By Marisa Garcia
Ensuring all passengers get fresh, comfortable cabin air is understandably complex. But airplane manufacturers have spent decades mastering the science.
Planes fly in conditions that are inhospitable to life. Outside temperatures can vary from -68º Fahrenheit to as low as -85º Fahrenheit. Outside the aircraft, pressure at 35,000 feet is only 3.47 pounds per square inch of absolute pressure (PSIA), compared to 14.67 PSIA on the ground.
Boeing’s Dr. David R. Space, an associate technical fellow in the Boeing Commercial Airplanes Environmental Controls Systems group, explained that aircraft air systems are designed to keep cabin pressure at a suitable level for humans, while ensuring that the air we breathe is fresh and that the temperature is comfortable. These processes are interrelated.
Cycling air through the cabin builds the pressure we need. Airplanes work on a 50/50 share of internal and external air, and the air is never static.
“The outside air portion comes into compressors and is compressed to a density which makes the oxygen safe to breathe,” Space told Travel + Leisure.
“That process makes the air hot, so it has to be cooled. The air then flows into a big chamber called a mixing manifold, where it’s mixed with recirculated air from the cabin, after that cabin air has been through a specialized HEPA (high efficiency particulate air) filter. The mixed air then travels through air ducts on the plane, from back to front, and to connecting ducts, where the ceiling meets the sideboard. At the same time, air leaves the cabin through return air grills, where the cabin meets the floor. Half of the cabin air is dumped overboard, keeping a continuous flow of air.”
As Space explained, the rate at which the air is dumped creates pressure in the cabin. The exchange rate of air in the cabin is higher than most other environments, like our home, office, or most other public spaces. “There are between 12 to15 air changes in an hour and 25 to 30 cycles through a HEPA filter,” he said.
The filters used to clean airplane air are of the same quality used in operating rooms. These HEPA filters can capture very small particles, including the majority of viruses and bacteria. The outside air is naturally sterile, because of the atmospheric conditions at altitude.
Cabin air management systems are even more sophisticated on modern aircraft, like the 787 Dreamliner, where the pressure is lowered to equal 6,000 feet of altitude. That’s a far more comfortable 11.78 PSIA, which also helps alleviate the fatigue we feel from flying.