Alert no. 420 | 14 December 2022 | Version 1

Bulldozer drops into a void above a conveyor feed valve point

What happened?

A bulldozer working on a coal stockpile dropped into a void above a conveyor feed valve point.

How did it happen?

During preparation of the stockpile for train loading, the location of the feed valve was miscalculated.

The feed valve location was not available on the GPS system in the bulldozer.

External reference points used by bulldozer operators to locate the feed valves were inaccurate.

Coal taken through the feed valve to the load out bin created a rathole, because the void did not reach the stockpile surface.

The coal bridge above the void failed beneath the weight of the bulldozer (see Figures 1 and 2).

Key issues

• The bulldozer operator did not have an accurate location for the feed valve in the stockpile.
• The stockpile profile used as the visual aid for the location of the feed valve was incorrectly positioned during stockpile preparation.
• Not all bulldozers in use on the stockpile were fitted with GPS units.

Recommendations

All Site Senior Executives should:

• clearly demarcate stockpile feed valve locations on the surface of coal stockpiles.
• have a system that manages movement of mobile equipment and personnel on coal stockpiles.
• utilise the advice given in MDG 28: Safety requirements for coal stockpiles and reclaim tunnels when conducting risk assessments relevant to working on coal stockpiles.

All operators should:

• confirm the location of feed valves under coal stockpiles before accessing the stockpile surface.
• keep their machine outside the nominated distance from the feed valve.