Hearing protection device

A hearing protection devices, also known as a HPD, is an ear protection device worn in or over the ears while exposed to hazardous noise to protect against noise-induced hearing loss. HPDs reduce (not eliminate) the level of the noise entering the ear. HPDs can also protect against other effects of noise exposure such as tinnitus and hyperacusis. There are many different types of HPDs available for use, including earmuffs, earplugs, and electronic hearing protection devices.[1]

Types

Earmuff hearing protection device.

Earmuffs

Different styles of earplugs are pictured. Left, pre-molded earplugs. Center, formable earplugs. Right, roll-down foam earplugs.

Earmuff style hearing protection devices are designed to fit over the outer ear, or pinna. Earmuff HPDs typically consist of two ear cups and a head band. Ear cups are usually lined with a sound-absorbing material, such as foam. The soft cushions seal around the pinna of the ears. The head band applies force/pressure to seal the ear cups over the ears.[1]

Earplugs

Earplug style hearing protection devices are designed to fit in the ear canal. Earplugs come in a variety of different subtypes.[1]

  • Pre-molded earplugs have a preformed shape and a push-to-fit design.
  • Formable earplugs are pliable and take the form of an individual's ear canal.
  • Roll-down foam earplugs are one of the most commonly used earplugs, and are made from slow recovery foam which expands after it has been "rolled-down" and inserted in the ear canal, creating a tighter seal.
  • Custom Earplugs are made individually for each user following ear impressions. Typically custom earplugs are purchased from an audiology clinic or hearing healthcare professional.

Electronic hearing protection devices

Some HPDs reduce the sound reaching the eardrum through a combination of electronic and structural components. Electronic HPDs are available in both earmuff and custom earplug styles. Electronic microphones, circuitry, and receivers perform active noise reduction, also known as noise-cancelling, in which a signal that is 180-degrees out-of-phase of the noise is presented, which in theory cancels the noise.[1]

Custom earplug hearing protection devices.

Some electronic HPDs, known as Hearing Enhancement Protection Systems,[1] provide hearing protection from high-level sounds while allowing transmission of other sounds like speech. Some also have the ability to amplify low-level sounds. This type may be beneficial for users who are in noisy environments, but still need access to lower level sounds. For example, soldiers who need to protect their hearing but also need to be able to identify enemy forces and communicate in noise, hunters who rely on detecting and localizing soft sounds of wildlife but still wish to protect their hearing from recreational firearm blasts, as well as users with pre-existing hearing loss who are in noisy environments may all benefit from Hearing Enhancement Protection Systems.

Electronic HPDs require the use of batteries and are typically more expensive than non-electronic types.

Use of hearing protection devices is recommended by the U.S. National Institute for Occupational Safety and Health, audiologists and other hearing healthcare professionals when exposure to noise meets or exceeds 85 dB-A as an 8-hour time-weighted average.[1] This level of noise may be encountered in both occupational and recreational settings. HPDs are recommended for use in settings where it is difficult to control the noise level, and the person exposed to the noise cannot be removed from the environment.

The amount of protection from noise can vary based on the physical fit of the device. Hearing protection devices with accurate placement (an airtight seal) and/or accurate insertion (deep into the ear canal) will provide the most attenuation of noise.[1]

In occupational settings in the US, the Occupational Safety and Health Administration (OSHA) regulations dictate whether employees are required to wear hearing protection devices or participate in a hearing conservation program.

Noise reduction ratings

Hearing protection device manufacturers are required by the EPA to label HPDs with a Noise Reduction Rating, or NRR. The NRR indicates the effectiveness of the HPD to reduce the level of noise, measured in decibels.[1] The higher the NRR, the greater the reduction of noise.

The NRR is measured by manufacturers using American National Standards Institute (ANSI) specified procedures.[1] The NRR tends to overestimate the amount of protection the HPDs provide in real-world conditions. These differences are most likely attributed to inaccurate insertion depth of earplugs. Because the actual amount of attenuation is typically less than the labeled NRR, the U.S. Department of Labor/OSHA suggest "derating" or reducing the NRR when using it to evaluate how much noise attenuation the user can expect from the HPD.[1] The EPA proposed new procedures for measuring the NRR for hearing protection devices in 2009, which would yield NRRs closer to those obtained in real-world conditions.[1] However, these proposed changes have yet to be implemented.[1]

Regulations and standards

United States

References

  1. 1 2 3 4 5 6 7 8 9 10 11 12 Rawool, Vishakha Waman (2011). "Chapter 6: Hearing Protection and Enhancement Devices". Hearing Conservation: In Occupational, Recreational, Educational, and Home Settings. Thieme. pp. 136–173. ISBN 1604062576.
  2. ↑ "1910.95(a)". U.S. Department of Labor. Retrieved February 20, 2018.
  3. ↑ "PART 62—OCCUPATIONAL NOISE EXPOSURE". Electronic Code of Federal Regulations. Retrieved February 20, 2018.
  4. ↑ "INSTRUCTION NUMBER 6055.12" (PDF). Department of Defense. Retrieved February 20, 2018.
  5. ↑ "Navy and Marine Corps Public Health Center Technical Manual NMCPHC – TM 6260.51.99-2 (September 2008)" (PDF). Navy and Marine Corps Public Health Center. Retrieved February 20, 2018.
  6. ↑ "Directive 2003/10/EC - noise". European Agency for Safety and Health at Work. Retrieved February 20, 2018.
  7. ↑ "ANSI/ASSE A10.46-2013 Hearing Loss Prevention for Construction & Demolition Workers". The American Society of Safety Engineers. Retrieved February 20, 2018.
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