Police say the explosives found at Dural were allegedly intended for an antisemitic attack. What was the explosive – and how is it typically used?
Counter-terrorism police in New South Wales are investigating after a caravan laden with explosives was found at a residential property in greater Sydney.
NSW police said on Wednesday there were indications the explosives – enough to create a 40-metre blast zone – would be used in an antisemitic attack. Police also said they believed the explosives were Powergel, potentially obtained from a mining site.
Powergel is the brand name for a range of explosive products used in mining. Trademarked by Orica, an Australian-based multinational and one of the world’s largest providers of commercial explosives, the products mainly consist of ammonium nitrate, a compound widely used in explosives and fertiliser.
Powergel can be cream, grey or black in colour with “a firm putty-like consistency”, according to information on Orica’s website. It is packaged in plastic “sausages” with wire clips at either end.
Orica was contacted for comment.
Powergel is used as an explosive in a range of mining settings, including in open-cut coal and metal mines, underground mines, and quarrying.
It is mainly made of ammonium nitrate, a chemical used in fertiliser to provide a source of nitrogen for plants. On its own, ammonium nitrate is a stable chemical at room temperature and requires extreme conditions – such as heavy impact or high heat – for explosion.
But ammonium nitrate becomes very explosive when mixed with fuel oil such as diesel, which is often the case for mining explosives, according to Gabriel da Silva, an associate professor of chemical engineering at the University of Melbourne.
“In an explosion, you need a release of gas and a release of energy. The ammonium nitrate decomposes to create a lot of gas, and the fuel oil in the presence of oxygen [from the ammonium nitrate] releases a lot of energy,” he said.
Da Silva said explosives used in mining such as Powergel were usually not “primary explosives”, or contact explosives, which are extremely sensitive to heat, impact and friction. “You would need some high explosive, like a blast cap, to detonate [Powergel] to initiate the explosion.”
He added that prepackaged explosives such as Powergel were typically “sensitised” – or made more explosive – with gas bubbles or small voids “that helps the shock wave propagate through the material … to then get a true explosion”.
NSW police commissioner Karen Webb told media on Thursday: “Whilst the explosive material was found in that caravan, there was no detonator with the caravan.”
Powergel also contains sodium perchlorate, an electrolyte which is not required for explosion.
In NSW, anyone who wants to use and store explosive substances must first apply to SafeWork for a licence. Licence applicants must first obtain security clearance to gain “unsupervised access to explosives, explosive precursors or concentrated ammonium nitrate”, according to SafeWork’s website.
Under the NSW Explosives Act, blasting explosives licence holders are able to use up to 50kg of blasting explosives and 100kg of ammonium nitrate a day. Anyone wanting to store more than 2.5kg of blasting explosives and 50kg of ammonium nitrate overnight must also apply for storage approval.
“A blasting explosive user licence holder must not allow people to have unsupervised access to explosives or security sensitive dangerous substances unless they hold a valid security clearance,” SafeWork’s website reads.
A spokesperson said licences for explosives were “only granted when SafeWork NSW is satisfied that security planning is adequate”.
“Compliance with the requirements of the NSW explosive legislation is monitored via a coordinated approach across multiple teams within SafeWork NSW,” they said.
“If they do have some of those packaged sausage-type explosives, the fact that they managed to get their hands on some of that … is of incredible concern,” da Silva said. “The controls on those and the paperwork is that needed to manage that is very extensive.”
