Say What? Hearing Loss is a Two Part Problem

By Lt Col David McBride and Lt Col Darryl Tong, RNZAMC

Noise Induced Hearing Loss (NIHL) is not a new phenomenon - the effects of noise were known to the ancient Egyptians and has been a problem for the military ever since.

There are numerous articles in scientific literature that discuss the problem, and there is even a text book on noise and military service. Soldiering is a noisy business by any standard.

NIHL is traditionally more common in some branches; most notably infantry, gunners, and armour. The risk depends on the energy of the noise or noise dose, measured by the intensity and the duration of exposure. Noise intensity levels are measured in decibels (dB) with "normal" conversational speech at approximately 65dB, a good argument at 85 or so, and an experienced Drill NCO capable of 100 dB on a good day. The upper limit of "safe" noise exposure is generally accepted at 85dB over eight hours, and if you are exposed for shorter periods the noise can be louder, with a three dB(A) increase halving the duration : 88 dB(A) for 4, 91 dB(A) for 2, 94 for two and so on. Any prolonged exposure to levels above 85 dB(A) for eight hours increases the risk of developing NIHL. Loss of hearing occurs when the delicate hair cells in the inner ear (that converts vibrations to electrical signals to the brain which interprets these signals as sound) are damaged by loud noise, which can cause immediate damage. Not surprisingly, small arms fire and artillery rounds are extremely noisy, typically over 160 dB. Safe duration? Thousandths of a second! At these levels, and without adequate hearing protection, NIHL is more of a probability than a possibility. The problem is that it starts to happen quickly, but takes a while to notice and by then it is too late. In one independent review up to a quarter of US troops returning from Iraq and Afghanistan were reported as having some degree of NIHL due to small arms fire, explosive blasts and other noise. Because NIHL is irreversible, most military nations, including New Zealand, have hearing conservation programmes (HCPs). Our programme can be found on the Intranet. Finland and Canada are good examples of where the HCP has been shown to work: a study of the HCP in the Finnish Army showed that hearing tests among NCOs and Officers improved between two study periods when the HCP was given a high profile. These HCPs are important for new recruits who learn about NIHL early in their training.

General Sir Charles Guthrie, Chief of Defence Staff in the UK in 2001, was extremely worried about the attitude of the Ministry of Defence to noise, stating that the "creeping advance" of health and safety legislation affecting the Armed Forces was creating a climate of "risk aversion". However, health and safety is about risk management, not aversion and more about force protection than avoidance of the issue. We identify our tactical risks very carefully, including strengths and weaknesses, and a deaf soldier will not be on the "strengths" side of the mission analysis equation. That is why there are medical standards for hearing – a grading of H2 or H3 really does mean something, and there are too many of us out there with that grading.

Risk management should start with reduction of the noise at source, but silencers on a 50 cal really do not work, and, although well designed, a LAV is not a Toyota Corolla. Operationally the main concern is compromised situational awareness - most notably interference with detection and localisation of auditory warnings and perception of orders. What we need to seek is a balance between good levels of protection without compromising tactical performance Innovation is the key in these situations and the good news is that Defence is looking at new types of hearing protection that "kick in" when the noise starts, and kick out again when it stops. This has been a problem because weapons noise occurs suddenly, but new "smart" designs of earplug react very quickly. LAV crew members are more fortunate with "Active Noise Reduction" (ANR) headsets which cancel out the noise of the vehicle but not communications. Early detection of NIHL is also a priority, and new forms of hearing test can detect hair cell problems before irreversible damage arises. All good, but how is this a two-part problem? NIHL from an occupational standpoint has been identified by the military and programmes have been devised for hearing conservation but what about the times when you are not in uniform - in other words when you are in civvies? This is the second part of the equation - NIHL from recreational activities. A growing concern among hearing specialists is the degree of hearing loss among young people due to iPods, MP3 players and other similar devices. Reminiscent of the concerns arising from the use of Sony walkmans in the 1980s, children and young adults are being literally bombarded with sound at higher volumes and for longer periods of time. At peak volume an iPod can reach levels of 120dB - the range between a jackhammer and a jet engine and devices are turned up to the maximum in order to drown out external noise, which is resulting in significant hearing loss at an early age in the United States. This is not some random propaganda exercise by a couple of dads with teenaged kids - one Finnish study found that up to 20 percent of recruits had a greater than 20dB hearing deficit in either ear as a result of leisure-time noise exposure, most commonly to loud music prior to basic training and exposure to loud noise in a military environment.

NIHL is really not too difficult to prevent. Ear plugs are good, but make sure a medic shows you how to use them. You have to keep the tip of your finger on them for at least a minute or they will expand out of your ear instead of blocking the ear canal. If you are on the range, wear your hearing protection till you are well off the firing point. If you are on exercise and know you will be involved in a fire fight, put the plugs in. Try not to listen to your iPod for more than an hour, and if others can hear it, it’s too loud. The secret is not to give your ears a good work out, they work much better with rest and relaxation and that way, just quietly, they will hopefully keep working for you for a long while yet. Symptoms of hearing loss include tinnitus (ringing in the ears), pain in the ear, muffled sounds and decreased ability to hear sounds that others are seemingly able to hear.

Recommendations

• Use protective hearing devices when provided
• Be familiar with the correct usage of protective hearing devices
• Limit the volume of personal music devices such as iPods and MP3 players
• Limit the amount of time using these devices (i.e. limit exposure time)
• Seek medical advice if you have concerns about your hearing

LTCOL McBride is a senior lecturer in occupational medicine at the University of Otago. LTCOL Tong is a maxillo-facial surgeon. Both are Territorial Force officers.