I think a lot of these precautions go back to the days of piston engine ac using high octane gasoline. As has been said, it's difficult to get kerosene to burn under these circumstances BUT kerosene in vapour form is a different matter if the temp and air mix is right.
I seem to remember that the USAF operated a turboprop back in the 60s called the C133 which had a habit of disappearing on overwater flights. Wreckage indicated an explosion in an empty tank and I believe it was concluded that the explosion was related to the use of the HF. Maybe someone has more info?