User Guide

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Technical Data Bulletin
3M Personal Safety Division
#234 Hearing Protection for Impulse Noise Published July 2015
Impulse noises are generally defined as sounds with short duration (less than 1
second) such as gunfire, explosions or the “pop” of a pneumatic nail gun. These
sounds typically have an extremely fast onset and often reach very high sound
pressure levels (SPL). In figure 1, for example, the sound of gunfire reaches a
peak SPL of 164 decibels (dB) in the first few tenths of a millisecond then
decays rapidly.
By comparison, continuous noises are generally defined as sounds that have a
longer duration (more than 1 second) such as most typical industrial noises,
noises from vehicles and aircraft, and noise from operating power tools at work
or at home.
What are the Risks Associated with Impulse Noise?
One commonly accepted approach to assessing the health risks for people
exposed to impulse noise is to measure the instantaneous peak sound pressure
level (L
pk
) rather than the average sound pressure level (L
avg
). When peak sound
levels exceed 135 dB, the risk of damage to the auditory system and other
adverse health effects increases significantly. Common health effects
associated with impulse noise include hearing loss, tinnitus, hyperacusis
(abnormal sensitivity to loud sounds) as well as non-auditory effects such as
hypertension, fatigue and other conditions related to stress.
Are Hearing Protectors Effective Against Impulse Noise?
When properly selected and worn according to the user instructions, hearing protection devices (HPDs)
help reduce exposure to both continuous noises as well as impulse noises. However, it is difficult to
predict the required and/or actual hearing protection obtained during exposure to impulse noises. For
gunfire, the weapon type, number of rounds fired, proper selection, fit and use of hearing protection,
the proper care and condition of the hearing protectors, and other variables will impact hearing
protector performance.
Traditional Passive Hearing Protectors
Passive hearing protectors are devices without electronic components. Traditional passive HPDs, such
as roll-down foam earplugs, push-to-fit foam earplugs and earmuffs, create a physical barrier that
reduces (attenuates) the sound level that reaches the wearers’ ears by a certain amount regardless of
the sound level to which the wearer is exposed. For example, someone who selects and wears 3M™
E-A-Rsoft™ FX™ Earplugs correctly and obtains 33 dB of noise reduction overall would be expected to