Everybody knows that if you're exposed to loud enough noise for a long enough time, you'll lose your hearing. But few people know that hearing loss is just one of the problems associated with noise exposure. Noise affects our ability to react to warning signals, and some research suggests that it may adversely affect vision, increase stress levels and raise blood pressure. These effects are called extra-auditory because they go beyond just experiencing a hearing loss.
Speech Interference. A mechanic working on an overhead crane fumbles a socket wrench. He yells down to warn you out of the way, but you can't hear him over the background noise. Today's your lucky day. The wrench lands with a clank two feet in front of you. But what about the next time? Can you act on warnings you don't hear?
Color Perception. Noise affects some people's ability to differentiate between red and green. Because red and green are used to indicate stop and go, safe and unsafe, on and off, and similar conditions, the inability to tell them apart could lead to a fatal injury.
Peripheral Vision. Another extra-auditory effect is reduced peripheral, or side, vision. Not being able to detect movement out of the corner of your eye might result in your being run over by a forklift or slapped on the side of the head by a moving crane load block.
Increased Stress. Did you ever want to strangle a neighbor who blared his stereo at night when you were trying to get some sleep? If so, you're aware of yet another extra-auditory effect of noise -- increased stress and irritability. It's fairly well established that people who are distracted, stressed out and irritable are more likely to make mistakes that could lead to injuries.
Blood Pressure Changes. Some people's blood pressure increases upon exposure to noise. If they have pre-existing cardiovascular problems, exposure to excessive noise could make things worse.
Startle Response. The startle response occurs when someone sneaks up behind you and yells "boo." Now you probably won't lose your hearing from someone sneaking up behind you to yell in your ear, but you could be fried, when in your startled state, you inadvertently touch that high-voltage circuit you were testing with your voltage probe.
OSHA Noise Standard
Curiously, OSHA's noise standard doesn't address any of these extra-auditory effects. It is only concerned with occupational hearing loss, and even in that respect, it doesn't do a very good job protecting workers. In fact, OSHA knows that significant number of workers will lose their hearing, in spite of the standard! How can this be?
OSHA allows people to be exposed to a level of 90 decibels (dB) for up to eight hours. As the noise level goes up, the exposure time must be reduced.
Ninety decibels is pretty loud. It is comparable to the noise of a fast-moving freight train about 10 feet away. Even though OSHA knew that some people exposed to 90 dB noise would develop a permanent hearing loss, this limit was chosen as a political compromise that considered economic concerns as well as employee protection.
Later, OSHA attempted to address the shortcomings with another compromise of sorts -- the hearing conservation amendment to the noise standard. In that March 1983 revision, OSHA called for noise monitoring and protective equipment in 85-decibel environments, if employees experience a standard threshold shift (STS) in their hearing capacity. Absent an STS, hearing protection is not required unless noise levels reach 90 decibels as an 8-hour time-weighted average.
In short, these were the best that OSHA could do given the political influences of the day. But here's the bottom line: contrary to popular belief, following the OSHA standard won't keep some workers from developing a hearing loss.
Some health professionals who recognized that the OSHA standard was not adequately protective took the initiative of setting voluntary lower limits. For example, for more than two decades, the Department of Defense has used an exposure threshold of 85 decibels. DOD policies also require that both civilian and military personnel wear ear protection above this limit regardless of how long they are exposed.
Engineering Controls
OSHA standard 29 CFR 1910.95(a) stipulates that when employees are subjected to sound levels exceeding those listed in Table G-16, feasible administrative or engineering controls shall be utilized."
Engineering controls are things that can reduce the noise level or eliminate it all together. For example, scrap grinders used in the plastics industry typically have sound levels over 100 dB. To control this noise, many plastics plants have built sound-absorbing rooms around their grinders. Because the enclosure absorbs the noise, sound levels in the rest of the plant are low enough that people don't need to wear ear protection.
Other examples of engineering controls include: installing mufflers on air exhausts; using plastic gears instead of metal gears; doing simple things like tightening machine guards so they don't rattle; or putting people in booths or control rooms that isolate them from the noise.
During the Reagan era, OSHA pulled a nasty trick on the working people it was supposed to be protecting. It issued an administrative enforcement directive which in essence torpedoed the universally accepted industrial hygiene principal of using engineering controls before relying on other, widely acknowledged, less effective controls, such as employee work practices and personal protective equipment.
OSHA's internal compliance document CPL 2-2.35A, titled 29 CFR 1910.95(b)(1), Guidelines for Noise, and dated Dec. 19, 1983, stipulated that if average 8-hour sound levels were less than 100 dB, employers had the option of doing a cost-benefit analysis to see if a hearing conservation program was less expensive than engineering controls.
Unlike the standard, this administrative policy was an executive fiat not subject to public comment. Although most of the CPL has been withdrawn, its spirit has been incorporated into Chapter III of OSHA's Field Instruction Reference Manual (FIRM), which you can find on the OSHA CD-ROM or on OSHA's web page, http://www.osha.gov. Paragraph C.3.b of the FIRM states:
"Current enforcement policy regarding 29 CFR 1910.95(b)(1) allows employers to rely on personal protective equipment and a hearing conservation program rather than engineering and/or administrative controls when hearing protectors will effectively attenuate the noise to which the employee is exposed to acceptable levels as specified in Tables G-16 or G-16a of the standard."
Given that safety and health professionals generally agree that protective equipment is the last line of defense for controlling hazards, I've been perplexed why there has not been public outcry about this arbitrary and capricious policy.
Noise Reduction Ratings
Many people do not understand the labels on ear protection that indicate the noise reduction rating or NRR. Take, for example, a foam plug that has a published NRR of 27 dB. Now, good old common sense tells you that if you've got a noise level of 107 dB, and earplugs with an NRR of 27 dB, when you put the plugs on, the noise level at your ear level should drop to 80 dB (107 dB-27 dB = 80 dB). That's just common sense right? Well, actually this is just another safety myth (see "Safety Myths: What Everybody Knows Is Simply Wrong," OH, October 1996).
Don't believe me? Check it out. If you consult OSHA's Figure II:5-1, Calculating Hearing Protector Attenuation of the OSHA Industrial Hygiene Technical Manual, you will find that the agency instructs its compliance industrial hygienists to first subtract 7 dB from the NRR to compensate for spectral uncertainty. This is because the acoustical spectrum of industrial noise is not a pure tone like that used during a hearing test. That means that our original 27 dB NRR now becomes: 20 (27 dB - 7 dB = 20 dB).
But we're not done yet. The technical manual then tells us to apply a safety factor. Now, in many scientific and engineering applications, safety factors of four to seven are pretty common, but OSHA requires a safety factor of only two. In other words, we divide 20 dB by our safety factor of 2 and wind up with 10 db. So we've now gone from a published NRR of 27 to an effective level of protection of only 10 dB.
All of this complexity creates a public misperception as to the meaning of NRR. What people fail to understand, and some experts fail to communicate, is that the testing protocol uses a test panel that in essence receives two hearing tests: one without ear protection and one with it. The NRR is then calculated based on the results of these two tests.
Summary
Noise exposure may produce extra-auditory effects such as interference with speech, changes in vision, increased stress, and high blood pressure.
Even if you comply with the OSHA standard, many of your employees may still suffer a permanent hearing loss. Even though OSHA's noise standard stipulates that engineering controls be used to reduce noise exposure, the enforcement policy ignores this requirement when sound levels are less than 100 dB.
Finally, remember that the NRR on a package of earplugs might not provide the protection you think it does. Find out what it means and protect your workers accordingly.
John Rekus is an independent safety consultant and author of the Complete Confined Spaces Handbook. With more than 20 years of OSHA regulatory experience, he specializes in conducting OSHA compliance surveys and providing safety training for workers and managers. He lives near Baltimore and may be reached at (410)583-7954 or via his web site at www.jfrekus .com.