Fire, a powerful force of nature, seems mysterious and unpredictable. But, did you know that it's actually a precise science? At its core, fire is the result of a delicate balance between three essential elements: fuel, oxidizer, and ignition source. Together, they form the fire triangle, a fundamental concept that explains the combustion process.
In this post, we'll delve into the fire triangle, exploring what each element brings to the table, and how they work together to create the perfect conditions for a fire to start and keep burning. We'll also explore how understanding the fire triangle can help us prevent and extinguish fires, and discuss the crucial role of Lower and Upper Explosive Limits in ensuring safety.
What is the fire triangle?
Fire triangle is a term used to visually explain the
combustion process. The latter in fact requires the presence of three elements,
which form the sides of our triangle, at the centre 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
For combustion to take place, three elements must be
present: the fuel , the oxidizer and
the ignition source . A fire 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, 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 ignition source 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.
How the Fire Triangle Works
To sum up, in order to have combustion, 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 dies out.
We can therefore put out a fire by exhausting the fuel,
reducing the oxidant, or removing heat to a temperature lower than that
necessary to maintain combustion.
A do-it-yourself experiment
To demonstrate the fire triangle, try this simple and
easy practise:
Light a candle and place a clear glass over it. Quickly
slide a piece of cardboard under the glass to trap the air.What happens? The
flame goes out. Why? The cardboard blocks oxygen from reaching the flame,
removing one side of the fire triangle and extinguishing the fire.
LEL and UEL
The Lower Explosive Limit (LEL) is the minimum concentration
of gas in the air required for a fire to start. Below this level, the mixture
is too lean to ignite. On the other hand, the Upper Explosive Limit (UEL) is
the maximum concentration of gas in the air above which a fire cannot start.
Beyond this level, the mixture is too rich to ignite because there's not enough
oxygen. Understanding LEL and UEL is crucial for safety in environments where
flammable gases are present.
