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Unbalanced load during mill reline ejects parts 65m

mill reline parts ejected
Parts were ejected up to 65m during a mill reline

The NSW Resources Regulator has advised of a dangerous incident during relining of a mill at a mine site.

During a planned shutdown for the relining of a mill, a maintenance worker was slowly working the mill in an anticlockwise direction. The mill was stopped on completion. The crew saw the mill begin to move in a clockwise direction and increase in speed.

The brake failed, followed by a loud bang and then metal parts were ejected from the brake unit up to a distance of 65 metres away. No workers were in the line of fire.

The Regulator said that “During maintenance activities the mill became unbalanced, causing it to rotate. Unbalanced loads must be considered as a potential energy source when completing and isolating work areas.”

Mill reline work known for safety incidents

In 2013 a maintenance worker was seriously injured during a ball-mill relining operation at a Western Australian mine when he was struck by a large liner plate weighing about 1.5 tonnes.

At the time of the incident, the worker had been preparing to remove two unsecured liner plates still in place inside the ball mill when the top liner plate was dislodged and fell, pinning him to the ground. A mechanical lifting device was required to lift the liner plate from the worker.

He sustained extensive injuries, including compound leg fractures, fractured vertebra, and crush injuries to his chest. The probable cause of the incident was the ball-mill liner plate was unsecured.

Contributory causes included:

• The unsecured liner plates were identified as a hazard but there were no controls in place to prevent their uncontrolled movement or prevent worker exposure to falling object hazards.

• The resting position of the unsecured liner plate was above the horizontal centre-line of the ball mill

• The workers undertaking the mill relining were not adequately trained and had not been assessed as competent for the task.

Mine maintenance should ensure when developing safe systems of work for mill relining operations, mine sites should apply the same rigour and standards as used for other workplace activities.

New mill designs and installations should include, where practicable, appropriate engineering controls to assist mill relining operations, such as fit-for-purpose equipment for handling mill liner plates. Mill relining tasks should always include a pre-task risk assessment.

Identify the potential for objects such as liner plates to fall during mill relining operations — during both removal and installation of lining — and implement controls to prevent:

• their uncontrolled movement

• workers entering the fall zone. Ensure competency-based training has been undertaken by those involved in the mill relining operation (including contractors).

This should include awareness of the increased potential for unsecured liner plates to fall if they are located above the mill centre-line, and the need to prevent the mill moving as the centre of gravity adjusts when liner plates are removed or added. Ensure critical tasks are supervised by competent persons.

Reference: Dangerous incident | IncNot 0034149

 

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