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Active hearing protection in the workplace

Investigating the requirements set out in European standards for active hearing protectors.

Unlike passive ear protectors, active ear protectors incorporate microelectronics to interact with the outer acoustic environment. At work, long-term exposure to high levels of noise can lead to permanent hearing loss, and employers must take measures to prevent this. The most effective way of reducing noise levels at work is usually to incorporate noise prevention measures into the design of installations, and to choose materials, procedures and working methods which produce less noise. Whenever this is not possible, employers must supply personal ear protection to all employees exposed to the noise hazard.

Ear protectors are available in a number of different styles. Basically, they provide attenuation of the noise levels by placing a barrier between the source of the noise and the wearer’s ears. Parts 1, 2 and 3 of the European standard EN 352 series contain performance requirements for ear protectors such as ear-muffs, ear-plugs and ear-muffs attached to industrial safety helmets, respectively. However, they also refer to other standards for the specific physical and the acoustic properties of the devices.

The noise attenuation provided by hearing protectors can be assessed by methods using human subjects (see figure 1) and an Acoustic Test Fixture (figure 2). Active protectors can offer enhanced noise attenuation by a number of different methods which are covered by the following standards.

Figure 1: Subjective testing carried out in a hemi-anechoic chamber

EN 352-4:2001 – ‘Hearing protectors – safety requirements and testing – part 4: level dependent ear-muffs’, is intended for ear-muffs which contain an electronic system that relays low sound levels detected on the outside of the ear muff to speakers mounted on the inside of each muff, while higher levels of sound are attenuated. This type of device can be used in noisy environments where the noise is non-continuous and allows necessary communication at low noise levels.

EN 352-5:2002 – ‘Hearing protectors – safety requirements and testing – part 5: active noise reduction ear-muffs’, is designed for ear-muffs that provide additional noise attenuation by means of an inbuilt noise cancellation circuit. These devices attenuate low frequency sounds such as machine noise, but allow the transmission of higher frequency sounds such as speech and emergency warning sounds.

Figure 2: Assessing hearing protection on the Acoustic Test Fixture (ATF)

EN 352-6:2002 – ‘Hearing protectors – safety requirements and testing – part 6: ear-muffs with electrical audio input’, covers products which incorporate an electrical communication device to allow wearers to communicate despite wearing hearing protection.

EN 352-7:2002 – ‘Hearing protectors – safety requirements and testing – part 7: level dependent ear-plugs’, is intended for ear-plugs which contain an electronic sound restoration system that relays low sound levels detected on the outside of the ear plugs to speakers mounted on the inside of each ear-plug, while higher levels of sound are attenuated. This type of device can be used in noisy environments where the noise is non-continuous and allows necessary communication at low noise levels.

EN 352-8:2008 – ‘Hearing protectors – safety requirements and testing – part 8: entertainment audio ear-muffs’, is available for non-industrial ear-muffs which are often used by air travel passengers where the low noise of the aircraft can be further attenuated, allowing sound and music played at lower levels through the ear-muffs to be heard. The entertainment signal may be relayed via a cable or radio or wireless to the headphones. A risk assessment of any work environment containing any noise hazard is essential and this assists employers in selecting the most appropriate type of ear protection to be used. SATRA has a comprehensive hearing protection test facility, including a hemi-anechoic chamber (figure 1) to conduct subjective attenuation testing and acoustic objective testing (figure 2).

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SATRA tests all types of ear-muffs, ear-plugs and safety helmet-mounted hearing protection to the EN 352 series of standards. Please email ppe@satra.com for further information.