Water-type fire extinguisher, c 1950s.
© Science Museum / Science & Society Picture Library
Water is the most widely used fire-extinquishing agent and is used on clas A fires. It is applied as a fine spray using carbon dioxide gas, generated within the appliance to expel it from the container at high presure. It has a cooling effect and the steam produced helps to smother the fire. Water is not suitable for use on clas B fires involving flammable liquids (which require chemical foam/powder or carbon dioxide), clas C fires involving electrical equipment (which require a dry chemical extinguisher), or clas D fires involving burning metals such as magnesium and sodium (which require special techniques). This sectioned fire extinguisher was made by Pyrene Co Ltd.