few years ago, Marc-André Lavoie was conducting an investigation into an accident where a worker broke his foot after being hit by a forklift. The forklift was backing up from outside into a noisy industrial environment.
“I asked them ‘Did you check the noise inside the building and the noise of the backup alarm?’ When I presented it to the safety guy, he decided to ignore my comments, and there was an issue there,” says Lavoie, president of Risk Marcker, an industrial hygiene solutions company in Dartmouth, N.S.
While noise was a factor, the issue that remains unclear, says Lavoie, is whether the backup alarm was too low or the worker’s hearing protection was too high, resulting in overprotection.
Overprotection occurs when a worker’s hearing protection device is providing too much attenuation — filtering out too much noise — for the environment and the work he is doing.
CSA Z94.2-14 Hearing protection devices — Performance, selection, care and use says if the sound level resulting from the use of a hearing protector is more than 85 decibels (dB), the protection is insufficient. A sound level of 80 dB to 85 dB is acceptable, (as is 70 dB to 75 dB) while the “optimal or ideal” sound level is between 75 dB to 80 dB, says the standard.
If workers are protected at 70 dB or below, they are at risk of overprotection, according to the standard.
Overprotection is a concern in environments with lower noise levels, including many manufacturing processes where the noise level is just above 85 dB.
A study by the National Institute for Occupational Safety and Health (NIOSH) in the United States found 90 per cent of industries are under 90 dB, says Theresa Schulz, hearing conservation manager for Honeywell Safety Products who is based in Church Station, Texas.
On the other hand, overprotection is not an issue in really noisy environments, such as steel mills or carpet manufacturing.
Overprotection can be a concern for many reasons, including the inability to hear backup signals from moving vehicles, such as forklifts, backhoe loaders, dump trucks or compactors. For example, a worker in an oil and gas refinery who has a noise exposure around 88 dB to 93 dB could be at risk.
“There’s moving things going on all around you, there’s vehicles, moving parts, that sort of thing. If a person has too much protection in that environment, they could be hurt by being run over by something, missing a warning signal… and frankly, it could be fatal,” says Schulz.
Overprotected workers may not hear general warning alarms properly.
“Noises are altered, so warning alarms or security alarms may not sound the same… If you have a worker engrossed in a task, they may not be attentive to sounds that are warning them of a danger or a machine noise telling them a malfunction is happening,” says Richard Quenneville, senior director of corporate services at T. Harris Environmental Management in Toronto.
“If you are overprotected, you may be unable to locate the origin of sounds so you may not react appropriately to warning sounds.”
Hearing protection can be customized to be more or less protective to certain sounds and help filter the proper nose while leaving room for others, such as alarms.
Communication between workers may also be hindered. For example, if a worker is exposed to 86 dB and he is getting 35 dB of attenuation with his earplug, that’s blocked him down to 51 dB and he can’t hear anything at that point, says Schulz. He is essentially in the “cone of silence” which can be a serious problem.
“You have introduced the feeling of isolation for the worker and the speech can be distorted or muffled and there’s a decreased voice discrimination for the hearing impaired or workers with English as a second language,” says Quenneville.
When workers cannot hear each other properly, they have a tendency to take off their hearing protection. A 2001 study published in the journal Noise and Health found the number 1 reason workers do not consistently wear hearing protection is interference with communication, cited by 70 per cent of the 124 workers surveyed. The second most common reason is interference with job performance (46 per cent) by making certain sounds from the machinery undetectable, according to the workers who were all employed in the printing industry.
When wearing earplugs, people tend to speak more softly because they sound louder in their own heads, contributing to workers having difficulty hearing each other. Workers should be told to speak up in noisy environments.
Even if workers are just popping off an earmuff or earplug here and there, these short, unprotected exposures can have a big impact.
“If you know you’re getting 30 dB of attenuation from earplugs, but over your eight-hour day there’s a five minute period — and it doesn’t need to be all at one time, it can be a minute here and two minutes there — that whole eight hours that you didn’t wear your hearing protection, it decreases your hearing protection overall by 6 to 7 dB,” says Schulz.
Safety professionals need to make this clear to workers and ensure they understand the negative effects of removing hearing protection. It’s important to get out in the field and talk to employees to see if there are any complaints about the hearing protection provided, says Quenneville.
Safety professionals need to determine whether or not communication between workers is critical, says Lavoie. If the communication is critical, then they are better off using hearing protection that uses active noise reduction, which relies on the principle of “destructive interference” to cancel noise.
“You have an earmuff that will record the noise and it’s a sound wave and it will communicate the mirror image of the noise that it received and the addition of the two will make a flat noise, so you don’t hear the annoying noise anymore,” says Lavoie.
To prevent overprotection, a hearing conservation program is necessary. Employers need to conduct noise mapping or sound measurements of the workplace to establish where the high-noise areas are. Workers should then wear personal noise dosimetry devices to determine their individual eight-hour noise exposures.
An octave-bend analysis is also useful to understand the significant frequencies that are impacting the workers.
“Be aware of the type of noise. If you have continuous noise sources or fluctuating noise sources based on the process or impulse noise sources, that’s all going to affect how you determine what hearing protection is required,” says Quenneville.
The CSA Z94.2-14 standard, specifically table 4, compares the eight-hour exposures to the recommended class of hearing protection. For example, if the exposure is less than 90 dB, the recommendation is a C-class hearing protection. If it’s greater than 90 but less than 95 dB, the standard recommends a B or BL class.
“The table basically is intended to provide the best balance of sufficient hearing protection and avoidance of overprotection,” says Quenneville. “If your gut reaction is just to assign the highest level of protection, then you’re getting into the realms of overprotection.”
The noise reduction rating (NRR) printed on the packaging of hearing protectors indicates the level of sound the device will block out.
There has been a trend in the industry to always look for a higher NRR, says Schulz, which leads to overprotection.
“We seem to get into this Tim The Tool Man Taylor thing: ‘A little bit is good, but more is obviously better.’ We have been chasing after higher and higher NRRs,” she says.
It’s important to note the NRR ratings are based on noise reduction obtained in laboratory conditions. It is recommended to use fit testing to estimate the hearing protector’s noise attenuation in the workplace.
“Find out if it’s not enough or too much or the old Goldilocks saying, ‘Just right,”
How the earplug should be worn is determined during a fit test. For example, the NRR might be 30 dB on an earplug but depending on how it’s worn, the worker might get as little as 18 dB of protection.
“A really deeply inserted well-fit foam earplug usually gives you the highest amount of protection. If you back it out just a little bit, you’re going to get a little less,” says Schulz. “You think of just the physics of how much foam is in that canal. Less of it is going to block less sound.”
Fit testing is not mandatory in all jurisdictions, but the CSA Z94.2-14 standard considers it a best practice.
Some employers are fit testing for both a low noise earplug and a high noise earplug.
“Some customers will say ‘I want 10 or 15 dB when noise is at 90 so I can still communicate... in a noisy environment, but when noise is above 90 or 100, then I need a lot of protection, so I rather have a different hearing protector,’” says Schulz.
Employers need to be careful of implementing blanket policies for hearing protection, as they can lead to overprotection.
“Lets say the dose of a person is 88 dB. Then you say ‘You must wear your earplug all the time.’ Well, if you didn’t identify the source, maybe it’s about 87 dB at a certain time or when a certain machine is working,” says Lavoie. “You get into this area ‘Well it’s mandatory hearing protection’ but in reality, it’s only when this machine or that machine is operating, so you set your protection for the highest noise, but the highest noise isn’t happening all the time.”
It’s very important to make sure warning signals and alarms are at the appropriate level. While a safety professional might think overprotection is the problem, it may in fact be that the alarms are not set up properly.
Employers should conduct a noise assessment of the workplace and the rule of thumb is that the alarm should be 6 dB to 10 dB above background noise.
The alarm should not be too much louder than the background noise because it can have a startling effect, says Quenneville, which can cause obvious safety issues in many processes.
A main takeaway for safety professionals on this issue is to make sure they are asking “Was that person wearing hearing protection and how much?” when they are investigating accidents — which is not asked as much as it should be, says Schulz.
“Once you start drilling down, why, why, why, to those third or fourth levels of ‘Why did that person not hear the forklift backing up or vehicle backing up?’ you’d start to maybe look for some of those kinds of things,” she says. “(Overprotection) is maybe more prevalent than what we have evidence of.”
This article originally appeared in the October/November 2015 issue of COS.
© Copyright Canadian Occupational Safety, HAB Press. All rights reserved.