Mod-01 Lec-03 Typical Examples of Explosions and Classification
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Mod-01 Lec-03 Typical Examples of Explosions and Classification

August 11, 2019

Good morning, in the last two classes we defined
an explosion as being produced, when
a blast wave is generated, and this blast wave is generated due to impulsive or rapid
release of energy. Let us qualify it a little better, you know supposing I have a region
or a zone or a small volume, in which let us say
some energy gets released. And then what happens is this energy release, drives the
blast wave which propagates out. And then what is happening is the energy release gets
redistribute, this energy release in this small
volume gets released or gets redistributed by the lead shock wave.
And this energy is at this particular time when the blast wave is here, the energy released
gets redistributed here, when the lead shockwave is here the energy gets redistributed in
this zone, and so on. It is essentially the redistribution of energy which is impulsively
deposited, which leads to an explosion. Now, when we say about this redistribution of
energy, it is this potential energy of the explosive or what is being released here which
gets converted into kinetic energy and potential energy, but it is all contained within the
lead blast wave as it were. There is something important in this, and
we have been telling this repeatedly in the last
two classes namely that the material does not move, it is the energy gets redistributed,
I think this point must be kept in mind as we
go along. We also told ourselves, well the way two points we said, if this energy release
gets into the thermal energy of the medium. Well, it is unavailable energy this
is unviable for deriving the blast wave. Second, we also told since the energy is redistributed,
when the blast wave or when the wave continually decays out and reaches a
faraway point. Let that means, we are looking in the far
field, well the energy could get conserved, we
will take a look at it in the subsequent classes. Therefore, this is the way we defined an
explosion, and we found that anyway the lead shock is something which is continually
decaying. In other words what did we tell ourselves, on a streak diagram in which the
y axis is t, the distance is x or very often
we will define it as the radius from here, let us say
R s. Well, they it decays out initially it travels a longer distance for a short time,
then it becomes an acoustic wave in the far field.
Now, what is going to happen? See it is continually decaying the energy gets
redistributed it is a terrible tangent problem, unsteady and therefore to be able to solve
it was difficult, and therefore what did we do?
We went through the non dimensional analysis through which we looked at the parameters,
and we got the dependence saying. Well, the distance by which the lead shock
travels at some time t, after the impulsive release of energy can be written as R s is
equal to A t to the power 2 by 5. The second point, we also said the velocity with which
the lead shock moves d s d R s by d t, which we said is equal to R s can B written as a
constant here A is a constant, t is the time can
be written as R s to the power minus 3 by 2. We also found out the rate at which the
blast wave decays and we found. Well, denoting it
by R s dot and we say well I am looking at R s 2 dot that is d 2 R s by d t square into
R s divided by R s dot square, we got it equal to minus 3 by 2.
In other words, R s is positive, R s dot squared is velocity which is anyway it is a
positive number, therefore it continually decays, and this is what we got from
dimensional analysis. We will also recall, we said there are different types of explosions,
we said there explosion could be occur in nature, we said naturally occurring explosions
naturally occurring explosions. We also talked in terms of accidental, we said well in the
kitchen something leaks, gas leaks and all of a sudden we have something like accidental
explosions. We also talked in terms of intentional explosions,
may be intentionally may be the during warfare somebody goes and drops a bombs at
some place or may be of flake we have these antisocial elements like terrorist.
Who go and plan some minds or by explode bombs in some crowded localities, we say these
are intentionally created explosions or we say well intentional explosions. We also
told, well an explosion could be use for constructive purposes like air bags in a for
surgery may be for making kennels and all that, well these were the different types
of explosions we talked off. Now, in today’s class to be able to relate
to the theory, which we must develop mind you
see we just developed some value of the shock based on dimensional analysis without
going into the detail physics of the problem, but we also found. Well, when I have this
lead shock across the lead shock there is a jump in pressure, a spontaneous jump in
pressure, because the shock wave from the ambient pressure it jumps to this value.
Behind it, you have the momentum of gases or the impulse of gases, it is necessary for
us to determine these quantities to find out,
what is the effect of the explosion on the things
around it. Therefore, to be able to do that, if we can
go through some of these examples of different types of explosions, maybe we will be better
equip to understand the theory. Therefore, in today’s class what I do is, we will take
a look at different types of explosions, and see
how they behave. And based on that, we will go back and try to again revisit the blast
wave generated from the energy source, and find out the parameters of a blast wave
which could cause some damage. Having said that, let me come to the first
slide which I want to show, I will get I will start
with the naturally occurring explosions one. You know let us get started with the slides
over here, may be the first type of the naturally occurring explosion, which all of us are
familiar is something like a lightning, see this particular slide shows a lightning here
what happens is here? The clouds which move, and during the movement
at high velocities they pick up a charge, become a charged as it were developed
high potential or high voltage and it hurts to the ground, and you have something like
an arc discharge. I took this slide from national geography, and what you have to find
is something like a like an arc discharge over here. And what happens? The arc discharge
releases rapid energy over here, and therefore what would happen then let us go
back and see what could happen? See you have something like an arc discharge taking
place, something like a line discharge. And therefore, I will start creating something
like a cylindrical wave, which propagates out from here this is R s dot that is the
velocity with which it goes, in the near field what
is going to happen? You have I again plot that t versus the x or the distance let us
say R s over here, initially it is start with high
velocity decays out in the limit, where in the wave
travels to far away, I hear rumble of thunder, if I am near to this I hear extremely loud
bang loud thunder, and far away I just hear the rumble of the thunder. We looked at this,
well this is the first naturally occurring explosions, lightning’s are frequent in
some places it occurs more often than known. Well,
this is the first type of naturally occurring explosions. Let us got to the next type, the next is the
volcanic eruptions, and you know in this picture again from national geography, I show
a volcano spoofing out fire, as it where I have a huge fire. And in this hot gases are
generated, the hot gases sometimes are charged, and therefore I could get arc discharge
and something like a lightening I could get a blast wave, but very often what happens
is? Some of these volcanos when they here up there is also some seismic activity, like
there is some tidal waves and or else the volcano is in the ocean.
And very often during the volcanic eruption some sea water enters into the volcano, the
volcano is pulling out these hot gases hot lava is what is there, molten lava is there.
When water enters, you know this water see this huge hot mass of lava and hot gases,
it is spontaneously flashes into vapor it become
superheated, and the type of energy is so high, that it creates an explosion something
like a physical thing wherein the phase of the
water changes. And we had this very famous explosion at Krakatau, this was something
like 40 kilometers west of java, and this happened on August 26 1883 mind you it is
quite old. But this explosion is extremely famous, in
fact what happened in this volcanic eruption is, something like over a distance of something
like 5000 4500 kilometers away the blast could be heard point one. Point two something
like over a distance of something like 500 kilometers, the buildings got shattered that
is the power of this particular explosion that is the blast wave generated, created real
lava in this naturally occurring volcanic eruption. Such type of eruptions do take place
now, and then and of late we have the tsunami, we have water in gracing and all
that therefore these are the types of sea second
type of naturally occurring explosions. We come to the third one and this is of particular
interest, because of late. We talk in terms of comets. We also talk in terms of asteroids in space,
what is the difference between an asteroid under comet, you know these are all loosely
from objects in space, and what happens is? When these are not planets actually, they
do not have a particular type of a trajectory and
they the asteroid consists of metal and rocky material. Whereas a comet consists of may
be ice, dust and also some rocky material with a result, when the comet approaches the
sun or near to the sun, you know the ice evaporates under comet as a long tail as it were.
Whereas an asteroid having metal is something which is more solid, sometimes these
comets and asteroids enter into the earth, like for instance. I say well the earth is here, above the earth
we have atmosphere for something like 15 to 20 kilometers high. And suppose some of the
comet or asteroid enters into the atmosphere, it immediately creates the kinetic
energy creates a blast wave something like a comet is entering, I have a blast wave here
to be able to equalize the velocity here, and
the velocity here the energy release is so high that it creates a blast wave. And this
blast wave can cause damage and one such comet,
one such asteroid you know in this slide, I
show a comet or perhaps an asteroid it is not very clear, whether it is really a comet
or an asteroid.
It enters the atmosphere at a distance of around 8 to 10 kilometers over a place known
as Tunguska in Siberia on July 30, 1908. You
know the blast wave it got generated during this re entry was so strong, that over a distance
of something like 150 kilometers, the trees just got fell unfortunately for a Siberia
being a desert there were not many buildings around, but buildings got demolished over
a distance of something like 5 kilometer and that is the type of the explosive energy released
that take place during the entry of an asteroid into the atmosphere. It is not that there is just one case of this,
you know you will recall around a few months back on 15th February 2013, over the Russian
town of Yekaterinburg. You know we had a comet entry, and this comet entered the
atmosphere at a distance around 5 to 7 kilometers above the surface of the earth.
And the blast wave which created the impact was felt at a city known as Chelyabinsk, which
is 200 kilometers away from the place where it really entered. In fact, due to this
blast wave or the impact something like 200 to
300 buildings got broken, hospitals got damaged. And in fact, you know this was the big
news in all the newspaper saying, meteor rattles Siberian city fortunately nuclear and
chemical facilities are safe, there were switched off for some time. And let us go ahead, you know the big bang
from this mid from this comet was such that as it strict over Russia. Well, it really
cause shockwaves, shatter windows, buildings got
broken, and it let to something like services like internet mobiles and all being affected. You know this is the type of power, which
is associated with a comet re entering, and there is lot of interest in comet and asteroids.
And in fact, it was told that it is about the
larger size, and now if I look at the size of this particular mean size of this comet,
it is around something like 17 meters or so in diameters,
so very small one. Compared to what was there, over Tunguska it is something
like 30 meters diameter. And mind you these are all small things which can really
cause so much of damage. And therefore, there is quite a lot of interest
on the blast waves generated, when a meteor or a meteor, let us say a comet or an asteroid
enters the atmosphere. And you know we have this problem like, when
this asteroid re entered here you find this brilliant flash due to energy release over
this Russian town as it were, and the blast wave
creating the damage. And since some asteroid is supposed to re
enter the earth, may be a comet is supposed to
an asteroid is supposed to re enter the earth, around let us say 2036 may be there is some
interest. I must also point out that one such huge asteroid is set to have re enter the
earth around 6 million years ago. And it is responsible
for the extinction of life at that time, including extinction of the dinasors. Well,
this is the third type of naturally occurring explosions. And the last one let us see what it is like.
We talk in terms of stellar explosions, explosions in the star, well you have the
star which is whose life is going to get over, it is
fuel is consumed. Therefore, it has just neutrons in it, they because of gravity the neutron
shrink it becomes very dense over here. And because of the density it explodes, high
density the neutron explodes lot of energy gets released, you have a brilliant flash
over here. And I also show something like a super nova
that is a stiller explosion in this; this is
again taken from the national geography. And what you find in these stellar explosions
is you know the type of temperature, which is
reached during the explosion is so very high, that the atoms or atoms combined to form heavy
substances like gold, silver, may be platinum. And you know the source of these
materials are set to come from on earth, is supposed to come from the stellar explosions. Well, these are the four types of naturally
occurring explosions having seen these four types of explosions. Let us quickly summarize
over here, the naturally occurring explosions are either, let us say lightening. Second
we say volcanic eruption volcanic eruptions in which some physical explosion
like sea water entering the volcano, can release huge amount of energy like the one
at Krakatau. Maybe we talked in terms of the third type, in which we have asteroid comets
entering the earth. And the last one we said, well it could be
stellar explosions. You know the stellar explosions cannot be heard for the simple
reason, we have vacuum between the star and us. And therefore, there is no question of
sound reaching us, there is no question of a
blast wave reaching us, but we must remember it is the light intensity which is seen. And
also we have the electromagnetic waves in form of the cosmic radiation, which we
perceive from the stellar explosions. Having said that lets come to the next type
of the explosion namely the accidental explosions, these accidental explosions are
occur quite frequently whatever be the type of precautions we take some over the other
an accidental occur, how do we define an accident? Let us first be very clear what
an accident means, when we say an accident it
means something like an unplanned event, something which we have not planed
accident. And how do you say well, anything can I go cross the road; something comes
and hits me say I meet with an accident. Therefore, for unplanned activity there is
always a chance that an accident takes place, and the word chance in Arabic is given by
the word azhar, something like azhar is a Arabic word. And therefore, whenever we talk
in terms of an accident likely, we associate the word hazard, whenever we move
substances which are somewhat likely to cause an accident. We say these are hazardous
substances and we must be careful. And most of the substances are hazardous under
some condition or the other. Therefore, let us
take a look at some of the accidental explosions and mind you, when we do risk analysis
we will address the hazardous nature of substances. And say how to take precautions to
avoid accidental explosions. Therefore I come back to the slide, I talk
in terms of accidental explosions mind you in
the first talk I said about, cooking gas exploding in the kitchen maybe there is a stove,
may be a cylinder the gas leaks mixes with air, somebody goes and pushes puts on the
switch or creates an electrical spark and bang, the entire building is there. These
accidents even in a metro like Chennai keeps occurring, and there are something like 3
to 4 such accidents in a year, and you see the
building getting demolished, the neighboring building getting demolished. We go to the next one this also shows the
same accident, wherein the liquid petroleum gas stored in a cylinder getting exploded
over here. Well, it is not only the gas from the cylinder
which explodes. You know in the previous one, well the gas leak it created within the
confinement of the kitchen mixture which could explode. Well, when we transport may
be some substances, which are reactive in this particular case, this happened on something
like 24th march 2012 about a year and half back.
What happened is this is a Korean ship, which was carrying an explosive substance or a
reactive substance which was toluene. And this toluene is somewhat volatile it formed
a vapor and it exploded. And it resulted in
a killing of a person mind you, at that particular time there were not many people in the ship,
but still it cause an explosion created havoc. And therefore may whenever we say, well we
transport energetic substances we have to be careful, list an explosion or a blast wave
is formed. This is something which has been in the news
for quite some time on July 9 2013; there was this huge number of oil cars or oil tankers
being taken. There were something like 72 wagons being pulled by 9 locomotives in
the township near to Quebec in Canada, and what happened was? May be after parking these
wagons safely the breaks were put on according to the drivers, but somehow the
break got released, and the wagons freely rolled. And when the wagons freely rolled
they picked up some velocity, and they derail one wagon on top of the other.
And during this process a leakage of the oil took place, and when leakage of the oil took
place it caught fire, and not only did it catch fire, the heats from the fire increase
the evaporation or the pressure in the containment
of the wagons, and it led to a huge blast. And in fact, the a township near Quebec by
name last magnetize got totally devastated, mind you the death rate was not very high,
but even then it was a major explosion. This shows the burning after the explosion
may be the oil spill getting burned, but remind you it is a major tragedy that means,
the spillage of oil from tankers causing an explosion, I will examine this a little later. But in our own country, you know we have these
on the roadways we move liquid petroleum gas in tankers, and when it heat
a particular vehicle in the Kerala’s state near
Quilon, this was on December 31 2009. The LPG spill caught fire, but somehow the fire
personal where able to douse the fire without really exploding. Mind you therefore may be some it points towards some precautions
which we must take, while handling the spills from tankers oil tankers. Well, this is what really happens? what happens
is a vapor gets generated, the vapor burns or rather you gave hot vapor which rapidly
burns forms a blast wave, and this is what happens in these oil tanker explosions,
namely a vapor cloud gets generated. You know one of the well documented oil tanker
explosions, this happened in the city of Illinois in US this was in crescent city.
And this was done by professor stellar in fact the previous picture which I show is also from
him. And what was done was, he was the first person who looked at accidental explosions
in a major way. And what let us take a look at this particular explosion in the crescent
city at Illinois. It was again a number of wagons, which derail and what happened? Let
us take a look at this happened on June 2 1970. In this particular case, you have these wagons
carrying in this case what was being carried was liquid propane, one after the
other. There is derailment one of the wagon jump against the other, and there is a spill
of liquid propane gas propane is essentially a
liquid, and when it meets the when it spills it evaporates you form a vapor of propane.
And when you have spill taking place, you have a fire and this fire if it heats this
particular wagon, the pressure inside it increases you have hot propane here.
And it when the pressure increases I said the wagon burst, you have a huge quantity
not only does the wagon burst, but have a huge
quantity of vapor which gets generated. At least to a huge ball of fire and this creates
a blast wave, and this is known as a liquid which is getting heated from some other source.
You have something like a boiling liquid, which expands expanding
vapor explosion it is known by the word BLEVE, boiling liquid expanding vapor explosion this
is what cause this explosion. We have such explosions happening in our country at BLEVE,
at Jaipur BLEVE happening in Jaipur, but it is happening in open atmosphere. It
is an in an unconfined gaseous explosion, and
these required some particular attention, we go to the next one. In addition to having something like wagon
exploding, when we have pipelines conveying, let us say liquid petroleum gas,
liquid natural gas, liquid propane and all that.
It is quite possible sometimes some leakage occurs in the pipeline, the vapor is released
or the liquid is released, it vaporizes over here catches fire and it creates an explosion. You know there are some typical explosion
which I would like to say one is, one happened at port Hudson in Missouri, this
picture I got from professor stellar. You know
you have at port Hudson in Missouri, wherein pipeline which was carrying, which was
carrying again I think it was again liquid propane, let us come back to this example. You know you have pipeline, this pipeline
was something like point 2 meter diameter, the pressure was something like 50 bar are
so at which it is communicated. There has been some rapture in the pipeline, and the
liquid propane is a liquid under atmospheric conditions at temperatures less than around
minus 45 degree centigrade. Therefore, may be liquid propane escapes, it forms a huge
fountain of liquid. And then it evaporates I get a fog and a smog
over here of propane, but this accident as is
seen their happens in the month of December, when it is quite cold. And the surface
wind at that condition was not very high; it was around 2.8 meters per second. And
therefore, the cold propane just collected on the ground as it were over the captured
pipeline. And it gradually move, you know there is no ignition source of the point where
the accident took place, and therefore it just moves it keeps mixing with air.
And downstream you know this is something like a value was there, there was a building
over here a concrete building, which housed some refrigeration units, such that may be
the food stuff could be kept cool, there was a refrigerator inside or a something to keep
the substances cold. And therefore, what happened is the gas, the vapor moves here it through the crevices in the door in window,
it moves in over here mixes well with air. And since there are some motors in the refrigeration
unit, well it catches fire develops a blast over here, and you know there are so
many different units here, that the fire the flame becomes something like an explosion
or a detonation. And we have the blast which takes place, and
this blast took place around 13 minutes, it took for the mixture to come and found this
blast. And once this blast comes this ignites the whole thing, and you had a huge explosion.
And this explosion was such that it could be heard something like 50 kilometers downstream,
and also it just annulled just designated the place as it were. This is the
explosion, which is involving liquid propane as it happened at port Hudson, I come back
to the slide again port Hudson on December 9 1970. We have a number of such explosions, and one
such explosion is sort of cataloged in literature, as being the largest man made
explosion ever. This happened in the Ural Mountains in Siberia and you know what was
done, you know you had a pipeline around 0.7 meter diameter. It was convey natural
gas which is essentially methane. And in this you know the pressure it was I think it was
designed for a pressure of something like 25
bar, it was operated at 12.5 bar, but then over a distance of something like, almost
like pipeline or something like 1 kilometer. There was this pipeline ruptured, and it was
downstream it was something like 1500 downstream of the supply point of the gas
to this pipeline. Nobody really notice that gas
was leaking, huge quantity of a leak and mind you it was June 14 1989, the spill
accumulated on the ground and does not mix well with air. And at that point what
happened is? You know as fate would have it. Let us go back and take a look at this
particular accident, and how it took place you know what happened is? We told
ourselves well you have the pipeline conveying this, conveying l and g. Therefore, over the ground you have I will
methane low temperature methane accumulating, it does not really mix such
so well with air. There is no accidental source after all it is a Siberian plane not very
well populated. And there are not no houses or
anything which can lead to ignition sources like spark over here. But, you know you will
also remember that if you look at the geographical part may be on the east you have
Vladivostok. And there is an train which runs from Vladivostok to Moscow, this is the
trans-Siberian railway, and this is the double railway line. And as fate would have it you
know this sort of spill took place over a long distance.
And there were this two tracks which was there, and along both the tracks in one the
forward train is going from Vladivostok to Moscow. In the other the train going from
Vladivostok to Moscow in one train, is going the other one along the other track you
have the train going from Moscow to Vladivostok. And both are adjacent to each other and because of this turbulence which is developed,
when two trains pass each other and it has it is ability to mix the gases a good
mixture got generated over here. And this being
electrical trains over overhead, we have the electrical spark which ignites and huge bang
took place, and this is the largest man made explosion ever.
It killed all the inhabitance of both the trains and something like. Let us get back
to the slide, something like 600 people got killed,
trees were decimated over a distance of 4 kilometers. I needs not only this pipeline,
you know in many chemical industries you have pipelines conveying explosive substances
from one container to the other, such many such incidence do occur in chemical plants.
One typical example which is often quoted in literature is the accident at Flixborough
in England on June 1 1974. Wherein it just created a goes down in England and that
town still continues to be a goes down, because of the damage it cause there. Let us go to the next example. Well, so far
what is it have done, I have looked at may be
the explosions accidental occurring from gas in a confinement, occurring from may be a
vapor unconfined geometry, we looked at pipelines, we looked at wagon derailment. And
now, we come to something like solids substances, like in this particular case this
accident took place on something like April 18th this year, something like 5 months
back. And what really happened? This was the factory in the town of west in Texas in
US. And there were making there were storing ammonium per chlorate, it is not very clear the thing is a still under investigation,
but apparently the ammonium per chlorate which let us say ammonium per chlorate is
a condensed phase substance. Let us take a look at it, we will be looking
at some of the explosions involving such substances. It is not ammonium per chlorate;
it is ammonium nitrate which is use as a fertilizer. You know this substance has both
fuel and oxygen unit, and if it begins to catch fire may be it gets heated and the rate
of releases high, and when a particular large quantity of ammonium per chlorate it is involved.
It goes into this chemical reaction which keeps on feeding back heat to it, and
you have such a powerful rate of energy released that a blast gets generated. This
is what happened in this particular case at the
Texas factory in the town of west, and the entire town of west got decimated. Well it
is a case of a solid substance like ammonium per
chlorate; we say it is a condensed phase explosion. We take a one or two more examples of this,
let us say you know in our own country at Sivakasi in Tamil Nadu, where we make this
cracker industry. The cracker industry involves some substances like carbon, sulfur
and ammonium nitrate mixed together, which are used in making crackers or making
fireworks. And to handle them even though they handle small quantities, very
often we find that not handling them properly leads to the accidental explosion. Wherein
people die every time we hear 3 people dead 10 people dead, the entire building gets decimated
like. What is shown over here, the due to a small
amount of this composition accidently igniting a blast is created the entire building
gets decimated people die. And one such case, which is very well cataloged
in literature involving ammonium nitrate is something which I will spend some
time on. This accident in was in the Texas City in
US, this is the southern it is a port city in
southern US. You know this happened in 1947, what is the thing what we are talking?
Again this involved ammonium nitrate, see ammonium nitrate if you see we said it is NH4NO3 it contains lot of nitrogen, it is
used as a fertilizer. You know and there is lot of
demand for fertilizer, because you would like to a fix nitrogen in the soil. Now, in this
particular case you know we do not want to use the real ammonium nitrate, but we would
like to make it a little more resistance to explosion.
And therefore, you have wax being coated on the ammonium nitrate crystals, such that it
is intensity of explosion or is susceptibility to burning and explosion is reduced.
Therefore, you have instead of AN ammonium nitrate, you have what is called as
fertilizer grade ammonium nitrate, which is essentially coated ammonium nitrate and
normally it is coated with wax. In this particular case, you have something like 7700 tons
of ammonium nitrate all in cartons or bags stored in the hull of the ship; you have all
these cartons of ammonium nitrate being stored in the hull of the ship.
Now, the hull of the ship is somewhat insulated you know heat cannot really go from
inside to outside or outside to inside, and if some temperatures increases over here,
you know it keeps heating it up. And therefore,
what was observed was may be at that in that particular accidents some temperature increased
due to some chemical reactions taking place inside, always there is some element
of reaction taking place. And when they found some smoke in the ship you have steam
which is available people spreads water, and steam on to the smoke which was being
created. Now, the temperature is going up, the steam
further contributed to the reaction. And therefore, you have something like a chemical
reaction gets terribly increased, because of
this there is the spiraling of the chemical reaction rate of chemical reaction if I say,
whereas time progresses builds up. And the rate of chemical reaction becomes so much,
that high intensity energy is getting release spontaneously, and you have a huge blast
wave which gets generated. The blast wave in this case was so strong, that the entire
hull of the ship got blown off.
And it carried over a distance of a few kilometers, why something like almost 600 people
died the over a distance of 16 kilometers from the sight of the explosion. Well nothing
remain people got knocked down, buildings got destroyed, over a distance of 60
kilometers trees were uprooted. And this explosion from Texas City could be heard at a
town 400 kilometers away, and that is the intensity of this explosion. Well, pictures shows the damaged cars, may be the hull of
the ship, and the buildings being damaged, which I again show in the next slide. Wherein after the aftermath of this Texas
City disaster, well nothing really remains. Therefore this is the type of explosions which
keep taking place, and what is it we have considered so far. Let us quickly review ourselves
such that we are, we can look at some other explosions and draw some examples. We tell ourselves, well the accidental explosions
maybe we say yes an accident is an unplanned event could be something like a
confined one using gases, it could be unconfined it could be something like wagons,
derailing. And have something like BLEVE boiling liquid expanding vapor explosions
BLEVE. We could also have we said solid substances like condensed explosions,
in which may be some chemical reactions occur like an in Texas may be at Sivakasi,
we have all this condensed explosions. We could also have the confined gaseous explosions
in a slightly different context, and a very deliberately brought this point out in
the next slide, wherein I show the example of
the explosion of a fuel tank. There was this particular aircraft which took off from New
York on July 17 1996; it was the TWA 800 flight. And since it was supposed to go over
a short distance, not all the fuel tanks in the air craft where fully filled with kerosene
or what we call as a jet fuel in New York. It
was the summer month minds you it happened on July 17th.
And therefore you know what was done was one central fuel tank was near empty,
because that much of fuel was not required for the flight from New York, I think it was
going to Europe. And therefore, the quantity of fuel which was loaded was not in all the
tanks 11 minutes after takeoff, the aircraft just exploded and it was a huge fireball.
And an analysis showed that the since the central
fuel tank was near empty that there was small amount of kerosene in it, aviation kerosene.
And you know on the ground, wherein you have lot of air available and explosive
mixture could not be generated, but the moment it goes to higher altitude, wherein
the air is small combustible mixture with air
got generated. And therefore, at that point some electrostatic
spark could have resulted in this particular explosion, it is again a confined fuel air
explosion. In which you had a huge fireball all
the passengers and crew of this flight, where killed in this particular explosion. You
know this is something which we will deal with in some detail, we will look at limits
of flammability of substances under what conditions
you could have an explosion. And we will we have to address some of these points
including the flash fire point of the volatile liquid fuels. You know it is not only the gas, the liquid
and the solids energetic solids, but dust can
explode. I would like to qualified further that is what did we tell now.? Well, I could have confined explosions, because
of may be some tankage may be you have gas which is mixture which is formed,
which is initially not flammable or initially not explosive, but which becomes explosive
under certain conditions. We tell ourselves not only solids and liquids and say gases
are explosive. You know that dust like for instance we consume wheat flour, we make bread
out of wheat flour may be we use sugar, maybe we use for icing fine powdered
sugar all these are explosives substances.
If it is mixed with air in sufficient quantities, it could explode and one such thing which
is the first recorded explosion was in Turin in Italy this was on December 14 1785.
Wherein you know you had this particular baker, who sends a boy to the godown collect
some flour, I think it was wheat flour or maize flour I am not very sure about it. And
this particular boy you know this was December
month, you know it is an evening quite dark, therefore this boy takes a candle in his hand,
and in the other hand he picks up the flour as it were being a boy he is playful, he tosses
the flour and this flour when it mixed with air exploded, and this was the first recorded
dust explosion. We have such explosion involving dust in large
number in US, wherein they handled the food crops in confinement we had this in Wichita
in US, wherein you have 7 people being killed in a dust explosion involving.
I think it was a wheat dust; you also have an
entire port terminal being destroyed in Brazil in November 2001, which was conveying the grain was being unloaded in the particular
port. Therefore, dust explosion is also an a
type of explosion which could occur. Having said that, we spend a minute or 2 on
the last type of explosions, which we said well it could be accidental. We call so talk in terms of physical explosion,
we already talked in terms of physical explosions, when we talked in terms of the
volcano in which the water get got into the volcano, got terribly heated up super heated
vapor formed where is an explosion. And in physical explosions is essentially a substance
which is not combustible or a high energy substance like water, which can create an
explosion. Let us take an example in a particular place in Canada near at Ottawa
at place known as Flin Flon. You know you had this copper smelter, and you know towards
the evening you know on a weekend day, you know people want to go home early. You had this smelter you have a evaporated
furnace or a furnace crucible furnace. And the furnace is hot people want to leave early,
but they have to cool down the furnace before they leave the work is over. Therefore,
to cool it further may be the operator he takes water in a pail and pushes into the
furnace, which is quite hot at that point and
time. And all of a sudden, because of the thermal inertia of the furnace the water just
flashes into vapor and creates a blast wave and injures people.
This is the type of explosion which I said happened on, I come back to the slide on
August 8 2000 at Flin Flon a town near Ottawa in Canada, wherein in a copper smelter
we had flash vaporization driving blast waves and an explosion. You know such type of
explosion was also, we must remember in the case of natural explosion at Krakatau,
wherein you had the huge explosion and this is the type of examples, which I collected
under accidental explosion. Now, I just spend a minute or 2 on intentional
explosions, lets come back to this. Unfortunately, you know the of late we find
these terrorists and the antisocial elements, engaging in this type of affair. And one such
example which I show here is happened on at Oklahoma City on April 15 1995, wherein
nice posh building which house may be children; a nursery you know was brutally
damaged by a blast. In which case you know a
truck carrying solid explosives was sparked nearby. Well it was ammonium nitrate, it
was little bit more energetic, we will get back into the details when we study the condensed phase explosion. And the blast wave
just ripped of this building, it is not only thus ((Refer Time: 49:16)) keep happen, it
is keep happening all over the world of late in
Afghanistan, in Iraq may be while in India. We have this improvised explosive devices,
we have minds being planted. And nowadays, we talk in terms of these explosions as low
intensity conflicts, and we have to design the system such that may be the buildings
or the type of the blast wave could be controlled
or may be this structure should be so strong, such that it does not really get affected
by this. Well, these are the intentional explosions. And you will also remember at the Boston marathon
a few months back, we had the terrorist putting the explosive or energetic
substance in a pressure cooker and killing people. Well these are the type of intentional
explosions. And before we complete this, I deliberately
brought this point of atmospheric dispersion, why is it atmospheric dispersion? You know
in the example of the Hudson explosion, wherein liquid propane went into the building,
it is by atmosphere that it is going. And in
fact, you know we have some cases of atmospheric dispersion causing disaster, one is in
our own country we had the Bhopal gas tragedy, which is stated to be the world’s worst
industrial disaster this happened on a cold day December 2 to 3 1984. And what really
happened, let us take a look at it, because it give some room for thinking. In this particular plan which was a carbide
plan, you know you stored methyl isocyanate in tank ages. And you know you have the valves
of this, somehow you know the somewhat like a wood, which will prevent water
in gracing into this was missing, when it was being clean some water got into the
tank, water got into the tank. And also the tank was little dirty you had something like
chloroform; you had some ion inside the tank. And when water comes in contact with
methyl isocyanate, it begins to react carbon dioxide gets generated, and these impurities
further let to the reaction with a result pressure in the tank got increased.
And normally you know in the plants you have something like refrigeration coils, which
will control the temperature of the system, it was December it was cold these were not
operational at that point in time. Gas got generated, the pressure went up through the
went valve a mixture of MIC and MIC gas got released, the scrubber was unable to
control the mass flow rate of it; the wind velocity was low at around 2.5 meters per
second. And being winter time the temperature on the
ground was lower than above with a result, we say atmospheric inversion the gas was not
able to diffuse up diffuse out into vertically. And prevent the methyl isocyanate
affecting the people downstream with a result it drifted, and whenever it came in
contact with people either they got blinded or
when the dosage went up they just die over here. That means, we are talking of the
atmospheric affects, you know even when we talk in terms of some gas from a pipeline
gases coming out, you know the ability for the gas to go out into the atmosphere.
We say an unstable atmosphere will allow the gas to get lost, does not happen under
certain conditions, and therefore atmospheric dispersion is an integral and an important
part of the explosion physics. And therefore, we say well we could have accidents due to
atmospheric dispersion. And the world’s worst case was in the case of the Bhopal gas
tragedy in which some 20,000 people killed were killed. Why we had also the great smog
of London this happened on December 5 1952, again in the winter time during winter
time people burnt more fuel to stay warm. And in those days may be the type of cold
was also not of that good quality, it created sulfur fumes and it got trapped on the over
the surface of the earth, this permitted into buildings and something like 12,000 people
got kill. You know in addition to may be pollutants and dispersion, we recognize that
the combustible gases could also move mix with air, and therefore atmospheric dispersion
becomes important. The last one is may be nuclear power plants;
you have loss of coolant type of accidents, in which you have hot metal coming in contact
with water generating hydrogen, and this hydrogen exploding. we had this in Fukushima
in December 2011 around 2 years back, we had this almost a imminent, but it did
not explode this was in 3 mile island on march 29 1979. We had this happening in Chernobyl
and the only thing which was done was the whole thing was engaged with concrete
and steel, and maybe it was it nothing more was allows to happen. This is the last slide which I show; this
is taken from Professor Dewey. And what is seen
here is, you know an explosion taking place, you see the blast wave from the explosion
preceding the matter from explosion, this is the blast wave which causes the damage. To some of them, you know we talked in terms
of different types of explosion. We talked in terms of the largest man made explosion.
We talked of nuclear explosions. Well we did not get into Hiroshima Nagasaki which
I talked of yesterday. Well, you could also have fission and fusion, and these again
generate we will not deal with fission fusion, but we will look at loss of coolant
type of accidents. We talked of explosion in a
fuel tank in the TWA 800. We talked of dust being explosive may be the eatable things,
which in fine powder becomes explosive. In our own country, we have the propellants
exploding in one of the assembly points in a in the Indian space program.
We also have the BLEVE type of explosion at Jaipur in an oil refinery on 29 October
2009, we had several such BLEVE explosions at Vishakpatnam, we also talked in terms
of the of the BLEVE explosion at Crescent City in Illinois. Well these are the different
types of explosions, and to just sum up the different categories of explosion, I will
just put it in a slightly different form. We tell
ourselves well, we looked at different types of
explosions, we find well the cause lot of damage to life and property. And I can tell myself well, the first type
of explosion which I can talk is, maybe a condensed phase explosion. In which solid
substance are associated, it creates more and
more heat, it is something like a feedback and the rate of reaction goes up. Well, it
is a thermal type of explosion. We talked in terms
of confined gas explosion in a room, in a confinement. We talked in terms of the unconfined
BLEVE type of explosion, unconfined explosions.
The fourth one we said well, why all this even a dust could explode, dust explosions
we talked in terms of the physical explosions,
that means some vaporization of the substances taking place. We talked in terms
of maybe we have finished confined, unconfined, solid substances. We talked in
terms of atmospheric dispersion. We talked in
terms of loss of coolant analysis maybe the nuclear explosions. Well, these are the
different categories of explosion, and having understood these explosions.
Our next step would be to go back look at the how release of energy from this explosion,
drives a blast wave we will try to model the blast wave. And try to find out how to
proceed further with calculations of the pressurize, calculations of impulse, which gets
transmitted by momentum to the body which is getting affected by the explosion, this
is what we will do in the next class.
Well, thank you.

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  1. The medium doesn't move – yet there is kinetic energy… If the potential energy of the explosion is transferred to heat energy, it cannot be used for work – yet, in a previous lecture you identified potential energy as a function of the heat capacity and temperature… Great anecdotal stories on historical explosions though. Is there away of deriving the dimensional result from Newton's laws and get the constants of proportionality?

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