Noise and vibration assessment of a roof bolting machine

In its 1996 National Occupational Research Agenda, the National Institute of Occupational Safety and Health (NIOSH) identified hearing loss as the most common job-related disease in the United States. Previous field studies by NIOSH have shown A-weighted sound levels at the operator’s station on roof bolting machines used in coal mines exceed 100 dB when drilling. Laboratory vibration measurements conducted while drilling indicated that drill steel acceleration levels greatly exceed those of the drill motor, drill motor cover, the roof support plate, and the drilled media. Sound level measurements performed with parts of the drilling apparatus and the drilled media wrapped in lead-fiberglass barrier-absorber blankets revealed that the drill steel is the dominant noise source. To evaluate the ability of a partial-height barrier to reduce operator noise exposure, 80% of the drill steel length was encapsulated in a quilted lead-fiberglass barrier-absorber sleeve. The partial-height barrier reduced the time-weighted average sound level (TWA) by 9.8 dB for the Mine Safety and Health Administration (MSHA) Permissible Exposure Level (PEL) criteria and 9.3 dB for the NIOSH Recommended Exposure Limit (REL) criteria.