MSHA statistics show that 98% of US roof fall injuries in underground mines are due to small rocks (average in size 900 x 500 x 100mm) that fall from the roof. These falls also account for 19% of fatalities. Typically these rocks fall between roof bolts or around temporary supports.

Some mines, particularly in the western US, use steel screen routinely. In the east, steel screen has been used traditionally as a secondary support in poor roof conditions and for rehabilitating roof falls or overcasts. But mines that have switched to installing steel screen on-cycle have found that the number of roof fall injuries can be reduced by as much as 90%.

Some underground mines have resisted the wide use of mesh partly because handling and installing full screens in low seam conditions is not very easy. In 2002, 73% of US underground coal mines were mining in heights of less than 60 inches.

To help overcome installation problems, NIOSH recently developed a new concept that employs a half screen that can be installed by a single roof bolt operator. Called the Personal Bolter Screen (PBS), this screen is 5 ft x 5 ft with a reinforced perimeter and weighs 11 lbs.

It can be installed with pattern bolting and has a 6 inch overlap of each screen. Its material cost is also comparable to roof straps and it affords 3 times the roof coverage. Single sheets of PBS can also be used for occasional supplemental support where roof conditions call for it.

“MSHA, NIOSH, support material suppliers, and equipment manufacturers are cooperating in a major effort to reduce the number of miners who are injured by rock falls beneath supported roof,” said NIOSH section chief, rock mechanics, Chris Mark.

“Currently screen installation tests are being conducted in coal mines of varying heights and with different bolter types to iron out the operational barriers to roof screen installation. By controlling the roof skin, coal mine operators can potentially prevent hundreds of injuries a year,” he said.