Decompression & hypoxia

Modern aircraft cabins are pressurized to simulate a much lower altitude than the aircraft actually cruises at — typically equivalent to around 6,000-8,000 feet, even when flying at 35,000+ feet, so passengers can breathe comfortably without personal oxygen equipment.

Decompression means cabin pressure drops unexpectedly, usually due to a fault with a door, window, or pressurization system. A gradual decompression may be hard to notice at first; a rapid decompression is sudden and dramatic — often with a loud noise, a rush of air, fog forming in the cabin, and the automatic deployment of oxygen masks.

Hypoxia is the shortage of oxygen reaching the body's tissues. At high cabin altitude without supplemental oxygen, hypoxia can impair judgment and coordination within seconds to minutes — which is why passengers are instructed to secure their own mask before helping others, since a confused or unconscious helper cannot assist anyone.

Cabin crew priorities during a decompression include securing their own oxygen quickly, following the flight deck's instructions (which will usually include an emergency descent to a safer altitude), and helping passengers with their masks once crew have their own oxygen secured.

Communication is critical but may be limited during the event itself; crew rely on training, briefings, and the flight deck's guidance rather than improvising, and passenger safety instructions (like the pre-flight safety demonstration) exist specifically to prepare people for this low-probability but serious event.

After the immediate event, crew monitor passengers for continued effects of hypoxia or anxiety, and the flight deck manages next steps, which may include a diversion depending on the cause and severity.