In an airplane cabin there are a lot of passengers in close proximity in a confined space. Often many people are coughing, sneezing and perhaps have other ailments. What is the air quality like, in airplane cabins ?
Question asked by Jurgen.
Air in an airplane cabin comes in from outside of the airplane. This ambient air at high altitudes, is clean and cold (as cold as -70 C or more). The air is essentially dry, sterile and dust free, but low in partial pressure of oxygen, in fact, too low to sustain life. Therefore, the air must be compressed to a density that is healthy for passengers and crew.
The airflow is continuous and is used for maintaining a comfortable cabin temperature, pressurization and overall air quality. About half of the air exiting the cabin is exhausted from the airplane through one or more outflow valves, which also control the cabin pressure. The other half is drawn by fans through High Efficiency Particulate Air (HEPA) filters under the cabin floor, and then is mixed with the outside air coming in from the engine compressors. The HEPA filters are very effective at trapping microscopic particles such as bacteria and viruses and can provide essentially particle free air in the recirculation system. Because of the way these filters are designed, their efficiency actually increases for particles both smaller and larger than the most penetrating particle size, which is about 0.1 to 0.2 microns. The efficiency of HEPA filters to remove bacteria and viruses is greater than 99 percent. Recirculating 50% of the air provides several benefits. It increases air humidity in the passenger cabin, which improves passenger comfort, especially on long haul flights. It also reduces level of ozone in the cabin air and improves engine fuel consumption.
The air flow in the cabin is from the ceiling area, towards the sidewalls and out through the grills at the floor level. The air does not flow lengthwise through the cabin. Thus if air might be contaminated in one area of the cabin, it will not be spread to other areas.
The air in the cabin is completely replaced every two to three minutes. The air is of much better quality than air in an average home or an office building.
A bit more about Captain Dan:
Captain Dan Baz enrolled in Flight School at the age of 16.
He has completed studies in Aircraft Engineering and Master of Business Administration. He has been at the controls of many different types of aircraft, from single engine Cessnas to large intercontinental jets on global routes.
Over the last four decades he has flown thousands of hours up in the blue sky.
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