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Focus on Safety: Hearing Loss Prevention

Ted Schorn
Click here to see this story as it appears in the August 2017 issue of Modern Casting

Hearing loss is the third most common chronic physical condition in the U.S., more prevalent than diabetes or cancer. Over 22 million people in the U.S. are affected, accounting for 13% of the working population. Industrial noise exposure is by far the leading cause of hearing loss, with three primary industrial sectors responsible: mining, construction and manufacturing. Among the manufacturing sector, the foundry industry is a leading contributor, according to report of the NIOSH Occupational Hearing Loss Surveillance Project (2003-2012).

According to the study, “Economic Impact of Hearing Loss and Reduction of Noise-Induced Hearing Loss in the U.S.,” an estimated 20% of all hearing loss in the U.S. is connected to industrial noise exposure and if this to be prevented, the economic benefit would be substantial—between $58 billion-$152 billion.

In understanding the statistics associated with hearing loss and foundry industry contribution, the Bureau of Labor Statistics provides helpful information. While traumatic hearing loss is considered a recordable injury, gradual hearing loss is considered an illness. Other recordable illness categories include respiratory problems, dermatological (skin) problems and poisonings. Figure 1 illustrates the rate of recordable illness over the years 2004-2015 (the latest available data-year) for all private manufacturing, the general foundry classification in the NAICS coding system and for ferrous and non-ferrous foundries (excluding die casting).

By far the largest single category of contribution to recordable illness is hearing loss.

Hearing loss is a recordable illness (and placed on your OSHA 300 log) if annual testing reveals a 10 decibel shift from the baseline hearing (averaged at 2000, 3000 and 4000 hz) in one or both ears. See 29 CFR 1904.10 for more information on recording this illness.

The contribution to illness of hearing loss occurrence can be observed by plotting the same years and industrial categories but including only hearing loss-related illness.

Recordable illness data is reported using a different scale than that of injury owing because recordable illness is far less frequent.

This is based on 10,000 “equivalent workers” annual rate of illness, not the 100 equivalent workers annual rate used in injury TCIR (total case incident rate) calculations (where the multiplier is only 200,000).

The statistics on the rate of hearing loss in foundries reveal the following:

Hearing loss is occurring at a substantially higher rate (roughly three times higher) in foundries than in all private manufacturing.

Hearing loss is by far the single greatest category of occupational illness in foundries.

Hearing loss rate is roughly the same in all types of foundries over the last five years.

In 2015, in the listing of the top 25 job classifications with the highest illness rates, the Bureau of Labor Statistics identified steel foundries 18th and aluminum foundries 25th among all classifications.

Industrial noise-induced hearing loss is completely preventable. Hearing loss reduces the quality of life and leads to isolation and challenges in socialization. In industrial and business settings, it can lead to other safety risks as employees do not hear instructions, assignments or warnings clearly. 

Corrective Measures
The metalcasting industry can do more to prevent hearing loss. To address any safety hazard, corrective measures should be considered among a range of options that vary in overall effectiveness. This is usually communicated via the diagram in Figure 3, drawn from the OSHA website.

The first and most effective means of protection is to eliminate the hazard, the source of noise and vibration. This may mean replacing equipment, outsourcing noisy operations or redesigning processes or products such that the noisy operation is unnecessary. In a foundry, this could mean determining an alternate means of removing gates and risers or automating noisy operations so that no worker is required to be in the area of high intensity sound.

The second most effective means of protection is to substitute the equipment that produces loud sounds for equipment that is specifically designed to operate more quietly. NIOSH encourages a program they call “Buy Quiet” and initiatives under the “Quiet by Design” program to connect suppliers who have constructed tools and equipment that reduce noise with manufacturers seeking to reduce ambient noise levels in their workplace. The purchase of new equipment should be evaluated from many perspectives—and safety is usually an important viewpoint. The safety evaluation should not be limited to injury prevention by examining guarding, e-stop locations and light curtain placement but also include the operating noise level and its contribution to the environmental sound level. Talking to suppliers about this issue during design and development is an appropriate step to protect the hearing of your workers.

The third most effective step to address hearing hazards is to control the noise at the source through maintenance practices, vibration padding, proper lubrication, adjusting air pressure, installing covers with sound insulating barriers and similar strategies to reduce the noise. Sometimes simply relocating equipment farther away from a wall reduces the reflection of sound waves into the workspace. Improperly maintained chains, gears and pulleys can be very noisy. Establishing an appropriate frequency of maintenance activities that keeps equipment running efficiently and more quietly would help reduce ambient noise levels. This kind of preventive action should be taken systematically and be periodically re-evaluated. When was the last time your job environment was surveyed for noise?  Has equipment been added, replaced or moved since then? Many factors can change the area profile of sound intensity and vibration. OSHA requires a new profile be prepared according to the following rule: “Monitoring shall be repeated whenever a change in production, process, equipment or controls increases noise exposures to the extent that: Additional employees may be exposed at or above the action level; or the attenuation provided by hearing protectors being used by employees may be rendered inadequate to meet the requirements of paragraph (j) of this section” [29 CFR 1910.95(d)(3)]. It is easy to get complacent about facility changes and their impact on sound intensity.

The fourth most effective step to address hearing hazards is to apply administrative controls such as limiting the time workers spend in a noisy area through duty cycling. This is less effective because it does nothing to address the source of the noise—it simply attempts to reduce the amount of exposure by procedural means. This certainly can be a part of an overall program to address hearing protection but by itself is not greatly effective because it relies on human adherence to procedures rather than getting to the cause of the problem.

PPE Least Effective
Perhaps surprisingly to some, the least effective method to achieve hearing protection is through the use of personal protective equipment. For many, hearing protection is something you stick into or over your ears to keep the noise out. In manufacturers with well planned, systematic hearing protection programs, PPE is the tool of last resort; the solution to a problem that could not be designed out or resolved in any other way. Part of the reason PPE for hearing protection is judged as the least effective solution to the problem is that while most hearing protection devices will attenuate sound to a reasonable degree in the laboratory, in real life they perform less well. Figures 4 and 5 reproduce data provided by NIOSH and available at the helpful hearing conservation website www.safe-at-work.com .They illustrate the actual average level of attenuation achieved compared to laboratory use.

The relative ineffectiveness of hearing protection devices (NRR = noise reduction rating) has been studied carefully by several researchers, and improper sealing of the ear canal is the primary cause. According to the report, “Measurement of Hearing Protection Devices Performance in the Workplace During Full-Shift Working Operations,” sealing problems have been found to result from the following list of issues:

Lack of use (utilization rate).

Poor fit.

Improper compatibility with other PPE (e.g. safety glasses or safety helmet).

Readjustment during use (most often, discomfort).

Equipment deterioration.

Abuse of equipment.

The explanation of why hearing protection devices are not worn consistently provided by workers frequently is that it interferes with communication. This particular objection has been studied closely by audiological researchers. Actually, for those with normal hearing profiles, there is a 7–12% improvement in speech recognition while in a noisy environment when wearing appropriate hearing protection, according to the report, “Speech Recognition in Noise Under Hearing Protection.” That is, for those with normal hearing, you are better off with hearing protection in place. The noise reduction prevents cochlear overloading and enables better signal detection. However, some types of hearing protection do reduce speech recognition in individuals with impaired hearing.

Specifically, hearing protection needs to be designed to uniformly reduce the decibel level of sound across all frequencies— typically those with hearing loss suffer in the higher pitch frequencies and attenuating these frequencies on top of the existing loss makes speech difficult to decipher. Hearing protection devices that are “flat attenuating” provide protection and benefit speech recognition even for those with hearing loss in noisy environments.

The foregoing discussion, and the types of problems observed in real world application of hearing protectors, explains why among other requirements, OSHA requires annual training where hearing protection is worn. This training is not simply a reminder to wear your earplugs on the shop floor.

Hearing protection required training must include:

Description of the effects of noise on hearing.

The purpose of hearing protection.

The advantages and disadvantages and attenuation characteristics of various types of protection.

Instruction on the proper fitment, care and use of protective devices.

Description of the purpose of annual audiometric testing and the test procedures.

It is also important that training be practical and demonstrated. For example, you can teach “the hum test” for proper earplug fitment (place one earplug in and hum; the sound should be considerably louder in the unplugged ear. If not, the earplug is not doing its job and is not inserted properly). Ear plugs when properly fitted should have a fair amount of resistance to being pulled out and should not be just hanging in the ear canal opening. Study of the proper use of these devices can make the training more practical and interesting.

NIOSH has several publications on the prevention of industrial hearing loss available for free download; especially helpful is publication 96-110, “Preventing Occupational Hearing Loss—A Practical Guide.”

Hearing is a precious thing and metalcasters have a stewardship responsibility to care for the health and well-being of the people entrusted to them. 

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