What Happens When A Plane Loses Cabin Pressure?

Commercial aviation is magical. You are cruising along in a pressurized metal tube at 35,000 feet, and while the outside temperature – at a crisp -66 degrees Fahrenheit – is cold enough to freeze you to death, you admire the view while staying warm and comfortable inside. So if that tube keeps you away from certain death by hypothermia and suffocation, what happens when something goes wrong and the cabin depressurizes? Let’s first understand what cabin pressure is and what can cause cabin pressure loss.

Think of the earth as a huge fish tank, with us standing at the bottom, which we will assume to be sea level. This fish tank is filled with air, just like our atmosphere. Due to gravity, the air above us exerts barometric pressure on the air below — i.e. the air around us — compressing it. Due to that high pressure, this dense air supplies more oxygen to your body with every breath you take. The higher you go, the less air pressure there is. This lack of pressure makes it harder to breathe because oxygen molecules in the air are not bunched as closely as they are at lower altitudes. 

Simply put, every breath puts less oxygen in your lungs, which drops blood oxygen levels in your body. This lack of oxygen to the bloodstream, called hypoxia, can incapacitate everyone onboard the aircraft, including the pilots. Let’s take a closer look at how this terrifying scenario can develop and what happens next.

To counter the high-altitude environment, a plane’s cabin is pressurized to simulate an altitude of around 8,000 feet. Why not sea level, where breathing is easiest? The pressure difference between sea level and 35,000 feet would put enormous internal strain on every inch of the airplane’s structure, similar to an expanding balloon. 8,000 feet is considered the cutoff point before entering a high-altitude environment, which helps sustain a passenger’s breathing needs while reducing pressure on the plane’s structure. Your ears might pop, but at least you are breathing comfortably.

There are a few reasons your flight might turn into a cabin depressurization nightmare. It could be due to a structural failure in the airplane, like a door, window, or pressure bulkhead failing, as occurred in a Boeing 737 after it suffered a door plug blowout. It could also be due to a malfunctioning pressurization system or incorrect control inputs. The cabin could be deliberately depressurized by the captain in case of a fire, to clear the smoke from the cabin. Then there is sabotage or terrorist activity, where an explosive rips out a section of the plane, causing rapid depressurization.

Let’s talk about what happens to the human body when a plane cabin loses pressure at high altitude. If the pressure loss is gradual due to slow or insidious decompression it will be difficult to detect until it’s too late, when passengers and crew members would experience symptoms of hypoxia. If undetected, it could lead to people being incapacitated and losing consciousness. 

A rapid or explosive decompression is quite dramatic. It causes a sudden drop in cabin pressure with a loud bang. This is preceded by air being sucked out of the cabin due to the pressure difference and a drop in temperature as the cabin air levels with the freezing outside air. Other dramatic effects are fog or mist engulfing the cabin, loose items and debris flying around, and, of course, lots of screaming.

The effects of cabin decompression on a person are mostly due to a lack of oxygen and the sudden pressure drop. The most critical medical complication is hypoxia. Low levels of oxygen in the bloodstream can cause passengers to experience impaired vision and judgment, drowsiness, slurred speech, memory loss, and impaired motor skills. Other medical issues include excessive bloating due to gas expanding inside your stomach, breathlessness, nausea, and ear discomfort.

The moment the flight’s cabin loses pressure, the plane’s pressure sensors set off alarms inside the cockpit. The pilots and crew put on oxygen masks, inform air traffic control of the emergency, and begin a rapid descent to minimize the effects of the pressure difference inside the plane cabin. The aim is to drop below 10,000 feet where the oxygen is dense enough for the passengers to breathe without masks. 

Inside the cabin, yellow masks drop down in front of each passenger. These are required to carry at least 10 minutes of oxygen, enough time for the pilot to get the plane to lower, breathable altitudes. To accomplish this, a Japanese Spring Airlines plane once dove from 36,000 to 10,000 feet in just 10 minutes. 

What should you do in the event of a cabin depressurization? First, put on the oxygen mask in front of you, then help others around you put theirs on. The best course of action is to fasten your seatbelt — if you haven’t already — and stay put in your seat while the pilots and crew handle the rest. Follow every instruction given by the cabin crew as if your life depends on it. It does.

Why should you rush to put your mask on? Airlines refer to time of useful consciousness, which is a specific period of time starting from the interruption of normal air supply until the time an individual loses their ability to perform normally due to lack of oxygen. Beyond this time, the individual will be incapacitated. At 18,000 feet, it is 20 to 30 minutes. At 35,000 feet, it is as low as 30 to 60 seconds. As such, it is beneficial to wear that oxygen mask pronto.

Can you be sucked out of the plane in the event of a cabin depressurization? Unless there is a large hole next to you, the chances are quite low. Even in that scenario, having your seatbelt buckled will probably save you — just one more good reason to buckle up.

Despite these harrowing scenarios, flying remains the safest way to travel. With modern technology, sensors, emergency descent protocols and redundant depressurization systems, cases of cabin depressurization are rare, and in the event of one, the chances of you walking away from it are quite high.