Combustible.

The look of utter disbelief on Dean's despairing face was amusing and it was all Sam could do not to laugh outright. They both knew that gunpowder residue was highly combustible but neither of them had anticipated that the spilt jar of black powder would cause such chaos.

Had Sam realised that his accidental spillage had gotten all over Dean's laundry bag he would have been more careful throwing the shovels in the trunk and the spark would not have made toast of Dean's every pair of jockey shorts.

"Well, Dean. You always told me you were red hot stuff!"