I found a picture of a car with melted door panels strangely compelling (it was first brought to my attention by Dave of The Stuffed Dog).
The picture is of (as far as I can tell) a 1997 Saturn SL that was parked too close to (but not inside) a forest fire. What is curious is that even though the door panels have melted, the windows are still intact and the tires have not exploded (apparently, heat related tire explosions can occur before the tire pressure is exceeded thanks to pyrolysis, which has absolutely nothing to do with anything). Also, an intact steering wheel is visible. This struck me as curious. Then someone in the lab mentioned that the Saturn was not made entirely of metal.
Of course! The dent resistant panels! The rust proof bumpers!
Saturn prides itself on the thermoplastic panels and bumpers used in their cars. As it turns out, a few different thermoplastics* are used in the construction of Saturn cars. I've listed these below, along with their softening temperatures:
GTX (fenders and quarter panels): 300-400° F
Pulse (door skins): 200-250° F
Thermoplastic Olefin (bumpers): 100-120° F
Pulse, a polycarbonate and acrylonitrile butadiene styrene blend is manufactured by the Dow Chemical Company. I am not sure which of the many flavors of Pulse is used in the doors of the Saturn SL; however, the properties of the various types of Pulse seem to be fairly similar, more or less. At any rate, Pulse is almost certainly the material that has melted and resolidified in the wacky news photo.
This is, of course, not the least bit surprising. Pulse is a thermoplastic. Thermoplastics are neat, fun, and generally well liked by the manufacturing industry because your can heat them up, pour them into a mold, and then watch them resolidify. This is a good thing in a factory. It's just that no car designer in their right mind worries about people who park too close to forest fires (especially after being told not to by Smokey the Bear). So no one considered the ramifications of bumpers that start softening around the temperature on a hot July in Phoenix, and doors that follow around the boiling point of water. And that's OK, I guess.
Also: because wood burns at about 617° F, it's not surprising that a plastic car would melt in close proximity to a fire, even with the lousy conduction of air. What is fortunate is that the temperature was not quite high enough for the melted pool of plastic to catch fire, as such events are quite volatile, and would thus make lousy wacky news photos.
So, to finally get to (or completely miss) the point of this diversion: Under no circumstances should you boil a Saturn in water.
* PDF version, which includes an important table
Wednesday, June 26th, 2002
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