Hearing Protection Device Evaluated Products List

Maintaining hearing health is important for force readiness and in all aspects of life.  Service members are at risk for noise-induced hearing loss from brief exposure to impulsive noise like weapons fire, and to the long-term effect of continuous noise from engines and other sources. Noise-exposed DoD civilians are also at risk for noise-induced hearing loss. One of the core objectives of the HCE is to prevent irreversible hearing loss among our Service members, veterans, and civilians.  To address this goal, HCE has been focused on improving the way hearing protection devices (HPDs), such as earplugs, are selected through the use of an evaluated products list.  The Hearing Protection Device Evaluated Products List (HPD EPL) addresses the competing needs of protecting hearing while maintaining situational awareness. The list helps Service members and noise-exposed civilians and their supervisors tailor HPD selection based on the HPDs ability to reduce noise exposure and preserve critical hearing for the mission or tasks being conducted.

Hearing-critical tasks (HCTs) are those tasks in which the only sense that can perform the task is hearing.  In the military, HCTs are often related to the speed and safety of an action.  HCTs can be categorized as

(1)    sound detection

(2)    sound identification

(3)    localization

(4)    speech intelligibility

Noise can mask the critical sounds. Also, HPDs can interfere with HCTs by blocking the sounds, however, some HPDs are designed to pick up hearing critical sounds while protecting from hazardous noise.  The HPD EPL provides information on how listed HPDs attenuate (reduce) noise and enable the wearer to localize sounds (locate the direction of sounds).  Currently, the list has a limited number of passive HPDs, but HCE is working to expand the list to include more passive HPDs as well as active and communication devices.  Passive HPDs are earplugs or muffs that have no electronics.  Active HPDs have electronics to reduce noise levels.  Those electronics may also enhance other, desirable sounds that a Service member needs to hear.  Communication HPDs may reduce noise passively or actively, but are able to connect into a radio or communication system.  Communication HPDs are tested for speech intelligibility.  

Noise environment for the military varies greatly from industry.  Flight decks, artillery fire, and tracked vehicles are more noise hazardous than most noise sources found in industry.  Noise is categorized as either continuous or impulsive.  Continuous noise can be found with any engines or machinery, while impulsive sounds are from gun and artillery fire.  At high levels and increased exposure, they are hazardous to hearing.

The devices on the HPD EPL have been assessed for noise attenuation using the latest standards from the American National Standards Institute for continuous and impulsive noise attenuation.  We use the below rating systems for continuous and impulsive noise attenuation.  The higher attenuation value, the more noise the HPD blocks.  The charts are further explained in the guidebook which can be downloaded from the Pueblo/GPO webpage.

Localization is the ability to determine the direction and distance, direction alone, or distance alone of a sound.  Localizing is important for safety and detecting danger.  For example, being able to determine where the truck with the back-up alarm is coming from is important in preventing accidents. The outer ear plays an important role in localizing sounds.  When the ear is covered by an earmuff, it is harder to localize sounds. An earplug can distort the frequency of a sound making it difficult to identify the direction of a sound. For Service members, the direction and distance to gunfire is also critical in detecting the location of enemies.  HPDs and other equipment such as helmets may interfere with cues that help with localization.  Some HPDs are designed to allow for localization. Selecting HPDs based on localizing as well as noise attenuation capabilities may be mission critical.

For devices on the HPD EPL, we compare the ability to localize with the open ear, to how well those same people are able to localize with HPDs being tested.  Three measures are used:

(1)    Front-back reversals

(2)    Percent angular error

(3)    Aurally-guided search

Front-back reversals occurs when a person confuses the direction of a sound by 180^o. Most people can easily distinguish between a noise in front of them versus one behind them.  A normal hearing person who is not wearing hearing protection will confuse sounds in front of them for a sound behind them less than 5% of the time.

Percent angular error is the percent of angle off from the direction of a sound. Percent angular error is a measure of how precise a person can localize.  Normal hearing people with the open ear will have a percent angular error of less than 5%.  As the angular error increases, a person may take longer to find a target or mistake the direction of a sound

Aurally Guided Visual Search (AGVS) measures the time required to find a visual target that is co-located with a sound source in the presence of other visual targets. Response time is important because it measures the functional impact HPDs have on localization capabilities.  Without a sound, people will take an average of 12 seconds to find the visual target.  With the sound paired with the visual target, people with normal hearing will take less than two seconds to find the target.  We use the term spatial awareness to describe localization on the HPD EPL.  The below rating system is used for spatial awareness.  Note the smaller the number, the better the device will help the wearer to localize a sound. Further explanation is available in the guidebook.

Communication is essential in military operations.  When working in a noisy environment, understanding communication can be difficult.  When communication is considered essential in a noise hazardous environment, HPDs with communication capabilities are used.  These devices are tested in conjunction with the entire communication series to ensure speech is at an acceptable level of intelligibility without interference from any one part of the system.  For military systems, speech intelligibility must score greater than 80% in a defined noise environment.  In general, the louder the environment, the harder it is to understand speech.

The below rating system is used as a guide to select devices for speech intelligibility.  The higher the number, the better speech is understood at 85 decibels (dBA).

Passive Hearing Protection Device Evaluated Products List

N.D. – No data available for this test

Disclaimer: This information is provided for education purposes only.  Reference to any commercial product or service does not imply endorsement by the Department of Defense or DoD Hearing Center of Excellence.

For further technical information including expanded testing data, please contact us via https://hearing.health.mil/hcehome/Contact-Us

References

American National Standards Institute/Acoustical Society of America

ANSI/ASA S12.6-2016 Methods For Measuring the Real-Ear Attenuation of Hearing Protectors

ANSI/ASA S12.68-2007 Methods For Estimating Effective A-Weighted Sound Pressure Levels When Hearing Protectors Are Worn

ANSI/ASA S12.42-2010 Methods For The Measurement of Insertion Loss of Hearing Protection Devices in Continuous Or Impulsive Noise Using Microphone-In-Real-Ear Or Acoustic Test Fixture Procedures

ANSI/ASA S3.71-2019 Measuring The Effect Of Head-Worn Devices On Directional Sound Localization In The Horizontal Plane

ANSI/ASA S3.2-2009 (R2014) Method For Measuring The Intelligibility Of Speech Over Communication Systems

Military Standards

MIL-STD-1474E std 15APR2015 Noise Limits

Testing Data

Gallagher, H.L., McKinley, R.L., Theis, M.A., Swayne, B.J., Thompson, E.R. Performance Assessment of Passive Hearing Protection Devices. AFRL-RH-WR-TR-2014-0148, October 2014.