There have been four recent free-fall incidents on tower cranes in Queensland, each where the load fell to the ground. Thankfully in all cases no-one was injured, but the potential for tragic consequences was very real.
In three incidents, the hoist rope broke and in the fourth the hoist brake did not hold the load. In two of them, a hook block weighing 500kg and a seven-tonne rubbish skip fell to the ground.
Workplace Health and Safety Queensland investigations show these incidents were caused by:
- electrical components being replaced with non-original equipment, resulting in a failure in the crane control system and the failure of the brake
- the upper hoist limit was not used and the hook block 'two blocked' and broke the hoist rope. Two blocking is when the hook block contacts the hook trolley or sheaves above.
To prevent free-fall incidents on tower cranes:
- only use ropes specified by the crane manufacturer and inspect the rope regularly for wear and tear, particularly the parts subject to the most wear
- monitor replacement ropes after a rope failure to check for accelerated wear—if the rope shows accelerated wear, seek written guidance from the crane manufacturer
- remove cranes from service if the hoisting or braking systems malfunction until they have been inspected by a qualified person who is a technical specialist—don't keep using them even if the fault is intermittent
- if a crane is involved in an incident, have it checked for mechanical damage before putting it back into service
- do not override safety features built into the crane by the manufacturer
- choose a crane that is suitable for the site you are working on—make sure the hook height is high enough for lifting, so that you aren't tempted to override built-in safety features.
A safety alert was issued after the first of these incidents and is available at worksafe.qld.gov.au.