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Halon fire extinguishers
offer inexpensive protection
against inflight fires.
By Mary Bernard |
When a Swissair MD-11 crashed in 1998 just 30 miles from the Halifax, Nova Scotia, runway it had diverted to, the incident quickly attracted the attention of the FAA, pilots and airline passengers alike. As the Transportation
Safety Board (TSB) of Canada concluded its investigation, it determined
the cause of the crash was likely a fire triggered by a wire-arcing event related to an inflight entertainment network power-supply cable.
But how could this incident have escalated to disaster with all of the airliner's
sophisticated technology and fire suppression equipment on board? Well, the fact that it did points out the urgency
with which all pilots need to quickly detect and extinguish an inflight fire.
Although inflight fires are rare, it is advisable for all aircraft to be equipped with some sort of fire extinguishing equipment. In the case of light aircraft—and most all homebuilts—this will typically
be a portable fire extinguisher. There are limited options for extinguishers, yet determining which one is suitable for your aircraft involves considering a number of factors such as the size of aircraft,
the type of fire to be extinguished, the space available for mounting,
price, practicality, maintenance requirements
and overall effectiveness.
 H3R’s line of Halon fire extinguishers for light aircraft includes a mix of straight 1211 units (with pressure gauges) and blended 1211-1301 units (disposable units without gauges).
Fire Categories
All extinguishers should carry a rating issued by Underwriters Laboratories, the U.S. Coast Guard or another similar
agency. The rating has to do with the type of fire that the extinguisher will address and a benchmark number indicating the extinguisher's effectiveness
against such a fire.
But to understand the rating, it is necessary to understand how fires are classified. A letter is assigned to indicate
the type of materials that may be involved. Class A involves cellulose
materials such as wood, cloth and paper; Class B involves liquid fuels; Class C involves energized electrical equipment; and Class D involves combustible
metals. A 5B:C rating, for example,
means that the extinguisher is appropriate for flammable liquid (Class B) or electrical fires (Class C), and the number indicates the extinguisher's effectiveness
for a fire of a given size. The most common types of fires in light aircraft fall under Classes B and C.
How Extinguishing Agents Work
Today's extinguishers can be divided into two primary types: Halon and alternatives such as carbon dioxide, foam, water and dry chemicals. Halons are chemical action agents (CAAs), meaning that they interact chemically with the fire by removing flame free-radicals. The alternatives to Halon are physical action agents (PAAs), which interact physically with the fire by
absorbing heat. Chemical action agents are generally more effective extinguishants
than the physical type, but the bromine they contain gives them greater ozone depletion potential. Let's start with the PAAs and look at some of the extinguisher types most commonly available to determine their suitability for aviation use.
Physical Action AgentsThe most common PAA extinguisher
types are carbon dioxide and dry chemicals, which are suitable for Class A, B and C fires, depending on the type of powder used.
Dry Chemicals. The National Institute of Standards and Technology (NIST) in 2001 issued a conference report evaluating the effectiveness of various extinguishing agents. They found that "dry chemicals provide rapid knockdown
of flames and are more effective than Halons in most applications."
The disadvantages, however, are significant, especially when it comes to aviation:
- Dry chemicals penetrate poorly behind obstacles and offer no direct cooling of surfaces or fuel.
- Without a doubt, they'll cause major secondary damage to your airplane
including electronic, electromechanical
and mechanical components. The chemicals are highly corrosive and unless washed off immediately—which is virtually impossible—they will corrode
surfaces and components and destroy
the aircraft (or at least the metal portions of it.).
- If discharged in a small space (such as the cockpit during flight), dry chemicals will cause loss of visibility
and respiratory problems. The discharge
creates a choking, blinding dust so instead of trying to fly the aircraft to safety, you’ll be hacking on dry chemical
powder.
Carbon Dioxide. CO2 is the most common inert gas used as a fire extinguishant. According to the NIST, carbon dioxide is “a clean, electrically non-conducive agent with good penetrating
ability.” It is discharged as a gas, but the dry ice that forms may also increase its ability to absorb heat. But again, the disadvantages for aviation use are severe:
- The gas itself is much heavier than Halon, so you’ll have to carry a bigger, heavier bottle to get the same extinguishing capability as Halon.
- If sprayed on avionics (or, for that matter anything electrical), it can shock-cool the components and render them permanently useless.
- Finally—and most significantly
—CO2 removes the oxygen from the air as it works to deter a fire, so you’ll be in danger of suffocating yourself if you use it in the confined space of an aircraft. The choice of carbon dioxide for a hangar or ramp may be appropriate, but not for the confined space of an aircraft cabin. (Needless to say, you don’t want to try to ventilate the cabin at the same time trying to knock down the fire.)
The Halon Advantage
Now that we’ve covered what you should not use in an aircraft, let’s look at what you should: Halon fire extinguishers.
According to H3R, a California-based supplier of Halon extinguishers, Halon, or halogenated hydrocarbon, is a blend of carbon, fluorine, chlorine and bromine.
But why is it so ideal for aviation use? Well, it’s clean, non-volatile and electrically non-conducive. Consider these advantages:
- Halon is an effective agent on Class B and C fires, the ones you’re most likely
to see in an aircraft.
- It works in gas form, so it will not
obscure your vision like the powder
emitted from dry chemical extinguishers.
Basically, it’s invisible.
- As a gas, it’s capable of getting into hard-to-reach places like the inner workings of your instrument panel.
- It’s a non-corrosive clean agent, which means it won’t damage items it comes into contact with.
- It won’t shock-cool your avionics.
- It’s lighter and more efficient
than CO2.
- Halons are low-toxicity, chemically stable compounds.
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At 5B:C, both of these units are rated equally, yet the RT A1200 (left) might make a better choice for aviators. It’s a 1211-1301 blend disposable unit (non-gauged), which means fewer maintenance
requirements, and it weighs less—3.3 pounds gross compared to 4.9 pounds for the gauged, straight 1211 C352TS on the right.
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Sounds perfect, right? Well, there are a few drawbacks.
We said that
Halon has low toxicity. But it’s not benign or entirely non-toxic, and you wouldn’t want to introduce it to your respiratory system given the choice. “But everyone, including the FAA, recognizes
that it’s better to put out the fire effectively than to worry about breathing the Halon,” says Chris
Dieter, marketing and distribution manager for H3R. “Breathing the carbon
monoxide from the smoke is bad in itself. When you do spray Halon, however, try to ventilate the space as soon as possible.”
A perceived disadvantage is availability.
As a chloro-fluorocarbon (CFC), the gas is subject to a ban that took
effect in 1994, and no new Halon is being made today. The only source is Halon recycled from existing extinguishers
and brought up to mil-spec standards. In the U.S., it is legal to buy, sell and use Halon fire extinguishers for aviation, commercial and residential applications.
But according to Dieter, no Halon shortage is imminent and “the eventual
demise of Halon will come not from insufficient supply, but from the development
of an equally effective agent that does not damage the ozone layer and is relatively inexpensive.” He says H3R estimates that Halon will be available
for at least the next 15 years.
Even so, the search is on to find suitable replacements for commercial aviation applications. A few alternatives
are already available—Halotron I is an example—but they’re still more expensive and only half as powerful as Halon. General aviation will undoubtedly
benefit from whatever advancements
are made in that arena.
Types of Halon
Halon comes in three primary types—Halon 1211, Halon 1301 or a blend of the two. Halon 1211 is a liquid streaming
agent—it’s stored as a liquid in the cylinder, but it rapidly turns into a gas when discharged. Nitrogen is used as the propellant, like in most fire extinguishers.
The benefit of liquid storage is that you can shoot the agent 6-15 feet on discharge, but the quick conversion
to gas allows it to start working on the fire immediately. H3R says that the majority of Halon extinguishers sold use straight Halon 1211.
Halon 1301 is a flooding agent that is stored as a gas and discharges as a gas. But according to H3R, there are no 1301 portable extinguishers in use except in the military, and you can’t buy one.
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These two 1211-1301 blend units are likely choices for pilots of one- to four-passenger planes. Both are 2B:C rated—the RT A400 (left) holds slightly less extinguishing agent compared to the RT A600 (right), and therefore weighs very slightly less.
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Halon 1211-1301 extinguishers contain a proprietary blend of the two types of Halon. The benefit here is that the 1301 component of the blend acts as a propellant in the place of nitrogen, which means that both the propellant (1301) and the agent itself (1211) work together to put out the fire.
“A Halon 1211-1301 blend is probably more effective than straight 1211, because you have two distinct agents working on the fire,” Dieter says, “as opposed to a mix with nitrogen,
which does nothing to put out the fire. That being said, if you have a bottle of 2B:C-rated Halon 1211 and a bottle of 2B:C-rated Halon blend, it’s hard to say one’s more effective than the other since the UL rating is the same for each.”
Another advantage of the 1211-1301 blend is that the extinguisher
itself is virtually maintenance free, with no pressure gauge. Gauged units (like straight Halon 1211 extinguishers)
are subject to maintenance regulations
determined by the National Fire Protection Association (NFPA): monthly visual inspections, a six-year maintenance check and a 12-year
hydrostatic cylinder test are required. Both maintenance procedures involve removing the extinguisher from the aircraft and taking it to an appropriate service company.
But the FAA considers the blended
units disposable extinguishers
because they don’t have pressure gauges
and can’t be recharged. Monthly inspections consist of hefting the unit to check the weight and visually
inspecting the unit for damage. In
addition, the extinguisher weight must be checked against the published gross weight every year to verify that no leakage has occurred. These minimal
requirements make blended Halon units ideal for the GA user who wants to mount the extinguisher in the airplane
and basically forget about it.
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Want a designer fire extinguisher? H3R’s line for light aircraft features two chrome-coated cylinders, which provide a classy, durable finish that won’t clash with your interior color scheme. Both the A344TC (2B:C, left) and C352TSC (5B:C, right) are straight 1211 units.
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Size, Weight and Price
For light aircraft use, Halon extinguishers
typically come with a 2B:C rating or a 5B:C rating. According to NFPA Code 408 (Standard for Aircraft Hand
Portable Fire Extinguishers), a 2B:C-rated
extinguisher is considered suitable for a one- to four-seat plane. For larger aircraft, you may want to consider a 5B:C unit. Either is suitable for most light aircraft fires, and either is small enough to be maneuverable in the cockpit.
The fine print on any extinguisher
will state not to use it in confined spaced of less than X cubic feet—check to make sure X isn’t smaller than your cockpit, and you’ll be fine.
H3R offers four 2B:C Halon units (two blends and two straight 1211 extinguishers)
and five 5B:C units (one blend and four straight 1211s). Gross weights for the 2B:C units range from 1.2 to 2.3 pounds, and the 5B:C units weigh between 3.3 and 5.6 pounds. Weight differences are due to cylinder materials (stainless steel vs. aluminum and plastic).
Prices for the 2B:C extinguishers range from about $70 to $100, and the 5B:C units are generally priced between $130 and $170. Distributors for H3R’s extinguishers include Aircraft Spruce, Chief Aircraft and Sporty’s Pilot Shop, among others. Shop around—prices may vary depending on the distributor. Buyers should be aware that shipment of any fire extinguisher requires special handling because it’s a pressurized cylinder—
anticipate extra shipping charges
from most distributors. Charges can range anywhere from a few dollars to $30, depending on how much the distributor
is willing to cover.
How to Help Yourself
Inhalation of toxic gases in smoke is a primary cause of fatalities in most fires, whether in an aircraft cabin or a high-rise building. Have a plan and know your emergency procedures. An adequate, well-placed and well-maintained fire extinguisher can prevent small electrical fires from escalating into major problems that will jeopardize structures or incapacitate the pilot. In any case, the first priority, after flying the plane, should be extinguishing the fire.
While modern aircraft benefit from flame retardant materials and high-quality extinguishers, survivable crashes are often followed by fire. In this case, the first priority for pilot and passengers should be to exit the aircraft. But if you can’t get out—due to injuries, damage to the aircraft or a fire standingin your way—an extinguisher can control a post-crash fire well enough to save lives. This being said, the pilot and passengers should be able to reach the extinguisher even if they are unable to get out of the aircraft. This means mounting it where it can easily be reached. And never allow an extinguisher to roll around loose in the cabin.
Epilog
By the time the Swissair pilots realized the seriousness of their situation, it was already too late. The fire had grown on what fed it: flammable materials and an air conditioning system that moved the fl ames toward the cockpit. Consider the following excerpts from the TSB findings and their implications for GA:
- ”The type of circuit breakers used in the aircraft were similar to those in general aircraft use and were not capable of protecting against all types of wire arcing events.”
- ”There were no built-in smoke and fire detection and suppression devices in the area where the fire started and was propagated, nor were they required by regulation.”
- ”There was no integrated inflight firefighting plan in place...nor was such a plan required by regulation.”
Most private pilots won’t face the kind of complexity the Swissair pilots did when attempting to detect the cause and location of an inflight fire, but swift diagnosis and action to extinguish the fl ames may still mean the difference between survival and its alternative. Homebuilders who construct their own aircraft have an advantage in that within reason they can include as many fire prevention technologies as they can afford. The use of flame-retardant materials in the cockpit, reinforcing the firewall, and installing fire safety equipment in a readily available position can all serve to reduce risk. In the end, a reliable and appropriate portable extinguisher may be the cheapest fire insurance policy a pilot can have.
By Mary Bernard
"KITPLANES" May 2005, Volume XXV Number 6
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H3R aviation fire extinguishers are sold through our distributor partners worldwide.
Email us for a distributor in your area, or call 800.249.4289.
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Aviation Fire Protection