Why is Water Remarkably Effective At Putting Out Fire?

Have you ever been in need of putting out fire? Did it happen recently? Or did it happen when you were a child? Regardless of when it actually happened, there’s a good chance that ‘water’ is the first word that came to your mind. You could call it intuition; or you could call it common sense. As children, most of us learnt this fact by way of practical experience (learning by doing). And some of us learnt it by seeing fires being put out by others (learning by seeing).

But why is water so remarkably effective against fire? You might have also heard about special fires where water-usage is not recommended. What’s special about those fires? Quite the intriguing list of questions we’ve got going here. Let’s get right into the topic, and try and understand the underlying phenomena.

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What Is a Fire?

Every item has an ignition point. This point is the temperature at which the item starts to discharge flammable gasses. These gasses together are what constitute ‘burning’. When an object is being ignited, the flame from the ignition source heats up the fuel (the object itself), and the fuel starts drying (because of the burning) and discharging flammable gasses past the ignition point. Once the fuel is hot enough, the gasses it produces (burning) spread over to other areas of the object, causing drying of burnt areas. As this happens, there is some unburnt / partially-burnt fuel that is discharged. And this is what we call smoke. If the smoke is hot enough, it could sometimes ignite and burn (provided that sufficient oxygen and fuel material are available). That is pretty much the basic explanation of the typical process behind ‘fire’.

The Fire Triangle – Why Water is Used in Putting Out Fire

The fire triangle is a simple model used to explain how most fires work. It depicts the necessary ingredients for combustion to occur. A typical fire needs all 3 ingredients shown: oxygen, heat, and fuel. Even if you remove one of these ingredients, the fire can no longer exist.

Consider a candle. If you put a lid on it, the fire goes out. This is because ‘oxygen’ supply is removed from the fire triangle (because of the lid). Consider a forest fire instead. In this case, fire fighters daringly do their best to cut across the fire’s path, and remove things for the fire to burn, so it can burn itself out. What they’re essentially doing here is removing ‘fuel’ supply from the fire triangle.

Now consider a building fire. Here, the building material itself is the fuel, and the oxygen supply is also pretty much abundant, as one cannot engulf the building in vacuum. The only other ingredient left in the triangle is heat. Firefighters try and control the heat of the fire by introducing water to the equation. Water essentially steals heat from a fire. How? Let’s look at that next.

Putting Out Fire Using Water

The special property of water is that it is non-combustible. This means that it does not have an ignition temperature. At very high temperatures, it undergoes something called thermal decomposition instead, which is not of relevance for our questions for this article.

For now, the notable point is that when water is introduced to a fire, it is of lower temperature, and does not combust. Instead, it consumes the heat from the fire, and undergoes a phase transition to ‘steam’. Therefore, water effectively removes heat from the fire triangle. In situations where neither the fuel nor the oxygen supply can be controlled, water is very effective to get the fire under control.

Over the years, human ingenuity has been able to invent and develop other far more effective ways of removing heat. But usually, these methods and materials are expensive and / or need special equipment to be deployed effectively and safely. Water, on the other hand, is available abundantly, is cheap, and reacts almost neutrally with fire causing no further complications or post-fire dangers. That pretty much explains why water is so effective at putting out fire. But what about those special fires where water-usage is discouraged? Right; onward to that question we go next!

The Fire Tetrahedron – Why Not To Use Water in Putting Out Fire

The fire tetrahedron is a more complicated combustion model that explains a broader class of fires than the fire triangle. The only new addition in the fire tetrahedron compared the triangle is the ‘chain reaction’ element. This represents scenarios where there is interaction between the various components that could cause a further chemical reaction. This chemical reaction could in turn worsen the fire.

Without going into the chemical technicalities, it suffices our purposes to know that there are certain classes of fires where introducing water could cause further danger. This is because water either directly reacts with the fire, or causes the other 3 elements left in the tetrahedron to undergo a chain reaction. Consider an electric fire for instance. Sure, water does not combust. But normal drinking water conducts electricity quite well to pose a danger if used against electric fires. This is the reason why non-conductive substances are used to put out electrical fires, and not water.

Similarly, there are other classes of fires, where water is not the best way to put out the fire. But for most typical fires we may come across, where the fuel and oxygen supply cannot be controlled, water is the first go-to solution. Of course, we could delve deeper and deeper, but I feel that this level of knowledge is sufficient for a curious mind to answer the questions we started out with. In case you feel the need to go deeper, do let us know by commenting below!

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Further reading that might interest you: 5 Reasons Why Nuclear Power Is The Future and Is It Okay to Kill Animals For Food?