- You know those oxygen masks the flight attendants promise will drop from the ceiling if your airplane starts to go down?

Do you ever wonder where all that oxygen comes from?

Is there one big oxygen tank above the luggage compartment or do I get my own oxygen tank?

It turns out it's neither.

There is no oxygen tank.

And the thing up there that does give you oxygen, brought a passenger plane down in the Everglades in 1996, killing all 110 people aboard.

(wind whirling) In case of emergency, oxygen masks may drop from the ceiling above you.

Place the mask over your nose and mouth and breathe normally.

Oxygen will be saved, even if the bag does not inflate.

But, How?

It doesn't make sense to put a big oxygen tank on most passenger planes, it would take up a lot of space and be really heavy to store enough oxygen gas for all of the passengers on a commercial flight.

But if the cabin depressurizes, while you're up in the sky, you're gonna need an additional oxygen source so you don't suffocate.

Above 30,000 feet, there's less than a third of the available oxygen that there would be down at sea level.

To keep a ready supply of oxygen without the weight of a pressurized tank, airlines use these.

This is a chemical oxygen generator.

It's about the size of two stacked soda cans and it's filled with Sodium Chlorate, Iron Powder, Barium Peroxide and Potassium Perchlorate.

When you pull your mask firmly towards you to start the flow of oxygen.

Pull your mask firmly towards you to start the flow of oxygen.

You're actually releasing a spring loaded striker that hits a percussive charge.

This tiny explosion starts a chemical reaction and the Sodium Chlorate begins to decompose into Sodium Chloride and Oxygen Gas.

The Iron Powder reacts with Oxygen and releases heat, keeping the decomposition going.

The gas flows out of the generator, down the tubing and into your mask.

As you take a big breath in, you might notice a burning smell.

This is totally normal due to the decomposition reaction above you, but can be understandably distressing in a plane where things are already clearly going wrong.

And don't be alarmed if the bag doesn't inflate, it's just there to hold extra oxygen.

So assuming you keep breathing in, you're likely inhaling all the oxygen before it has a chance to back up and fill the bag.

The reaction also gives off a little bit of Chlorine Gas, which is why the Barium Peroxide is there.

Barium Peroxide helps to soak up the Chlorine that you really don't want to inhale.

Now, the generators are only designed to provide about 12 to 22 minutes worth of breathable oxygen.

The designers assume that if the masks are needed, the plane is also probably going into an emergency descent profile.

AKA it's getting back to the ground as quickly and safely as possible.

So the chemical core is actually cone-shaped, it's wider at the beginning when you'll likely need more oxygen and then smaller at the end, when you've hopefully descended back down to a safer altitude.

The exothermic reaction keeping you alive, can reach temperatures above 1000 degrees Fahrenheit.

That sounds kind of frightening.

But it's not the only place where we use this kind of technology.

In fact, two other confined spaces, submarines and the International Space Station, both use oxygen candles to create breathable O2 in emergencies when normal oxygen generators go down.

These candles are basically bigger versions of the oxygen generators found on flights.

On May 11th, 1996, ValuJet 592 took off from Miami International Airport.

Six minutes after takeoff, the crew heard a loud bang and the Pilot, Captain Candi Kubeck, reported that they were experiencing electrical problems.

Flight Attendants saw smoke in the cabin and just three minutes later, the flight crashed into the Everglades, killing all five crew and all 105 passengers aboard.

Captain Kubeck had the unfortunate distinction of becoming the first female pilot to die in a commercial plane crash.

So, what happened?

Underneath the front of the plane there were 144 expired and soon to be expired, chemical oxygen generators in the cargo compartment on their way to a ValuJet facility in Atlanta.

A maintenance company had recently removed them from two other planes.

Normally, you're supposed to put a safety cap on these things to keep them from activating.

But this contractor was in a hurry and instead just wrapped the discharge lanyard around the canister and taped it in place.

This same contracted company would later be found guilty for mishandling these hazardous materials and one of their mechanics is still on the run from the FBI.

The oxygen generators wound up in ValuJet 592's cargo compartment, loosely packed and unsecured.

An oxygen generator likely activated sometime between loading and takeoff.

Maybe caused by a jolt on the runway, which started a fire in the cargo hold below the passenger's feet.

You might think that airplanes would have some sort of fire suppression system in case a fire starts in the cargo compartment.

And had this been a typical fire, they did.

The compartment was designed to have very little ventilation with the idea that if a fire started, it would quickly use up the available oxygen and self extinguish.

Now, the idea of using a sealed compartment to squelch a fire, isn't a bad one.

If I place a jar over a candle, cutting off its oxygen supply, it'll burn through the oxygen around it in the jar and then go out.

Unfortunately, in the ValuJet accident, what was on fire were literal oxygen generators.

So they were just pumping oxygen into the small space.

So what if we add an oxygen source to our candle setup?

If I let a jar sit over a mint plant for awhile, the plant will give up oxygen.

When I place the oxygen rich jar over a candle, the candle inside burns longer, than a candle in a jar filled with just normal air.

The same thing happened in the ValuJet cargo compartment.

The release of oxygen from the generators, kept the fire burning longer and hotter than it would have otherwise.

And stored right beside the oxygen generators, were three large airplane tires.

Investigators suspect that the extreme heat of the fire caused the explosion of one of the tires.

Hence the loud bang that the cabin crew heard.

In fact, the fire got so hot that it melted some of the aluminum structures of the airplane.

Meaning it likely reached over 1000 degrees Fahrenheit.

It quickly destroyed electrical connections causing the pilots to lose control and crash into the swampy Everglades below.

After the disaster, new safety regulations were put in place.

More safety staff, better fire detection and suppression systems.

So no more relying on it burning through a limited supply of oxygen And a ban on chemical oxygen generators as cargo on passenger planes.