A Primer on Fire Extinguishers

It was at 4,500 feet on a dark night near Purcell, OK, when the rear seat passenger of a Piper Warrior noticed the seat getting warm and the smell of smoke. Very quickly, the passengers found themselves attempting to control an in-flight fire with...


As a Part 91 operator, why do you care if your extinguisher is approved by UL? It comes down to quality. UL-approved extinguishers meet industry standards for safety in storage and use. It means, if properly maintained, the tank won’t corrode and burst at 10,000 feet. The valves and o-ring seals won’t crack and leak at -20 F. The handle won’t fall off when you bring it up to use it. The additional cost to have the UL rating is insignificant and, considering the number of years the extinguisher will hide in your airplane, becomes meaningless as a decision factor. It’s pointless to buy anything else.

What kind of ­extinguisher to use?
In choosing a fire extinguisher, you need to consider the aftermath of using it. Once the fire is out, improper extinguisher selection may cause short-term and long-term issues with the pilot/passengers as well as the aircraft.

A carbon dioxide extinguisher, while effective in smothering a fire, can also be effective in smothering the occupants. The enclosed space of an aircraft cabin will trap the gas and, unless you’re using oxygen or you can get your nose right up to the cabin vents, the accident report may show cause as pilot incapacitation. CO2 can be deadly in an airplane cockpit.

Dry chemical extinguishers can cause visibility and breathing problems if used in the close-in environment of the cockpit. The chemical powder can cause almost immediate problems with avionics and the corrosive nature of the extinguishing agent can have you cleaning and treating the airframe for years.

Other types, like water, may be good for one type of fire (paper/wood combustibles) but not good for another (like electrical and/or flammable liquid); the effects of water on avionics is so obvious it doesn’t warrant discussion.

The far-and-away best, FAA-endorsed, choice for aircraft fire extinguishers is the Halon extinguisher. Halon dispenses from the extinguisher in an easily aimed, longer range stream that vaporizes almost instantly when it comes in contact with a hot surface and stops a fire by displacing the oxygen feeding the fire.

Halon is incredibly effective in stopping fire. It has been found to stop combustion in extremely low concentrations (well below 5 percent); it is so effective at fire control it is used in sealed ultra-high-voltage switch boxes (at power stations and such) to eliminate arcing of the contact points, thus stopping the arc-induced wear on the contacts. And, unlike CO2, Halon has low toxicity so the airplane can be landed after the fire is out.

If Halon is the perfect fire extinguishing agent, why doesn’t everyone use it for everything? Well, it’s been found to have some undesirable effects on the earth’s ozone layer (this has been contested by several organizations). Halon, it was discovered in the ‘80s, floats around in the stratosphere and breaks down over time (50-100 years), releasing chlorine that is destructive to ozone. In 1994, the Montreal Protocol ozone-protecting international treaty ended Halon production. Halon continues to be stockpiled for use in aviation and other industries requiring its unique capabilities because of its ideal aviation fire-fighting qualities. Because of its limited use, Halon extinguishers are expensive compared to the others; a decent one for aircraft will run about $150-plus. But, a pocket full of money is worth little at 10,000 feet as you notice a glow under the instrument panel.

Not described in AC 20-42C is a fairly new product that, according to the manufacturer, has been FAA-approved as a substitute for Halon. The fire-fighting agent, called “Halotron I,” has been developed as an ozone-protecting answer to Halon. From available information, Halotron has the benefits of Halon but the knock-down effectiveness of Halotron is slightly less and requires a little larger quantity fire extinguisher to provide equivalent protection.

Regardless of extinguisher type, all should have a label describing proper operation the pilot needs to familiarize him-/herself with prior to flying the aircraft. This is especially true of rental pilots who may deal with several different brands of extinguishers.

Continued air­worthiness of fire ­extinguishers
As a piece of emergency equipment, the FAA requires air carriers to have a maintenance program for fire extinguishers. Part 91 operators should also be equally concerned with their extinguishers, so let’s move on to extinguisher care.

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