For what it's worth, you have to rear-end a Crown Vic at something like 70 mph to make it explode! It's basically the same old story as those old GM pickups with the saddle tanks mounted outside the frame. Sure, they'll blow up. If you hit them hard enough. Or if you do like Dateline did and strap on a few pounds of explosives! And, incidentally, the accident that caused all the controversy over those GM pickups came up when one got T-boned at something like 73 mph!
I remember reading somewhere that overall, the death rates of GM's big pickups from that era were slightly LOWER than their Ford and Dodge competition. Interestingly, even the Pinto, that infamous
Barbeque that Seats Four had an overall death rate about similar to other small cars of the time.
As for hanging gas tanks out behind the rear axle, car makers had been doing that almost since the dawn of automotive history. Just about every RWD car ever made, at least until they started coming up with independent rear suspensions and finding ways to get the gas tanks up under the back seat, had the tank mounted behind the rear axle. I think the problem with Ford, though, might have been that their design was a bit different. Most RWD cars just strapped on a wide, but shallow gas tank under the trunk. Ford made the gas tank more vertical and put it right behind the rear axle. The result was that the trunk had a nice, deep well behind the gas tank, and a more shallow shelf up over the tank and the rear axle, where the spare tire went. Other cars had trunks that were wider and went further forward, but didn't have that nice deep well.
Well, when a car gets rear-ended, especially a body-on-frame car, the first place it usually buckles is right over the rear axle. Now you'd think that having a gas tank further forward would be safer, and a Crown Vic has its tank further forward than something like a Caprice, Diplomat, etc. But when the car buckles, the tank would get pinched between the trunk well and the rear axle, and rupture.
I used to have a Gran Fury, and it had a little shield mounted between the rear axle and the gas tank. It just looked like it was made out of rubber, and I don't know if it would've done much good in a rear-ender. But evidently, Chrysler saw fit to put it there, so maybe they knew something that Ford didn't?
Still, I wouldn't be afraid of a Crown Vic just because of the fire incidents. If you spend most of your time stopped along high-speed freeways, then you might want to reconsider. But they're not going to blow up if someone backs into it in the parking lot. Or bumps it at 11 mph with a '72 Impala...
http://www.motherjones.com/news/feature/1977/09/compress.mov