RedactedNarrative: The operator and three other occupants were in the vessel as it was being backed into the water. Only the propeller was in the water when the operator told the driver of the pickup to stop. The operator said that he turned on the blower and then immediately tried to start the boat. On the second turn of the key the engine housing exploded into the air and a stream of fire ran down a channel from the stern to the bow. The two occupants sitting on the port side near the open channel were burned as they tried to exit the boat. The operator and front occupant did not get injured. The fire exstinguisher was used and the fire was put out. The 3 year old occupant and his mother were taken by abulance to Independence ER for severe burns.