- main or a day tank - are OK until you have a fuel system fire.
Granted, a pretty rare event, but if it happens and if you don't have a remote
shut off or a shut off valve outside of the engine room then the entire contents of the fuel tank
(one gallon up to +20 gallons) can feed the fire.
Not a good thing.....
If you have a large enough dry chemical extinguisher (at least 5-lb, 10-lb better yet) you can usually - note usually - get the fire out, but you will still have fuel freely flowing into the engine space.
Again, not a good thing.....so have a plan for immediately shutting off/plugging the fuel outlet. After you have shut off the batteries! You don't need damaged energized electrical wiring
re-igniting the fuel with you inside the compartment trying to stop the leak!
A fire fighting "trick" that is very handy to know, eventhough it is sort of a "last chance" way of getting the fire out, is to pour water
into the fuel tank via the deck
fuel fill. Water
is heavier than fuel, so sinks to the bottom of the tank - where the gravity fuel outlet is. After a few seconds you will have non-flammable water coming out of the leak instead of a flammable liquid.
Depending on the size of the hole and the shape of your fuel tank, a couple of gallons of water may be enough to do the trick, although you can pour in more to be safe.
You will still need to extinguish the burning fuel that has already leaked out, but at least gravity is not adding more fuel to the fire.