They come in an array of styles, sizes, and types--which will soon become more confusing.
If a newer system best suits your needs, don 't put off the purchase.
The U.S. Coast Guard requires motor boats to carry fire extinguishers and the wisdom of
that is beyond question. But here are many choices to be made--how many, how large, what
kind, where to put them. Our aim is to provide an overview and some general discussion of
fire extinguisher needs.
Fire extinguishers are classified according to the kinds of fires they can combat. Class A
fires involve ordinary solid combustibles: paper, wood, plastic, rubber and textiles.
Class B involves combustible liquids, oil, fuels and greases. Class C fires include
electrically live appliances or connections. On a boat, class B is the most serious worry
and is the minimum requirement for all Coast Guard-approved extinguishers, though most are
rated for class C and many for class A, as well (see Figure 1].
The Coast Guard has two size classes, although Underwriters Laboratories' ratings are much
more commonly known [see Figure 2 for a comparison of CG and UL. ratings). A UL. rating of
40B, for example, means four times the capacity of a 0 B-rated model against a class B
fire. No number accompanies the C rating; it only indicates safety for electrical fires.
We did not perform tests on fire extinguishers. The UL tests are universally recognized
and our tests would only be repetitive.
Effective Fire-Fighting Agents The most widely used fire-fighting agent is water,
and that's always available to a boater. But boat fires most often involve grease, oil, or
fuel--most boat fires begin in the engine compartment--and water is the last thing to
throw on that kind of fire. Burning oil can be dispersed by the water, instantly producing
a widespread, nastier fire. If you keep a bucket handy, make sure you don't use it on any
oil or electrical fire.
Carbon dioxide effectively smothers fires, but is not commonly used in small boat systems.
It's not safe in an enclosed, occupied space (because it displaces the air and
asphyxiates living/breathing creatures) and it
will drift or blow away in the open. CO2 extinguishers are also large and heavy
compared to others of similar capacity.
Most marine fire extinguishers today use either dry chemicals or Halon gas. Dry chemicals
are used in portable, hand-held extinguishers. They spew a mist of powdered chemical to
smother the fire. "All-purpose" or "multipurpose" models use ammonium
phosphate, which is effective against all three kinds of fires. They carry UL class A, B,
and C ratings. Sodium bicarbonate models aren't effective against class A fires, but are
particularly effective against burning grease. They have UL class B and C ratings. Both
dry chemicals leave a messy, corrosive residue that complicates cleanup after a minor fire
and can damage electronic equipment, which must be checked very thoroughly before being
put back in service.
Halon gas has become the mariner's favorite, but it will no longer be available after this
year (see "End of the Road for Halon"]. Halon is a
heavier-than-air gas that chemically interferes with combustion. Although UL-listed for
extinguishing all types of fires, its effectiveness on class A fires is limited. It's most
effective in a closed space, such as an engine compartment, and less so in open spaces
where the gas can drift or blow away too quickly. When that happens, the concentration of
Halon can fall below that needed to quell the flames and the fire could re-ignite. Halon
is used in all remote-mounted extinguishers for automatic protection of engine
compartments, as well as in portables. It's relatively non-toxic and, unlike dry
chemicals, leaves no messy, damaging residue.
Automatic Extinguishers Remote-mounted extinguishers, designed for permanent mounting in
an inboard-engine compartment, are automatically triggered by heat, much like the
sprinklers in a commercial building. A metal or glass-enclosed link melts or breaks at the
prescribed temperature to discharge the gas. They're completely mechanical; no electricity
is needed for them to work. Coast Guard-approved remote extinguishers have a pressure
switch and a separate indicator light to warn if the extinguisher has discharged.
Also available are models with a manual cable release to enable the skipper to poll the
cord from the helm and discharge the Halon even before the automatic valve opens, if
trouble appears obvious. Remote extinguishers range in list price from less than $200 to
over $1,000, depending on the size and choice of options. Remote extinguishers can't be
recharged after use: they must be replaced. Replacements for discharged Halon cylinders
are often offered at one-third to one half of list price.
Diesel engines present a special problem, though. A diesel will continue to run in a Halon
atmosphere and consume the Halon, thereby reducing its concentration and allowing the fire
to re-flash. It's important to shut off the engine immediately to prevent that. Some
automatic engine shutoffs, actuated by the remote extinguisher's indicator switch, are
available. One special, manually-operated remote extinguisher is made for outboard motors.
It's discussed in the sidebar below.
In general, with a gas engine as well as with a diesel--and whether you do it manually or
have an automatic switch do it for you-you should be prepared to shut down the engine at
the first hint of an engine fire.