There are a lot of factors that go into ensuring your safety on a day to day basis. Whether it is your climbing equipment; gloves; footwear; eye, head and hearing protection; or even your work apparel, there are a multitude of new materials and components that can make your job safer, more comfortable and more efficient. When it comes to hearing protection, there are several issues that can factor into your selection of hearing protection.
Will doubling up or wearing dual protection ‑ an earmuff in addition to earplugs — provide added protection against extreme noise levels? According to Howard Leight by Sperian, the answer is yes, but perhaps not as much as you thought.
According to Brad Witt, audiology and regulatory affairs manager for Howard Leight by Sperian, dual protection is not required by OSHA regulations for general industry in the U.S., but NIOSH recommends dual protection for any exposures over 100 dBA, and some companies require it for employees with progressive noise-induced hearing loss despite normal protective measures.
However, Witt cautions, there are also risks associated with dual protection. “Using earplugs and earmuffs concurrently seriously isolates the wearer, so it is warranted only in extreme noise levels,” he stated. He also suggests dual protection is overused. “When a high-attenuation earplug or earmuff is properly fitted and the user is motivated to use it correctly, some hearing professionals say the need for dual protection is rare.”
So how much protection will doubling up provide? That depends on the fit, said Witt, but it “is not simply the combined ratings of the earplug and earmuff. There is a ceiling effect that limits the amount of combined protection. Even if wearing a perfectly fitted earplug and earmuff with ideal attenuation, we would still hear sound transmitted through our bodies and bones to the inner ear.”
As for a rule of thumb for estimating the effects of dual protection, OSHA recommends adding 5 dB to the Noise Reduction Rating (NRR) of the higher rated device. But this sacrifices some accuracy, said Witt, “An earmuff typically adds about 4 dB to the NRR of a well-fitted foam earplug, and about 7 dB to a well-fitted pre-molded earplug.” He also said that an earmuff with moderate attenuation provides the same effect as a high-attenuation earmuff when either is worn over a well-fitted earplug.
“The key to obtaining maximum benefit from dual protection is proper fit, especially the fit of the earplug,” Witt stated. “When a poorly fitted earplug is worn with an earmuff, the resulting dual protection is little more than the earmuff alone.”
Absorbent pads for earmuffs
Earmuff users know that anything interfering with a good seal around the ear — thick hair and eyeglass frames or large earrings — can potentially compromise the attenuation of the earmuff. Workers who wear absorbent pads might also wonder if their earmuff attenuation is being compromised.
Absorbent pads typically come with an adhesive backing that attaches directly to the earmuff cushion. As an option, the punched oval center may also be placed inside the earcup to protect the foam filling of the earmuff. These pads are ideal for humid and moist environments, for users who perspire heavily, or for settings where the same earmuff is shared among multiple users.
According to tests conducted by Howard Leight by Sperian, the addition of absorbent pads causes a mild drop in attenuation of about 2.5 dB in the low frequency response (500 Hz and below) of the earmuff, but no significant difference above 500 Hz. The addition of the punched oval center into the earcup actually increases attenuation in the earcup by about 1 to 2 dB in the high frequencies (4,000 Hz and above).
If these results are applied to the NRR, the addition of the pad would decrease the NRR of an earmuff by 1 dB or less. Using the pad with the punched oval center pad in the earcup would decrease the NRR by about .5 dB. These minor changes in overall attenuation (1 dB or less) are within the standard deviation of the testing, and will likely be unnoticeable and insignificant to most users when compared with the benefits of extra comfort, longer wear time and additional hygiene provided by absorbent pads.
“When headset radios first appeared in stores several decades ago, they were not marketed as hearing protectors,” said Witt, adding that this was, “a good thing, since they offered very little attenuation of noise. At some frequencies, the headsets were even found to amplify background noise (with the radio turned off) due to resonance in the earcup.”
To be a hearing protector, said Witt, an earmuff must be designed to be a hearing protector from the start. “Ideally, a radio headset should allow the enjoyment of music at safe levels, but also reduce the background disturbance in a noisy environment.”
Today’s new hearing protectors with built-in radios contain circuitry that limits their maximum radio volume. But the questions that concern many are: When using these earmuffs in an industrial setting, won’t the radio simply add more noise to damage hearing? And what are the noise levels under the earcup when the radio is turned on?
“When two noise sources are added together, the decibels are added logarithmically, not arithmetically,” Witt explained. “For example, the sum of two 90 dB sound sources would equal 93 dB.”
“Since the radio output is limited to a safe maximum, the radio adds very little noise to effective exposures in high noise levels,” said Witt. “In a high-noise job that is also repetitive or monotonous, a radio earmuff can add significantly to worker satisfaction and enjoyment, without sacrificing hearing protection.”
Information provided by Howard Leight by Sperian. For more information, visit www.howardleight.com.