Here's a post from another site for your info. Has anyone contemplated installing or actually installed breakaway valves at critical places (e.g. wing root, firewall)? If so, what are the pros and cons and what are the best valves? Does anyone know what valves are used on military light aircraft like the Cessna 172 military versions?

http://www.homebuiltairplanes.com/forums/general-experimental-aviat...

Pretty much every military helicopter and aircraft in the US has them. The US Army has effectively reduced the rate of deaths due to fire and smoke in survivable crashes of its helicopter fleet to the single digits for roughly the past 20 years through the use of improved fuel tanks and breakaway fuel lines. It's not unusual to find the tank sitting completely outside of the helicopter but still full of fuel.

For small aircraft, you would ideally want to have the valves at the tank and at any point the line is firmly anchored (at the firewall for example). This would also reduce the risk of fires associated with the engine being broken from its mountings in a crash sequence.

WT