Fire extinguishers on the boat

Two fire extinguishers from Rob MacFarlane’s boat Tiger Beetle with sturdy metal handles and nozzles.
Two fire extinguishers from Rob MacFarlane’s boat Tiger Beetle with sturdy metal handles and nozzles.
Two fire extinguishers from Rob MacFarlane’s boat Tiger Beetle with sturdy metal handles and nozzles.

My boat Tiger Beetle is a 45-foot sailboat, basically a long fiberglass tube with three exits onto deck from the interior: a large foredeck hatch anybody can get through, the companionway with a ladder and steps, and a smaller hatch aft set into the cockpit floor. You need relatively narrow shoulders to fit through the cockpit hatch. These are the ways out if there’s a fire inside the boat.

I keep two types of fire extinguishers onboard: three small dry chemical ABC units for attacking a generic fire, and one Halotron 1 unit specifically for an engine box fire. The dry chemical extinguishers are the inexpensive Kidde 1A 10BC, plastic valves, USCG certified. They are charged with monoammonium phosphate. This chemical is good for ordinary dry combustibles (paper, cloth, wood), flammable liquids (diesel, gasoline, alcohol) and energized electrical equipment.

My dock neighbor, Tim, is a retired Fresno Fire Department captain — his phone number is “911” and he’s worked most fires one can think of: chemical, metal, vehicles, structures, wild land. He and I had a discussion about fire extinguishers as he was returning from having his inspected and re-certified.  I showed him my extinguishers and he strongly suggested that I do NOT want plastic valves on the extinguishers — if I drop the extinguisher the valve can break off, at which point I’ve made a huge mess and no longer have a useful fire extinguisher. Much better to have an aluminum valve so that if dropped it may bend but it’s designed not to break off and I will still have an extinguisher that works.  

Tim pointed out that if there’s a fire in a confined volume, such as inside the boat, there is a short list of things to do:

1. Recognize there’s a fire (have a smoke detector that sounds an alarm).

2. Make sure you have an exit and can get out.

3. Notify someone that can help (if possible).

4. Only attack a fire if you can keep yourself between the fire and the exit – be certain you can get out if the fire doesn’t stop. In other words, always approach a fire with your back towards the exit — never let a fire block your way out.

5. Smoke is deadly, particularly in a confined space, burning plastics and resins are especially nasty.

I have three mounted extinguishers, each located near an exit: one up forward by the foredeck hatch, and two aft outboard on either side of the companionway. If there’s a fire inside the boat there will be at least one extinguisher I can reach without having to pass the fire to get to the extinguisher.  And getting to that extinguisher will put me at an exit. Tim’s suggestion is to put the biggest, best fire extinguisher at the best exit and consider fighting the fire from there.

A significant fire source on Beetle is the propane-fired stove; it’s the one place I can expect to have an open flame on board. For convenience I’ve mounted the propane shutoff solenoid switch at the stove. For safety reasons that switch is also wired through a circuit breaker in the nav station on the other side the boat — both the circuit breaker and the switch have to be turned on to get propane to flow and either control will shut off the propane. I can kill the propane without going near the stove.

Some boats keep a fire blanket in the galley, the idea being to drop it over the stove top and smother a fire. Tim’s suggestion here is simpler — keep a pot lid handy while cooking. If there’s a fire on the stove, put the lid over the pot or pan and turn off the stove. If done carefully, the lid can shield the wrist from flames as the lid is maneuvered into place. Leave the lid in place until it cools down – don’t invite re-ignition by lifting the lid to look.

With an electrical fire the first thing to do is de-energize the circuit. After that, consider an extinguisher or some way to smother the fire (I was the person smothering the fire with a towel on a friend’s boat and towels can get hot). I know where the battery shut-off switches are and have fused all wires at the battery. In an electrical fire it’s likely that what is actually burning is the wire’s insulation.  

Another boat neighbor, Jeremy, had a significant electrical fire in the engine box of his boat. The main positive cable from the starter motor passed above the transmission coupling on its way to the battery; he was motoring along when that cable fell onto the coupling, the metal coupling cut through the insulation, and the cable immediately shorted to ground as the engine and shaft are grounded. The result was lots of smoke from burned insulation and the heat even melted through the adjacent Morse cable transmission shift lever. He later found that the starter cable was never fused at the battery — such a fuse would have minimized the time the circuit was energized.

If there’s an engine box fire the first thing to do is turn off the motor. If the motor won’t stop and there’s time, consider blocking the air intake — this will kill the motor and it doesn’t require opening up access to the engine and introducing more oxygen which can feed the fire. Don’t slap a hand over the intake since the suction created by the engine can damage skin. Use something else to block the intake: a book, towel, dinner plate, block of wood — lots of things can be used to shut down the motor this way. 

Dry chemical extinguishers make an enormous mess when fired off, and one fired into the engine box while the motor is running will allow the engine to suck in powder through the motor’s air intake, which can damage the engine. There are better ways to handle engine room fires than powder extinguishers.

The better extinguisher I have is five pounds of pressurized Halotron 1 liquid. Halotron 1 boils at room temperature, turning into a gas that interferes with the chemical reaction of fire (I haven’t yet found an explanation of what is really going on during the chemical reaction). The Halotron 1 extinguisher on Beetle was sized specifically to the motor box volume. I asked fire extinguisher professionals to engineer the fire protection system. To squirt the Halotron 1 into the engine box I added a circular 1-inch diameter knock-out plate in the plywood box wall. This was easy to do with a plunge router. I cut most of the way through the half-inch thick plywood, leaving a thin veneer on the inside. The hole is sized to the extinguisher nozzle. If there’s a box-fire I can knock out the bit of remaining wood, poke the nozzle in the hole and discharge the extinguisher contents into the box without ever having to open the box. This is useful as I don’t introduce extra oxygen to the problem.

Tim also said to resist the urge to be curious and open the engine box to see what happened. Let it cool down first, it’s not going anywhere. The last thing I want is a re-ignited fire in the engine box.

One detail I definitely know is that I have a fiberglass boat constructed with resin, which is basically flammable oil in a solid form. If the resin holding the hull together ignites and starts to burn it is extremely difficult leaning towards impossible to put out. Essentially, if the hull catches fire I am in danger, skip the extinguishers, head for the exit and get out and away from the boat. To that end I work diligently to minimize ignition sources, look for wire chafe possibilities and protect against it, fuse everything attached to the batteries and don’t block paths to the deck.

I’m off to fetch new extinguishers, preferably those with metal handles that can be recharged!  

Rob MacFarlane has singlehandedly raced and cruised for 30 years on San Francisco Bay, the US West Coast, across to Hawaii, Mexico, Canada, and French Polynesia. He is currently in Southern California waiting for countries to lift Covid-19 restrictions so he can continue cruising the South Pacific aboard his 1983 Morgan N/M 456 IOR two tonner, Tiger Beetle. A retired database architect, he likes the idea that design and function can create simplicity.

By Robert MacFarlane