Noise Reduction for Hearing Protection
Noise Reduction for Hearing Protection
Noise reduction is the amount by which hearing protection reduces the sound level reaching your ears. It is measured in decibels (dB).
As a general workplace exposure guideline, 85 dB(A) for 8 hours is commonly used as the maximum daily noise exposure before hearing protection and/or noise controls should be considered. Above this level, prolonged exposure can increase the risk of permanent hearing damage.
It is important to understand that decibels are logarithmic, not linear. This means that a small-looking increase in dB reduction can represent a significant improvement in the amount of sound energy reaching the ear.
23 dB vs 31 dB of reduction
| Hearing protection | Noise reduction | Sound energy reaching the ear* |
|---|---|---|
| Option 1 | 23 dB | ~0.50% |
| Option 2 | 31 dB | ~0.079% |
The difference is 8 dB, but it is not simply an 8% improvement.
A reduction of 31 dB provides approximately 6.3 times less sound energy reaching the ear than a 23 dB reduction.
In other words, moving from 23 dB to 31 dB of noise reduction represents about an 87% further reduction in sound energy reaching the ear.
For example, if the surrounding noise is 100 dB:
23 dB reduction → approximately 77 dB at the ear
31 dB reduction → approximately 69 dB at the ear
That additional 8 dB of protection can therefore make a meaningful difference, particularly in high-noise environments or where workers are exposed to noise for extended periods.
*The percentages refer to sound intensity/energy, not a percentage reduction in perceived loudness. Actual protection depends on fit, frequency, the hearing protector's rating and how it is worn.
Fitment
Fitment is extremely important with hearing protection. The stated noise-reduction rating assumes the hearing protector is being worn correctly and forms a proper seal. In real-world use, a poor fit can dramatically reduce the protection actually achieved.
Why fit matters
Hearing protection works by creating a barrier between the noise and the ear. If there is a gap around an earplug, earmuff, microphone/earpiece, or other hearing-protection device, sound can travel through that gap and bypass much of the protection.
How much noise is too much?
Whether the exposure standard (85 dB(A) averaged over eight hours) is exceeded depends on the level of noise involved and how long workers are exposed to it.
Peak noise levels greater than 140 dB(C) usually occur with impact or explosive noise such as sledge-hammering or a gun shot. Any exposure above this peak can cause almost instant damage to hearing.
Decibels (dB) are not like normal numbers. They can’t be added or subtracted in the normal way. The decibel scale is logarithmic. On this scale, an increase of 3 dB represents a doubling of sound energy. This means that every 3 dB increase in noise level can cause the same damage in half the time.
Table 1 provides examples of the length of time a person without hearing protection can be exposed before the standard (LAeq,8h = 85 dB(A)) is exceeded.
Noise level dB(A) Exposure time before standard is exceeded
80 16 hours
82 12 Hours
85 8 hours
88 4 hours
91 2 hours
94 1 hour
97 30 minutes
100 15 minutes
103 7.5 minutes
106 3.8 minutes
109 1.9 minutes
112 57 minutes
115 28.8 seconds
118 14.4 seconds
121 7.2 seconds
124 3.6 seconds
127 1.8 seconds
130 0.9 seconds
Essentially, a worker who is exposed to 85 dB(A) for eight hours receives the same noise energy as someone exposed to 88 dB(A) for four hours, with the balance of the day in a very quiet environment. In both cases the exposure standard is not being exceeded. However, being exposed to 88 dB(A) for more than four hours would mean that the standard is exceeded. Similarly, if a worker is exposed to 121 dB(A) then the exposure standard would be exceeded after only 7.2 seconds.
