Solution Summary: Non-electronic Level-dependent Hearing Protectors
Non-electronic level-dependent hearing protectors use an acoustic filter to reduce noise exposure while maintaining the wearer's ability to hear speech and alarm signals.
Description:
Non-electronic level-dependent hearing protectors (NELDHPs) help reduce hearing loss and tinnitus due to noise overexposure without blocking important sounds like coworkers' voices or backup alarms. Traditional (passive) hearing protectors reduce noise at the ear canal uniformly across all levels. In contrast, NELDHPs block noises above a certain level. As impulsive sounds become louder, the valves in these style of ear plugs become more effective at blocking harmful noise. NELDHPs will attenuate frequencies differently from typical passive foam or premolded ear plugs.
NELDHPs perform a similar function to electronic level-dependent hearing protectors (ELDHPs), but they work through a different mechanism. While ELDHPs use a microphone to pick up sounds and then reproduce them electronically inside the ear canal at a safe volume, NELDHPs use a special membrane called an acoustic filter. This filter sits within the hearing protection device. All noise must pass through it on the way to the listener’s ear canal. The filter is air permeable, which improves ventilation and may increase the user’s comfort.
Many brands of NELDHPs have removable filters for maximum utility. When the filter is taken out and replaced with a plug, the listener receives the same protection they would get from a similar hearing protection device like a standard rolled or molded earplug. If the filter is removed and the channel between the general environment and the ear canal is left open, the listener does not receive any hearing protection.
3M Combat Arms Ear Plugs
- Cost: $16.96
- Noise Reduction Rating (NRR): 7-23
- Material: elastomeric polymer
Photo courtesy of 3M
Westone DefendEar Hunter Passive Ear Plugs
- Cost: $129.99
- NRR: 4
- Material: silicone
Photo courtesy of Westone
Risks Addressed:
Repeated overexposure to noise causes permanent hearing loss and ringing in the ears (tinnitus). It has also been associated with hypertension and other cardiovascular diseases (Girard et al, 2015).
The Occupational Safety and Health Administration (OSHA) requires that workers’ LAeq (similar to an 8-hour time-weighted average) remain under 90 decibels, while NIOSH has recommended that it remain under 85 decibels. NIOSH’s recommendations are more protective and preferred for maximum hearing conservation. Table 1 shows how long a worker can safely be exposed to different levels of noise (measured in A-weighted decibels, or dBA) according to both OSHA and NIOSH criteria.
|
dBA |
OSHA |
NIOSH |
|
80 |
32 hours |
>24 hours |
|
85 |
16 hours |
8 hours |
|
90 |
8 hours |
2.5 hours |
|
95 |
4 hours |
47.6 minutes |
|
100 |
2 hours |
15 minutes |
|
105 |
1 hour |
4.7 minutes |
|
110 |
30 minutes |
1.5 minutes |
|
115 |
15 minutes |
28 seconds |
|
120 |
7.5 minutes |
9 seconds |
|
125 |
3.8 minutes |
3 seconds |
Table 1
How Risks are Reduced:
NELDHPs prevent hearing loss by blocking harmful levels of noise from entering the ear canal. They are similar to non-level dependent (passive) forms of hearing protection in shape and size, but they block noise selectively. NELDHPs use a special membrane to filter out louder noises. This means that the user’s hearing is protected without masking lower-level noises that are important for safety and communication, such as back-up alarms and coworker’s voices. While softer noises are often muffled by traditional passive hearing protection like foam ear plugs, a 2011 study confirmed that NELDHPs preserve the wearer’s ability to understand normal speech (Norin, Emanuel & Letowski, 2011).
Many tools frequently used in the construction industry, like powder-actuated nailers and pneumatic nail guns, produce high level impulse noise, which is loud but short in duration. This kind of noise has been shown to cause more damage to hearing than equivalent levels of continuous noise (Starck, Toppila & Pyykkö, 2003). If you are exposed to impulse noise, it is especially important to wear appropriate hearing protection. NELDHPs have been shown to reduce the impact of impulse noise on workers' hearing (Fackler, Berger, Murphy & Stergar, 2017). Workers may also be more likely to consistently use hearing protection that does not interfere with their ability to hear coworkers and alarm signals.
Effects on Productivity:
n/a
Additional Considerations:
Noise Reduction Ratings (NRR) are based on laboratory tests that may not fully represent real-world conditions. OSHA recommends “derating” the published NRR on hearing protection devices to adjust from C-weighted noise levels to A-weighted noise by subtracting seven. This derated value can be subtracted from an A-weighted noise exposure measurement to estimate the noise level that reaches the ear.
Hearing protection devices should be used as a last resort when substitution, elimination, and engineering controls are not achievable. Buying quieter tools and machinery can eliminate the need for hearing protection. Administrative controls and work practices can also be used to reduce the amount of time any one employee spends in a noisy area. If these practices are not sufficient to reduce workers’ noise exposure to 85 decibels or less, employers must provide appropriate hearing protection devices as part of a written hearing conservation program.
Contributors:
Sara Brooks, MPH, CPH - CPWR The Center for Construction Research and Training
William J. Murphy, Ph.D. - NIOSH
Availability
3M
To obtain information, visit Combat Arms Ear Plugs
