Figure A. Noise Dose: Ambient vs. In-Ear Measurements, Underground Coal #1

The tragedy at Massey Energy’s Upper Big Branch mine in West Virginia in April was a wake-up call for safety professionals in all industries. Among the many hazards miners face is the danger of hearing loss. Ninety percent of all coal miners above the age of 50 have a hearing impairment, and by the time they retire, they are nearly guaranteed a moderate hearing loss. At least 80 percent of American miners are exposed to noise levels exceeding 85 dBA, and 25 percent are exposed to noise levels higher than the 90 dBA permissible exposure limit (PEL).

A noisy job site
Miners are exposed to noise levels from above 70 dBA to 140 dBA in continuous, intermittent and impact exposures. Underground mines are a reverberant chamber where sound waves bounce off cave walls as roof bolters, shearers and conveyors contribute to the cacophony. Surface miners are exposed to sounds from augers, bulldozers, crushers, draglines and hydraulic shovels.

In this environment, the ability to hear has great implications for personal and team safety, especially during a crisis. Miners must maintain clear communication with co-workers while remaining distinctly aware of their environment.

Regulations
Hearing conservation regulations for mining have relied heavily on engineering and administrative controls to protect miners from hazardous noise exposures. In 2000, MSHA updated its Occupational Noise Exposure standard (30 CFR 62) to reinforce the use of controls. While the updated regulation requires the use of “all feasible engineering and administrative controls” to reduce noise levels to the 90 dBA PEL, the use of hearing protectors in lieu of such controls is not acknowledged

But due to the nature of mining, even with various controls in place, noise levels are hard to control. So, what’s one to do to prevent occupational hearing loss among miners?

Performance-based hearing conservation
In a field study conducted by Dr. Kevin Michael and Dr. J. Alton Burks at two underground coal mines, two groups of miners who were air arcing encountered extremely high noise exposures. They had been using dual protection (earplugs and cap-mounted earmuffs) in noise levels upwards of 125 dBA.

For this study the miners wore standard earplugs and used in-ear dosimeters integrated into cap-mounted earmuffs. This measurement accounted for the ear’s actual noise exposure and provided realtime monitoring throughout the workday. In addition, ambient noise dose measurements were taken with conventional dosimeters.

It was determined that by continuously monitoring noise dose during the course of the work day, miners could be protected well below the 90 dBA PEL — and many below the 80 dBA action level. (Figures A and B below). With these data, the hearing conservation program managers had a leading indicator as to whether a miner would need to use dual protection. Instead of serially comparing audiograms to determine hearing loss, in-ear dosimetry could identify after day one whether or not a miner was at-risk for occupational hearing loss.

Motivate workers to be responsible
Sadly, hearing loss is accepted as part of the job, and miners share the following objections to the use of hearing protectors:
  • “I can’t hear roof noises” - In fact, machine noises may actually “mask” roof noises more than a well-fit hearing protection device would. Miners who maintain healthy hearing and wear their hearing protectors properly can hear roof noises better than those with hearing loss .
  • “If MSHA’s not accepting it, I’m not wearing it.” - While MSHA does not accept hearing protectors as the first or only line of defense from hazardous noise, it does require the voluntary use at 80 dBA, mandatory use at 90 dBA and dual-protection at 105 dBA.
  • “I can’t communicate with my co-workers.” - Removing protectors for even a few minutes can reduce the overall effectiveness of their published attenuation.
  • “I don’t need them. I’m used to the noise.” - The ear cannot “get accustomed” to noise. If a worker has lost some hearing, wearing HPDs is more important than ever to prevent further loss. To educate miners (and their families) about hearing loss, instill the following beliefs and practices:
  • Your hearing is a key sense and is yours to protect – Miners have the right to maintain good hearing. While mine operators have the responsibility to provide a safe workplace, it’s up to each miner to ensure the workplace is safe.
  • Some hearing protectors enhance speech communication – While many miners object that hearing protection devices (HPDs) isolate them from their environment, there are models of earplugs and earmuffs that better enable intelligibility of voice, signals and alarms.
  • Hearing loss is cumulative – Unlike other injuries or diseases, noise-induced hearing loss is usually not traumatic and often goes unnoticed in its early stages. It accumulates over time with every unprotected exposure to hazardous noise, and its effects are realized long after the damage has been done.
  • HPDs should be part of everyday life – Talking about noise hazards present in everyday activities — recreational shooting, using power tools, auto racing — brings the hearing conservation message “home” in a meaningful way.


Figure B. Noise Dose: Ambient vs. In-Ear Measurements, Underground Coal #2

References

1 R.J. Matetic. “Hearing Loss in the Mining Industry: Overview of the NIOSH Hearing Loss Prevention Program at the Pittsburgh Research Laboratory.”

2 http://www.msha.gov/30CFR/62.0.htm

3 Burks, Dr. J. Alton and Dr. Michael, Kevin. “A New Best Practice for Hearing Conservation: The Exposure Smart Protector™ (ESP).” Noise-Con 2003.

4 Merry, Carol and Stephenson, Mark. “What about hearing roof noises?” The Holmes Safety Association Bulletin (October 1998). http://holmessafety. org/1998/OCT98.pdf