Quote:
Originally Posted by tophcfa
Being trapped for over three hours in a germ tube, while breathing recirculated air, is a very bad idea.
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That is probably the most widely circulated rumor on how an aircraft cabin air system works. It's almost as bad as the STD in The Villages rumor.
THE TRUTH ABOUT CABIN AIR
Filthy, germ-laden, rotten, disgusting, wretched, skanky, rancid, putrid, fetid, and fart-filled are just a few of the adjectives used to describe cabin air, and legion are the accounts of flyers allegedly made ill by microscopic pathogens circulating throughout a plane. In reality, the air is very clean.
On all modern aircraft, passengers and crew breathe a mixture of fresh and recirculated air. Using this combination rather than fresh air only makes it easier to regulate temperature and helps maintain a bit of humidity (more on the humidity in a moment). The supply is bled from the compressor sections of the engines. Compressed air is very hot, but the compressors only compress; there is no contact with combustion gasses. From there it is plumbed into air conditioning units for cooling. It’s then ducted into the cabin through louvers, vents, and the eyeball gaspers above your seat. The AC units are known to pilots as “packs.” That’s an acronym for pneumatic air cycle kit. Usually there are two per plane.
The air circulates until eventually it is drawn into the lower fuselage, where about half of it is vented overboard—sucked out by the pressurization outflow valve. The remaining portion is remixed with a fresh supply from the engines and run through filters, and the cycle begins again.
Studies have shown that a crowded airplane is no more germ-laden than other enclosed spaces—and usually less. Those underfloor filters are described by manufacturers as being of hospital quality. I needn’t be reminded that hospitals are notorious viral incubators, but Boeing says that between 94 and 99.9 percent of airborne microbes are captured, and there’s a total changeover of air every two or three minutes — far more frequently than occurs in offices, movie theaters, or classrooms.