CLEANING AIRCRAFT AIR WOULD MAKE FLYING A LOT SAFER AND HEALTHIER IN COMMERICIAL JETS.

*We draw today from The Economist, Sept. 19th-25th, 2009 Edition.

One of the common and most pervasive concerns of passengers on commerical jets is the fact that many become ill during the flight. No matter what airlines tell you, having a large group of people couped up in a relatively small area for an amount of time increases the risk of catching an infection.

Viral diseases like Swine Flu have spread quickly around the world because of air travel. There are also pollutants to worry about such as engine fumes leaking into the passenger compartment.

A new developement could help ease this situation and help passengers and crew breathe more easily. Just this week (Sept. 19, 2009), two British firm; BAE Systems (a defense and Aerospace giant) and Quest International (a small producerof equipment used to sanitise the air in hospitals and nursing homes) have announced that they had successfully adapted Quest's technology for use in aircraft. They made this bold claim on behalf of their new company, called AirManager. Uniquely, it can be retro-fitted during a routine overnight service and uses less power than a light bulb, but is capable of zapping just about all the bacteria, viruses and other biohazards in cabin air, as well as destroying chemical contaminants and pollutants. And it kills nasty smells as well.

Basic Air Flow:
Air has to be pumped into the fuselage of an aircraft once it flies above 3000 meters (9,800 feet) because from there the air outside starts to become thin with too little oxygen to keep people alive. In the early days of commercial flight, when piston engines turned propellars, electrical generators were used to provied the power to pressurise the cabin. But with the arrival of faster, higher flying jets, aircraft makers found it more efficient to pressurise the fuselage by "bleeding" some of the air entering the compressor stage of the actual jet turbine (before it was mixed with fuel of course). At first, only fresh air was taken from the engines, but as jets have become more fuel efficient, air bled from the engine has been mixed with recycled air from the cabin. Why? Because the big fans mounted on modern "high bypass" jet engines achieve thrust more efficiently by sending a larger volume of air around the turbine as opposed to through the turbine. Thus, with less air now available in the compressor, any that is bled off means the turbine has to work harder, which in turn only adds to precious fuel consumption. A compromise was reached: a 50:50 mixture of fresh and recirculated cabin air is used although pilots can reduce the amount of fresh air to save fuel.

Mixture:
The mixed air is maintained in the cabin at a pressure which is equal to an altitude of 2,500 meters and is passed through the well known HEPA filters. (high efficiency particulate arrest) Provided they are cleaned regularly, and that is a big "IF", HEPA filters can grab a sizeable amount of microscopic particles. Still, some nasties get through.

Clean The Air:
The new AirManager system is said to kill 99.999% of all pathogens in a single pass. Even on a short flight, the cabin air will pass through the filters around 30 times. Quest says the mechanism is a non-thermal plasma using a high voltage screen to strip electrons from some of the molecules in a gas. The plasma is confined using an electric field grid and the cabin air is passed through this. The free electrons disrupt the molecular bonds of any particles in the air, causing them to break up into electrically charged pieces. A second electrically charged filter trap grabs these pieces like fly paper.

Cost:
Each unit costs $16,000. Not too bad but the bigger the plane, the more of these gadgets are needed. Still, in the long run, it would be worth the passenger comfort and health to install these small, energy efficient cleaners. They would all pay for themselves in a year by reducing the air that has to be bled from the turbines;  thus letting the new engines work as designed for maximum fuel efficiency.

Dr. Haberstroh is a Somerville and Boston Chiropractor.