Uploaded by quimicadascoisas on 15.05.2012

To know the chemistry of things is the first step
to understand and to be able to act on the world around us.
To demonstrate this, today we talk about fire!
Fire, or rather, combustion,
is actually an oxidation-reduction reaction
with a large release of energy.
And why is it important to know this?
First of all, to fight a fire!
As with any other chemical reaction
fire exists only in the presence of reagents
which in this case are fuel (inflammable materials)
and a oxidizing agent, which is usually oxygen from the air.
And, as in many other chemical reactions
fire occurs only if the reagents are at an elevated temperature.
Therefore, fire breaks out when the combustible material
is heated to its ignition temperature
in the presence of a oxidizing agent.
After the combustion reaction starts
it generates the heat needed to heat up more combustible material
and the fire spreads.
However, we just need to remove one of the essential components
fuel, combustible material or heat source
and the chemical reaction of combustion ceases.
That is, the fire goes out!
Why is water so effective in fighting fire?
Because it decreases fuel temperature
therefore stopping the reaction.
Another way to fight fire is to deprive it of one of the reactants.
For example: the so called dry powder extinguishers
spread a powder layer on the materials,
preventing oxygen to feed the fire.
On the other hand, common carbon dioxide extinguishers
produce a gas fog, for the same purpose:
keep the oxygen away!
When possible, we take out the other reactant, fuel.
In wildfires, this can be done with a suppression fire
or opening a firebreak
which is basically a strip of land with no vegetation.
Some examples of the use of chemicals in fighting fires
require more in-depth knowledge of chemistry.
Such is the case of "Halon" extinguishers
and their more ecofriendly substitutes, like heptafluoropropane.
These are compounds with a very effective extinguishing effect
because they interfere directly in the combustion chemical reactions, inhibiting them.
The diversity of combustible materials that surround us
has contributed to increase the complexity of firefighting.
But, since fire is a chemical reaction
we can count on the developments of chemistry
to better understand and control it!
To learn more about the chemistry of fire, please visit our website aquimicadascoisas.org
or find us on Facebook!