenuation and speech intelligibility and has generated great interest in our pilot community." Lieutenant General John Bradley, chief of the Air Force Reserve, personally tested the earplugs during several F-16 sorties and called the technology "phenomenal," endorsing ACCES as the preferred solution for hearing protection for the Reserve. (The author wishes to acknowledge technical contributions to this article by Mr. John Hall, an audiologist with the AFRL Human Effectiveness Directorate's Battlespace Acoustics Branch.)
Mr. John Schutte (Ball Aerospace), of the Air Force Research Laboratory's Human Effectiveness Directorate, wrote this article. For more information, contact TECH CONNECT at (800) 203-6451 or place a request at http://www.afrl.af.mil/techconn_index.asp . Reference document HE-H-05-03.