Coal Inspectorate | Alert | No.424 V 1 | 14 February 2023

Dozers entrapped in stockpile voids above feed valves

What happened?

Two recent incidents have resulted in coal mine workers being exposed to an unacceptable level of risk when bulldozers they have been operating on coal stockpiles have sunk into voids above feed valves.

The first incident occurred at a surface coal mine on 27 January 2023. Coal taken through the feed valve to the load out bin created a “rathole”, because the void did not reach the stockpile surface (see Figure 1, below). The coal that bridged above the void, due to the “rathole”, failed beneath the weight of the bulldozer. This resulted in the bulldozer inverting and becoming engulfed with coal, with the operator trapped in the cabin for approximately 10 hours (see Figure 2, below).

The second incident occurred at an underground mine on 30 January 2023. In this case the separation distance of the bulldozer from the caving profile visible above the feed valve was insufficient to prevent the entrapment occurring.

These two events follow an early event in December 2022, which was communicated to industry through the publication of Safety Alert 420 Bulldozer drops into a void above a conveyor feed valve point.

How did it happen?

Initial information suggests that these events have occurred due to failures to implement controls capable of ensuring operators are informed about and aware of hazard areas and exclusion zones on stockpiles.

Key issues

Directives have been issued to operators of coal mines requiring them to take particular actions to ensure risk to coal mine workers operating bulldozers on coal stockpiles does not reach an unacceptable level. The directives require operators to review their systems associated with the provision of equipment and training to coal mine workers, communication systems and emergency procedures relevant to stockpile operations.

It is the responsibility of operators and Site Senior Executives to ensure plant provided to workers is safe and risk from operations is managed to an acceptable level. However, all workers operating bulldozers on stockpiles should ensure:

• they are aware of the location of feed valves under coal stockpiles before commencing any operations on the stockpile;
• bulldozers they are operating are at all times kept outside the nominated clearance distance from the feed valves; and
• they do not operate bulldozers on stockpiles unless they are satisfied that the equipment provided is fit for purpose and is fitted with emergency equipment, as required by the mine’s safety and health management system.

References and further information

The Queensland and New South Wales mines inspectorates have published information aimed ensuring risk from operating bulldozers on stockpiles is managed to an acceptable level. In December 2022, a bulletin was issued in Queensland following a similar incident. The NSW guideline MDG 28 Safety requirements for coal stockpiles and reclaim tunnels was issued in 2013.

• Safety Alert 420 Bulldozer drops into a void above a conveyor feed valve point.
• MDG 28 Safety requirements for coal stockpiles and reclaim tunnels.