The explosion of a tanker carrying ammonium nitrate emulsion (ANE) on the Great Central Road could have been prevented, according to report findings.
The incident occurred approximately 150 kilometres east of Laverton in October 2022, with the driver lucky to escape injury.
The road train included a dolly and two aluminium tankers, carrying 61 tonnes.
At about 9.30am, the driver noticed black smoke coming from the rear trailer, then stopped and attempted to extinguish a fire on the rear passenger side wheels of the rear trailer using two dry chemical powder extinguishers and a nine-litre water extinguisher.
Due to the intensity of the fire, the driver was unsuccessful, so disconnected the dolly and rear tanker, before driving the rest of the road train to a safe distance.
Emergency services and the mine site emergency response team attended the incident scene, where at 11:33am, the tanker exploded, causing several spot fires around the site. Luckily no one was injured.
As a result of the explosion, a crater, approximately 15 metres by 17 metres wide and one metre deep was formed.
A 100-kilogram piece of steel shrapnel was thrown approximately 413 metres from the blast site, while a 31kg piece of the trailer’s turntable was found 672 metres away.
Following the incident, the WorkSafe Group of the Department of Mines, Industry Regulation and Safety (DMIRS) investigated, with a 120-page report now released.
Though it found that incidents of this type are rare, it found that improvements are required to better prevent and respond to tyre fires on vehicles transporting ANE and similar products.
According to the DMIRS report, the likely cause of the tyre fire was a loss of pressure in an air supply line that caused the trailer’s brake system to overheat and set grease alight on the brake drum.
The report said dry chemical powder fire extinguishers are not effective for cooling purposes and cannot prevent re-ignition of flames.
Although the portable fire extinguishers complied with the regulatory requirements, the number and type fitted to the vehicle were inappropriate for the type and size of fire.
“Water and/or foams are the most appropriate firefighting media for tyre fires,” the report said. “Dry chemical powder and carbon dioxide may not be as effective since burning tyres have enough heat energy to reignite after flame knockdown and require continuous cooling with water or aqueous foam.
“Fighting tyres with water requires significant quantities to cool the tyre and extinguish the fire. Foam or encapsulating agents have the added benefit of being a good blanketing agent that will adhere to the surface of a burning object and suppress the fire.”
DMIRS’ chief dangerous goods officer Iain Dainty said it was fortunate the explosion occurred in a remote location and that no one was injured.
“Our report contains 16 recommendations for industry, and everyone involved in transporting dangerous goods must understand their responsibilities,” Dainty said.
“The explosion would not have occurred if the driver had been able to extinguish the fire, and there are practical measures to reduce such risks.
“Transport operators can also modify the design of their tanker trailers to better protect them from fires.”
Dainty added that the incident has already seen more transport companies and mine sites take additional measures to reduce the likelihood of fires on trucks carrying ANE and similar products.
“Operators are increasingly upgrading fire-fighting capability and making design improvements, and I encourage all interested parties to adopt such practices.”
As a result of the investigation, the state government has directed the department to introduce legislative amendments and develop a new Code of Practice to ensure the risk of such incidents is kept as low as possible.
Two other trucks carrying ANE have caught fire this year, one in New Norcia in June and another in Newman in August. While these fires were left to burn out after the drivers tried to extinguish them, the ANE did not explode.
Dainty said the incident was the world’s first known detonation of ANE during transport since bulk movement of the product was introduced in the 1980s.
“Given the significance of this event, we immediately sent a team to the remote eastern Goldfields to investigate the scene and probable cause,” Dainty said.
“The blast was equivalent to between one and three tonnes of TNT, but this was a fraction of the explosive power as the road train was carrying 33.8 tonnes of ANE.
“Emergency Response Teams felt the blast wave at their position 3km away, while workers at a mine site around 25km away felt vibrations and saw windows rattling.”
A condensed version of the report featuring information for transport operators and drivers, including the 16 recommendations, can be found here.