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Coal Inspectorate | Alert | No.386 V 1 | 19 February 2021

Unplanned vehicle movement - Failure of Battery Isolator and Braking System

What happened?

A Komatsu 930E-2 rear dump truck ascending a ramp incurred a fault and lost all power and propulsion, coming to a complete standstill on the ramp. The operator exited the cabin and descended to ground level to reset a battery isolator. When the operator stepped off the access ladder the rear dump truck began to roll backwards. It gained speed, travelling an estimated distance of 200 metres down the ramp and came to rest on a bund. A grader and another rear dump truck had to take evasive action.

How did it happen?

There was an existing issue on the main battery power isolator where it was difficult to initiate it into the ON position due to the mechanism being tight to turn. When the battery isolator has been reset it has not been fully turned, locked, and engaged into the ON position, allowing the isolator to trip to the OFF position, likely from vibration during operation of the truck.

Before the incident, the Komatsu rear dump truck has incurred the same fault and lost all power and propulsion on flat ground. The operator exited the cabin and reset the battery isolator. An intrinsic condition exists with the vehicle's operational design, inhibiting the application of the park brake if the vehicle monitoring identifies movement above 0.5 mph (0.8 kph) to ensure the integrity of the park brake system is maintained as its reliability will be degraded if it is applied at speed.

When the vehicle lost all power, both electrical and mechanical, the park brake, being spring applied and oil release, has lost hydraulic pressure and would have tried to engage whilst the vehicle was still moving forward, degrading the effectiveness of the park brake system. Vehicle diagnostic, monitoring and protection systems would have been rendered ineffective due to the loss of the main electrical supply. The operator was not aware of the above condition when the rear dump truck has returned to service. When the second loss of power event occurred on the ramp, the park brake integrity has failed resulting in the unplanned movement.

Key issues

Recommendations

Investigations are ongoing and further information may be published as it becomes available. The information in this publication is what is known at the time of writing.

We issue Safety Notices to draw attention to the occurrence of a serious incident, raise awareness of risks, and prompt assessment of your existing controls.

References and further information

Investigations are ongoing and further information may be published as it becomes available.

The information in this publication is what is known at the time of writing.

RSHQ issues Safety Notices to draw attention to the occurrence of a serious incident, raise awareness of risks, and prompt assessment of your existing controls.

Authorised by Peter Newman - Chief Inspector – Coal

Contact: Mark Lydon, Inspector of Mines (Electrical) , 0436 950 514

Issued by Resources Safety & Health Queensland

Safety: This information is a guide only and is issued to promote safety through experience. It is not to be taken as a statement of law and must not be construed to waive or modify any legal obligation.
Placement: Place this announcement on noticeboards and ensure all relevant people in your organisation receive a copy.

All information on this page (Unplanned vehicle movement - Failure of Battery Isolator and Braking System - https://www.rshq.qld.gov.au/safety-notices/mines/unplanned-vehicle-movement-failure-of-battery-isolator-and-braking-system) is correct as of time of printing (17 Apr 2021 11:35 am).