You won't. It's one of those things that can only happen when there are a whole series of things going wrong in a very small time frame. The KJ fuel tank is plastic (asis the case with most modern vehicles), so if there is a VERY substantial rear impact, it may rupture. Actually, its less likely to rupture than a steel tank - mostly it just deforms.
Petrol doesn't explode, as you see it on tv and films. Many years ago I was on a course (paid for by Her Majesty's Government) and just for a laugh, a couple of us stuck 8oz of C4 under the target car's fuel tank, trotted back about 50 yards and then hit the remote. There was an almighty bang when the C4 detonated, but rather than a huge wallop as the fuel tank detonated with immediate and impressive flames(as they always do in films) we simply got showered in petrol. Now - if someone had then struck a match and ignited the vapour that came off our soaked clothes - it would not have been a barrel of laughs.
Google/search news sites for accidents of this kind - very rare.