Synergist - August 2009

A gun blast can be well above 140 dB. Both OSHA and ACGIH indicate that the unprotected ear should not be exposed to continuous, intermittent, or impact/impulse noise above this level.

Impulse noises complicate efforts to obtain accurate noise exposure measurements. Standard noise dosimeters are designed to evaluate continuous noise exposure. Using these devices to evaluate impulse noise can dramatically underrepresent actual exposures.

An alternate method is to use an integrating sound level meter fitted with a quarter-inch microphone. The microphone will allow the meter to integrate impulses greater than 140 dB. Some instruments also include the ability to count the number of peaks in excess of 140 dB, which is necessary to meet the requirements of the Department of Defense standard for determining single vs. double hearing protection (MIL-STD-1474D). Data collected with this equipment is a more reliable measure of exposure, but the equipment is expensive and somewhat delicate, and may not be able to capture automatic firearms discharge. Additionally, the lack of criteria and regulations for impulse noise make results difficult to interpret.

They can also feel rushed prior to the start of firearms qualifications tests, especially if the instructor doesn’t wear earplugs or doesn’t understand how to insert them properly.

Ear muffs, on the other hand, are
quick and easy to put on, but do not
typically attenuate noise above 110 dB
and often interfere with helmets and
other gear. Unless the side arms are
thin, safety glasses lessen the effective-
ness of ear muffs. Furthermore, built-in
communications systems may not be
compatible with ear muffs. Some em-
ployees like to use electronic level-lim-
iting ear muffs, which provide
protection at unpredictable and inter-
mittent intervals while allowing speech
and warning signals to be heard—a fea-
ture particularly helpful for those al-
ready suffering from hearing loss.
However, electronic ear muffs perform
better than non-electronic versions
only at low frequencies.

Controlling Firearms Impulse Noise

Even though obtaining accurate and reliable exposure data is difficult, OHS professionals must still recommend controls to minimize exposures. Engineering control options are generally limited; sound suppressors, for example, tend to impair marksmanship. Thus, OHS professionals must select appropriate hearing protection. Although standard earplugs provide enough protection to reduce TWA exposures below exposure limits, the consensus of the scientific community is that impulse sound is likely more damaging to hearing than continuous sound of the same exposure.

Selecting proper hearing protection presents several challenges. Foam earplugs provide excellent noise reduction and do not interfere with other safety equipment worn by security personnel, but proper use requires training, and inserting them can tax employees’ patience. Earplug users, especially those with hearing loss, complain that they cannot hear commands and are worried for their physical safety during drills.

Have you ever had to explain to workers or management that the Noise Reduction Rating (NRR) so boldly marked on a package of hearing protectors didn’t actually describe how much protection a wearer would receive? If so, you’ll be happy to hear (no pun intended) that a change to the NRR is in the works.

Thirty years ago, the U.S. Environmental Protection Agency (EPA) issued hearing protector labeling requirements, using the authority given it by the Noise Control Act of 1972. Since that time, numerous studies have shown that most wearers would achieve much lower noise attenuation in real workplace situations. It was clear that change was needed.

In 2003, EPA hosted a workshop to discuss hearing protector labeling and testing issues and listen to recommendations from stakeholders, including ANSI, NIOSH, the military, various professional organizations and hearing protector manufacturers.

Then, in late 2007, ANSI issued a new American national standard (ANSI S12.68-

2007) that described new methods for computing and using NRRs.

The proposed NRR will simplify the selection of appropriate hearing protection.

First, it will no longer be necessary to subtract 7 dB from the NRR when comparing to A-weighted decibel levels. In addition, applying correction factors, like the 25–70 percent factors recommended by NIOSH, may not be needed in order to better predict protection.

Second, the prominent single number will be replaced by two numbers that represent a range of protection. The lower number will represent the amount of protection that most individually trained wearers can achieve. The higher number will indicate the amount of protection that a few motivated proficient wearers can achieve. A smaller range between the high and low numbers would indicate less variability among wearers. This two-number system is not unlike the EPA fuel economy standards, where different driving conditions result in different miles per gallon ratings.

It’s uncertain when the EPA will issue a proposed ruling, what it will look like, or how long the process will take. We also don’t know how OSHA will address the proposed changes. But we can be certain that change is on its way.