Oxygen as fuel

This may possibly be the stupidest question ever. (yeah I know “there are no stupid questions, only stupid people”. In this case it may be both)

But since oxygen is flammable, why can’t it be used as a fuel source without any additional help from agents like gasoline?

Mods, not sure if this a GD or GQ. But it seems to me like it has a definite answer. If not, please move as you see fit. (as if you need my permission. :rolleyes: )

Oxygen isn’t flammable. When something burns, it combines with oxygen. Oxygen by itself does not burn.

Well that’s certainly a good explanation.

So why do places that have oxygen have warning signs about open flames?

I guess what i was thinking was using an electrical charge to ignite the oxygen. Of course as you say since oxygen isn’t flammable, that wouldn’t work. I just wonder why so much caution about smoking or an open flame near oxygen? I always thought it was because it would ignite the oxygen.

Obviously I’m missing something. Perhaps this should just be closed.

Thanks, Doc.

The warning signs make sense. More oxygen in the air makes things burn faster and hotter. A cigarette butt that may otherwise have smouldered and gone out could burst into flame, or make other things burst into flame, e.g. dust on the ground, paper, etc.

Normal air is about 1/5th oxygen. In an oxygen-rich environment, things burn faster (or explode), hence the warning. IIRC, aluminum would burn if the air were 100% O2.

As part of a chemistry experiment, we generated bottles of O[sub]2[/sub], then placed smoldering chemicals within. When we lit a sample of phosphorous, it smoldered like a cigarette. But when we placed that inside an O[sub]2[/sub] bottle, it lit up like a light bulb.

Fluorine gas is even more reactive than oxygen. Water will burn if it’s in a fluorine atmosphere.

In reference to the water/fluorine thing, The Master says it here: Water contains hydrogen and oxygen. Why doesn’t it burn?

The warning signs are posted at storage points for oxygen because accidental release of the gas can allow the other materials in the vicinity to burn magnificently, even materials you wouldn’t think would burn well or at all.

Over thirty-five years ago, three American astronauts died in a flash fire that erupted in their command module during a pre-mission simulation. The test took place in a nearly-pure oxygen environment, and some fairly innocuous materials – synthetic netting and strips of velcro were specifically cited – were ignited by an electrical spark. In the oxygen atmosphere, the fire incinerated the inside of the module and killed its occupants in a matter of seconds. As bizerta pointed out, aluminum tubing in the module melted and burned.

In my line of work, we sometimes use oxy/acetylene torches. When the acetylene is first lit, it burns in normal air with a dirty yellow color and puts off clouds of black soot. It’s OK for lighting your cigarette, maybe. But once the oxygen is fed to the flame, the soot disappears and the flame becomes a translucent blue. We use it to burn through steel rebar and bridge beams.

The Apollo 1 astronauts died so fast and horribly because the capsule was highly Oxygen-enriched. Our dear Dr. Matrix is of course correct.

Oxygen assists combustion. Light a candle. What is really burning? Not the wick, the wick is wicking up the wax, just as it becomes soft and liquid enough to be wicked up by the wick, in what is generally known as…a wicking action. :smiley:

The wax burns at the tip of the wick, and is allowed to burn by the presence of oxygen in both the wick, and wax, and the air around the candle.

Light a small candle. Get a big mayonnaise jar. ( This harkens back to what is now regarded as the Golden Age of The Straight Dope, when all fine scientific queries were answered at The Straight Dope Science Labs ). Light the candle, and put the long large jar over it, so it’s covered. Now, watch. The candle is nice and new, and would burn steadily until it is out of wax and wick, but for one major problem.

The candle is using the oxygen trapped in the sorta-sealed area under the mayonnaise jar. Once that oxygen has been depleted, the candle will slowly sputter and go out. It does not have enough oxygen to sustain its burn.

Not all things need lots of oxygen to burn. As AWB points out, even water can burn if it is in the right atmosphere. Magnesium burns very happily under water.

** The Flaming Cubes [b/]. BAND NAME !!! :slight_smile:


Sorry about that, T-Bone. I did preview my post, but didn’t scroll down for a simul-post, ya beat me to it on Apollo.

My bad.

Even steel burns with enough oxygen in the right conditions. Most of the cutting with an acetelene torch is not merely melting the steel. The cut is started with a neutral flame which has a correct mixture of oxygen and fuel, the blue flame TBone2 mentions. When the cut is started a lever on the back of the torch adds more oxygen, dramatically accelerating the cut. That’s why acetelene cutting torches only work on ferrous metal. For nonferrous metal (though it works on steel too) a plasma cutter is used which cuts with a jet of ordinary compressed air that has of course been ionized and superheated by an arc.

To add an aside about liquid oxygen which is much more hazardous than the gaseous state because of concentration I saw a demonstration when I was in the navy that was enlightening. A clean cotten glove was placd on the concrete and a bit of liquid oxygen dripped on it. Using a very long cord the heavy steel tow bar of a pieve of ground support equipment was dropped on the glove which exploded, knocking the towbar back upright. We were told that getting LOX on a fuel or oil spill would cause an explosion by itself with no other ignition.

This is used to good effect in Thermic-Lance Boring.

Have you done the trick where you turn off the acetylene, and burn through the rest of the piece with the oxygen alone? Makes a much more ragged cut, but it can work…

Steel wool will burn very hot, with out any enhancements.

OK, to make sure you get what’s going on, oxygen by itself doesn’t burn, and fuel by itself doesn’t burn. Fire is when the oxygen and the fuel combine chemically, releasing heat. No oxygen, no fire. No fuel, no fire. When firemen spray water on a fire, they are doing two things…cooling down the fuel, and preventing oxygen from reaching the fuel. Without oxygen, a wood house won’t burn.

Now, why does oxygen cause things to burn? Isn’t it odd that we have this element present in the air that spontaneously combines with things under the right conditions? Yes, yes it is. The presence of oxygen in the air is unstable. Without the constant influx of oxygen from plants all the oxygen in the air would get used up pretty quickly. Within a very short while, all the free oxygen in the air would be consumed, just like burning a candle inside a mason jar. Once the oxygen is gone, fires don’t sustain themselves, and go out.

But WHY does oxygen do this? Chemical reactions seek an equilibrium. If you combine two substances with high energy states, they may combine into a third substance with lower energy, releasing the energy as heat. Oxygen and Carbon combine to make Carbon Dioxide. Carbon Dioxide has less energy than free Oxygen and Carbon, and when it forms it releases heat. The released heat can be seen in the glowing gasses that make up the flames in a fire.

No, I haven’t tried that Anthracite but I might when I get a chance. Makes a perfect demonstration of the process to show burning rather than just melting. Terminology changes over the years. My grandma was a pipefitter in the Washington shipyards in WWII and always referred to her job as “oxygen cutter.”

I have another anecdote to add to Lemur’s contents. When I was working at Biosphere II we experienced a depletion of oxygen from some overlooked elements, soil microbes and millions of square feet of exposed concrete. The crew inside became winded doing small tasks and a candle flame could not be sustained. You should have seen the crew come to life after we hooked up a tanker truck full of LOX to the south lung.

And, of course, in a predominantly hydrogen or other reducing gas atmosphere, oxygen will be a “fuel” – entering into combustion with the hydrogen, methane, or whatever that constitutes the atmosphere into which the jet of it is released and ignited.

Consider this-
in the atmosphere of a gas giant, rich in hydrogen ad methane, an opened gas bottle of oxygen will burn with a flame practically identical to that of a bottle of H2 on earth.
So yes, oxygen does burn, even without igniting ferrous metal.

Hello, Pollycarp…
…we would have posted at the same time if I had been logged in properly.