By Phil Mercer in Sydney

As Australian fire fighters continue to battle the arc of flames that threatens Sydney, a specialist police task force formed to crack down on suspected arsonists is keen to make its mark.

However, as Australia's biggest city prepares for a fresh onslaught of bush fires this weekend, the depressing reality that many were started on purpose is beginning to sink in.

Whereas most of us have a flirtation with a partner, these people get their kicks from the fire

Dr Richard Kocsis, forensic psychologist

Authorities claim about 40 of the fires still raging across New South Wales were probably lit deliberately.

Those responsible face up to 14 years in prison and hefty fines.

Dr Richard Kocsis, a forensic psychologist, has studied serial arsonists.

Fire demons

His investigations produced 'Project Firebug' - a 10 year profiling of offenders. Dr Kocsis says they are driven by many different demons.

Arson is hard to investigate as evidence is destroyed

"Generally there's six broad motives for arson," he said.

"They are profit, vandalism, excitement, revenge, crime concealment and what I like to call 'extremist'."

These are the people urged on by sexual gratification.

They will choose low-risk targets such as rubbish bins or bush land and usually leave "some evidence of sexual activity in the area".

"You've got some kind of offender who's made some kind of association between sexual perversion and fire lighting," Dr Kocsis said.

"Whereas most of us have a flirtation with a partner, these people get their kicks from the fire."

Expert advice

Arson is a difficult crime to investigate because the evidence is mostly destroyed.

Victims pay a heavy price for the arsonist's "thrills"

The 35-member police arson squad - Strikeforce Tronto - will call on advice from forensic and psychological experts.

The New South Wales Rural Fire Service Commissioner, Phil Koperberg, believes some arsonists were simply thrill seekers, who enjoyed the excitement of the chaos they cause.

"In the past what we have invariably had as a motive is the sense of wanting to see the excitement of people responding to drama," he said.

Over the years volunteer fire fighters and security guards have been caught lighting fires.

Experts say they crave attention and want to engage in acts of heroism.

Dr David Indermaur, of the University of Western Australia's Crime Research Centre, told the Sydney Morning Herald that some arsonists were lonely people "disempowered around Christmas time", looking to take their frustrations out on society.

Stopping re-offending

Three teenagers - all boys aged 15 - have already been arrested on suspicion of starting fires at Shellharbour to the south of Sydney.

They may escape formal charges if they agree to psychological counselling.

According to Dr Kocsis such help may stop them re-offending.

"If we've got children who are fascinated by fire or by fire brigades, having good educational programmes to actually impress upon them the dangers of fire are quite effective," he said.

Australia's Bureau of Crime Statistics recorded more than 6,000 acts of arson last year, almost double the figure for 1995.