Be careful after fueling up.
Refueling Danger
According to BoatUS Marine Insurance, the industry has seen several explosion claims that occurred right after refueling.
Gasoline, like other vapors, has an "upper explosive limit," or UEL. Too high a concentration means it can't ignite. A leaking fuel-fill hose can allow gas to collect in the bilge, making vapor concentration too high to ignite. This prevents engines from starting because there are too many gas fumes and not enough air to support combustion inside the engine.
But as fresh air gets mixed with the vapors, say after opening the engine cover, the fumes become less concentrated than the UEL, and a spark from a faulty starter or bilge-pump switch can ignite the fumes in a spectacular way. If your boat refuses to start right after fueling, immediately check for a gasoline spill.