CRIME scenes devastated by fire are to be preserved to allow for CSI-style investigations.

Fire chiefs say they deal with 20,000 deliberately set fires each year. In Glasgow alone 558 cases of wilful fire raising were recorded in 2011-12.

The Scottish Fire and Rescue Service, Police Scotland and Scottish Police Authority Forensic Services have now signed an agreement to share skills, resources and training to ensure scenes are preserved for forensics.

"Rather than us putting the fire out and then the police coming to investigate, we will all be engaged at the scene of incidents and we now have three national specialist units to investigate wilful fire raising," said a spokeswoman for Scottish Fire and Rescue.

Tom Nelson, director of the Scottish Police Authority Forensic Services, said residues of blood, petrol and even fingerprints can all be found within a charred crime scene if it is treated appropriately.

"When the fire service goes in its priority is to put out the fire and make sure people get out safely," he said. "But what this agreement allows us to do is work on joint training and a joint approach to ensure we have material preserved at the crime scene for evidence.

"As scientists we go in to identify the seat - or origin - of the fire, take samples of debris and look for residues of accelerants such as petrol.

"The most important thing for us is for the scene to be as intact as possible. It could be, in the case of a murder, there are the remains of a weapon with blood still on it. We could still find fingerprints after a fire. There is a lot of potential evidence.

"As forensic science advances we can get meaningful information from smaller and smaller samples. However, protecting the integrity of the crime scene is vital in giving us a complete understanding of how the fire started and who was responsible. "

The aim is also to prevent repeat offending by fire raisers.

The move follows the death of three members of the Sharkey family, who were murdered when their home in Helensburgh, Argyll and Bute, was set on fire in July 2011. Thomas Sharkey, 55, son Thomas, 21, and daughter Bridget, eight, were killed.

Scott Snowden, 38, and Robert Jennings, 50, were convicted in July this year of murdering them.

Police launched an internal review into how they investigated deliberate fires in Helensburgh before the Sharkey murders following speculation that if a number of "historical" fires had been investigated fully at the time, the killings could have been averted.

Between 2010 and 2012 there were 56 reports of wilful fire raising in Helensburgh. But the figures show reports of fire-raising in the town fell to just two in 2012/13 after the Sharkeys' killers were arrested and remanded.

Chief Officer Alasdair Hay said: "Those responsible for deliberately setting fires should note how determined we are to prevent them endangering people and damaging property.

"Fire is incredibly unpredictable and is completely beyond the control of those who start it. People who set fires deliberately are endangering lives by their reckless, criminal actions.

"Scotland's firefighters attend about 20,000 deliberately set fires each year, which shows the importance of our expert officers working to identify the causes and supporting the police with evidence to track down those responsible."

Chief Constable Sir Stephen House said: "This protocol will help shape a modern and effective response to wilful fireraising that can be held up as an example of excellent joint working."

In 2011-12, 57 people were killed in fires in Scotland, a 10% increase on the previous year. However, overall police reports of fire raising fell to 3066 in 2012-13.