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Control of Workplace Hazards for the 21st Century
Setting the Research Agenda

White Paper: Engineering Noise Controls and Personal Protective Equipment

The purpose of these brief summaries or "white papers" is to outline topics for discussion of new or enhanced research on control technology and personal protective equipment. Specifically, the summaries are intended to initiate, not limit, dialog at specific sessions of the conference "Control of Workplace Hazards for the 21st Century: Setting the Research Agenda" to be held March 10 –12, 1998, in Chicago Illinois.

The opinions and conclusions expressed are not considered as final statements of NIOSH policy or of any other organization.


When Federal regulations to protect workers' hearing were enacted, the legislators intended for engineering /administrative control to be used to reduce the noise exposures of workers to safe levels. It was clear that engineering/administration controls were the preferred method and that personal protective equipment (PPE) was to be used only as an interim measure if neither engineering nor administrative controls were feasible.

The issue of feasibility was the focus of much litigation as industry contested citations on the grounds that engineering control were neither economically nor technically feasible. When OSHA proposed new regulations in the mid 70's, there was a great deal of concern about whether or not the proposed lower limits were reasonable or even possible in view of the economic and technical aspects of current engineering control technology.

In an effort to answer the question of technical feasibility of engineering noise controls, OSHA funded Bolt, Beranek and Newman to conduct a broad assessment of the status of available engineering controls. On an industry-by-industry basis BBN catalogued those machines requiring noise control for the 19 categories in general industry (SIC 20 through 39). For each machine/process BBN also identified the expected degree of difficulty in quieting them with engineering controls. The following categories were employed to define the status of the existing technology:
off-the-shelf treatment
substitution of quieter machines/processes
custom retrofit using existing technology
redesign of machines/processes using existing technology
breakthrough required

The last category recognized the fact that certain equipment/processes were not amenable to engineering controls. Some examples included:
engine test stands previously treated for noise reduction,
certain maintenance operations in which maintenance personnel must work for long periods of time in high noise areas not normally occupied by workers,
certain riveting and grinding operations, and
specialized equipment such as oxygen lances, rock drills, weaving looms, spot-welding equipment and painting spray guns.

A similar, but more focused and detailed, technical assessment of feasible engineering controls for mining equipment was published by the former Bureau of Mines in 1983. Again, as in the OSHA study, some machines/processes were identified for which further development was required, but in the main technology was deemed feasible. More recently, MSHA as part of its ongoing rule making activities related to occupational noise has determined that engineering/administration controls are feasible: The Agency has concluded that the coal mining industry as a whole, and the metal and non-metal industry as a whole, can meet this requirement at a PEL set at a TWA8 of 90 dBA.

In support of MSHA's conclusion, the noise exposures of coal miners collected by MSHA inspectors from 1986-1992 were recently analyzed. For both the 1993 MSHA study and the 1976 BBN study for OSHA, the following distribution of daily noise doses were revealed.

Table 1. Percent of coal miners (MSHA, 1993) and manufacturing sector workers (BBN, 1976) exposed to noise.

Daily Noise Dose


Equivalent TWA


Percent of Coal Miners


Percent of Workers Exposed ( SIC 20-39)

< 100

< 90

76.5 77.8
100-200 90-95 19.5 13.9
200-300 95-98 3.0 5.4
>300 >98 1.0 2.9
  Total 100.0 100.0

Simply put, these data show that compliance with a PEL of 90 dBA can be achieved for 96% of the coal miners with a reduction of 5dB, or less, and for 99% of the miners with a reduction of 8 dB, or less. The BBN study projected that the application of "best effort" engineering/administration control procedures would achieve compliance with the 90 dBA TWA (8 hours) for 99.4% of the workers in those industries represented by the 19 SIC codes. BBN stated further that it was not unrealistic to expect that these levels of reduction are achievable with engineering controls.

Yet, by the mid-80's policies had begun to evolve in both OSHA and MSHA that effectively reversed the preferred hierarchy of controls. In 1983, OSHA policy (CPL 2.45A CH-12) provided that if an effective hearing conservation program is in place, no Standard Threshold Shift has been detected, and adequate hearing protectors are utilized, no citation will be issued for noise up to a TWA8 of 100 dBA if the costs to implement the hearing conservation program are less than those of engineering or administrative controls. A disparate policy with regard to mining sector developed within MSHA: while continuing to require the metal and non-metal mining industry to consider engineering controls for compliance, MSHA began permitting the coal mining industry in 1985 to use hearing protectors in lieu of engineering controls.

Finally, the demise of U.S. Environment Protection Agency's Office of Noise Abatement and Control signaled a lack of commitment at the Federal level to the development of quieter products in this country. It is not surprising that since the mid 80's little effort has been expended by industry in fostering the development and implementation of inherently quieter machines and processes to achieve compliance with workplace noise regulations.

The regulatory agencies need to revisit and reassess their policies on the use of engineering controls. It is encouraging that MSHA in its current rulemaking is proposing to reestablish the primacy of engineering/administrative controls. Is not encouraging that MSHA will maintain a PEL of 90 with a 5-dB exchange rate. In the BBN study was a projection of what percentage of workers would be exposed to hazardous noise for two different target controls levels: 90 dBA or less as compared to 85 dBA or less. Also shown in Table 2 are the NIOSH estimates of the percent of workers at risk of developing material hearing impairment over their working lives. If noise controls were implemented for noise levels of 85 dBA and above, fully 96.4% of workers in the 19 industrial segments would be exposed to noise levels of 85 dBA or less.

In order for a research agenda for control technology to have a customer base, regulatory pressures need to be reasserted. The first step would be to eliminate the approach to protecting workers' hearing through the sole use of PPE. When other types of health and safety hazards are present in the workplace, engineering/administrative controls are always utilized as the first line of defense to eliminate or minimize the potentially harmful effects of the hazards. Yet, a peculiar rationale for noise, in effect a double standard for noise, has been adopted in addressing the problem of noise-induced hearing loss: preservation of workers' hearing is not important enough to require the same level of protection provided to them for other hazards. Although they are intended to be an interim, temporary element in a hearing loss prevention strategy, hearing protectors have become the only strategy available to at least two generations of American workers. The problems with total reliance on hearing protectors are:

Table 2. Percent of workers that would be exposed for two noise reduction targets: 90 dBA and 85 dBA. Also shown are the percentage of workers expected to develop hearing impairment from a work-life exposure to the noise levels.


Percent of Workers

Noise Level 90 dBA Exposure Limit(1) 85 dBA Exposure Limit1 Percent at Risk of Hearing Impairment(2)
< 80 dBA 47.0 47.0 3
80 - 85 18.5 49.4 15
85 - 90 33.9 3.0 29
90 - 95 0.2 0.2 43
95 - 100 0.2 0.2 56
100 - 105 0.2 0.2 75(3)
> 105 nil nil 953

Personal Protective Equipment

Workers are reluctant to use hearing protectors because they are uncomfortable, interfere with communication, interfere with hearing critical machine operations, and cut the workers off from their environment.

Present EPA Noise Reduction Rating scheme over estimates the amount of protection really available to the average wearer by as little as 40% and by as much as 2000%. The derating strategies of OSHA and NIOSH have high face validity, but have not been evaluated in the field to see whether they help or not.

Management relies upon hearing protection to the extent of assuming that if hearing protectors are used, there is no noise problem.

Because of 1, 2, and 3 above,, the hearing conservation program becomes a hearing loss documentation program.

Best Estimate of Present Situation

In the 1980's National Occupational Exposure Survey, NIOSH found that companies did not apply all aspects of a hearing conservation program evenly. Table 3 shows that more companies provided hearing protection than provided noise monitoring and more companies provided noise monitoring than provided audiometer. The trend was similar for all business sizes, small, medium, and large.

Table 3. Prevalence of Hearing Conservation Program Elements by Company Size.

Percent of Companies Providing Element

Company Size Audiometry Monitoring Hearing Protection
Small 0 0 16.5
Medium 5.2 4.5 37.9
Large 18.7 29.5 83.5

The elements audiometry and hearing protection are only implemented if the results of monitoring shows workers being exposed above the permissible exposure limit and no noise control elements has been introduced. Yet, it is unlikely that controls will be introduced when hearing protectors are being dispensed to workers whose noise exposures are unknown in the first place.

There is the wide-spread expectation that hearing conservation programs can be as effective in preventing hearing loss as can noise control programs that reduce the noise to less harmful levels. This implies that a noise control capable of reducing the exposure level by 10 dB will be no more effective than a hearing protector that reduces the noise exposure level by 10 dB; the hearing protector is certainly less expensive than noise control. The flaw of this expectation is that a noise control outcome affects all persons in the area which a hearing protector provides more than 10 dB of noise reduction for some workers and less than 10 dB of noise reduction for others.

In 1976, BBN provided additional data about the cost of a hearing conservation program. The results are displayed in Table 4 expressed in 1997 dollars. Also shown in Table 4 are OSHA's estimates from a cost analysis done in 1983 and from a penalty assessment action in 1992.

Table 4. Costs per worker of hearing conservation program elements

BBN Cost Impact Analysis
$70 per worker ($26 for monitoring, $44 for audiometric testing)

OSHA 1983 Analysis
$63 per worker ($28 for monitoring, $15 for hearing protection, $20 for training)

USDOL 1992 Analysis
$87 per worker (distributed between monitoring, audiometry, hearing protection, and training)

There are 30+ million American workers exposed to noise levels in excess of 85 dBA and a large proportion of them are not in hearing conservation programs providing any elements. A 1995 Michigan Department of Public Health found that 45% of companies employing workers with noise-induced hearing loss had no hearing conservation program.

A recent market analysis found that $180 million are expended annually for hearing protectors and that $120 million are expended for audiograms. So little is spent on noise monitoring and noise control that it is not possible to track expenditures. If a full hearing conservation program were available to all occupational noise exposed American workers, the market should be approaching $1.9 billion per year for every year that noise control is not on the national agenda. Instead, $320 million is spent going through the motions, less than 17% of what is needed.

Recommendations: Research & Related Activities for Noise Control and Hearing Protection

The following recommendations are tentatively offered:

1. Current and legacy noise control technologies should be evaluated in terms of their applications - some materials used 25 years ago may not be available or may have proven to have health-hazardous properties.

2. A database of control technologies that work should be created. The database would apply to retro-fitting noise controls.

3. Information management research could develop:

a. a user-friendly computer-based model to guide those responsible for compliance (plant engineers, safety officers, industrial hygienists) through the intricacies of identifying, selecting and implementing engineering noise controls. Such a model would also permit the user to evaluate alternatives to arrive at an optimal control strategy.

b. a computer-based system that contained a database of new products that are already available.

4. Health Communication research could focus educating management (especially the financial types) and the general public about the benefits of a quiet workplace.

5. On an industry-by-industry basis:

a. Establish a knowledge base of current noise control technology, publicize it, and make it readily available. Identify technology gaps that are either true barriers to the development of quiet machines/processes, or will further enhance the technical/cost effectiveness of current technology.

b. Conduct joint research/demonstration projects to fill the technology gaps and evaluate new emerging technology.

c. Adopt voluntary noise standards to label products used in the workplace.

d. Provide Federal funds to jump start the activities identified above, or to match other sources of funding for there activities.

6. Initiate research methods for active noise control of stationary and mobile noise sources.

7. Develop hearing protection devices that employ active noise control, active level-dependent attenuation technologies, and communication functions.

8. Develop hearing protection devices on the basis on wearer comfort and enhanced speech understanding.

1. From BBN Economic Analysis Report 3246, April 1976

2. From NIOSH 1972 Noise Criteria Document

3. Based on extrapolation from NIOSH 1972 noise criteria document

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