The DMP has warned crane operators and other competent persons to properly inspect head sheaves on their machines prior to operation.
At a mine site in July 2014 a nylon head sheave shattered in half under load and fell two metres to the ground, “narrowly missing” a rigger standing below the boom.
The auxiliary hook head sheave weighed about two kilograms, and landed within the rigger’s exclusion zone.
An incident report showed the crane was working within its limits, and there was no side loading of the boom head sheave during the lift.
Recommendations from the Department of Mines and Petroleum in Western Australia suggested that crane inspection programs must include inspection and assessment of sheaves.
A contributing cause was that damage to the head sheave was not identified during the daily pre-start inspection of the crane.
It was noted that head sheaves must be inspected for alignment, damage such as cracking, wear, mobility and extreme soiling, before starting a crane operation.
In addition, special attention was given to discourage the practice of double blocking, or allowing the headache ball to make contact with the head sheave, including when moving or packing up the crane.
It was also advised that crane maintenance records must be checked and cranes examined for damage prior to entering mine sites.