[Trevor Booth]

The case for fuel cells in side mounted tanks.
I have attached (hopefully) a couple of sketches representing a tube frame chassis before and after a frontal impact. This is very simplified and indicates the likely deformation. The difference between a tube frame and a mono is basically that a tube frame has little or no progressive crumple. This is due in part to the slenderness ratio of long thin members evident in a tube frame chassis. The front and rear sections are usually well supported with braces and may form a very rigid structure or "box". The cockpit area is most likely to suffer deformation of members 1 & 3 and probably outwards being "driven" by the engine mass behind it. In this event the fuel tanks are likely to be deformed and possibly rupture. A rigid tank with no foam is not what I would call safe, foam will help, two shorter tanks on either side are better than one long tank, but a flexible fuel cell with foam is less likely to rupture. Wheels and suspension components are unlikely to rupture a tank in a frontal impact. The photo of the Ford crash indicates that the wheels have not impacted the tank or if they did it was not a severe impact. It is possible to construct a tube frame chassis to minimise collapse of the passenger area but one needs to be careful that the chassis is then not too rigid and having little capacity to absorb energy. In this event the occupants become a write off and the car survives!!
If you want to be safe a fuel cell will give you the best chance and of course proper connections, clamps , hoses etc (not water delivery hose which I have seen on some cars)

The other consideration is a side impact, there are many documented cases of a massive fire after a side impact. An escape of fuel similar to the Ford crash could result in an explosion and a fire suppressant system will do very little in this situation.
Cheers