Fire Triangle - Role of Water Additives

Role of Water Additives

The role of water in extinguishing a fire can be summarized as follows: The main effect is cooling down the fire by absorption of heat energy either at the fuel surface or in the gas phase. A contributing effect is diluting the atmosphere by adding vapor and thereby removing oxygen from the fire The main limits to the use of water are directly linked to the physical-chemical characteristics of water itself: - Water cannot be used on certain type of fires :

• Fires where live electricity is present- as water conducts electricity it presents an electrocution hazard
• Hydrocarbon fires - as it will only spread the fire because of the difference in density
• Metal fires - as these fires produce huge amounts of energy (up to 7.550 calories/kg for aluminum) and water can also create violent chemical reactions with burning metal (by oxidization)
• Fat fires - as vapour will carry and spread burning oil everywhere.

Since these reactions are well-understood, it has been possible to create specific water-additives which will allow:

• A better heat absorption with a higher density than water
• Carrying free radical catchers on the fire
• Carrying foaming agents to enable water to stay on the surface of a liquid fire and prevent gas release
• Carrying specific reactives which will react and change the nature of the burning material

Water-additives are generally designed to be effective on several categories of fires (class A + class B or even class A + class B + class F), meaning a better global performance and usability of a single extinguisher on many different types of fires (or fires that involve several different classes of materials).