A couple of people have already posted similar, but as someone who works for an oil company, I will just reiterate that it's the vapour that ignites, not the liquid (You can drop a lighted match into petrol and it wont ignite, its the vapour it reaches first that does) and aviation fuel sitting on hot tarmac would generate a lovely flashpoint for any source of ignition. Remember Buncefield? mmmmmm lots of warmed up aviation fuel helped that along!