Mining Project: Inventive Methods for Evaluating the Translation of Hand-arm Vibration to the Ear Canal in Miners

Research Summary

Noise-induced hearing loss (NIHL) continues to be a prevalent issue within the mining industry despite research efforts from public health institutions, the implementation of hearing loss prevention initiatives, and the improvement of hearing protection technologies. Pending further updates, mining still has the highest prevalence of hazardous noise exposure of any major industry sector. NIOSH estimates that 76% of U.S. miners self-report working in an environment where the time-weighted average (TWA) exceeds the NIOSH recommended exposure limit (REL) of 85 dB, and 25% of these are exposed to a noise level exceeding the Occupational Safety and Health Administration (OSHA) permissible exposure limit (PEL) of 90 dB. Proportionally, mining employees currently accrue the most hearing disability and have the highest prevalence of moderate or worse hearing impairment when compared to all other industry sectors. The most recent statistics show that workers in the mining sector lose approximately 3.45 healthy years per 1,000 workers due to hearing impairment. Pneumatic drill operators are a sub-class among all machine operators that are most susceptible to both noise and vibration exposure.

The jackleg drill was chosen for the purposes of this pilot project research because drill operators are known to accumulate the most rapid noise dose accumulation among all machine operators in western hard rock mining. Use of the jackleg drill has also been associated with vibration white finger (VWF) in miners—a condition which has shown an association with increased risk of NIHL in numerous studies. Nevertheless, though these studies have suggested an increased risk of NIHL in workers with VWF, recent research confirms that the relationship remains poorly understood.

As a proof of concept, NIOSH’s Spokane Mining Research Division (SMRD) constructed a prototype monitoring system that measured the transmission of hand-arm vibration from the point of contact to the hearing anatomy. Pilot research was executed in two phases. The first phase included a series of beta tests that were conducted at SMRD. The first iteration of beta tests included impulse response tests using an electrodynamic shaker table to identify a transfer function. This was followed by simulative grip tests that utilized a commissioned jackleg drill to simulate apparent vibration levels and confirm prototype utility. During the second phase, the research team collected measurement data from study participants at a local university's research mine facility, with the participants performing jackleg drilling and bolting tasks while being monitored by the prototype. All measurements were captured using general purpose tri-axial accelerometers.  Approval of the study protocol was obtained by NIOSH’s Institutional Review Board (IRB).

The overall research aim for the pilot project was to determine whether hand-arm vibration (HAV) could be measured as it translates through the hand-arm-shoulder system to the hearing anatomy. This objective was achieved by demonstrating the feasibility of measuring vibration transmission on the human body using the prototype monitoring system and determining whether the vibration intensity levels observed during prototype testing were significant enough to warrant further investigation.

The findings from this pilot project contributed to mixed exposures research studying the effects of simultaneous vibration and noise exposure on the human body. The data from this study will be used as an attempt to better characterize the nature of this type of exposure. While the monitoring methods used in this pilot have been implemented in previous research, the prototype monitoring device and system is novel to this field of study. An internal technical report will be generated to disseminate research findings and in an attempt to gain insight on how to improve upon prototype design and measurement strategies. If prudent, findings will also be used to develop a peer-reviewed manuscript in addition to a follow-up research proposal that will investigate the potential mechanisms behind vibration exposure and developing NIHL. The follow-up research project will attempt to determine whether the low-level exposure experienced around the hearing anatomy is significant enough to contribute to human hearing impairment.