Part of a heavy vehicle could have avoided bursting into flames and becoming airborne, an investigation found.
Authorities recently examined circumstances that led to a road train’s wheel igniting 34 tonnes of mine blasting oxidising agents called ammonium nitrate emulsion.
Investigators discovered the detached dolly and tanker trailer were completely destroyed. The blast left a 17 metre long by 9 metre wide and 1.1 metre deep crater on Great Central Road, near Gold Road Resources’ Gruyere mine – about 1000km east of Geraldton.
They collected more than 50 kilos of solidified molten aluminium shrapnel, indicating the vehicle tank melted and lost containment prior to detonation. It also shows the explosion moved upwards instead of occurring within the tanker.
The heaviest piece of steel shrapnel weighed over 100 kilos and was discovered 413 metres from the blast site. The crew also recovered a 60 kilo brake drum at 97 metres and 31 kilo dolly turntable fragment at 672 metres.
Nearby vegetation was also heavily damaged, with 7 metre tall trees uprooted and other shrubs “completely flattened” even at distances of between 40 and 50 metres.
“The blast overpressure at 120 metres may have been of the order of 14 kPa, which gives a rough estimate of the size of the explosion of approximately 1-3 tonnes of TNT equivalent. This is a small fraction of the potential explosive power of the 33.85 tonnes of ANE initially present in the tanker trailer,” the State Department of Mines, Industry Regulation’s incident investigation report said.
The department’s Dangerous Goods Safety team concluded a tyre fire caused the incident and this could have been prevented.
“The likely cause of the tyre fire was a loss of pressure in the air supply line that operates the tanker trailer’s braking system. This caused the brakes to be applied and overheat, leading to a fire on the rear tri-axle passenger-side tyres on the rear trailer,” the report said.
“It was a preventable incident because it was caused by a tyre fire and a range of practical improvements can be made to vehicle and transport operations to better prevent and respond to tyre fires. Had the driver been able to extinguish the fire it would not have progressed to an explosion.”
The department also declared the incident was the world’s first detonation involving ANE during transport.
Nobody was injured and the only the rear tanker, dolly, ANE and gravel road was damaged.
Investigators made the following recommendations
- National Transport Commission should review Table 12.1 Note 4 of the ADG Code
- intensify vehicle maintenance schedules when driven on poorly maintained gravel or dirt roads
- consider the practicality of fitting fire screens beneath loads of ‘AN explosion risk goods’
- inform firefighters when it is safe to fight a vehicle fire and when evacuation processes should be undertaken
- protect critical components of the vehicle’s running equipment from rocks and debris for safe vehicle operation
- fit vehicles transporting ‘AN explosion risk goods’ with a hub and tyre temperature and pressure monitoring system
- conduct fire tests on steel tankers to determine the effectiveness of new emergency venting requirements AS 2809 part 4 (2022)
- industry develops a national code of practice to provide detailed guidance on the safe road transport of ‘AN explosion risk goods’
- carry an appropriate means of vehicle operator communication to raise alarm and provide essential information to emergency services
- provide drivers with a journey management plan formulated after a risk assessment, and avoid using poorly maintained gravel roads where possible
- fit mudguards with heat shielding properties (e.g. stainless steel) to protect the tank or cargo containing ‘AN explosion risk goods’ from the heat radiation of a tyre fire
- conduct fire tests to determine the rate of decomposition and explosive potential of ANE in open fires where the fuel and ANE entrapment are similar to the Great Central Road incident
- fit vehicles with a sufficiently large pressurised foam or water-based firefighting system
- consider automatic fire suppression systems for tyres of vehicles transporting ‘AN explosion risk goods’
- increase emergency evacuation distances in the Australian and New Zealand Emergency Response Guide Book, Guide No. 140 to 1.6km for fires involving ANE and ANSOL
- appropriately train and accredit drivers in the safe and secure transport of ‘AN explosion risk goods’.
