Health authorities confirmed the 35-year-old suffered severe burns and remained in a serious but stable condition on Thursday after being flown from Canberra Hospital to Sydney's Concord Hospital.

But emergency medicine specialist at the Calvary Hospital Dr David Caldicott, who teaches first responders how to deal with vehicle explosions, said such instances were not uncommon.

"Burns are inflammations from heat and with any inflammation it develops over a period of time," he said.

"So it is possible to suffer life threatening burns and be walking and talking but be in a critical condition hours later."

Mr Caldicott recalled treating victims of the 2002 Bali Bombings at the Royal Adelaide, many of whom chatted and waved while being wheeled off the aircrafts.

They were in chemically induced comas six hours later due to heightened swelling of their burns.

"The other thing with a burn that if it is deep enough it actually kills the nerves in your skin and becomes insensate, meaning you won't feel the actual skin because the nerve endings have been killed," he said.

"While you can't feel the skin it often reflects significant injury to the muscle so thats another way in which burns might not be appreciated. In many ways, the most painful burns are superficial burns."

Dr Caldicott said a person's psychological state was also a key factor in their physical capability after suffering from serious injuries.

The Canberra man was airlifted from Canberra Hospital early Thursday evening to one of two adult specialist burns units in New South Wales to receive further treatment for his burns.

ACT Policing confirmed the man presented himself to the hospital on Wednesday night after walking from the scene where he had parked a van and ignited several gas cylinders outside the headquarters of the ACL building in Deakin.

ACL managing director Lyle Shelton was quick to label the fire a deliberate attack against the organisation's conservative political stance, but police determined there was no political, religious or ideological motivation behind the explosion after interviewing the man.

Speaking to Fairfax Media on Thursday, Mr Shelton cast doubt on police claims.

"There's a whole bunch of things that just don't add up," he said.

Mr Shelton told ABC radio the clean up of the ACL will begin in the new year while the organisation reassessed its security.

Police earlier said they were conducting a thorough investigation into previous threats to the ACL, despite dismissing political, religious or ideological motivation.

They would not provide any further detail on their investigations when asked on Friday.