Let's put the risk in perspective.
Do you ever drive on the freeway? You are in a vehicle constructed of combustible materials which emit poisonous fumes when burned, carrying 10-20 gallons of highly volatile fuel sloshing around in a tank held in place by metal straps exposed to salt crusted roads, surrounded by hundreds of other drivers in similar conveyances, all travelling at 65-75 mph... and you lived to tell the tale.
The best defense against fire is to ensure that you are on top of your maintenance. Make sure your hoses and lines are in good shape, your extinguisher(s) are charged and well -located, you have adequate exhaust blowers, and you know how to maintain your boat.