“……the gas cap of the saw had vibrated off and the fuel in the saw was spilling out onto his gear and all around him…” While the roof operations were progressing, an evacuation tone was hit due to the deteriorating conditions. After all were removed and par was verified the roof was reevaluated for stability and crews were sent back onto it to continue operations. As this was taking place the operating crews were being assembled and these crews were placed into service. As they were rotated out for rehab along with equipment, new crews were placed into operation. As luck had it, several of my firefighters along with my deputy chief and the deputy chief of a mutual aid company were working on one particular section when the firefighter operating the K-12 noticed the strap of the saw was on fire. As he started to react to the strap fire, the gloves he was wearing caught and then his boots until he was fully engulfed. It was unknown at that point that the gas cap of the saw had vibrated off and the fuel in the saw was spilling out onto his gear and all around him. He immediately tossed the saw which was still running and in doing so he splashed even more fuel around himself. As the people around him realized what was happening and started to react, he tried to run and was immediately stopped by the two deputy chiefs working with him. They were able to put the fire out and except for a few scary seconds and a scorched saw all was well. The issue here was through out most of this call, all that you kept hearing inside the command bus where I was operating was safety officers ordering people on the roof to pack up. If this firefighter had not been packed up I am sure he would have suffered severe if not fatal injuries. The second issue is that if this firefighter had checked his tool he might have been able to see the saw fuel cap was not tightened and could have tightened it preventing this event from occurring. It is now part of our operating procedures that any tools being used will be checked the same as or airpacks and any other suppression gear.