• Question: If hydrgen is flammable and it is one of the elements to make water, why does a fire go out if you put water over it?

    Asked by milachinchilla to Davie, Gemma, James P, James V, Nuala on 28 Jun 2012.
    • Photo: Gemma Purser

      Gemma Purser answered on 28 Jun 2012:

      Hi Milachinchilla,

      I like how you have thought about this question! good theory! Its all to do with bonds and reactions and energy. Hydrogen gas is known as H2, that is two hydrogen atoms bonded together by electrons. In the presence of air (containing oxygen) if you put a little bit of energy in it causes a reaction which breaks that bond and it releases lots more energy, in the form of heat and light.
      If you add water to things that are on fire it stops the reactions because the water absorbs the excess energy which is needed to keep the reactions going. No more energy means no more bonds broken so the flames are put out.

    • Photo: James Verdon

      James Verdon answered on 28 Jun 2012:

      Fire is basically the reaction of any other element with oxygen. So when hydrogen burns, it combines with oxygen, so 2 hydrogen atoms and one oxygen atom combine to form H2O, or water. So water is basically hydrogen that has already been burned.

      Another reason water can be used to put out fire is because it smothers the supply of oxygen. When, for example, wood is burning, the carbon atoms in the wood are combining with oxygen to make CO2. By smothering the fire with water, we cut off the supply of oxygen, so the fire stops. This is how fire blankets works as well – by smothering the supply of oxygen. Other fire extinguisher types, like foam, work in a similar way. Stop the supply of oxygen and you stop the fire.

      In the opposite way, by blowing gently on a small fire you can increase the supply of oxygen, helping the fire to get going better.

    • Photo: James Pope

      James Pope answered on 28 Jun 2012:

      Hi milachinchilla,

      I’ll add to this that like water, oil which is made up of carbon and hydrogen atoms and what we use to make petrol and burn in power stations for energy can also be used to put out a fire, as in it’s raw form it doesn’t burn and just smothers the fire.

      Though, it goes without saying, don’t try it at home 😉

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