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Understanding boat fires

Here is some insight from Daniel K. Rutherford's three decades as a marine investigator:
• Most fires, excluding arson, are fuel- or electrical-related — "If it's a fuel fire, we're probably dealing with a leak in a hose or fitting, maybe a tank," he says. "It's probably a single-source leak of some kind that results in gas vapor accumulation with some sort of an ignition spark."

• Reaction time is essential — "If you have a Type ABC extinguisher on board and hit the fire quickly, you have a good chance of putting it out. Believe it or not, the fuel burning is not a super-hot fire. But once the fire spreads into the fiberglass or wiring or hoses, then it's fully involved with multiple sources and much more difficult to fight."

• False sense of security — "The insidious thing about electrical fires is that you can put the fire out, but until you disconnect the electrical circuit you're not putting out the source," Rutherford says. He recalls a case in which a boater was installing a freshly charged battery at the start of a season, not knowing that the conductor that led to an aluminum panel had shorted out. This caused a spark that ignited gases from the battery. The boater emptied his fire extinguisher snuffing out the flames. "But the conductor wasn't removed, so the battery terminal was still glowing hot and reignited the fire, which subsequently destroyed the boat."

• At the marina — Most boat fires at marinas are caused by problematic shore power connections. Both ends need to be clean and free of any evidence of corrosion and inspected regularly for evidence of arcing or melting. The cause of these fires usually is not at the pedestal, but at the boat.

• Away from the docks — "Under way fires on smaller boats with outboard engines are almost always fuel-related, with fires starting in the powerhead or at the fuel line connection at the engine," Rutherford says. "On I/Os, the fire typically starts at the exhaust hose from the exhaust elbow to the transom. This is caused by rust and scale accumulation within the manifold that eventually blocks the outgoing water flow that cools the exhaust before it gets to the rubber hose leading out of the transom. Heat builds up, the hose catches fire and the driver doesn't usually know because the smoke is light and any odor is trailing the boat. The engine is running fine. The hose eventually melts and, since it's in close proximity to fiberglass or electrical wires, it's too late."

See related articles:

- Setting boats ablaze in the name of safety

- Use the right extinguisher

October 2012 issue