RedactedNarrative: The houseboat was parked on Beer Can Island for 5 days. During that time the river level dropped significantly causing the stern of the houseboat to lower creating a significant angle from bow to stern. As a result, the rear of the swim platform was under water. This created a trapped pocket of air under the swim platform where any gas vapor would be ventilated from the blowers and would not be ventilated to the outside air because of this trapped space under the swim platform.  The 4 blowers were running for approximately 20 minutes as Operator was going to fill up on gas and water at the marina. One of the blowers squeaks initially and then goes away after a few minutes. Operator was on the upper deck when attempted to start the port engine when the explosion occurred.  Operator used multiple fire extinguishers to put out the fire at the engine compartment. Vessel 2 was tied to and moored near the swim platform. Operator pushed the fishing boat away from the houseboat as there was fire around this boat. Operator used river water to extinguish the flames near the swim platform. The fishing boat only sustained damage in the form of soot rom the fire and a plastic fitting melted.  Operator stated he had not replaced or modified the two engines or generators in any way other than winterizing all 3. Operator stated he had not made any changes to the wiring in the engine compartment. 
  
  Investigator located numerous cut wires, exposed wires and spliced wires in the engine compartment, which could be possible ignition sources. Very few of the wires were labeled and tracking each individual wire through the houseboat was not possible.  Both engines and the generator looked to be unaltered mechanically and I did not observe any obvious potential ignition sources.   Water was still intruding through the hull in various places, but the bilge pump was keeping up.  Investigator observed the Halon fire suppression system capsule was still intact. The ventilation hoses were noticeably burned. No other noticeable damage was observed in the engine compartment other than the generator being off its mount and breaches in the hull. The 3 engine hatch doors broke from their hinges and the carpet edge closest to the rear of the engine hatch doors was melted. There was damage to some of the interior walls from the pressure of the explosion. 
  
  A Fire Consultant performed the fire investigation for the insurance company.  Consultant stated it was his opinion that the houseboat was not designed to be beached because the angle the houseboat was at resulted in the swim platform being underwater. As a result, any gas fumes were not allowed to be ventilated out the transom and away from the boat because they were trapped in the pocket of air under the swim platform. Subject also stated the amount and proximity and use/disposal of smoking materials (cigarettes) at the stern of the boat could have been a possible ignition source.  Consultant stated he was not able to pinpoint an ignition source, but noted there were numerous exposed wires, cut wires and non-marine wire connections, which could have all been possible ignition sources. Consultant stated it was his belief there was not much of a fire after the explosion as evident from minimal fire damage and described the incident as a “flash fire.”
  