Fire Protection for Passengers

Now that an effective system for fighting fires on the main decks of cargo airlifters has been developed, it’s time to consider the same protection for passengers on airliners. The next time you’re on an airliner, look up. Do you see anything like those little circles denoting the water spray of a fire extinguishing system found in every public building? Nope. Yeah, there are fire alarms in the lavatories, to alert the crew if the used paper towels in the trash bin catch fire, but there’s no suppression; a flight attendant has to rush into the lavatory with a hand-held extinguisher.

As far as the rest of the passenger cabin, there’s no fire detection or suppression whatsoever.

Federal Express (FedEx) has developed a system for detecting and combating fires in the cargo containers crammed onto the main decks of its airlifters. Basically, upon detection by infrared of a heat source indicating fire in one of the containers, a ceiling mounted nozzle deploys, plunges through the cargo container, and squirts a foam suppressant. Pretty neat, and long overdue, as fires are three times more likely on cargo airplanes than on passenger planes. (See Aviation Safety Journal, ‘New Fire Suppression System for Cargo Aircraft’)

There are a number of reasons why passengers should have similar protection:

— Are people less valued than cargo? That is the implicit message of the current disparity.

— There are more electronics being installed in the cabin of a modern jetliner, with all their potential for an electrical fire. Consider new seats that transform into lie-flat beds; these seats feature five or more electrical motors, associated wiring, etc.

— More electrical systems are now contained in the cabin sidewalls, where arcing could lead to a fire between the sidewall panel and outer skin of the airplane that spreads and finally bursts through with deadly effect.

— There is a moral imperative here: are people going to be allowed to burn to death, or die from noxious smoke inhalation, when life saving technology is available?

— Why should airliner cabins be prone to uncontained fires when every square inch of every public building requires detection and suppression? The example of a nursing home is instructive. The residents have limited mobility (old age, requiring walkers, or bedridden), they can’t get out of the building quickly, so fire suppression covers every area of the facility (rooms, halls, common areas, etc.). Airline passengers are like nursing home residents; healthy, yes, but their mobility is restricted until the airplane on fire can conduct an emergency landing. Passengers have to remain in their seats until the word is passed to evacuate.

Burned out interior of a Continental B737 that overran the runway at Denver 20 December 2008. Fortunately, no one was killed, but the adsence of fire protection in the main cabin heightened the risk of serious injury and death.

Burned out interior of a Continental B737 that overran the runway at Denver 20 December 2008. Fortunately, no one was killed, but the adsence of fire protection in the main cabin heightened the risk of serious injury and death.

The FedEx system would not be suitable for passenger airliners, as it relies on argon and foam to quench the fire. But a system based on ultra-fine water mist has been tested successfully in a retired B737 airliner. The system used the airplane’s on board potable water supply, atomized the fluid, routed it under low pressure though plastic piping, and squirted it out of nozzles placed between overhead bins.

To those who have witnessed the tests, the mist is so fine that it almost doesn’t even feel wet. But it does work, quenching fires and, maybe even more importantly, delaying flashover – the ignition of flammable gases near the ceiling – which can be deadlier than the actual fire.

Objections to the system seem to focus on three aspects:

1. It uses the airplane’s water supply to save weight. One of the objections is that a passenger may want a drink, and if this system is used fire firefighting, there won’t be any water for human consumption. This really was a serious objection. One can only ask who’s going to want a drink when the airplane’s on fire?

2. The second objection is that the water mist would interfere with the workings of aircraft electronics. Tests have found this not to be the case.

3. The third objection is cost. Let’s suppose the system costs $100,000 to install in a 100-seat airliner. That works out to less than $2 per passenger ticket over the course of a year’s flights. Say the system has a design life (before overhaul) of eight years. The price is about 25¢ a ticket. In other words, trivial.

This is doable.