About 60 percent of all arson fires are started with gasoline, and this substance leaves clues at the fire site. Gasoline which is poured on the floor usually burns downward and produces a burn pattern or hole. The highly volatile air and vapor mixture that forms above gasoline rises to the ceiling where it ignites and causes severe ceiling damage. Samples for laboratory analysis should be taken from the burned floor area. They should include fire-damaged flooring material, undamaged flooring material (for comparisons), and flooring material that may have absorbed gasoline at the edge of the burn pattern or hole. Samples should be covered and kept from drying out. Laboratory analysis involves the detection of tetraethyllead (from leaded gasolines), thylene dibromide (a bromide compound), hydrocarbons, and methycylopentadienyl manganese tricarbonyl (a manganese compound). Lead and manganese compounds remain as residues from the fire. A sample is treated with a strong acid that destroys everything except these heavier metals. They are then identified with a gas chromatograph. Bromine is freed from a sample with distilled water and identified by the use of a specific ion electrode that reacts only with this element. Finally, a gas chromatographic column can be used to identify the hydrocarbons present in the water used for the bromine extraction. References are not provided.