Bottom line up-front: Having any rated fire blanket aboard and at hand in your bunk or chart table is a great idea; they’re cheap, effective and clean. A combination of ABC and BC dry chemical extinguishers, mounted in intelligent locations is recommended – and don’t be shy about having more than the minimum USCG requirements. A fire port on an inboard engine enclosure is also recommended. Be aware of the unique hazards presented by Li-based batteries (large and small) and have a plan to match. Make sure your installation includes a tested, high-quality battery management system. Class-D extinguishers are not needed with LiFePO4 batteries.
Discussion
The large (~6X6 ft for ~$45) fire blanket referred to above is essentially the same as the one I showed in my ‘Yacht Fire Safety’ presentation (slide 27/35), and what I have on Frolic. Another smaller (3X3 ft for ~$15) option, less $ and space claim, is this:
http://www.amazon.com/Hot-Headz-Fir...8&qid=1461002996&sr=8-1&keywords=fire+blanket
The smaller fire blanket is certainly better than nothing, and should be suitable for a galley fire, and either is much more convenient than dumping a pound or more of dry chemical (fine powder) in the cabin (what a mess!). I’m tempted to switch to it, and move the bigger blanket to my garage. Note that the larger blanket can be wrapped around a person with clothes afire, while the smaller blanket is probably too small for that. But wool blankets will fill that function. If you have a galley fire involving propane, don’t forget to stop the gas flow as quickly as practical.
After the galley, the next most likely fire sources are the engine or an electrical fault. Engine fires are likely to involve fuel (or on some boats hydraulic fluid) and best attacked via a fire port with a good B-rated handheld extinguisher. The fire port is a small hole in the engine enclosure that allows you to attack an inboard engine fire without opening the enclosure and feeding the fire with clean air. Electrical fires may involve burning solids, like plastic and wood, and if so an A-rated extinguisher is recommended. For these reasons, it is recommended to have at least one good ABC extinguisher on hand. But be aware that ABC agents are ammonium phosphate based powder which are somewhat corrosive to metals, and irritating to breathe. If the amount of solid involved in the fire is ‘small’ then most BC dry chemical extinguishers (sodium or potassium bicarbonate) should be adequate, and they are less corrosive and irritating than ABC dry chemical. Note that while both sodium- and potassium-bicarbonates are rated BC, potassium-bicarbonate is roughly twice as effective by weight. A big boat could consider the bulkier and heavier CO2 (BC) extinguisher, but beware of using CO2 in a confined space (suffocation risk). So-called clean BC agents are available ($$$) and their advantage is that they become gaseous when discharged so no cleanup is necessary, and in normal use they aren’t an asphyxiation hazard. But beware of fluorinated agents (most clean agents and all Halons) as firefighting byproducts include seriously toxic gases. There are no toxic byproducts or other inhalation issues associated with the dry chemicals, they are just messy. Finally, keep in mind that in a pinch, BC agents can be augmented with the vastly available A-rated agent available to a floating yacht: sea water (another use for the scared sailor with a bucket). But be very careful if you have an inverter on – while fairly harmless with exposed 12 VDC circuits, salt water and 120 VAC can be shocking. In fact, for any electrical fire it’s generally a good first step to disconnect the batteries and make sure that the electrical system is down.
One of the most important things about extinguishers is how they are installed. Rather than mounting an extinguisher in the galley so that you may be compelled to reach thru fire to get it, mount the extinguisher near where you sleep and/or in the cockpit. Mount them with metal brackets (throw away the cheap plastic ones) so they are available when you need them. Don’t be shy about having more firefighting equipment aboard than the minimum USCG requirements! Think through the most likely scenarios and be prepared for those and similar.
Regarding Li-ion battery fires… Recommended protection depends on the type of Li-based battery and its size and support system (ie, battery management system). A class-D (rated for metal fires) extinguisher is really only needed for Li-based batteries that include a significant amount of Li metal in their construction, and only if the first recommended action – tossing the burning battery overboard – isn’t an option (got tongs and a metal bucket?). Most house batteries installed on yachts these days are LiFePO4 and these are currently the safest Li-based batteries for this application, especially if installed correctly with a high-quality battery management system. But, like any battery, they can fail, and unlike lead-acid, the electrolyte is flammable. However burning metal isn’t a primary fire source so a class D extinguisher isn’t needed for LiFePO4. And, unlike more energy-dense Li-based batteries, a LiFePO4 is very unlikely to produce enough heat to create an open flame or to melt through the boat bottom. But if a LiFePO4 (or any Li-based) battery does have a thermal event (and like any high-density electrical storage device, they can), then be prepared to deal with a lot of toxic smoke that may render the cabin uninhabitable for a while. The discharged gas, while not at flame temperature, is hot enough to ignite nearby solids, for example thin plastic or wood, paper, etc. Such a secondary fire would call for an ABC extinguisher, or a good douse of water. As with any big battery, mount the LiFePO4 in an enclosure that isolates it from such easily combustible materials. Other higher energy density Li-based batteries may warrant a stainless steel enclosure.
