 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. 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 redistributed. This energy release in the 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 release gets redistributed here, when the lead shock wave 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 which gets redistributed. I think this point must be kept in mind as we go along. We also told ourselves well there were two points we said if this energy release gets into the thermal energy of the medium well it is unavailable energy this is unavailable for driving 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 far away point 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. 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 rs well it decays out initially it travels a longer distance for a short time then it becomes an acoustic wave in the far field and what is going to happen. See it is continually decaying the energy gets redistributed it is a terrible transient 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 rs is equal to at to the power 2 by 5. The second point we also said the velocity with which the lead shock moves ds drs by dt which we said is equal to rs can be written as a constant here a is a constant t is the time can be written as rs 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 rs dot and we say well I am looking at rs 2 dot that is d 2 rs by dt square into rs divided by rs dot square we got it equal to minus 3 by 2. In other words rs is positive rs dot square is velocity which is anyway it is a positive number therefore it continually decays and this is what we got from dimensionals analysis. You will also recall we said there are different types of explosions we said that the 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 maybe intentionally maybe during warfare somebody goes and drops a bomb at some place or maybe of late we have these antisocial elements like terrorists who go and plant some mines or explode bombs in some crowded localities we said these are intentionally created explosions or we say well intentional explosions we also told well an explosion could be used for constructive purposes like air bags in a for surgery maybe for making canals and all that well these were the different types of explosions we talked of. 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 equipped 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 start with the naturally occurring explosions one you know let us get started with the slides over here maybe 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 you have the clouds which move and during the movement at high velocities they pick up a charge become charged as it were develop high potential or high voltage and it earths to the ground and you have something like an arc discharge I took this slide from National Geographic and what you find is something like a like an arc discharge over here and what happens the arc discharge releases rapid energy with over here and therefore what would happen 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 RS dot that is the velocity with which it goes in the near field what is going to happen you have I again plot the T versus the X or the distance let us say RS over here initially it starts at high velocity decays out in the limit where in the wave travels to far away I hear a 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 lightnings are frequent in some places it occurs more often than not well this is the first type of naturally occurring explosions let us go to the next type the next is the volcanic eruptions and you know in this picture again from National Geographic I show a volcano spooing of fire as it were I have a huge fire and in this hot gases are generated the hot gases sometimes are charged and therefore I could get our discharge and something like a lightning I could get a blast wave but very often what happens is some of these volcanoes when when they erupt there is also some seismic activity like there is some some tidal waves and or else the volcano is in the ocean and very often during the volcanic eruption some seawater enters into the volcano the volcano is spooing out these hot gases hot lava is what is there molten lava is there when water enters you know this water sees this huge hot mass of lava and hot gases it spontaneously flashes into vapor it becomes superheated and the type of energy is so high that it creates an explosion something like a physical thing wherein the face of the water changes and we had this this very famous explosion at Krakatov this was something like 40 kilometers west of Java and this happened on August 26 1883 mind you it's quite old but this explosion is extremely 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 havoc 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 ingressing and all that therefore these are the types of the 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 and a comet you know these are all loosely formed objects in space and what happens is when these these these are not planets actually they don't have a particular type of a trajectory and they they the asteroid consists of metal and rocky material whereas a comet consists of maybe ice dust and also some rocky material with the result when the comet approaches the Sun or is near to the Sun you know the ice evaporates and a comet has 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 like for instance I say well the earth is here above the earth we have atmosphere for for something like 15 to 20 kilometers high and suppose some of the comet or asteroid enters into the atmosphere it immediately creates the 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 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's not very clear whether it's really a comet or an asteroid it entered 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 fortunately for a Siberia being a desert there were not many buildings around but buildings got demolished over a distance of something like 5 kilometers and that is the type of the explosive energy release that takes place during the entry of an asteroid into the atmosphere it's 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 Ekaterinburg you know we had a comet entering and this comet entered the atmosphere at a distance of around 5 to 7 kilometers above the surface of the earth and the blast wave which it created the impact was felt at a city known as Chilean Binsk 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 it was a big news in all the newspaper saying meteor rattles Siberian city fortunately nuclear and chemical facilities are safe they were switched off for some time and let's go ahead you know the big bang from this meet from this comet was such that as it's strict over Russia well it really cost shockwaves shattered windows buildings got broken and it led to something like services like internet mobiles and all being affected you know this is the type of power which is associated with a with a comet re-entering and there's a lot of interest in comet and asteroids and in fact it was told that it's about the largest size and now if I look at the size of this particular mean size of this comet it's around something like like 17 meters or so in diameters a very small one compared to what was there over Tunguska it's something like 30 30 meters diameter and mind you these are all small things which can really cost so much of damage and therefore there's quite a lot of interest on the blast wave generated when a meteor or a or a meteor let's say a comet or an asteroid enters the atmosphere and you know we have this problem like like when this asteroid re-entered here you find this brilliant flash due to energy release over over this Russian town as it were and the blast wave creating the damage and since some some asteroid is supposed to re-enter the earth maybe a comet is supposed to an asteroid I'm sorry is supposed to re-enter the earth around let's say 20 36 maybe there is some interest I must also point out that one such huge asteroid is said to have re-entered the earth around 6 million years ago and it is responsible for the extinction of life at that time including extinction of the dinosaurs. 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 you have the star which is whose life is going to get over its fuel is consumed therefore it has just neutrons in it there because of gravity the neutron shrink it becomes very dense over here and because of the density it explodes high density the neutron explodes a lot of energy gets released you have a brilliant flash over here and I also show something like a supernova that is a stellar explosion in this this is again taken from from the national geographic and what what you find in these stellar explosions is you know the the type of temperature which is reached during the explosion is so very high that the atoms or atoms combine to form heavy substances like like gold silver maybe platinum and you know the source of these materials are said to come from on 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's quickly summarize over here the the naturally occurring explosions are either let's say lightning second we say volcanic eruptions volcanic eruptions in which some physical explosion like like seawater entering the volcano can release huge amount of energy like the one at crack at all maybe we talked in terms of the third type in which we have asteroids comets entering the earth and the last one we said well it could be stellar explosions you know these stellar explosions cannot be heard for the simple reason we have vacuum between the star and us and therefore there is no question of 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 let's come to the next type of the explosion namely the accidental explosions these accidental explosions are occur quite quite frequently whatever be the type of precautions we take some over the other an accident occur how do we define an accident let's first be very clear what an accident means when we say an accident it means something like an unplanned event right something which we have not planned accident and how do you how do you say well anything when I go cross the road something comes and hits me say I meet with an accident therefore for unplanned activities there is always a chance that an accident takes place and the word chance in Arabic is is given by the by the word other something like other 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 there are hazardous substances and we must be careful and most of the substances are hazardous under some condition or the other therefore let's 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 see how to take precautions to avoid accidental explosions therefore I come 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 maybe 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 in a metro like like Chennai keeps occurring and there are something like three to four such accidents in a year and you see the building getting demolished the neighboring building getting demolished we we go to the next one this also shows the the same accident wherein the liquid petroleum gas stored in a cylinder getting exploded over here well it is not only the the the the the gas from the cylinder which explodes you know in the previous one well the gas leaked it created within the confinement of the kitchen mixture which could could explode well when we transport maybe some substances which are reactive in this particular case this happened on something like 25 24th March 2012 about a year and a 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 it it formed a vapor and it exploded and it resulted in a in killing of a person mind you at that particular time there were not many people in the ship but still it caused an explosion created havoc and therefore may whenever we say well we transport energetic substances we have to be careful lest 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 this huge number of 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 maybe after parking these wagons safely the brakes were put on according to the drivers but somehow the brake got released and the wagons freely rolled and when the wagons freely rolled they picked up some velocity and they derailed 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 heat from the fire increase the the evaporation or the pressure in the containment of the wagons and it led to a huge blast and in fact the the township near Quebec by name last magnet is got got totally devastated mind you the death rate was not very high but even then it was a major explosion this shows the the burning after the explosion may be the oil spill getting burned but you mind you it is 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 these on the roadways we we move liquid petroleum gas in in in tankers and when it hit a particular vehicle in in in the Kerala state near Kuala Lumpur this was on December 31 2009 the LPG spilled caught fire but somehow the fire personnel were able to dose the fire without it really exploding mind you therefore maybe some it it points towards some some precautions which we must take while while handling the the 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 have 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 in the city of Illinois in US this was in Crescent City and this was done by professor Sturlow in fact the previous picture which I show is also from him and what what was done was he was the first person who looked at accidental explosions in a major way and what let's let's take a look at this particular explosion in in the Crescent City at Illinois it was again a number of wagons which D derailed and what happened let's 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 jumps against the other and and there is a spill of liquid propane gas propane is essentially a liquid and it when it meets the when it spills it evaporates you form a vapor of propane and when when you you have a 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 such as the wagon burst you have a huge quantity not only does the wagon burst but have a huge quantity of vapor which gets generated it leads 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 causes this explosion we have such explosions happening in our country at believe at at Jaipur believe happening in Jaipur but it is happening in open atmosphere it is an in an unconfined gaseous explosion and the these these require some particular attention we go to the next one in addition to having something like a wagon exploding when we have pipelines conveying let's say liquid petroleum gas liquid natural gas liquid propane and all that it is quite possible sometimes some leakage occurs in the pipeline the the 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 explosions which I would like to say one is one happened at Port Hudson in Missouri this this picture I got from professor Strelow you know you have at Port Hudson in Missouri wherein a pipeline which was carrying which was carrying again I think it was again liquid propane let let us come back to this example you know you have a pipeline this pipeline was something like 0.2 meter diameter the pressure was something like 50 bar or so at which it's communicated there has been some rupture in the pipeline and the liquid propane is a liquid under atmospheric conditions at temperatures less than around minus 45 degrees centigrade therefore maybe 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 as is seen there happens in the month of December when it is quite cold and the surface wind at that can 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 ruptured pipeline and it gradually moved you know there is no ignition source at the point where the accident took place and therefore it just moves it keeps mixing with air and downstream you know this was something like a valley was there there was a building over here a concrete building which housed some refrigeration units such that maybe 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 and 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 you have the blast which takes place and this blast took place around 13 minutes it took for the for the mixture to come and form 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 anal just decimated 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 catalogued 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 conveying natural gas which is essentially methane and in this you know the the pressure it was I think it was designed for a pressure of something like like 25 bar it was operated at 12.5 bar but then over a distance of something like almost like pipeline of 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 noticed that gas was leaking huge quantity of leaked and mind you it was June 14 1989 the the spill accumulated on the ground does not mix well with air and at that point what happened is you know as fate would have it let's go back and take a look at this particular accident and how it how it took place you know what happened is we told ourselves well you have the pipeline conveying this conveying LNG therefore over the ground you have methane low temperature methane accumulating it doesn't really mix such so well with air there is no accidental source after all it is a Siberian plane not not very well populated and there are not no houses or anything which 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 maybe on the on the east you have Ladiwa stock and there is a train which runs from Ladiwa stock to Moscow this is the Trans-Siberian railway and this is a double railway line and as fate would have it you know this sort of spill took place over a long distance and there were these two tracks which was there and along both the tracks in one the forward train is going from Ladiwa stock to Moscow in the other the train going from Moscow from Ladiwa stock to Moscow in one train is going the other one along the other track you have the train going from Moscow to Ladiwa stock and both are adjacent to each other and because of this turbulence which is developed when two trains pass each other and it has its ability to mix the gases a good mixture got generated over here and these being electrical trains over overhead you have the electrical spark which ignites it and a huge bang took place and this is the largest man-made explosion ever it killed all the inhabitants of both the trains and something like like let's get back to the slide some something like 600 people got killed trees were decimated over a distance of 4 kilometers and it's 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 incidents 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 ghost town in England and that town still continues to be a ghost town because of the damage it caused there let's go to the next example well so far what is it I have done I have looked at maybe the the explosions accidental occurring from gas in a confinement occurring from maybe a vapor in unconfined geometry we looked at pipelines we looked at wagon derailment and now we come to something like solids solid substances like in this in this particular case this accident took place on something like April 18 this year something like five months back and what really happened this was a factory in the town of west in Texas in US and they were making they were storing ammonium per chlorate it's not very clear the thing is still under investigation but apparently the ammonium per chlorate which let us say ammonium per chlorate is a condensed phase substance let's let's take a look at it we will be looking at some of the explosions involving such substances sorry it's not ammonium per chlorate it's ammonium nitrate which is used as a fertilizer you know this substance has both fuel and oxygen in it and if it begins to catch fire maybe it gets heated and the rate of release is high and when a particular large quantity of ammonium per chlorate 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 release 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's a case of a solid substance like ammonium per chlorate we say it's a condensed phase explosion we take a one or two more examples of this let's say you know in our own country at Shivakashi 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 three people dead ten people dead the entire building gets decimated like like what is shown over here the due to a small amount of this composition accidentally igniting a blast is created the entire entire building gets decimated people die and one such case which is very well catalogued in literature involving ammonium nitrate is something which I will spend some time on this this accident in was in the Texas city in US this is the southern it's a port city in southern US you know this happened in 1947 what what is the thing what we are talking again this involved ammonium nitrate see ammonium nitrate if you see we said it is NH4 NO3 it contains lot of nitrogen it is used as a fertilizer you know and there is a lot of demand for fertilizer because you would like to fix nitrogen in the soil now in this particular case you know we we don't 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 its intensity of explosion or is susceptibility to 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 normally it's 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 temperature increases over here you know it keeps heating it up and therefore what was observed was maybe at that in that particular accident some temperature increased due to some chemical reactions taking place inside always there is some element of reaction taking place and when they form some smoke in the ship you have steam which is available people sprayed 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 terribly increased because of this there is a spiraling of the chemical reaction rate of chemical reaction if I say as time progresses builds up and the rate of chemical reaction becomes so much that high intensity energy is getting released 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 site of the explosion well nothing remained 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 picture 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's 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 may be we say yes an accident is an unplanned event could be something like a confined one including gases it could be unconfined it could be something like wagons derailing and have something like believe boiling liquid expanding vapor explosions believe we could also have we said solid substances like condensed explosions in which may be some chemical reactions occur like in Texas may be at Shivakashi we have all these condensed explosions we could also have the confined gaseous explosions in a slightly different context and I 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 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 aircraft were fully filled with kerosene or what we call as jet jet fuel in New York it was the summer month mind 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 there was small amount of kerosene in it aviation kerosene and you know on the ground wherein you you have lot of air available an 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's again a confined fuel air explosion in which you had a huge fireball all the passengers and crew of this flight were killed in this particular explosion you know this is something which we will deal with in in some detail we will look at limits of flammability of substances under what conditions you could have an explosion and we have to address some of these points including the flash fire point of the volatile liquid fuels you know it's not only the the gas the liquid and the solids energetic solids but dust can explode I would like to qualify it further that is what did we tell now well I could have confined explosions because of maybe some tankage maybe you have gas which is a 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 maybe we use sugar maybe we use for icing fine powdered sugar all these are explosive 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 1785 wherein you know you have you had this this particular baker who sends a boy to the go down to collect some some flour I think it was weak flour or me's flour I'm 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 in large number in U.S. wherein they they handle the the the food crops in confinement we had this in Vichita in U.S. wherein you you have seven people being killed in a dust explosion involving I think it was a wheat wheat dust you also have an entire port terminal being destroyed in Brazil in November 2001 which was conveying the the the the the grain was being unloaded in the particular port therefore dust explosion is also and type of explosion which could occur having said that we spend a minute or two on the last type of explosions which we said well it could be accidental we also 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 it got into the volcano got terribly heated up super heated vapor formed as 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 in a particular place in Canada near Ottawa at a place known as Splinflon 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 reverberatory 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 maybe the the operator he takes water in a pail and pushes this into the furnace which is quite hot at that point in 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 Splinflon a town near Ottawa in Canada where in in a copper smelter we had flash vaporizing driving blast waves and an explosion you know such type of explosion was also we must remember in the case of natural explosion at Krakatov 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 two on intentional explosions let's come back to this unfortunately you know the the off 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 a nice posh building which housed maybe children a nursery you know was was was brutally damaged by a blast in which in which case you know a truck carrying solid explosives was parked nearby well it was ammonium nitrate it was a little bit more energetic we will get back into the details when we study the condensed face explosion and the blast wave just ripped off this building it's not only this type you know we keep happening it keeps happening all over the world of late in Afghanistan in Iraq may be while in India we have this improvised explosive devices we have mines being planted and nowadays we talk in terms of these explosions as low intensity conflicts and we have to design the system such that maybe the buildings or the or the type of the blast wave could be controlled or maybe the structure should be so strong said that it doesn't 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 terrorists 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 why is it atmospheric dispersion you know in the 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's take a look at it because it gives some room for thinking in this particular plant which was a carbide plant you know you stored a methyl isocyanide in tankages and you know you have the valves of this somehow you know the the the the the somewhat like a hood which will prevent water ingressing into this was missing when it was being cleaned 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 iron inside the tank and when water comes in contact with methyl isocyanide it begins to react carbon dioxide gets generated and these impurities further led to the reaction with the result pressure in the tank got got increased and normally you know in in the plants you have something like refrigeration coils which will control the temperature of the of this system it was December it was cold these were not operational at that point in time gas got generated the the pressure went up through the vent 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 the the temperature on the ground was lower than above with the result we say atmospheric inversion the gas was not able to diffuse up diffuse out into vertically and and and prevent the the the the methyl isocyanide affecting the people downstream with the result it drifted and whenever it came in contact with people either they got blinded or when the dosage went up they just died over here that means we are talking of the atmospheric effects you know even when we talk in terms of some gas from a pipeline gas is 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 kill were killed why we had also the great smog of London this happened on December 5, 1952 again in the in the winter time during winter time people burned more fuel to to stay warm and in those days maybe the type of coal was also was also not of that good quality created sulfur fumes and it got trapped on the over the surface of the earth this permeated into buildings and something like 12,000 people got killed you know in addition to maybe pollutants and dispersion we recognize that the combustible gases could also move mixed with air and therefore atmospheric dispersion becomes important the last one is maybe in nuclear power plants you have 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 two years back we had this almost imminent but it did not explode this was in Three Mile Island on March 29, 1979 we had this happening in Chernobyl and the only thing which was done was the whole thing was encased with concrete and steel and and and maybe it was it nothing more was allowed to happen this is the last slide which I show this is taken from professor Dewis work and what what is seen here is you know an explosion taking place you see the blast wave from the explosion preceding the matter from the 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 could 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 maybe 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 in in in the Indian space program we also have the belief type of explosion at Jaipur in an oil refinery on 29 October 2009 we had several such believe explosions at Vishak Patnam we also talked in terms of the of the believe 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 they cause lot of damage to life and property and I can tell myself well the first step 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 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 believe 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 in 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 how to proceed further with with calculations of the pressure rise calculations of of impulse which gets transmitted by momentum to to the body which is getting affected by the explosion this is what we will do in the next class well thank you