As I understand it, jet A and jet A1 are NOT wide cut fuels. JP4 is the wide cut fuel. Wide cut means a larger number of the fractions of oil distillation. This is what makes JP4 lethal to handle. At room temperatures in an open container, jet A is too lean to burn, avgas is too rich and JP4 is just right. I have watched the old demo - toss a cigarette butt into a can of jet A and avgas no problems, but I've never met any survivors using JP4. It certainly impresses the apprentices when someone flicks a butt into a can of fuel!!!