People have long been aware of the ba­sic principles of acoustics. The ancient Greeks built their amphitheaters so the ac­tors voices could be heard without any dis­tracting noise. The great European concert halls were designed so audiences could hear the music, but not its echoes.

And people, of course, have always been upset by excessive noise. In the 19th Cen­tury they complained about horse hooves clattering against the cobblestones.

The real problems with noise, how­ever, came with the arrival of the indus­trial revolution and its loud machinery in enclosed spaces. Since many years passed without much concern for work­ers’ limbs or lives, noise control was hardly an issue. But, as concerns for workers’ safety have grown, so too has the awareness of the deleterious effects excessive noise can have on hearing.

Considerable progress has been made in a number of ways. But, since factors such as unsafe machinery or a potentially gaseous environment can result in a cata­strophic accident, and hearing loss is usu­ally gradual and not immediately noticed, the latter tends to not get as much attention as it should. Many corporations don’t see hearing loss as a required issue in risk man­agement and don’t see the need to invest in measures for noise control. Regulatory rules, while admirable in some ways, leave something to be desired in others.

Four recognized regulations for noise control come from the International Stan­dards Organization (ISO), American Coun­cil of Government Industrial Hygiene (ACGIH), Mine Safety Health Administra­tion (MSHA), and Occupational Safety and Health Administration (OSHA). In terms of stringency ISO comes in first, ACGIH and MSHA second, and OSHA third.

One issue has to do with enforcement. For instance MSHA inspectors are required to visit mines once or twice a year. OSHA, with fewer inspectors for the number of in­dustrial sites it regulates, might get to any particular site once every four or five years.

OSHA sets down specific guidelines. For instance, a worker’s exposure to the 120 decibels of a jet engine can be for only a half hour a day, whereas 85 decibels in a typical industrial setting is acceptable for an eight hour day. Many safety experts say this is all to the good, but express the wish that OSHA would get in line with international standards, such as ISO, which take into account not only imme­diate hearing damage but also the long-term injury, analogous to repetitive strain injury. There are some encouraging signs, however, says Alex Gomez, general man­ager of Super Soundproofing Co., San Marco, CA.

 “The most obvious trend, and one that is continuing, is that actions are being taken to reduce noise levels, whether within an industrial, commercial or home setting.” In fact, Gomez explains, the increase in the density of homes is leading developers to sound-proof various rooms or an entire home. This general awareness is being translated into local regulations, which, in turn, affect commercial and industrial sites. “Many corporations want to reduce their external noise levels to become good neighbors,” Gomez says.


This, in turn, is encouraging progressive industrial sites to look more closely within their work environments. “We’re seeing more industrial managers asking us to contain sound within an area, or isolate offices from the industrial setting either through acoustical tents or creating a new room for the equipment,” says Gomez.

“Often the best and most cost effective way to determine what the noise or acoustic environment should be is before the plant is constructed,” says Michael Gendreau, president, Cohn Gordon & Associates, San Bruno, CA. Potential sound problems can be solved in the design phase, he explains. For instance, specifying equipment which make less noise and laying the machinery out in a considered manner, especially making sound barriers part of the design can be much more efficient.

“There are many scenarios you can work with,” says Gendreau, ‘‘and you can do something similar when you upgrade your equipment.” As an example he cites that many clean rooms have small fans that act as filter units. “You can have a half dozen fans, run them fast, and make a lot of noise,” he explains. “Or you can have twice as many fans, which don’t run as fast, make a lot less noise, and use much less electricity. You have a higher cost up-front, but you save later.”

Even with existing equipment there is much you can do. Once you determine the noise level, you can design appropriate stuffing material, mufflers or other silencing techniques. You can erect a barrier or enclosure. Or you can take the machine back to the manufacturer and ask him to modify it so that it’s quieter.

What’s making this more and more possible, Gendreau continues, is that over the past several years software has been developed and become more and more sophisticated in taking noise from different areas and modeling different ways to control it, including noise inside and outside the plant. Some sounds are more difficult to subdue than others, says Gomez. “Low frequency sounds, like the low rumblings of a motor or the low hum-
ming from a generator or compressor create a hazard over time.” He mentions that
whereas the sound of a human voice is measured in inches, the wave length of
these low frequency industrial sounds are measured in feet. ‘For example, if the motor
is running 100 cycles a second, you have a 20-foot wave length,” Gomez says. “That means you have to have 8 to 10 inches of concrete block to stop it.”

Add to that the way these sounds can bounce off bare walls and ceilings, and you
add to the already unacceptable level of noise. As a distributor of soundproofing solutions and materials, Gomez says that one solution to stop the transfer of noise through walls is a visco-elastic adhesive which is applied between two sheets of the wall. It serves to dampen the reverberations of sound within a room.

A newer technology has come on the market in terms of earmuffs for individual worker protection, Gomez says. “Previously there has been open cell foam which absorbs the sound. The newer technology blocks out the sound.”

A company that provides instrumentation to document and monitor noise is Occupation Health Dynamics, LLC (OHD), based in Birmingham, AL. OHD is the sole U.S. distributor for the products of CirrusResearch, ELC, based in the U.K.

There are two main types of instruments, explains manager of noise instrumentation, Jeffery Griggs, sound level meters and noise dosimeters. The meters refer to instruments that measure noise coming from an area or a machine. The dosimeters are devices an individual wears during a shift which provide a representative noise exposure.

General noise monitoring is a mature concept which has been around for some 40 to 50 years. From the 195Os through the 1970s, noise was measured via analog in which the meter fluctuated as the noise went up or down. Then came digital, which started with a number, and gave a more accurate reading of what went up or down from there. Then, during the 1980s, the digital devices became capable of integrated noises, of doing the math, so you got a time weighed average over a period of time.

Dosimeters have been around 30 to 40 years and have gone through similar evolvements to more complex and accurate levels. The big news here, says Griggs, is that “noise dosimeters are headed toward wireless.” Though they’ve been around 10 to 12 years, Griggs says, “The early evolution was not capable of meeting industry needs. That has changed over the past year or so and we have introduced a product that meets all of the product standards of the U.S.”

Griggs adds that early in 2007 his com¬pany will be introducing a dosimeter with dual and multiple channels. This means that a worker will be able to see how well his noise environment measures up to ISO, OSHA, and other standards. “The wireless product will be less intrusive, lighter, take up less space, be easier to wear and won’t have the safety issues which come with cords.”

It's an example of cost effective ways to protect a worker’s hearing. This is a message that should not have to be shouted.


 

© 2008 Facility Safety Management - All Rights Reserved -