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Aviation Halon Fire Protection

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Cockpit Fire Extinguishers   "The Aviation Consumer"

In our view, there's only one choice: Halon.
Better buy it while you still can.

We would never suggest that the average 30-year-old airplane is a firetrap, but there's enough gasoline, oil and worn electrical wiring in close proximity to make an in-flight fire a real possibility. That's why most pilots carry fire extinguishers.

Under FAR Part 91, they aren't required but they most definitely are for commercial operations, for large (more than 12,500 pounds) and turbine powered multiengine airplanes and under transport aircraft certification regulations. As it usually does on matters of safety, the FAA has both rules and suggestions on the subject of fire extinguishers. The suggestions are found in Advisory Circular 20-42C.

It strongly encourages the use of Halon-filled extinguishers as the fire fighting agent of choice in aircraft. Only problem is, Halon has been judged a danger to the ozone layer and it's no longer in production. You can still get it, but it's getting increasingly expensive. Should you cut the price corner, then, and make do with a cheap hardware store extinguisher? We think that would be a mistake.

What Is This Stuff?

Halon is a halogenated hydrocarbon, consisting of a potpourri of carbon, fluorine, chlorine and bromine. It's stored as a liquefied gas in the extinguisher and comes in several varieties denoted by four-digit names, such as Halon 1211 and Halon 1301. (for the curious, those numbers signify the number of carbon, fluorine, chlorine and bromine atoms present in each molecule
of the agent.)

Halon 1211 is what's known as a "streaming agent," because when discharged, it shoots out in a stream of mostly liquid. Halon 1301 is a "flooding agent" and discharges mostly as a gas, giving better penetration into compact areas such as those under the panel.

Halon 1301 is less prone than Halon 1211 to making undesirable decomposition products in an enclosed space. These variants of Halon have different properties but both are very effective in interrupting combustion, as opposed to smothering the fire, as other agents do. Also, Halon leaves no residue to corrode avionics or airframes.

The downside of Halon is that it and other CFCs were the subject of a 1987 United Nations protocol signed by the United States and nearly 100 other nations, which essentially banned production of Halon for most purposes by the year 2000. In November 1992, that cutoff was accelerated to January 1994 with a more than $40 per pound excise tax on the Halon being imposed
here in the U.S.

The only Halon sources today are from existing first-run stocks and recycled material collected from old fire extinguishing systems in aircraft, computer rooms, libraries, etc. At least aviation is permitted to continue to use Halon "until further notice," because the United Nations has recognized that no effective substitute agents for firefighting in aircraft yet exist. Heavy Halon users such as the military and airlines, where Halon-charged systems protect engine, lavatory and cargo compartments are scrambling for an effective replacement agent.


The search for a replacement is being pushed by Boeing and the Air Force and coordinated through the FAA's Atlantic City Technical Center. We see this process taking months, if not years. The saving grace, if there is any, is the economic incentive for manufacturers and airlines to get this settled, quickly. It's hardly a Manhattan Project, but the airlines need a solution and GA will probably tag along.

Meanwhile, what is the Bugsmasher crowd to do? To begin with, we recommend, without hesitation or equivocation, that every aircraft should have a properly maintained extinguisher on board. Even beyond the specter of in-flight fires (a recurring nightmare for us all), why stand by helplessly watching your machine melt to puddles of molten aluminum when a shot or two from an extinguisher could put out a fire caused by a carb backfire or an electrical short?

Few ramps are equipped with sufficient extinguishers, so carry your own for less than the cost of a $100 hamburger. Not to sound like environmental clods, but we say better to have a few holes in the ozone layer than your pants on fire: Go with Halon, as the FAA recommends.

Here's why: the FAA estimates that as of 1990, 250,000 Halon fire systems were in use, containing about 50,000 tons of the product. Aerospace uses consumed only about 5 percent of that total. The occasional discharge of 2 1/2-pound Halon bottle carried in a Cherokee is insignificant in this calculus. Driving the point home is that from a GA perspective, no other agent is, in our opinion, as safe as Halon for humans or equipment in the cockpit. The options to Halon just aren't acceptable.

The Choices

The fire threat in an aircraft is a mixed bag of ordinary combustible materials; fabrics, headliners, rubber and such, making up what's known as Class A fires. Fires fueled by flammable liquids are Class B fires and those involving energized electrical equipment in which the non- conductivity of the agent is critical are called Class C blazes. Any agent for aircraft needs to be effective on these types of fires, relatively light in weight and of low toxicity in the closed cabin environment. Remember, a standard part of most in flight fire checklists is to cut off ventilation, so check your AFM.

Extinguishers are rated by Underwriters Lab on their effectiveness against the various classes of fires. For example, 5B:C means that the extinguisher is appropriate for flammable liquid or electrical fires, with the numbers indicating relative effectiveness on a benchmark size fire. Extinguishers rated as 4B should be twice as effective on flammable liquid fires as ones rated 2B,
and so on.

The Big Chill

Carbon dioxide is a popular agent and you can buy extinguishers appropriate for Class B and C fires. You'd think that since CO2 is an inert gas it would be ideal for closed-cabin use. That's not quite right, for several reasons. For one thing CO2 extinguishers are heavy. To get the same firefighting potential out of CO2 for B and C class fires as a 3 pound bottle of Halon, the CO2 extinguisher will tip the scales at upwards of 14 pounds and costs $250. Try to muscle that up under the panel to put out a smoldering circuit breaker.

More to the point, in concentrations necessary to extinguish a fire, a blast of CO2 won't leave you enough oxygen to sustain life. You need about a 34 percent concentration of CO2 to snuff out a fire. At concentrations above 9 percent, loss of consciousness will occur, death follows for concentrations above 20 percent for more than 20 minutes.

CO2 is also hard on avionics. On discharge, gas expansion results in a rapid cooling that will cold-shock components into oblivion. So in addition to killing yourself and your passengers, you'll trash your radios.

Cheap But Deadly

Dry chemical extinguishers are ubiquitous around hardware stores. Little wonder, since they are effective on a side range of fires. Twenty bucks will get you about 2 1/2 pounds of monoammonium phosphate, a common dry chemical agent. Blow a bottle in an aircraft cabin, however, and you'll likely be scraping a layer of it off the windows in order to maneuver the aircraft to a safe off-airport emergency landing. It will also corrode the avionics to the point where thousand of dollars of unnecessary damage may be done by the extinguisher itself. We can't say this strongly enough: If you have a dry chemical extinguisher in the cockpit, know that the cure for fire may be as bad as the disease.

How They Work

Halon does none of the these bad things and it's several times more effective per unit of weight than CO2. Not all is a bed of roses, however, Some decomposition products of Halon in a fire may result in dizziness, impaired coordination and reduced mental acuity. In balancing these risks against the fire itself, the FAA says carbon monoxide, heat, smoke and oxygen depletion, are more immediate dangers than are the decomposition products of Halon.

Just to see how effective these agents are, we compared Halon against CO2 and a dry chemical bottle. This was purely backyard pyromania; we claim no scientific basis for our tests. Still, the results were impressive. For a test bed, we glued upholstery fabric to foam backing somewhat similar to the material used for aircraft interior panels. We dabbed on a shot glass full of gasoline and ignited the panel.

Our Halon extinguisher put out this blazing mess with just a squirt or two and in minimum time. There was no reignition after only part of the 2 1/2 pound bottle was used. We were happy that the extinguisher had enough for another go,
if needed.

Using a fresh, identical panel, we next tried the CO2. It took about twice as long as Halon to put out the blaze. Worse, once the fire appeared to be out, it flamed right back and needed to be smothered again with the CO2. By the end of the second try, the bottle was nearly empty and this fire was not particularly large.

The several types of dry chemicals we tried were nearly as effective as Halon in extinguishing the fire. The resulting mess was a sight to behold, however, with powder swirling in the light breeze and coating everything in sight. The air was full of a biting, sour-tasting white dust. We can only imagine trying to fly in a closed cabin with the stuff in the air; parachutes would be preferable.


Where To Get It

Most of the aviation discount houses carry what we learned is about the only remaining type of Halon extinguisher easily available to pilots. It's made by Incendex International, Inc. of Montreal, Canada, and is filled with a mix of Halon 1211 and 1301 called Halonaire. It's UL rated as 5B:C, although the box says it's suitable for Class A fires, too. Street prices are about $80 for a 2 1/2 pound extinguisher and $50 dollars for a smaller unit. Go for the larger size, it's not that big and you surely don't want to run out if smoke and flames threaten.

Although we would prefer to see a directable hose attached to the extinguisher to permit aiming the discharge at the fire while holding the bottle upright (as the instructions direct), this extinguisher put out a robust stream of the gas/liquid mixture. We're sure it would reach up under the panel, if need be.

The distributor of the Halon extinguisher, NFPA, Inc. 1-800-249-4289) in San Francisco, says the extinguisher has a 20-year shelf life, with interim maintenance consisting of a monthly inspection to ensure that the nozzle is unobstructed. To check the contents, you can either heft the unit, or weigh it, to see if it's the same weight as when new. It's non-refillable, according to the distributor and manufacturer, but the 20-year shelf life should largely preclude the need for refilling to maintain a full charge.

If you have a Halon extinguisher now and you either used it or the gauge/hefting test says that it needs to be refilled, take it down to the nearest fire extinguisher services shop. Chances are good that one with a metal valve/trigger assembly can be refilled with recycled agent and basically overhauled with replacement of the rings and seals for about $40 per pound of agent used. Many shops won't recharge similar units with plastic valves/triggers, but some will, and there isn't any harm in asking around.

Current stocks of Halon at many aviation supply houses are reported to be good and will probably last for some time. (One supplier told us that there were literally hundreds of the Incendex bottles in stock.)

We were unable to track down Incendex and were told by one source that it's still in business while another said it has been liquidated. In any case, current stocks must last until a manufacturer comes forward or a suitable replacement is found. Panic isn't in order but it makes sense to buy sooner rather than later as prices will continue to escalate.

Aviation fire extinguishers are sold through aviation distributors world wide.
or email us for a distributor in your area


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