As a fire investigator in Strahclyde, Scotland we have encountered a number of incidents were petrol has been introduced into a building, an ignition source applied and an explosion causing extensive structural damnage has occured. A number of factors can influence how the vapour air mixture once ignited will affect the structure, these factors can include the characteristics of the vapour/gas involved and the characteristics of the structure such as room geometry, confinement, ventilation openings. A useful reference is " Gas Explosions in Buildings and Heating Plant" by RJ Harris. The Ignition Handbook is also another excellent source of information. I would agree with some of the previous posters that if petrol/gasoline has been used within the area you could still find useful samples.

John