Previous research by the Mine Safety and Health Administration has shown that roof bolter operators are often exposed to excessive levels of respirable silica dust. Nearly 5000 samples taken from 2000-04 showed 20% exceeded a respirable silica dust concentration of 100mg/cu.m – a level MSHA considers excessive.

Currently roof bolting machines use a vacuum dust collection system to capture dust as holes are drilled. In this system operator exposure occurs when the operator empties the chamber of the collector and the canister filter.

Researchers from the National Institute for Occupational Safety and Health took to the lab to compare exposure levels of using this system compared to installing vacuum bags in the dust collector.

The tests showed 99.6% of the test dust fed into the collector was captured by the dust bags. It was found the canister filter collected five times less dust with the vacuum bag compared to without.

A RAM-1 dust monitor showed respirable dust levels in the collector exhaust to be more than two times higher when tests were conducted without the bags in place. The aerodynamic particle sizer also showed the number of total dust particles emitted from the exhaust was two times greater.

“Since nearly all the dust is contained in the bag, operator exposure is improved when emptying the collector box’s main chamber. Filter loading is greatly decreased when using the bags, enabling longer periods of drilling without filter removal/cleaning,” NIOSH said.

“Filter air emitted from the collector has less respirable dust and fewer total dust particles when the bags are used.

“These results show that benefits from the use of the bags are realised in all areas of operator exposure.”

To use the bags in underground coal mines, they must be accepted by MSHA as an exceptional item for the specific dust collection system and machine model. The collector must also have a pre-dump option and a retrofit kit inside the collector to connect the bag.