The Flammability of Oxygen: Does It Burn?

Here's What Happens When You Smoke Near an Oxygen Tank

Young woman starting camp fire

BROOK PIFER / Getty Images

Despite popular opinion, oxygen is not flammable. You can prove this by preparing oxygen gas and bubbling it through soapy water to make bubbles. If you try to ignite the bubbles, they won't burn.

A flammable substance is one that burns. Though oxygen does not burn, it is an oxidizer, which means it supports the process of combustion. So if you already have a fuel and a fire, adding oxygen will feed the flames. The reaction can be dangerous and violent, which is why it's never a good idea to store or use oxygen around any sort of flame.

For example, hydrogen is a flammable gas. If you ignite bubbles of hydrogen, you'll get a fire. If you add extra oxygen, you'll get a big flame and possibly an explosion.

Smoking and Oxygen Therapy

If a person on oxygen smokes a cigarette, they won't explode or even burst into flame. Smoking around oxygen is not particularly dangerous, as least as far as fire is concerned. However, there are good reasons to avoid smoking if you or someone nearby is on oxygen therapy:

  1. Smoking produces smoke, carbon monoxide, and other chemicals, which reduce oxygen availability and irritate the respiratory system. If someone is on oxygen therapy, smoking is counterproductive and harmful to their health.
  2. If burning ash falls from a cigarette and starts to smolder, the extra oxygen will foster a flame. Depending on where the ash falls, there may be enough fuel to start a significant fire. The oxygen would make the situation that much worse.
  3. An ignition source is needed to light a cigarette. Oxygen could cause the flame of a lighter to flare or a lit match to burst into an unexpectedly large flame, leading to a burn on the person. Or it could cause them to drop a burning object onto a potentially flammable surface. Oxygen flare-up fires do occur in emergency rooms, so the risk is present, although somewhat reduced in a home setting.
  4. If oxygen therapy is conducted in a hospital, smoking is prohibited for several reasons. Aside from the negative health effects on the smoker, secondhand smoke is produced and can be inhaled by others. Plus the residue from smoking remains even after the cigarette is extinguished, making the room unhealthy for patients who come in afterward.
  5. In a medical setting, there may be other gases (e.g., anesthesia) or materials present which could be ignited by a spark or a cigarette. The extra oxygen makes this risk especially dangerous since the combination of spark, fuel, and oxygen could lead to a serious fire or explosion.

Key Takeaways: Oxygen and Flammability

  • Oxygen does not burn. It is not flammable, but it is an oxidizer.
  • Oxygen feeds fire, so it's dangerous to use around something that is burning because it will help the fire burn much more quickly.
  • Patients on oxygen therapy who are smokers are not going to burst into flame or explode if they smoke. However, the risk of a fire or accident is greatly increased. And smoking negates some of the benefits of using oxygen.

Test It for Yourself

It seems almost unbelievable that pure oxygen doesn't burn, yet it's quite easy to prove for yourself using the electrolysis of water. When water is electrolyzed, it splits into hydrogen gas and oxygen gas:

2 H2O (l) → 2 H2 (g) + O2 (g)

  1. To perform the electrolysis reaction, unbend two paperclips.
  2. Attach one end of each paperclip to the terminals of a 9-volt battery.
  3. Place the other ends close to each other, but not touching, into a container of water.
  4. As the reaction proceeds, bubbles will rise from each terminal. Hydrogen gas will bubble up from one terminal and oxygen gas from the other. You can collect the gases separately by inverting a small jar over each wire. Do not collect the bubbles together because mixing hydrogen and oxygen gas forms a dangerously combustible gas. Seal each container before removing it from the water. (Note: An excellent option is to collect each gas into an empty plastic bag or small balloon.)
  5. Use a long-handled lighter to try to ignite the gas from each container. You'll get a bright flame from the hydrogen gas. The oxygen gas, on the other hand, will not burn.