Coal Inspectorate | Alert | No.445 V 1 | 09 February 2024

Uncontrolled movement of longwall transformer cart

What happened?

On 21 December 2023, an underground coal mine longwall transformer cart was being trammed into position when it moved down the grade in an uncontrolled manner for approximately 20 metres until it came to rest against a stationary load haul dump (LHD) machine.

Four coal mine workers (CMWs) were in the vicinity of the longwall transformer cart at the time of the incident. None were in the travel path of the out-of-control cart, however, the potential for a serious incident was evident.

Background information

• Equipment such as longwall transformers, emulsion pumps, shearer water pumps and tanks are often mounted on carts that require hydraulic power to release brakes or power the traction system.
• When the carts are to be moved or relocated hydraulic power is typically supplied to the carts from a LHD hydraulic power take-off circuit. Hydraulic wander hoses connect the LHD to the cart.

How did it happen?

• CMWs hydraulically connected the LHD to the longwall transformer cart.
• The operator function tested the hydraulic operations in the inbye direction and then in the outbye direction. The transformer cart was then trammed outbye approximately 50mm and a noise was heard.
• The transformer cart then moved inbye in an uncontrolled manner for approximately 20 metres before being stopped by another LHD (refer Figure1).
• The mine investigation identified that:
  • wander hoses from the LHD to the transformer cart were incorrectly sized and connected to the wrong manifold. his resulted in increased back pressure in the return hydraulic oil circuit. The increased back pressure in the return circuit caused the transformer cart brakes to release. The cart then moved down the grade in an uncontrolled manner.
  • CMWs were not familiar with the functionality of the LHD power take-off circuit or the transformer cart traction brake circuit.
  • CMWs had no ability to identify excessive back pressure in the return oil circuit.

Recommendations

All site senior executives should:

• provide machine specific technical training for LHDs and transformer carts in combination and individually.
• consider providing a method for monitoring return oil circuit back pressure.
• consider using a second LHD as a brake vehicle.
• review standard work instructions to ensure that CMWs have clear directions on how hydraulically connect LHDs to hydraulically powered carts.
• review the risk assessment for operation and maintenance of transformer carts and similar, including no-go zones.

All supervisors should:

• ensure you know and understand the standard work instructions.
• ensure that the standard work instructions are available to CMWs.
• ensure that CMWs conduct risk management before moving carts.
• ensure that only competent authorised persons conduct the task.
• provide leadership and guidance to CMWs, under your control.

All operators should:

• ensure you know, understand, and comply with the standard work instructions.
• conduct hazard identification and risk management before starting a task.
• report any unusual event to your supervisor.