According to the Department of Veteran Affairs, noise-induced hearing loss is the most pervasive disability resulting from military service. The damage caused from elevated noise levels is often painless and can go largely unnoticed. By the time one begins to realize their hearing has begun to deteriorate, substantial permanent damage will have already occurred.
Being able to recognize situations in which noise levels rise to harmful levels and taking the necessary preventative precautions will protect you from noise damage. Hearing loss is permanent, but it is also completely preventable.
Hearing Conservation Program
The goals of the Hearing Conservation Program are to reduce hazardous noise sources, prevent noise-induced hearing loss, and ensure auditory fitness-for-duty for service members and civilian workforce.
Commanders, commanding officers, and officers in charge shall ensure their Marines, assigned Sailors and exposed civilian personnel are trained, fitted for hearing protection devices, and tested for hearing loss.
Effects of Noise
Physical and Psychological
Short term exposure to loud noise can cause a temporary change in hearing (your ears may feel stuffed up) or a ringing in your ears (tinnitus) that may go away within a few minutes or hours after leaving the noise. Repeated exposure to loud noise, however, can cause tinnitus and/or permanent hearing loss.
The effects of exposure to loud noise aren’t limited to hearing-related issues. Loud noise can create physical and psychological stress, reduce productivity, interfere with communication and concentration, and contribute to workplace accidents and injuries by making it difficult to hear warning signals. The effects of noise-induced hearing loss can be profound, limiting your ability to hear high frequency sounds, understand speech, and seriously impairing your ability to comprehend and communicate.
The quality of your hearing also has a significant impact on your combat effectiveness. Sound is often the first source of information a war fighter has before direct contact. Unlike visual information, sound comes to us from all directions, through darkness, and over and around many obstacles to vision.
Garinther and Peters conducted a study in which they looked at tank crew performance in a tank simulator at varying speech intelligibility levels. The study noted the following reductions in combat effectiveness when noise levels were high enough to impact communication:
- Mission time – time required to identify targets (Time increased from 40 seconds at good intelligibility to approximately 90 seconds at poor intelligibility).
- Mission errors – Percent of commands not correctly communicated to gunner (1% at good intelligibility, 37% at poor intelligibility)
- Gunner accuracy – Percent of time correct targets hit by first round (90% at good intelligibility, 42% at poor intelligibility).
- Mission completion – Percent of targets correctly identified (98% at good intelligibility, 68% at poor intelligibility). The number of times the wrong target was hit also increased as speech intelligibility decreased and the number of times the enemy defeated the friendly tank during the simulation increased four times from 7% enemy kills at good speech intelligibility to 28% at poor speech intelligibility. In every situation tested, poor speech intelligibility negatively impacted performance.
Hazardous Noise Levels
Sound volume is measured in units called decibels (dB). Sounds of less than 75 decibels, even after a lengthy exposure, are unlikely to cause hearing loss. However, extended or repeated exposure to sounds at or above 85 decibels (approximately the level of a vacuum cleaner) can cause hearing loss.
Loud sound does not have to be physically painful to be harmful. The damage can occur at different thresholds depending upon the duration and intensity of the noise. The more intense the noise, the more quickly it can cause damage. A general rule to follow is that if you need to raise your voice to be understood by someone standing three feet away from you, then the noise is probably too loud.
Noise intensity is often referred to as loudness or impulse noise. Impulse noise is high-level, short duration burst of pressure that can immediately cause hearing damage (e.g., weapon fire or blast). Impulse noise greater than 140 peak decibels (dBP) is considered hazardous. Repeated, unprotected exposure to hazardous impulse noise will cause permanent hearing loss and possibly ringing in the ears (tinnitus).
The duration of exposure to loud noise is referred to as a steady state of noise, measured on the A-scale (dBA) to account for the relative loudness perceived by the human ear. Steady-state noise can be continuous and not vary with time, intermittent if broken by periods of very low noise levels, or fluctuating if the sound pressure varies over a wide range.
Extended or repeated exposure to sounds at or above 85 dBA will cause hearing loss. Brief exposure to elevated sound levels can initially lead to a temporary reduction in hearing or ringing in the ears, which can recover if the exposure is not severe. However, the risk of hearing impairment is also cumulative over the course of a working day. The louder the noise and the longer the duration of exposure at that volume, the greater the potential for permanent hearing loss.
Noise can be controlled by various measures. From most effective to least effective, the strategies employed are to reduce the noise, reduce exposure to the noise, and finally protect personnel who must be exposed to the noise.
The purpose of engineering controls is to reduce or eliminate the noise at its source or along the transmission path to the worker’s ear. This generally entails modifying or replacing equipment or making related physical changes to the environment in which it’s located. Some examples of engineering controls include the following:
- Use low-noise tools and machinery
- Place a barrier between noise source and worker
- Enclose or isolate noise
- Weld parts rather than rivet
- Use acoustical materials
- Install silencers, mufflers, or baffles
For every doubling of the distance between the source of the noise and the worker, the noise is decreased by 6 dBA.
Administrative controls are changes in the workplace or schedule that reduce or eliminate the worker’s exposure to noise.
- Limit time of noise exposure/alter work schedule
- Display signs and labels for hazardous noise areas and equipment
- Provide quiet areas for breaks
- Train workers on sources of hazardous noise in and away from the workplace
- Increase distance between source and worker
Hearing Protection Devices
When engineering or administrative controls cannot eliminate the noise hazard, personnel operating in those environments are required to wear hearing protection devices (HPD). There are a number of different types of HPD:
- Noise/Ear muffs
- Combat Arms Earplugs
- Tactical Communication and Protection System (TCAPS)
All hearing protection devices are provided with an NRR (Noise Reduction Rating), which is the degree to which it is able to block out noise or “attenuate” sound. This measurement is stated in decibels; a plug with an NRR of 26 blocks out a maximum of 26 decibels of noise.
That said, the NRR is based on the attenuation of continuous noise and may not be an accurate indicator of the protection attainable against impulse (peak) noise.
Consistent noise becomes damaging at the following thresholds:
- 85 dBA = Prolonged
- 100 dBA = 15+ minutes
- 120 dBA = 9 seconds
- 140 dBA = Immediate
All personnel are required to wear HPDs when engaged in work that exposes them to noise that equals or exceeds 85 dBA as an 8-hour TWA. If exposure exceeds 100dBA during an 8-hour TWA, double hearing protection should be worn (i.e., wear earplugs and earmuffs simultaneously).
Anyone exposed to any single impulse noise level that exceeds 140 dBP should wear an HPD; if the impulse noise exceeds 165 dBP, double HPDs should be worn.
Commands or units are required to provide or coordinate training regarding potentially noise-hazardous areas and sources, the use and care of HPDs, the effects of noise on hearing, and the command’s Hearing Conservation Program. Commanding officers (CO) and officers in charge (OIC) will ensure supervisors, managers and personnel exposed to hazardous noise receive training on their role in preserving the mission's hearing readiness. While the provision of annual training is the command’s responsibility, COs, OICs, supervisors and managers are encouraged to collaborate with MTF occupational audiology subject matter experts to provide quality, meaningful HCP education and training. The training is mandatory for all Marines, assigned Sailors and hazardous noise-exposed civilian personnel.
Marines receive a reference (baseline) audiogram as part of their initial physical examination conducted at MTFs while at the Recruit Depot or Officer Candidate School (OCS). Marine Corps civilians will receive a reference audiogram prior to assignment to a noise hazardous operation.
Hearing tests (audiometry) are performed to detect changes in hearing readiness before hearing loss becomes a mission impairment or impairs quality of life. Marines and assigned Sailors are annually monitored for hearing changes. Civilian personnel enrolled in the HCP should receive an annual monitoring audiogram while occupationally exposed to hazardous noise.
The commander and supervisor will take action to prevent further hearing loss when notified of early changes in personnel’s hearing, such as significant threshold shifts (STS). These actions will include the following: evaluation of the work-site for additional engineering controls by a qualified engineer, IH, OH professional, occupational audiologist or safety specialist; determining adequacy of HPDs; and ensuring that HPDs are properly worn.