Fire triangle: when does combustion occur?
Does combustion always occur in the presence of a gas leak? We often hear in the news about buildings in which explosions have occurred following gas leaks, so it is likely that instinctively we will answer yes to this question, but the correct answer is no. Let's see why!
What is the fire triangle
Fire Triangle is a term used to visually explain the process of combustion. The latter in fact provides for the presence of three elements, which form the sides of our triangle, at the center of which is the fire. Let's see what the three elements in question are and what the relationship between them is.
How combustion occurs
In order for combustion to take place, three elements must be present: the fuel , the oxidizing and the ignition source . A fire it occurs , therefore, only in the presence of these 3 factors. Let's see in detail what it is.
Fuel is any substance, organic or inorganic, capable of igniting. In our case therefore the gas.
But what is the oxidizer? The oxidizer is the substance that acts as an oxidizer of a combustible substance during combustion. The most common oxidizer is oxygen.
The ignition source is any heat source capable of starting combustion. To do this, the primer must have a temperature equal to or higher than that of the mixture and the contact between the two must occur for a sufficient time. Combustion stops if one of the three elements is missing.
To learn more about the dynamics of combustion you can read: How combustion works .
How the fire triangle works
To summarize, for combustion to occur, all three elements must be present in the minimum quantity necessary to start the process. If one of the three elements is missing, combustion cannot occur or, if in progress, it extinguishes.
We can therefore put out a fire through the exhaustion of the fuel, the reduction of the comburent or the removal of heat to a temperature lower than that necessary to maintain combustion.
A do-it-yourself experiment
To verify this, you can do a very simple experiment, which anyone can do at home. All you need is a candle, a jar with lid and a lighter . You simply proceed by lighting the candle and inserting it into the jar. Once the lid is closed you will see that after a while the candle goes out. What happened? The flame has consumed all the oxygen, i.e. all the comburent, and the combustion reaction can no longer take place.
L.I.E. and L.S.E.
At this point some of you are probably wondering what the necessary concentration of gas in the air to have combustion. This percentage is called L.I.E., lower explosive limit , and varies according to the type of gas. Of course there is also a upper explosive limit (L.S.E.) beyond which the mixture cannot explode because the gas has oversaturated the environment and the oxidizer is therefore not sufficient.
Anyone wishing to delve deeper into this topic can read the article: What is L.I.E?