Stamped Caution by Raymond Z. Gallun, Science Fiction, Fantasy 12+

📖 Ten minutes after the crackup, somebody phoned for the Army. That meant us. The black smoke of the fire, and the oily residues, which were later analyzed, proved the presence of a probable petroleum derivative. The oil was heavily tainted with radioactivity. Most likely it was fuel from the odd, conchlike reaction-motors, the exact principles of which died, as far as we were concerned, with the crash.