Hearing Protection Devices

No one really knows when people first discovered that by covering their ears or the ear canal with their palms or fingers, it is possible to effectively reduce the level of unwanted sound – noise – but this method, which has been known for centuries, has proven to be the only way to protect against loud sound.

Unfortunately, with this level of technology, there were no other means of hearing protection. The most effective solution to the hearing protection issue is to control the noise level in the ear canal. Currently, we have various types of hearing protection devices: earmuffs, earplugs, earmolds (fixed or variable, two or three cuffed, soft, silicone, fiberglass, etc.) or head harnesses.

Antinoise earmolds are inserted into the outer ear canal. A variety of different shapes and sizes of earmolds are available to suit most people. Available in soft enough material to protect against sound and can be shaped to suit the individual hearing canal characteristics. Variable earmolds precisely match an individual shape of the ear canal. Vinyl, silicone, elastomeric compounds, fibrous materials and wax, staple fiberglass, and closed cell foams can be used to make earmolds.

According to HomeCareChoices blog, half-shell earmolds are worn on the outer ear canal. The use of half-shells is similar to the fingers that cover the outer ear canal. Half-shells are made in one size that is designed for use by most people. This protection is held on the ear by a lightweight arch.

Earmuffs consist of two plastic “cups” connected by a metal or plastic arch. The cups completely cover the ears, with a special cushion that ensures a completely sealed ear area. Inside the cushion there is usually foam or liquid material. Most earmuffs are equipped with a gasket that effectively absorbs sound, resulting in more effective noise reduction at frequencies above 2000 Hz. The arch can be placed on the head, around the neck or under the chin, although the effectiveness of protection depends on it. In other cases, earmuffs may be attached to a “hardhat”. Compared to simple earmuffs, this “hard” design does not provide a close contact on any type of head, therefore, the effectiveness of noise protection is reduced.

In the USA, there are more than 100 manufacturers of hearing protection devices. Despite the variety, disposable noise-resistant inserts are most often used, the production of which makes more than half of the whole sales.

Modern Hearing Protection

For the most effective prevention of hearing loss, it is advisable to work outside the zone of harmful noise exposure. For this purpose, closed production areas with sound insulation are used, where you can talk freely, and a noise level does not exceed the value that poses a threat to human health.

Another option for effective hearing protection is to reduce the noise level of a source to acceptable levels which is often achieved by changing the design of equipment, as well as improving noise control devices.

If it is not possible to eliminate the source of noise or to reduce the noise level, the last resort is using hearing protection devices. However, the effectiveness of the latter can often be limited if other protection measures are not available.

Maximum efficiency is achieved when such devices are worn at all times. Regardless of design, the effectiveness of protection is reduced with a reduction in the duration of use of these devices. For example, the protection effectiveness is significantly reduced if earmolds or earmuffs are removed to talk to a colleague for a few minutes when exposed to noise.

Assessing the Effectiveness and Use of Hearing Protection Devices

There are many ways to evaluate the effectiveness of hearing protection devices. The most common is a single-digit system, i.e., the noise reduction rating (NRR) used in the United States (U.S. Environmental Protection Agency 1979) and the European Single-Number Assessment (ISO 1994). There is also a European three-digit evaluation method (ISO 1994).

Finally, methods have been developed to determine the degree of attenuation for each hearing protection device in each frequency range equivalent to one octave in width. In the United States, this method is called the Octave Band (OBM) method, and in Europe, it is known as the Assumed Protection Grade (ISO 1994) method.

These methods are based on audiometric thresholds, where the actual attenuation of the noise level at the respective hearing protection thresholds is determined experimentally as required by the standards.

In general, the audibility threshold in the sound range is determined in the laboratory for the protected and unprotected ear. In the USA, the acoustic samples are performed by a specialist, while in Europe the measurements are performed by a person using hearing protection device and the specialist providing assistance.

The difference between the protected and unprotected ear thresholds is the actual reduction in noise levels. This data is obtained for a defined group of 10 workers in the United States, with each participant taking measurements 3 times; in Europe, the group consists of 16 and the measurements are taken once. The average attenuation and the corresponding standard deviations are then calculated for each octave frequency band.

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