MSHA said the accident involved a drill station canopy on a Fletcher roof bolting machine at a district three underground mine.

A roof bolter operator was nearly struck in the head by the canopy as it suddenly fell after being momentarily stuck in the raised position. Fortunately, the operator was not injured.

The Fletcher drill station canopy support assembly consists of three nested square tubes raised up and down by a hydraulic cylinder.

MSHA said the incident apparently occurred because the bolt attaching the canopy and the square tubing to the hydraulic cylinder became loose. Without this bolt connecting the tubing and cylinder, when the bolter operator activated the lever to lower the canopy, only the hydraulic cylinder retracted.

The square tubing and canopy remained in the raised position for a few seconds and then suddenly dropped and nearly struck the operator.

“Although the recent accident occurred as a result of a 3-inch-long bolt backing out of the cylinder rod, a similar scenario could result on the "older" style tubing/ cylinder attachment,” MSHA said.

“Prior to 1992 the top of the cylinder rod was threaded and the tubing assembly attached with a nut. It is even more important that older machines with this design be checked due to a shorter thread engagement length at the connection point.”

MSHA issued a number of practices mines could follow to ensure a similar incident did not re-occur.

“When lowering the canopy the bolter operator should pay special attention - if the canopy does not immediately begin to lower when the lever is activated, this could be a warning sign. If this happens, do not continue to attempt to lower the canopy. Stop immediately and inspect the bolt or nut.

“Check the retaining bolt or retaining hex nut weekly, making sure it is properly tightened

(torqued to 150 ft-lbs).

“If the bolt or nut is loose, reinstall it by first using Locktite on the threads.

“A cap is available from Fletcher to prevent dirt and loose coal from accumulating in the access hole to the bolt or nut. Use of this cap will make the weekly torque check much easier.

“Remember - do not pressurize the canopy against the mine roof. (Pressurizing the canopy can damage the tubing/cylinder connection).”