How loud is too loud?

Save your hearing with effective protection

Noise is the sign of progress on a jobsite. The hammering, the revving, the shrill shriek of saws and grinders testify that raw materials are being transformed into a finished project.

But it’s also a sign of danger. While the activity that produces the noise may be dangerous to workers, the sound itself puts the sense of hearing at risk.

Research bears this out. Studies have found that 25 year-old carpenters have the hearing loss commonly found in 50-year old non-noised exposed males.

It’s no wonder, when you consider that equipment decibel ratings on jobsites often fall between 75 and 120 dB(A) and ambient noise levels range from 65 to 91 dB(A). OSHA identifies any sound level higher than 90 dB(A) to be above the Permissible Exposure Limit (PEL). NIOSH recommends employees should be enrolled in a hearing protection program at levels above 85 dB(A).

The dB(A) rating of a sound characterizes its strength or loudness. Like the Richter scale used to measure earthquakes, the decibel scale works on the order of magnitude. A sound that is 10 dB is 10 times more powerful than a sound at 0 dB. A 20 dB sound is 100 times more powerful than a sound at 0 dB; a 30 dB sound is 1,000 times more powerful; 40 dB is 10,000 times more powerful . . . you get the idea.

How noise hurts
Unlike other jobsite injuries, hearing damage results in little or no pain, and once it happens, it can’t be repaired.

There are fine hairs on the cochlea, a component of your inner ear, that transfer sound from the environment to nerve endings. Like a wind blowing across a tall grassy plain, those hairs bend and flex. The louder the noise, the greater the bending and subsequent nerve stimulation.

A loud noise is like a strong wind. It bends the hairs and over-stimulates the nerves. Over time and extended exposure to loud sounds, nerve damage occurs.

As shown in Table 1, there are several jobsite activities that produce sound levels greater than 85 dB(A). As the dB(A) level increases, the time a person can be safely exposed to it decreases, as shown in Table 2.

For example, a hammer drill produces a sound level of approximately 100 dB(A). If you operate a hammer drill for more than two hours a day without hearing protection, you could exceed OSHA’s PEL and be at risk for hearing loss.

Exposure varies greatly
“The tough issue is that noise varies greatly on construction sites and that workers get discrete exposures throughout the workday,” says Mark Stephenson, research audiologist at NIOSH.

“Workers must wear hearing protection when they need it, not all day. Welders don’t wear welding goggles all day — only when they are welding — so it makes sense that hearing protection only needs to be worn when it’s needed. That means it must be convenient to use.”

Stephenson and others continue to research ways to protect hearing on noisy jobs and have identified many aspects that can help protect hearing.

The first step is quantifying the noise level and establishing realistic expectations for hearing protection for a specific job. You can use averages found in Table 1 or you can measure sound levels on your jobsite. NIOSH studies have found that actual readings from your jobsite may be more meaningful to workers.

Once the noise levels are defined, NIOSH recommends first looking at ways to eliminate or reduce the noise at the source, followed by looking at ways to reduce or eliminate the employee’s presence/exposure to the noise.

If those two steps do not minimize exposure, then consider using hearing protection devices (HPDs). A wide variety of earplugs and muffs can be used.

Selecting the right HPD depends on the job and the exposure. “If a worker is exposed to different levels of noise, more than one type of HPD may be needed. It’s not a good idea to go with the highest noise reduction rating HPD. Overprotection discourages use because the worker can’t hear warning sounds or verbal instructions while wearing the HPD,” he says.

The Noise Reduction Rating (NRR) labeled on the HPD is not the best indicator of protection that device will offer on a jobsite. Instead, Stephenson recommends looking at the device’s NRR_SF rating, which uses the “subject fit” test to measure the HPD’s noise-reducing ability. “It gives a real-world estimate of the device’s ability to offer protection,” he says.

To figure the effects of an HPD, take the noise level and subtract the HPD’s NRR_SF  rating from it, which identifies the level of noise the worker will be able to hear using the HPD.

“Jobsite studies reveal that in 90 percent of the cases, construction workers are exposed to sound levels at or below 95 dB(A), the level that OSHA mandates protection. Generally, an HPD with an NRR_SF of 10 to 15 dB(A) is appropriate for many construction jobs.”

Similarly, if the worker is exposed to various levels of noise on different tasks, different HPDs may be needed. “It’s like shoes. You wouldn’t wear heavy insulated boots in the middle of summer. You should match the HPD to the job. One style will not likely meet all of your hearing protection needs,” he says.

HPD convenience and fit are also very important. “Workers often need protection only for a short time while doing certain jobs. The HPD needs to be easy to use,” he says.

The HPD must also match the job. For example, if the job requires frequent donning and taking off the HPD and it’s a dirty environment, compressible earplugs may not be the best choice because they will get contaminated by workers rolling them in their fingers for insertion. Pre-molded earplugs, a semi-aural protector or muff may be a better choice.

Technology continues to redefine hearing protection. Active noise reduction technology which, oversimplified, cancels out the sound wave before it goes into the ear, is getting better and less expensive, says Stephenson. “These units produce a sine wave that is out of phase and cancels it. It’s best for low, loud sound levels such as around heavy equipment or powder-actuated tool use,” he says.

The protection must fit
Individual fit is also important. While one HPD may fit 95 percent of the population, that last five percent will find it unusable and an effective option must be found. “If you wear size 15 EEE shoes, you don’t go without shoes just because they are hard to find. There are options out there, it’s just a matter of finding them, he says.

Training is the final and perhaps most important aspect of hearing protection. “Every trade has different needs and within those trades, hearing protection needs vary depending on the job. Workers need to know when they need to wear hearing protection and have a variety of HPDs available so they can select the one with which they are most comfortable. When workers help select the HPD, they are more likely to wear it,” he concludes.

Published in the May/June 2002 issue of Contractor Tools and Supplies magazine.

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