Page 22 - Occupational Health & Safety, September 2017

HEARING PROTECTION
New ANR Technology in Triple Hearing Protection Safely Extends Work Time
There is certain class of occupational environments where engineering controls are not feasible and double hearing protection is inadequate.
BY MADELEINE CISSNHA
ave you ever wished that your employees could spend more time safely doing their job in noisy work environments? Maybe you’ve let go of that dream because the
ous noise level is over 105 dB(A), double up on the hearing protection, especially if the person is already losing their hearing.
The combined attenuation of an ear plug and an ear muff is not simply the algebraic sum of the per- formance of each individual protector. This is due to an acoustic and vibratory interaction between the ear muff and the ear plug that causes them to behave to- gether as a system rather than as independent hearing protectors. Generally speaking, when you combine two hearing protectors, ear muffs over ear plugs, you can expect an increase of between 3 and 10 dB over the higher performing hearing protector. OSHA recom- mends using 5 dB as the benefit offered by combining hearing protectors. Even with the prescribed derating methods, this will often provide enough attenuation to satisfy your employee’s safety requirements.
Nevertheless, there is certain class of occupational environments where engineering controls are not fea- sible and double hearing protection is inadequate.
Double Hearing Protection Plus New ANR Technology = Triple Hearing Protection
Triple hearing protection can provide the extra at- tenuation unattainable by the combination of two passive hearing protectors. Triple hearing protection combines the conventional double hearing protection offered by two passive hearing protectors (ear muffs over ear plugs) with an ANR hearing protection com- ponent enclosed in the tip of the ear plugs. The lat- est ANSI measurement standards now recognize this new technology and make provisions for measuring and reporting the attenuation in accordance with na- tional standards.
Active noise reduction has been prevalent as a technology in circumaural headsets for several de- cades, but the advent of high-speed processing capa- bilities has matured the technology to a point that it can be miniaturized and placed deep in the ear canal. A typical active noise reduction circuit contains a microphone, a controller, and a speaker. The micro- phone measures the sound present in the occluded space between the tip of the ear plug and the ear- drum. The microphone signal is then processed by the controller which generates an “anti-sound” that is delivered to the occluded space by the speaker. The in-ear microphone measures the residual noise that is left after the combined ear muff and ear plug have done all they can do, and the active noise reduction attenuates this noise further offering a third layer of hearing protection.
performance limitations of even double hearing pro- tection won’t keep them safe from long-term hear- ing loss. If your team members are part of that select group of workers who are exposed to an eight-hour time weighted average of 115 dB(A) or more of con- tinuous noise, one solution to this problem may be “triple hearing protection.”
Before introducing what triple hearing protection means and the new active noise reduction (ANR) technology behind it, let’s quickly review single and double hearing protection.
Double hearing protection, the use of two different hearing protectors simulta- neously (ear muffs over ear plugs), may be advised or even required in certain workplace scenarios.
Single and Double Hearing Protection Review
The U.S. Occupational Safety and Health Administra- tion (OSHA) states that hearing protectors must re- duce an employee’s eight-hour time weighted average noise exposure to at least 90 dB(A) or less (85 dB(A) if a standard threshold shift has been identified). The majority of workers in noisy environments need less than 10 dB of attenuation from their hearing protec- tors in order to meet this requirement. Most com- modity hearing protectors (ear plugs or ear muffs) can deliver at least 10 dB of attenuation when worn properly in single hearing protection configurations.
Double hearing protection, the use of two differ- ent hearing protectors simultaneously (ear muffs over ear plugs), may be advised or even required in certain workplace scenarios. OSHA guidance for double pro- tection indicates that if an employee has progressive noise induced hearing loss, the employer may require the use of double hearing protection. The Mine Safety and Health Administration (MSHA) goes a step fur- ther and mandates that double hearing protection is required when an employee’s eight-hour time weight- ed average noise exposure is at or above 105 dB(A). The National Institute for Occupational Safety and Health recommends the threshold for using double hearing protection should be at or above 100 dB(A). These regulatory agencies explicitly or implicitly have one recommendation in common: when the continu-
22 Occupational Health & Safety | SEPTEMBER 2017
www.ohsonline.com