Oxygen is scarce above 10,000 feet, yet we take for granted that as the plane slices through the stratosphere at 35,000 feet, we’re on the inside, breathing easy. That’s all thanks to cabin pressurization, first introduced in 1939 with the Boeing Stratoliner. This invention revolutionized air travel, allowing aircraft to fly higher in low-friction atmosphere while maintaining cabin air pressure and oxygen levels equivalent to those at 8,000 feet.
Modern aircraft are equipped with ventilation systems so efficient you hardly notice they are there. Air flows constantly into the cabin via ceiling ducts and back out through vents near the floor. It is refreshed every few minutes, more often than in your home or office.