Before Commercial Airplanes Were Pressurized, Passengers Required Oxygen Masks at High Altitudes

Before pressurized cabins changed aviation forever, flying high was a serious and risky business. In the 1930s, commercial aircraft reaching altitudes of 10,000–12,000 feet (about 3,000–3,600 meters) didn’t have the technology to maintain breathable air pressure inside the cabin. So how did passengers survive the thin air? They wore bulky oxygen masks for the entire flight, and yes, it looked as dramatic as it sounds.

In the 1930s and early 1940s, cabins were not sealed or pressurized, so flying above 10,000–12,000 feet meant passengers and crew were exposed to dangerously thin air and low oxygen levels (hypoxia). Photos at the time show passengers wearing prominent, often bulky, face masks made of rubber or fabric. They resembled early military aviation masks more than the small, modern emergency masks. These were connected via a tube to an onboard, manual oxygen supply system. Oxygen usually flowed continuously, which could be inefficient and contribute to frost accumulation in cold cabins.

A major innovation in the late 1930s was the Boothby-Lovelace-Bulbulian (BLB) mask, developed at the Mayo Clinic in 1938. This was a more effective oronasal (covering both nose and mouth) mask design that reduced oxygen waste and was quickly adopted by the military and airlines. It was more comfortable and reliable than earlier “pipe-stem” devices or ill-fitting masks.

Oxygen mask technology improved significantly during World War II, with advancements like the A-14 mask (an enhancement of the BLB mask) that incorporated automatic diluter-demand systems for more efficient oxygen use, primarily for military pilots.

The early 1940s marked a pivotal transition with the introduction of the first commercial airliners featuring pressurized cabins, such as the Boeing 307 Stratoliner in 1940. This technological leap allowed aircraft to maintain a comfortable, near-sea-level cabin environment at high altitudes, making routine oxygen mask use obsolete for passengers.

The need for passengers to routinely wear oxygen masks disappeared as pressurized airliners became more common. Oxygen masks transitioned from standard equipment to the emergency backup systems we know today, used only in the event of a sudden loss of cabin pressure.