Hydrogen and Oxygen

• Water is a chemical compound that consists of two parts of hydrogen and one part of oxygen by volume. Compounds rarely have any of the chemical characteristics of the elements of which they are made. In the case of water, it is easy to see why this is so.
  
  

Hydrogen and Oxygen

• A mixture of two parts hydrogen and one part oxygen is very unstable. A small spark will cause the mixture to explode violently, as the hydrogen burns in the oxygen. This is the process, however, by which water is formed. When iron combines with oxygen, the result is rust. When carbon combines with oxygen, the result is carbon dioxide. When hydrogen combines with oxygen, the result is water. Water does not behave like either hydrogen or oxygen any more than rust behaves like iron or carbon dioxide behaves like carbon.
  
  

Putting out Flames

• Flames are one indication that a chemical reaction is taking place. Chemists call that type of reaction "rapid combustion" while most other people simply call it "fire." It occurs when three requirements are met: there must be a fuel, the fuel must be hot enough to keep the reaction going, and there must be oxygen.
  
  Putting water on flames deprives the reaction of two of those essential elements: heat and oxygen. When water evaporates, it absorbs heat from the fuel and cools it below its kindling point, the temperature at which it will burn. And if the fuel is covered with water, oxygen cannot get to it to support the combustion.
  
  

Warning: Do Not Use on...

• Water is not always the best choice for putting out a fire, however. If the fuel is oil or gasoline, water cannot cover it, because those petroleum products are lighter than water. They will float, and as a consequence, the flame will spread. Water should not be used on electrical fires because it can conduct electricity.