RedactedNarrative: I, Game Warden was on patrol aboard my patrol vessel on July 1st, 2018 at Boulder Beach at Lake Mead at approximately 1458 hours when I heard a call over the National Park Services (NPS) radio channel of a vessel (V1) on fire at the fuel dock in Hemenway Harbor. 
  
       V1 was a 1988 Carver yacht, 27 feet in length, stern drive, duel engine, model 27 Santego .
  
       Owner had recently purchased V1. He operated the vessel for the first time on June 30th, 2018. V1 was not fueled that day. V1 ran without issue. On July 1st, 2018, Operator took V1 out for a day trip with his family.
  
       V1 started without issue. V1 was taken to the fuel dock. Operator said the engines were turned off followed by the main power breaker. He filled both tanks full and turned the main breaker switch back on. Operator turned the blower switch on for unknown amount of time before attempting to start the engine. No witnesses were able to verify if the blowers were operating. During fueling, the cabin door was left open. The engine would not start. Multiple attempts were made to start V1. Operator asked the fuel dock employees for a tow back to his slip. Fuel dock employees gave Operator a jump box to start the battery. The fuel dock employees explained how to use it. 
  
  Subject1 attached the jump box cables, matching corresponding colors, to the port battery. Operator, Subject1, and subjecr2 said that as the jump box was turned on, an explosion happened. The explosion knocked subject3 into the cabin. Immediately after the first explosion, a second explosion happened in the cabin, causing V1 to “jump”. Subject1 and Subject3 ended up in the water. They were pulled out. The 6 remaining family members were taken off of V1. V1 was doused with fire extinguishers and water from a fire boat. V1 was beached at the shore nearby. 
  
       From the incident Subject1 received inhalational burns, 2% total body surface area burned, partial thickness burns to his left thigh, left arm, left ear and diffuse first degree burns. He was airlifted and taken to UMC hospital. Subject3 received burns to  40% total body surface area, deep partial thickness burns to his face, neck, anterior chest, bilateral upper extremity, and bilateral lower extremity. He was taken by ground to UMC hospital.
  
       Over the next couple of weeks, I interviewed witnesses and examined V1.
  
  Conclusion:  Fuel vapors were present in the engine compartment. The vapors entered the cabin. An ignition source ignited the vapors in the engine compartment which created the first explosion. The first explosion injured Subject3 and Subject1, knocked Subject3 into the cabin, and ignited the vapors in the cabin which created the second explosion. The second explosion caused the vessel to “jump” and the starboard cabin window to blow out. Fuel vapors were present in the vessel which could have been caused from two things. Either there was fuel in the engine compartment from a possible leak in the fuel system or the hull had filled with fuel vapors during fueling and was not sufficiently ventilated to eliminate the vapors. A fuel leak prior to the explosion was undetermined because of the intensity of the explosion and fire. It was undetermined if the vapors were present from insufficient blowing time, lack of power supplied to the blowers, or a failure in the ventilation system because of the intensity of the explosion and fire. The ignition source was by or near the jump box or battery.