Flares will burn, and keep burning, once lit. I wouldn't consider them to be especially spicy in the whole context though, since anything that has set them off has already lit the rest on fire.
Coincidentally, I'm a volunteer firefighter, and helped put out a fully-involved car fire yesterday. The interior was GONE, except for seat springs and the like. Fuel too, of course, and the tires. The alloy wheels were more interesting, guessing there was magnesium sparking off in great showers of brilliant white. We're concerned around things like gas shocks and bumper / hatch struts, because they will pop off with some violence; we found a hatch strut yesterday, probably 20' _behind_ our truck after we were done. If there had been road flares in the mix, I'd be thinking, "oh, that's pretty".