Fire is likely the greatest threat a recreational sailor can expect to encounter. Unfortunately, everything needed to start a fire is always onboard. Preventing fires should always be a high priority in the management of any vessel. Since fires occur on even the best managed boats, it is the master’s responsibility to ensure that appropriate fire-suppression equipment is onboard and that a fire emergency plan has been prepared, studied by the crew and is readily available, should it be needed.
A brief review of what you already know. A fire, whether controlled and beneficial or uncontrolled and dangerous, requires three elements: fuel, oxygen and a source of ignition. All three are virtually always available on a boat. With the exception of metal-hulled vessels, the boat’s very structure can provide all the fuel needed. Even in metal construction it is common to use combustible materials in the interior bulkheads and furniture. The 21 percent oxygen content of the air we breathe assures an adequate supply of this ingredient. The boat’s electrical system, the galley stove, an oil lamp or other fuel-burning appliance, a fuel leak adjacent to hot engine metal, or failure of the engine’s raw water cooling system can all provide an ignition source. Spontaneous combustion in improperly stored oily rags starts many fires.
The Coast Guard regulations specify the minimum fire extinguisher requirements for recreational craft. The limitations inherent in these requirements must be recognized; they represent the minimum equipment that satisfies the bureaucracy’s view of your safety. The required equipment list will likely fall short of what you believe necessary. A prudent mariner will assume that, regardless of precautions, a fire will occur and will have to be dealt with. Have a plan
Crew and passenger actions upon detection of a fire must be pre-planned. There is no time for discussion or debate during a fire. The boat’s fire emergency checklist should be reviewed by everyone onboard and posted where it can be referred to without delay. Doing the right thing the first time is critical to your success in dealing with a fire onboard. It is generally agreed that the outcome is often decided in the first two minutes after the fire is detected. Coast Guard data shows that approximately 90 percent of fires originate in the engine compartment. The data also shows that only a small percentage of those fires are successfully brought under control with use of the typical dry-chemical extinguisher carried on most recreational vessels.
Deciding how to achieve an acceptable degree of onboard fire safety can begin with a review of the three means by which a fire may be extinguished: excluding the oxygen required for combustion, removing all unburned fuel, cooling the burning material to a temperature below which the fuel won’t burn. A bucket of water works by cooling the blaze; however, it should not be used on fires involving liquid fuels that can be spread by the addition of the water. Use of water on electrical fires is generally undesirable, although on a boat where low-voltage DC power is involved, it can be useful if nothing else is available. Just as in dewatering a flooding bilge, a frightened man with a bucket can move a surprising amount of water. Water-foam extinguishers can be very effective, operating by simultaneously cooling burning fuel and excluding additional oxygen. However, this type of extinguisher is rarely found on small craft. Dry chemical
Gas-pressurized, dry-chemical extinguishers are the most common type used on recreational vessels. These extinguishers blanket the fire with an inert gas that is generated by the reaction of the fire’s heat with the extinguisher’s chemical powder. Once the available oxygen surrounding the burning material has been consumed, combustion will stop. However, the fuel may still be at a temperature high enough to immediately rekindle the fire should the oxygen-excluding gas blanket dissipate. For this reason, any seemingly extinguished fire must be considered a continuing hazard until everything has cooled almost to room temperature. Dry-chemical extinguishers are inexpensive, making it feasible to carry them in relatively large numbers. They require no service, other than an occasional shake to loosen the powder and a check of the pressure gauge to ensure that it is indicating in the green arc. Their major limitations are their limited stream range, requiring that the user be quite close to the fire when discharging the extinguisher, the need to direct the discharge stream accurately at the base of the fire and the limited duration of operation of the small units most often used. Although insignificant compared to the damage done by even the smallest fires, the residue from a dry-chemical extinguisher can create a major mess.
Although most of the portable extinguishers presently offered for use on boats are dry-chemical units, some new, no-residue extinguishers are now available. Offered in 5- and 11-lb units, they are rated as 5BC and 1A10BC, respectively. These extinguishyrs contain Halotron 1, an approved replacement for the now-banned Halon 1211 previously used in handheld extinguishers. These extinguishers are not inexpensive, carrying typical list prices of $260 for the 5-lb model and $516 for the 11-lb unit.
One of the most serious limitations on the use of any portable extinguisher for fighting a fire in an engine compartment, or other enclosed space, is the need to gain access to the space to direct the extinguishing agent at the fire. Opening an access hatch can deliver enough oxygen to turn a smoldering fire into an inferno. At a minimum, all engine and other machinery compartments should be fitted with small fire ports into which the nozzle of the fire extinguisher can be inserted without allowing the entry of a significant amount of air. Carbon-dioxide units
The shortcomings of dry-chemical extinguishers in all applications, including boats, led to the development of extinguishers that discharge either a vaporizing liquid or an inert gas. These extinguishers operate primarily by depriving the fire of oxygen. Carbon-dioxide extinguishers, once the standard for engine space protection, operate by excluding oxygen and, when directed at the heart of the fire, rapidly cooling the fuel to a temperature below that required to support continued combustion. Although very effective, this type of extinguisher requires a rather large and heavy wall container to safely deal with the pressure required to maintain the CO2 in liquid form. The carbon dioxide that excludes oxygen from the fire can also asphyxiate the occupants, making it dangerous to use this type of extinguisher below deck.
The need for extinguishing systems that can be used safely in occupied spaces and would not create the collateral damage caused by water, water-foam or dry-chemical agents led to the development of Halon chemical extinguishers. These extinguishing agents and their replacements operate by simultaneously reducing the oxygen available and by rapid cooling.
Although the Halon 1301 and 1211 agents were highly effective, they are chlorofluorocarbons and considered a hazard to the Earth’s atmospheric ozone. Due to this concern, they, along with a host of other related chemicals, including many refrigerants (R-12 and others), were banned by the Montreal Protocol. Many alternate hydrochlorofluorocarbon chemicals, including refrigerant R-22, will be phased out in the coming years. Halon replacements
At this time, two chemicals are available for use in fire-suppression systems suitable for boats: FE-241 and FM-200. These extinguishers are designed for fixed installation and are equipped with automatic-release, heat-sensitive discharge valves. FM-200 is considered safe for use in an enclosed, occupied space. The concentration of gas required for fire suppression is about 7 percent of the air volume, somewhat higher than when 1301 and 1211 were used. Safe concentration for FM-200 in occupied spaces has been established at 9 percent in areas without mandated egress times and 10.5 percent where evacuation times have been set. If one of these devices discharges, it is unlikely that anyone will need to be urged to leave the compartment. FM-200-filled extinguishers are more costly than those filled with FE-241. An FE-241-filled extinguisher, capable of protecting a 100-cubic-foot volume, carries a list price of $275. Filled with FM-200, the cost is $375. The cost differential increases with the volume of space to be protected due to the need for increasingly more FM-200.
|
These portables by Fireboy-Xintex are highly pressurized, using argon gas, that enables a user to stand as far as 10 feet away from a fire.Since FE-241 and FM-200 are flooding devices, the size of the extinguisher required to protect a compartment depends on the total volume in the space. A typical 75-cubic-foot engine space on a sailboat will require 3.9 lbs of FE-241 or 5.0 lbs of FM-200. The extinguisher for either agent measures 3 inches in diameter and 15 inches long. The amount of chemical per cubic foot does not vary linearly; therefore, it is necessary to consult the manufacturer’s data sheets to determine the appropriate size unit for a particular application. Extinguishers are normally equipped with an automatic, heat-activated release valve set at 165° F (74° C). A combined automatic/remote manual activation system operates at 175° F (79° C) or by pulling a mechanical release. It is advisable to check the maximum normal operating temperature in any compartment where an extinguisher installation is planned. There are a number of boats where an equipment space, typically a generator compartment, may routinely reach temperatures very close to 165° F. To maintain Coast Guard approval of the extinguishing system, the mechanical discharge cable must be installed when the higher release temperature valve is used. The cost differential for a remote-release-equipped extinguisher is typically less than $25, plus the cost of the remote cable assembly that varies with the length of the cable and ranges from about $50 to $120.
The discharge of a properly sized and installed FE-241 or FM-200 extinguisher in an engine space will extinguish the fire; however, it may not shut down an operating diesel engine. Should the engine continue to operate, it will simultaneously pump some of the fire suppressant from the space and draw in an additional quantity of oxygen-containing air. This can allow the fire to re-ignite. For this reason it is necessary to install an automatic engine shutdown accessory if the system is to meet Coast Guard requirements. The automatic diesel engine shutdown accessory will cost about $240 additional.
In the event an automatic system discharges into the engine or generator compartment, do not immediately open any inspection ports or hatches to check on the state of things. It is best to wait a few minutes for things to cool down. Allowing the entry of air to the compartment will dilute the concentration of extinguishing gas, and this could well allow the fire to start anew.
A fixed-installation fire-protection system for the engine and other machinery spaces is not cheap, but its cost will be instantly forgotten if you ever need it to fight a fire onboard your boat.
� Contributing Editor Chuck Husick is a sailor, pilot and instructor for the Ocean Navigator School of Seamanship.
