Hearing Protection

by Peter Cronhelm

My day job is a Safety Manager in a large manufacturing facility.  One of the safety issues I deal with at work is the prevention of hearing loss.  The corporate Hearing Protection Program includes annual employee audiometric testing as well as location sound surveys and the implementation of hearing protection policy and equipment to protect the employees from excess exposure to noise.

 Part of my job is to ensure the hearing protection equipment we use is sufficient to protect employees against the high noise levels they are exposed to in different areas of the plant.

  It was during this task I realized just how effective sound suppressors are at reducing the level of sound reaching a shooter’s ear.  In fact a reasonable sound suppressor is a great deal more effective at preventing shooting related hearing loss than any earplugs or muffs.

 Consider that most foam type earplugs have an NRR (Noise Reduction Rating) of 29-32 dB.  Most PVC type earplugs have NRR’s in the 25-27 dB range and earmuff performance varies widely from 20-30 dB depending on the model.

 Hearing protection is rated by the NNR system developed by the EPA.  Each device is tested and given an appropriate number representing its noise reduction capability.

 Industrial OH&S standards for calculating noise reduction from a hearing protection device require the NRR rating number to be reduced by 7 dB.  The 7 dB subtraction is made because the NRR is assigned under ideal conditions in a laboratory setting.  Therefore, it doesn’t necessary reflect the device’s actual noise reduction in the real world.

 The internationally recognized limit for hearing damage from impulse sound is 140 dB.  To ensure no hearing damage can occur, a hearing protection device must reduce noise exposure at the ear to 140 dB or less. 

 Lets have a quick look at the real world performance of the three types of hearing protection:

 

Device

NRR

Less 7 dB

Max SPL

Foam Plugs

29-32

22-25

162-165

PVC Plugs

25-27

18-20

158-160

Muffs

20-30

13-23

153-163

 

The Max SPL column shows the maximum noise level the hearing protection device can protect from.  Above this level, noise greater than the 140 dB limit is still reaching the ear.

 The real world performance of typical hearing protection devices are not very impressive.  All rifle cartridges from the 223 Remington and up produce a muzzle signature louder than 165 dB.

 That means even the best hearing protection devices are potentially exposing shooters to noise levels high enough to cause permanent hearing damage.  Add in a muzzle brake or the confines of a shooting range and the noise level at the shooter’s ear increases even more as sound waves are reflected back towards the shooter.

 On the other hand, the majority of modern sound suppressors are capable of reducing the muzzle signature of all but the biggest cartridges down to the 140 dB limit.  Typically only the .338 Lapua and .50 BMG are intense enough to require hearing protection on a suppressed rifle.

 Suppressor sound measurements are taken one meter to the left of the muzzle.  Sound levels at the shooter’s ear are typically a few decibels lower than the official muzzle signature rating because suppressors direct residual noise forward.

 Some suppressor manufacturers are even advertising their products meet government standards for noise reduction.  None of the hearing protection devices I am aware of can make this claim with respect to high intensity impulse noise.  I have been shooting for more than 15 years and have never heard any sort of claim regarding the hidden danger of hearing protection devices.  It was only when my job and my interest coincided that I became aware of this information.

 Sound suppressors also protect the hearing of bystanders and prevent the painful experience of being exposed, unprotected to an unexpected shot.  Sound suppressors in the hunting field reduces the public’s exposure to annoying gunshots and totally prevent the hunter’s exposure to the shot when there is not time to put on hearing protection.

 Countries and governments that do not allow their citizens access to sound suppressors are causing the citizens under their protection to be exposed to harmful sound levels during recreational hunting and shooting activities.  British hunters and shooters sued their government on Occupational Health & Safety grounds for the right to use sound suppressors as hearing safety equipment and they won. 


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