Coal stacker boom luffs uncontrollably after bolt failure, prompting safety alert and structural review of bulk handling equipment in Queensland mine

A coal mine worker narrowly avoided injury when a raw coal stacker boom suddenly and forcefully luffed upward during a lowering operation, according to a safety alert issued by Resources Safety & Health Queensland (RSHQ).

The incident, which occurred at a Queensland coal mine, is under active investigation by the Coal Inspectorate. Early findings suggest the uncontrolled movement was caused by the mechanical failure of bolts securing the bottom of a hydraulic luffing cylinder (HLC) used to control the boom’s vertical motion.

Mechanism of Failure

According to Coal Inspectorate Alert No. 456, issued 12 May 2025, the bottom end of the HLC became detached after both sets of clevis bolts securing it to the stacker structure failed—first on the western side, then on the eastern side. The failure eliminated the boom’s downward force, allowing the counterweight on the opposite end to swing downward and rapidly drive the boom upward in a catapult-like motion.

Although the operator was on the stacker platform at the time of the uncontrolled luffing, no injuries were reported.

The bolts were found to be significantly worn, and in some cases, threads on the nuts had stripped. Failures of this kind have previously resulted in fatalities.

Historical Context and Design Concerns

This type of failure is not without precedent. Similar past incidents—where structural or mechanical failures in stackers or other bulk handling machines led to rapid and uncontrolled boom movements—have caused severe injuries and fatalities. In response, equipment design standards have evolved to mitigate the risk.

The stacker involved in the incident was originally designed to the German BG1986 standard, which has since been superseded by DIN22261 and updated Australian Standard AS 4324.1 (1995, revised in 2017 and scheduled for further revision in 2025). The incident has raised renewed concerns about the longevity and safety of aging equipment operating under outdated standards.

Recommendations for Industry

The Inspectorate has urged all coal mine operators and maintenance teams to take immediate action. Key recommendations include:

• Structural reassessment: Engage a qualified structural specialist to review all stackers and similar equipment against current standards such as AS 4324.1 and ISO 5049-1.

• Component inspection: Give priority to parts operating in tension (e.g., hydraulic cylinder connections) where failure can release stored energy uncontrollably.

• Preventive maintenance: Recognise that bolts and structural fasteners degrade over time through corrosion and wear, reducing the effectiveness of original safety margins.

• Redundancy in design: Consider upgrading to dual-cylinder systems that can retain control in the event of a single-cylinder failure.

“Maintenance records alone are not enough,” the alert stated. “Inspection must verify that physical integrity and current configuration comply with up-to-date design and operational standards.”

Ongoing Investigation

The incident is still being investigated, and the Coal Inspectorate has indicated that further information will be released once it becomes available. The alert serves as a formal reminder for all operations to reassess their control systems for managing stored mechanical energy, particularly in legacy plant infrastructure.

The full alert is available on the RSHQ website, and mine operators are encouraged to place it on site noticeboards and share it widely with relevant personnel.

Contact:
Queensland Mines Inspectorate
QldMinesInspectorate@rshq.qld.gov.au
resources.qld.gov.au (for safety notices and hazards database)

Issued by:
Resources Safety & Health Queensland
Authorised by: Jacques le Roux, Chief Inspector – Coal