RedactedNarrative: Operator left cover to engine compartment open during fueling.  He failed to ventilate following its completion.  While leaving the marina he heard a bang and saw that the engine compartment cover was blown off and the engine compartment was on fire.  He attempted to fight the fire with an extinguisher onboard to no avail.  All occupants left the vessel and were rescued by a near by boat.  One occupant sfufered burns to her arm.