Fire Control using Water and Carbon Dioxide Video Lecture | Science Class 8

hello friends this video on combustion
and flame part 7 is brought to you by
exam feel calm no more fear from exam so
now knowing this concept of auto
ignition temperature and a flash point
we will see that how water helps to
control fires have you ever seen that if
a building catches fire or if a shop
catches fire what happens people call
fire brigade and what do they do they
try to put off the fire using water now
why water helps to extinguish fire and
what does that property in water with
which helps to get away with fires now
water cools the combustible substance
now we saw that there are three criteria
of combustion right three what were the
three criteria the first criteria was a
fuel or a combustible substance the
second criteria was the presence of air
or oxygen and the third criteria was the
presence of heat so that the substance
can reach its ignition temperature and
can catch fire now if we want to put off
the fire so let's say something has
already caught fire but now we do not
want that fire so how do we put off that
fire if any of these criteria is not
fulfilled
there will be no combustion so there
will be no fire now what does water do
water is quite cold and therefore
whenever you put water into a hot over a
hot substance it reduces the overall
temperature of that substance so
basically instead of providing heat you
are actually provided making the
substance more cold so you are reducing
the temperature of the combustible
substance
now when you reduce the temperature so
what happens again the substance
temperature comes below the ignition
temperature so below the ignition
temperature a substance cannot catch
fire and that is why the fact it doesn't
catch fire again and that's how the fire
stops because what is fire fire is
nothing but a result of reaction of the
substance with oxygen right so right now
the substance is still in contact with
oxygen but it is not able to
you release enough energy because it has
not reached its ignition temperature so
that is how the file is put off so
because the temperature falls below the
ignition temperature
so using water this criteria is not
fulfilled and that is why there is no
file and that is how the concept of
water as a fire extinguisher works now
water cannot be used as a fire
extinguisher in all the scenarios for
example if you take example of spaces
where there are a lot of electrical
equipments or electrical wires for
example in office spaces where you have
a lot of computers lot of machinery
factories or industries where there are
a lot of electrical equipments involved
water is not a good choice as fire
extinguisher
can you tell why because when I am
talking about water I am NOT talking
about your distilled water I am talking
about normal water which contains
dissolved mineral soils etc in it so
this water is a good conductor of
electricity so normal water so when I
say water is a good conductor of
electricity I mean not pure water at the
normal which we use in our day-to-day
life that is not distilled water so this
water is a good conductor of electricity
now since it is a good conductor so what
happens is when you put water on
electrical equipments which has caught
fire so the chances of getting electric
shock is very high because water will
also start conducting the electricity
which might the electric current which
might be present on those electrical
wires or the electrical equipments
therefore water is not at all a good
choice to be used as fire extinguisher
in edweb in fire involving electrical
equipments so which is alternative
choice the alternative choice is carbon
dioxide
now what special is there in carbon
dioxide that
can control fire because carbon dioxide
cannot act as a cooling agent but it can
do something else
so what carbon dioxide actually does is
it acts as a blanket over the substance
which has got fired
now this one as I again said there are
three criteria correct the first
criteria for combustion is pool second
criteria is oxygen or air and third
criteria is heat now water acts as a
fire extinguisher because it attacks the
third criteria but carbon dioxide
attacks the second criteria because
carbon dioxide is a gas and oxygen is
also a gas this carbon dioxide is
heavier than oxygen so carbon dioxide is
heavier when compared to oxygen now
since it is heavier so it settles down
so as I decide what happens is carbon
dioxide acts as a blanket surrounding
this entire substance so let's suppose
this is a wire just an example this
brown coloured line which you see that
is a wire and it has caught fire so over
this wire with fire the carbon dioxide
will act as a blanket so here you will
have the carbon dioxide blanket and
where is oxygen oxygen is present in the
surroundings so maybe oxygen is present
here now basically if you see due to the
presence of this blanket of carbon
dioxide the contact between oxygen and
the substance this is the substance so
the contact between oxygen and the
substance is being cut due to the
presence of carbon dioxide in between
now since the supply of oxygen is cut
therefore there is no oxygen supplying
so there is no combustion so there is no
fire so that is how carbon dioxide acts
as a fire extinguisher now how do we
actually for example in case of water we
just bring water maybe in buckets or in
pipes and we try to extinguish fire but
how do we do it with carbon dioxide so
carbon dioxide is present in liquid form
in fire
extinguishes if you look in in your
office paces you will see the red
colored fire extinguisher boxes inside
that you have carbon dioxide in liquid
form and when it is released it
neutralizes the oxygen that is actually
causing the file so another advantage of
using carbon dioxide as fire
extinguisher is that files do not record
immediately because of lack of oxygen
because all the oxygen is being sent out
by carbon dioxide so it actually
neutralizes with the oxygen so there is
no rule oxygen surrounding the
substances and as a result there is no
file
in fact the carbon dioxide which is
directly released from the extinguishers
that is also at ice cold temperature so
it is extremely cold so there are
certain precautions which needs to be
followed while applying carbon dioxide
on of in office pieces which have got
fires so what we learnt is we can
control fires either by using water or
by using carbon dioxide but the basic
concept of controlling fire is that one
of the three criteria needed for
combustion needs to be a bit limited
that is one of those criteria need to be
falsified and then combustion cannot
happen so there will be no fire thank
you
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