http://osf02.ktu.edu.tr/~ulutas/hoover/engine_fires.html 

My opinion " this is a more rare occurance - cutting the metal fuel line "
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The more common problem is the steel pipes in the fuel pump coming out and the fuel pump spraying fuel all over the place, which can catch fire.

Buy and use the expensive ful line and clamps. Not the silly sollys or crazy clints crap and you shouldn't have too much trouble. P.S. do the clamps up tight.

yeah the most common cause is neglect! fuel lines cracking or fittings coming loose. Fitting a filter between pump and carb is silly.

My Kombi fuel lines are well clamped, but something occurred the other day that made me wonder about the cause of VW engine fires.
The HT lead from coil to distributor dropped off at the coil end where it points down. The engine had been cutting out before it just died in traffic.
While the connection was loose, I guess there might have been some sparking.
Is it possible this could cause engine fires, not only the usual suspect of the heat of the engine itself?
I thought it worth raising this issue, it might be an idea to make sure your coil to distributor HT lead in particular is well secured.

YES - especially in a Type 1 upright motor running a PICT carb.
The Pict 34 often leaks at the bushing and drips petrol - right onto the side of the distributor.

Check your PICT's