Protecting Against Extreme Noise

Often at noisy facilities, there is one process or area that generates extremely loud noise. It typically is task-specific (such as tank cleaning, motor run-up tests or demolition projects) or tool-specific (a bead blaster, arc welder or jackhammer, for example). All the workers recognize it, even those who work several departments away.

Engineering controls often are infeasible, and it's common to hear the safety manager describe the noise level in words such as, “We can manage all the other hazardous noise levels at our facility, but not THAT one!”

When faced with noise exposures over 105 dBA, well-intentioned safety managers often ask which of the various contradictory de-ratings should be applied to the noise reduction rating (NRR) on the hearing protector package. “To estimate the noise protection, do we divide the NRR by 2, subtract 7 or de-rate the NRR by 70 percent?” (All three methods have been proposed at one time by various government bodies.)

After applying de-rating schemes, earplugs or earmuffs alone often are not enough to protect against extreme noise. Safety managers resign themselves to their most costly administrative control: limiting the number of minutes a worker is allowed to work on the extreme-noise job. They then rotate other trained workers into the area to supply a new pair of “fresh ears.”

To add to the confusion, hearing experts typically disagree with the regulatory definitions of safe noise. Published noise-dose tables defining safe, time-weighted noise exposures simply fall apart for extreme noise. Using its 5 dB exchange rate and 90 dB criterion level, OSHA¹ defines maximum permissible unprotected noise exposure as 115 dBA for 15 minutes — an overexposure most hearing conservation professionals consider to be unacceptable. In contrast, NIOSH² recommends that no worker be exposed to more than 28 cumulative seconds of noise at 115 dBA (and no other noise) in any workday.

Even the audiometric results may not correspond with extreme noise exposures. Among hearing conservation professionals, it is common to hear anecdotal reports of higher rates of hearing loss among workers exposed to moderate noise (90-95 dBA, for example) than extreme noise (over 105 dBA).

“My workers in 112 dB know they've got to take it seriously: They fit the hearing protectors well and wear them religiously,” one safety manager surmised. “My workers in 92 dB figure it's okay to cheat the system and remove their protectors for a few minutes here and there throughout the shift without any consequence. They're wrong.”

What hearing protectors can defend against continuous extreme noise levels over 105 dB? Is there any way to leave a skilled worker safely in extreme noise for several hours? And most importantly, how can we document that with any degree of certainty?

CONVENTIONAL METHOD: DUAL PROTECTION

Dual protection, using earplugs and earmuffs simultaneously, is sometimes the only available method to achieve maximum protection from hazardous noise. While dual protection typically lengthens the allowable exposure time, it comes at a cost: Using earplugs and earmuffs concurrently significantly can isolate the wearer, making it difficult to communicate or hear warning signals.

Dual protection is not required in OSHA regulations for general industry, but it is required in mining operations governed by MSHA³ for noise exposures over 105 dBA (8-hour, time-weighted average). Similarly, a guideline document from NIOSH² recommends dual protection for any exposures over 100 dBA (8-hour, time-weighted average). This recommendation is viewed by some to be overly cautious, perhaps based on the blanket assumption that noise-exposed workers do not wear their hearing protectors properly.

Some companies have adopted internal safety policies requiring dual protection in specific work locations or for certain noisy tasks. OSHA⁴ even has affirmed an employer's right to require double protection for particular employees, specifically when the audiogram indicates a decline in hearing thresholds despite normal protective measures.