Oxygen Supplies Aboard Modern Aircraft

If a sudden decompression were to happen inflight, each passenger and crew member would have their own oxygen supply. We will take a look at the systems installed for both the passengers and flight crew!

Passenger’s Oxygen Supply & Canister

The passenger’s oxygen supply is delivered via the overhead compartment where the oxygen-producing canisters are stored. Typically, an oxygen canister contains a sodium chlorate pellet within the cylinder and an igniter. The igniter can be triggered by pulling sharply on the oxygen mask’s tubing. This activates the chemical reaction in which heat and lots of oxygen are produced and supplying the passenger with oxygen for about 12-15 minutes. This gives the pilots enough time to descend the aircraft to a lower altitude where passengers and crew can breathe without the assistance of oxygen.

It’s important to remember that oxygen canisters can cause fires because their surfaces can get extremely hot while generating oxygen. Anything nearby that happens to ignite will burn intensely because of the rich oxygen supply.

The general features of the oxygen canister and mask located in the overhead compartment above the passenger’s seats.
credit: scienceabc.com

Flight Attendant’s Oxygen Supply

The Flight Attendants have portable oxygen cylinders attached to a mask that can be carried around the cabin by hand. This is so that they can assist other passengers while still receiving their own supply but can be mobile around the cabin.

Although designs may vary, each aircraft carries several oxygen cylinders to be used by flight attendants during an emergency.
credit: collinsaerospace.com

Captain & First Officer Oxygen Supply

The Captain and First Officer both have their own individual oxygen masks that are connected to a centralised oxygen tank under the cockpit or in the forward cargo compartment of the aircraft. This oxygen tank is capable of delivering oxygen to the two pilots and also two observers (if present).

A diagram of the location of pilot’s masks and the oxygen cylinder.
credit: aircraftsystemstech.com

As you might imagine, it’s important that pilots can continue to perform complex tasks. Their masks are designed to provide pure, pressure-fed oxygen directly into their lungs. These masks will provide pilots with adequate oxygen at any altitude in an unpressurized aircraft. They are called “quick-donning” because they can grab and secure them on their face within 3 or 4 seconds.

Oxygen settings & harness

There are three settings of oxygen that the pilots can use. They are:

  • N (Normal, preserves oxygen supply by regulating the percentage (flow) of oxygen with outside air depending on cabin altitude)
  • 100% (Pure oxygen, not mixed)
  • Emergency (Pure oxygen, under positive pressure, normally used to displace fog and smoke for better visibility)

These settings may be automatically controlled (i.e. certain aircraft will automatically provide pressure breathing above 27,000 ft. even though the emergency mode is not selected)

These masks hermetically seal to the face and are securely held in place by inflatable harnesses attached to the mask itself. This is important because the higher you fly, the more critical mask fit becomes.

Designs may vary from aircraft to aircraft but a generalised diagram of the pilot’s oxygen mask can be seen above.
credit: captainjetson.com

Regulations require that the crew be able to remove quick-donning masks from their stowage boxes, secure them to their faces, and receive oxygen within five seconds—using just one hand. This may seem like an unnecessarily short time, but if you are already hypoxic, the faster you re-oxygenate, the more likely you are to survive.

Smoke protection

Smoke is a serious concern for pilots. Occasionally, you may hear about an airliner making an emergency landing because of smoke on the flight deck. The mask protects our eyes from the smoke so the crew can get the aircraft safely to an airport.

Built-in microphone

These fancy masks are equipped with a built-in microphone. The mic allows the pilots to communicate with air traffic controllers and with each other via the cockpit intercom. Effective communication is critical during an emergency.

Pilots wear oxygen masks quite a bit!

Unlike the yellow passenger masks, flight crew masks get used more than you might think. They are tested carefully before every flight. There are also times during a normal flight that they are required to wear them as a precaution. During the cruise, when one of the pilots leaves the cockpit (bathroom break!) the other pilot must wear the oxygen mask. They do this in case of an emergency. With only one pilot at the controls, he or she will be really busy should an emergency occur while the other guy is “taking care of business.” Having the mask already on saves precious seconds should something go wrong.

A demonstration of how quick-donning masks can quickly be put on and secured in an emergency (aboard a 737).
credit: youtube.com/aviationfocus

Night flying

Even at a comfortable cabin altitude of 5,000 feet, the brain isn’t getting as much oxygen as usual. One of the problems that occur at this altitude is the degradation of night vision. During preparations for a night-time approach and landing, pilots will often grab the mask and breathe 100% oxygen for a few minutes. It gives their brains and eyes a little pre-landing oxygen boost. The difference is noticeable. After only a few breaths, colors become more vivid; lights and stars become brighter.

As you can see, different systems are in place aboard modern aircraft to ensure the safety of the passengers and flight crew during an emergency.


Sources:

Cover Photo: https://qph.fs.quoracdn.net/main-qimg-879902d0437acb0290e7bd4d9ca27bfa

https://science.howstuffworks.com/transport/flight/modern/question258.htm

Do Airplanes Really Carry Oxygen For The Oxygen Masks?

https://www.collinsaerospace.com/what-we-do/Business-Aviation/Cabin/Oxygen-And-PSU-Systems/Portable-Oxygen-Systems/Portable-Oxygen/Integra-Pulse-Portable

https://www.aopa.org/news-and-media/all-news/2016/september/pilot/oxygen-masks-101

https://www.google.com/amp/s/captainjetson.com/featured/how-do-airplane-cabin-passenger-oxygen-masks-work/%3famp

https://www.aircraftsystemstech.com/2017/05/aircraft-oxygen-systems-and-components.html?m=1

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