RedactedNarrative: OPERATOR 1 AND PASSENGER 1 WERE DOING MAINTENANCE ON VESSEL 1 WHILE CHECKING THE SPARK PLUGS ON VESSEL 1. AS OPERATOR 1 REMOVED A SPARK PLUG AND STARTED THE VESSEL THE OTHER SPARK PLUG SPARKED. THE SPARK FROM THE SPARK PLUG CAUSED FUMES IN THE ENGINE COMPARTMENT TO CREATE A FLASH FIRE. THE FIRE CAUGHT PASSENGER 2 AND THIS CAUSED THEM TO SUSTAIN INJURIES. THE OPERATOR WAS NOT INJURED AND THERE WAS NO DAMAGE TO VESSEL 1.