How To Handle An Engine Compartment Fire

The most natural reaction to an engine compartment fire is also the worst — opening up the hatch to see what's going on. Doing so provides a rush of oxygen that could easily turn a smoldering fire into an abandon-ship conflagration. A fire port or automatic fixed extinguishing system is the safest approach to contain and extinguish an engine compartment fire. Here's a look at how both options work, along with installation considerations for each.

Fire Ports

The American Boat and Yacht Council (ABYC) recommends that all inboard and sterndrive vessels not protected by a fixed fire extinguishing system have a suitable means of discharging fire extinguishing agent into the space without opening the primary access panels. Fire ports are small hatches or ports that allow discharge of a portable, clean agent fire extinguisher directly into the engine room without opening panels (and providing additional oxygen to the fire).

Note the term "clean agent" simply means the extinguishing agent leaves no residue behind (more on this in a moment). The dry chemical powder extinguishers typically found onboard are effective, but the powder is highly corrosive and the residue is difficult to remove. In some cases, dry chemical residue can actually cause more damage to the engine than the fire itself.

Of more importance from a firefighting standpoint, however, is that dry chemical extinguishers have to be aimed directly at the base of the fire to be effective, something that's likely impossible when using a fire port in a cramped engine compartment.

Fire Port And Portable Extinguisher Installation

Fire ports are simple to install. Select a suitable location and, using the pattern provided by the manufacturer, drill or cut the mounting hole. Seal any exposed coring to prevent moisture entry, then mount the fire port per the instructions. For gasoline-powered vessels, mount the fire port as close to the carburetor as possible for maximum effectiveness.

When selecting a portable fire extinguisher for use with the fire port, ensure the port is large enough to accept the extinguisher discharge nozzle. The extinguisher must also be able to be properly discharged in accordance with the manufacturer's instructions (such as a vertical discharge position) and be sufficiently sized to service the entire engine compartment.

Fixed Fire Suppression Systems

While the use of a fire port and portable extinguisher is preferable to opening an engine compartment to fight a fire, there are several drawbacks:

• The rate of discharge, distribution, and effective concentration of extinguishing agent is reduced.

• Fire detection and action depend on human intervention.

• The crewmember or operator must ensure the discharge of the agent is continuous and complete.

• The longer discharge time required to empty a portable unit into the space gives the fire more time to produce additional toxic fumes and by-products before being extinguished.

A fixed fire extinguishing system, by comparison, provides quick, automatic discharge of extinguishing agent as soon as trouble starts. "Automatic" is a key word here, but the system should also include a manual discharge control located outside the engine compartment, enabling immediate discharge of the system in the event you or a crewmember spots a fire before the auto-discharge mechanism kicks in.

How They Work

Automatic extinguishers use mechanical triggers (e.g., glass, metal) that break or melt at a predetermined temperature, typically around 175 F. Extinguishing agent is then released, flooding the entire engine compartment and extinguishing the fire (as opposed to the point-and-shoot method required with a portable dry chemical extinguisher).

You may remember halon was the clean agent extinguishant of choice for putting out engine compartment fires in the past. However, it's also an ozone-destroying chlorofluorocarbon, and as such, its production has been banned since the mid-1990s. If you have a halon system, note that it can still be used, as long as the system passes its annual inspection.

Today's fixed systems typically use FM-200 (heptaflouropropane) or FE-241 (chlorotetrafluoroethane) as a fire suppressant. High concentrations of FM-200 and FM-241 are deadly, but pre-engineered units contain amounts that are below toxic levels when installed in the size compartment they are designed to service. CO2 is an additional suppression system option.

Fixed fire suppression systems can be customized for your particular vessel, but most boaters will simply buy an off-the-shelf, or "pre-engineered," system based on the size of their engine compartment. This type of system is both cheaper and easier to install.

Planning The Installation

The first step in planning a fixed install is determining what size unit is required to adequately service your engine compartment. Start by calculating the cubic volume of the engine compartment, which can be found by multiplying compartment length times width times height. If the space contains fuel, water, or holding tanks, you can calculate their gross volume and subtract that from the overall cubic volume of the engine compartment (giving you its net volume). Another option is to ignore the space taken up by installed equipment. Doing so provides an additional margin of safety by providing more extinguishing agent.

Once you've calculated engine compartment volume, refer to the manufacturer's specifications for choosing the correct size unit. If your engine compartment opens to an adjoining bilge or compartment, you'll have to add its volume to the engine compartment's volume prior to selecting a system. Select a size that meets or exceeds your requirements. If in doubt, go larger.

A good pre-installation tip is to mount a thermometer in the engine room and measure the temperature during normal operation. Engine room temps are typically around 130 F, but keep in mind a poorly ventilated or well-insulated compartment can exceed the temperatures required to discharge the system.

Installation

Cylinders for larger, fixed systems are typically mounted vertically on the forward or aft bulkhead, while the smaller cylinders for pre-engineered systems can be installed either vertically (with the sensor/discharge port up) or horizontally on an engine compartment bulkhead or overhead (depending on the unit). Although you'll always want to follow specific manufacturer instructions when installing a fixed system (see page 78 for step-by-step installation), there are some general guidelines that can be applied to most any installation:

• Install cylinders and controls so they are protected from weather and mechanical damage. Cylinders must be both securely mounted and accessible for maintenance (i.e., removal for weighing, inspection).

• If mounting the cylinder on a bulkhead, locate it as high up and as close to centerline as possible, with the actuator pointing toward the opposite bulkhead or the engine. If mounted on the engine compartment overhead, the actuator should be in the center of the compartment with the cylinder parallel to the keel, the top facing the bow, and the actuator pointing down. Having the unit centered and up high helps ensure the sensor will more readily detect a fire from all points of the compartment and quickly discharge, blanketing as much of the space as quickly as possible.

• Do not mount the unit on the underside of a hatch or access door, which could be blown open or off in the event of an explosion. Avoid locating sensors near engine exhaust manifolds, turbochargers, or other engine components that could cause the unit to accidentally discharge due to radiated heat.

• Don't mount the extinguisher near exhaust or intake vents, which could delay discharge by reducing engine compartment temperatures near the sensor.

• Ensure the system is installed so it doesn't trap or rest in water, which could lead to corrosion.

• Never combine the volume of two smaller, separate cylinders in an effort to meet the volume of a single cylinder. The two cylinders could discharge at different times, failing to blanket the compartment with a high enough concentration of extinguishing agent to extinguish the fire.

• As mentioned, all automatic installations should be equipped with some type of manual discharge control, the most common being a pull cable and release mechanism. The pull handle should be installed near the helm, if possible, but outside the engine compartment in any case. Route the cable between the pull handle and cylinder with as few bends as possible. If installing the handle at the helm, following the steering or engine control cable run works well in many cases. An audible and visual alarm at the helm (to alert you in the event the system discharges) is also desirable.

In Case Of Fire

Whether you use a fire port or an automatic fixed system, shut down the engine as soon as possible in the event of a fire. A running engine can pump fire suppressant out of the engine compartment while continuing to suck in fresh air. Most automatic units have an option for installing an automatic engine shutdown, another excellent idea that is often a manufacturer's requirement for diesel engines.

Many automatic extinguishing systems also have the ability to shut down additional equipment, such as generators or exhaust fans (to prevent venting of the extinguishing agent from the space). If your engine utilizes a mechanical shutdown (air or fuel starvation), discuss the options for converting it to an electrical shutdown system with the manufacturer.

Because a clean agent unit kills the fire without damaging the engine and components, boaters can often restart the engine and return to port under their own power once the initial cause of the fire has been corrected. As such, make sure you have the ability to bypass any shutdown systems installed to bring the engine back up once the fire has been extinguished.