 Good morning. In today's class we will discuss a few case histories of explosions which involve detonation. Let me get started with the first one which is supposed to be the worst case history ever. This involves an accidental leak of liquid propane from a pipeline. Before getting into the details, let me first tell you when it occurred and what happened. The pipeline ruptured at a place known as Port Hudson. It was in the Franklin County. This is in Missouri and the leak happened on December 9, 1970. You know it so happened when liquid propane was being transported in a pipeline. This pipeline was of diameter something like 0.2 meter diameter at a pressure of something like 65 bar. From the site of the place where it was being transported, this particular accident happened at Port Hudson. This particular place was in a valley like for instance you had the topography of the place something like a valley. Something along the slope of the hill you have the pipeline which is sort of buried pipeline and it is transporting liquid propane at a high pressure. Why it is transported at high pressure is you know you propane is a gas normally it liquefies or it becomes a liquid at minus 42 degree centigrade. However at high pressure you can still transport it as a liquid. In this particular pipeline which was somewhat old something like 40 years old a small at the weld fracture at the weld sort of a leak developed and liquid propane started gushing out from this particular pipeline. Let me put it in a buried context and then let us go ahead and see what happens. You have the buried pipeline over here leak develops and liquid propane gushes out of the particular hole or the weldment wherein the failure has happened. The movement the liquid propane starts to gush out you know upstream of the particular leak people stop the supply but then there is lot of propane here and something like 2300 kg of propane got spilled from this particular leak. You know when liquid propane comes out you know the liquid propane is initially at the ambient temperature mind you it is a December month. The ambient temperature was something like 1 degree centigrade being a winter month and there was this wind along the valley along the slope of the mountain at around 2.5 meter per second this is the wind speed. You have the propane gushing out and the movement it gushes out you know from the high pressure region it sees the atmospheric pressure and because of the atmospheric pressure it flashes into vapor. The movement it flashes into vapor it absorbs that means the liquid flashes into vapor and therefore it absorbs the heat and therefore what happens is even though you have gas which is which should be there at atmospheric pressure because of the removal of latent heat you have liquid droplets which are being formed you have something like a fog of droplets which are being formed and you have a spray and the nearest place from which people could observe was something you have a highway which is something at a distance of around 800 meters away from this particular place where the leak develops. Therefore a few witnesses observed this this particular spray and this spray was something like almost like 15 to 20 meters high that means you have a huge spray of the the gaseous vapor you have the droplets of vapor which are being formed. Well this is what happened and as I said the nearest place was the highway and then because of the wind conditions you know this particular cloud now you have something like a whitish cloud which is being formed this cloud moves along the wind speed and the wind speed drags it along the ground and therefore you know the atmosphere transports this cloud and we will be studying about atmospheric dispersion at that point we will again revisit this example but this this cloud gets transported along along the valley at a place something like a 600 to 700 meters away you had a concrete warehouse you know you had this building and this was a two-story building in the bottom you had something like four or five rooms which housed a deep freeze unit you know in this deep freeze unit you had something like four deep freeze units in this thing and as the cloud moved you know you it was a winter month everything was closed and through the sliding doors of this concrete warehouse what happened is through this concrete through the sliding doors the cloud sort of diffused in and you had a mixture of propane with air being formed over here I will revisit it of the mixture gets formed therefore you have the cloud which comes in here maybe at the point of spill itself the gushing was so heavy because of the high pressure that a pit of width around three meter diameter and a depth of something like two meter diameter got formed that means that is the speed and because of the high velocity it also entrained air and therefore you have in this sort of spray which is being formed here air and propane available and this air propane blew into this particular warehouse and you had conditions wherein you could have a flammable mixture or even a detonable mixture but let us revisit this problem the leak happened when the time was around 10 25 p.m. it is at night you know the place is not heavily habited and therefore you have just a few houses and and maybe it is essentially a wooded area and for sometime like 20 minutes nothing really happened the cloud gets drifted along the valley and and what happened is it did not see any any sort of a ignition source or any spark or anything which could ignite it and it just entered this warehouse wherein these refrigeration units were there in the refrigeration units you have these control motors of the refrigeration system that is in the defreeze units control motors let us say and the heat source in these motors plus the spark from these motors it it ignited a flame in this particular warehouse therefore you know you know to ignite a propane air mixture you need something like like 0.2 milli joules of energy whereas to cause detonation in propane air you need something like 100 kilo joules of energy therefore to have a detonation being initiated in this place is just about impossible and therefore let us say a flame gets started because of the blockages which are available in this particular room which is housing these defreeze units the flame develops into a fast deflagration and then probably into a detonation and when you have a detonation or a very something like a quasi detonation I will again discuss this a little later what happens is the pressure behind it ruptures the the the the the warehouse which means it should have been a detonation to have ruptured this and you have the cloud which is available and this this shock wave created ignites this particular cloud over here and what people observe is up till around 10.45 pm nothing really happens when at 10.45 pm 20 meters after the leak originated you see a lightning in in the in in the leakage area just a brilliant flash as it were saying that something all of a sudden has happened followed by the loud bang mind you before this loud bang from this lightning of the propane air cloud which is formed over here prior to that a bang was heard when this thing got initiated a detonation got formed here therefore you have a detonation which occurred here due to blockages flame to detonation transition which creates a blast wave and or a shock wave and the shock wave ignites it that is when people observed a lightning in the sky in in in the valley and this caused the detonation and therefore you have something like a waiting period of something like 20 minutes after which you create a detonation and this detonation was so strong that maybe people who are witness to this particular accident from the highway when when they were just toppled down and even at a distance of something like almost like 20 kilometers away it is reported that one of the cops who are driving his vehicle he lost balance because of the wind effect and that was the powerfulness of this particular explosion therefore you find that in this case the accidental leak of something like liquid propane forms something like a cloud of fog of cloud which which has something like 2300 kilograms of propane apparently nothing really happens because of atmospheric dispersion and because of the intense velocity and turbulence with which the liquid propane is gushing forward it entrains the the air mixes with air you have a flammable cloud formed right here but this cloud keeps drifting gets into the warehouse gets ignited in the warehouse where it meets its first ignition source forms a flame it becomes a detonation knocks out the warehouse and the shock from this warehouse is what causes the particular detonation the detonation was so strong let us put some numbers into it like 10 kilometers of wooded area around the site that is got got got damaged buildings around 10 kilometers got damaged and we if we if you look at it you know we are seeing that the sky got lit up or lightning sort of thing happened 20 minutes afterwards that means you waited for 20 minutes and therefore whenever you have a leak you know the longer it takes longer it takes to ignite the more and more of the of the of the combustible cloud gets formed and you run into the danger of forming a large explosion and this is what happened which means you know for an explosion to occur again redraw what what we are learning what we have you need a fuel in this case it is C3H8 propane you need air to mix together and in this particular case there is no doubt that because of the high level of turbulence with which the spray is getting formed that it get mixed over here you have a mixable cloud and once the the the the valley gets lit then what happens is the heat from this sort of divorce you know it it it it feeds into the fuel rich propane which is still available and you see a red glow of fire which happens afterwards it consumes the the the remnant of the propane air or propane rich mixture which is formed therefore you have something like a fuel you have air you have an ignition source within the air warehouse which starts a blast wave or which starts a detonation this detonation breaks through the door and windows of this warehouse and ignites the cloud and this is what happened in this particular case well this is a well recorded case and the atmospheric dispersion has been done we will do the atmospheric dispersion a little later but this is one of the instances of an of an practical explosion of an accidental explosion having said that let's come to the next example we will we will look at some other gas let's take a look at let's say natural gas you know natural gas is widely used nowadays and the reason is you have the gas fields from which the natural gas is taken and is transported in pipelines and one such pipeline in in the in Ural mountains had massively let's let's take a look at it this pipeline was something like almost like 0.8 meters in diameter it was conveying natural gas natural gas is mainly methane CH4 compared to propane which we just now talked of mind you in this case it was liquid propane we are talking of gaseous methane over here which is being transported this was being transported at a pressure of something like 25 atmospheres and the pipeline was designed for 50 atmospheres the reason I give this is the following in a over a length of something like 1 to 2 kilometers may be the pipeline got ruptured and that means it's a massive massive leak and the operators who are supplying this pipeline this was from the gas field in western Siberia they found that well the pressure has gone down they pump more and more thing therefore you had a huge spill of me of natural gas which was being formed now why did this accident happen let's let's put some dates into it this happened on June 4th 1989 in the Ural Mountains and the the the leakage was something like 1400 1400 kilometers downstream of the gas supply station and the I'm sorry the the diameter of the pipeline was 0.7 million 7 meters not 0.8 meters and it cracked as I said over a distance of 1 to 2 kilometers giving a massive leak therefore what happened you have a massive leak of methane taking place a huge cloud of methane and during the leak because of the large thing it does not enter in too much of air unlike in the in the previous case wherein you had liquid methane flashing into vapor drawing lot of because of the high turbulence with which it's getting out it is turbulently entraining lot of air and forming a cloud at the exit itself at the exit of the leak itself in this case you know it is not entraining it's not able to entrain so much of air you have a cloud of methane plus a little bit of air which is being formed now this particular place where this leak happened was at a place known as near to us to a place known as Eufa and it was this it was between Eufa a place and the other place is Asma in Siberia and at a distance of around 500 kilometers from Eufa this is where the the the spill took place in this part of the of the terrain you have the Trans-Siberian railway you know in in USSR in in Russia you have this Trans-Siberian railway railway line running between Ladivostok in the east that is near to Japan to Moscow and this is a double track railway line that means you you have two railway lines two trains can go up and down and at this particular place near Eufa you have this Trans-Siberian railway and as luck would have it just after this leak got developed you know you had the leak taking place in this particular region you have a cloud of of natural gas that is methane and mix partly with air and at this point two trains were traveling simultaneously in the opposite directions that means you have a train going from east to west the other going from west to east and whenever the trains are traveling you have intense turbulence in the region between the trains and this turbulence help to mix the methane that is you should have put a CH4 the methane and air together you form a good combustible or a detonable mixture and these are electric trains and you have these electric trains that means you you have overhead electrical line you have sparks available always available here and this spark ignited the cloud here and when this ignited you know the force of the detonation was so large it formed a detonation it could not have formed a directly a detonation because spark does not have an energy we saw that to be able to directly form a detonation in methane air mixture which is stoichiometry requires something like 10 to the power of almost 3 kilo joules apparently a flame got formed you have the blockages due to the railway carriages over here wagons and in this wagons may be some 500 people were traveling essentially school children and you know when these wagons are there it creates turbulence it creates blockages the flame becomes a detonation and in the detonation because of the force of the shock wave in the detonation something like 28 carriages were just blown off from the track and also that the track of the two railway lines also blew away that was the force of this explosion and all the 500 people who were in these carriages got got killed and that was the force of this particular explosion therefore to sum up we can say that this particular explosion which not not only blew off the carriages but also demolished the railway line and over any area of something like 3 kilometers square what happened is that the trees were uprooted the buildings were decimated and this is the force of this particular explosion therefore what do we learn from this particular example this is known as the the largest ever man-made explosion and as I said this happened in the Ural mountains and the it happened on June 4 1989 well there have been case studies of this particular explosion including the dispersion of methane gas we will look at the atmospheric dispersion later but what really formed is the is the turbulence created when the two trains were moving as fate would have it we had two trains moving through the particular cloud of methane at the same time created turbulence mixed with air you had the electrical spark and we had the fire triangle wherein in this case you have methane gas you have air over here you have the spark which creates a flame the blockages of the train cause it to become a detonation and the wagons just just get blown off and this is the case of a natural gas explosion which happened in Ural mountains on June 4 1989 since we are with natural gas let's take one one more example of a case study of an explosion this happened in Cleveland in Ohio this this was on October 20 1944 you know this involved the the same natural gas but a liquid natural gas you know when when we talk of natural gas which is methane you know people prefer to transport it as a liquid because it's denser and it is the the temperature of the liquid natural gas is something like minus 161 degrees centigrade at atmospheric pressure we have LNG which is liquid natural gas maybe it's it's non-corrosive it is it is a harmless liquid non-corrosive it doesn't have a particular smell and this is being this is transported from all over the world in tankers maybe through pipelines and and through through wagons and the reason being you know you have an insulated container which can hold this particular low-temperature thing and or in the hull of a ship and you transport it in this case it was a storage area wherein you had tanks something like four four four storage vessels in which liquid natural gas was being stored as I said liquid natural gas is stored at cryogenic temperatures 161 it is formed by the mixed refrigeration cascades cascade process at these low temperatures and stored over here you know it so happened one of the containers developed a leak and the liquid natural gas escaped from this case from from the from the storage bin or from the storage vessel now we said well liquid natural gas is at low temperature let's put it in terms of Kelvin you have 273 minus 161 which is equal to 2 over here 1 might be something like we are talking of 112 Kelvin which is the temperature of your your liquid natural gas and you know at this particular temperature since the temperature is low liquid methane let's say what is the molecular mass whether it is denser or heavier you know if you talk of CH4 the molecular mass is 12 plus 4 16 grams per mole when we talk of therefore it compared to air whose molecular mass is something like 28.8 let's say 8 gram per mole it is lighter and therefore whenever let's say in the in the previous example when we say LNG leaks now it tends to diffuse into the atmosphere being a light gas but in this case you have the liquid methane which is at low temperature the gas coming out is at low temperature of the order of this low temperature and because of this low temperature it is much much heavier than air we can have an expression we can find out what its density is because the in proportion to the molecular mass therefore you have 16 divided by 288 you have the temperature in Kelvin which is equal to something like 112 that means the we are looking at the density therefore it is 112 divided by we are we are talking of 28.8 here 16 by 28.8 the ambient temperature let's say is 27 degrees centigrade that is 300 Kelvin well this becomes heavier than air and this becomes around 1.5 and therefore the leak from this of the low temperature natural gas sort of hugs the particular ground in other words let's let's let's draw this again we have the natural gas at the low temperature escaping from the storage vessel and being a low temperature gas it sort of hugs the ground it is on the ground the conditions of the air they are not specified but perhaps you know it would have been a low wind and the and the low wind speed and therefore the the liquid natural gas or the natural gas hugs the ground and travels forward there was a sewage plant at some distance from the storage area and in a sewage plant you know you have these perforations on the ground you have the sewage gas coming over here you have these process and when this heavy gas goes here it enters the sewage sewage area and enters the sewage area and enters the sewage pipeline and therefore you have natural gas that is methane gas you have sewage gas you have air in it all these things get mixed in this particular sewage line and when the when the mixture of sewage gas the the natural gas and air are mixed together you know because of the velocity apparently some spark occurs inside and there is a flame being formed well I cannot expect to directly initiate a detonation a flame gets formed because of the blockages which are available surface roughness of the pipelines etc this flame becomes a detonation and what happens you know whenever you have the sewage lines which are laid you have the man man manhole covers which are kept on the on the roadside and the sewage line is over here the manhole covers sort of sky rocket because of the detonation which occurs in this particular sewage line they sort of skyrocket up and it enters the houses causes fire in the houses and causes a lot of discomfort and this is the case of we say an LNG getting into an explosion in this particular case also we talk in terms of a low temperature methane mixing with air also mixing with sewage gas in the sewage line and how does it go it is transported by atmospheric dispersion the low temperature gas which is heavier gets into the sewage line and that's where the the explosion occurs and well the incidents occur later on and therefore you have a spark in the particular sewage line which causes the explosion well this is the case of the Cleveland explosion which happened on October 20th 1944 and in this particular case in addition to to blowing up homes in blowing skyrocketing of the of the manhole covers you know you you sort of destroyed the the it destroys the township as it were therefore whenever we talk in terms of LNG and you know LNG is an important fuel as on today it is being transported as I said by ship and you know whenever we talk of LNG leak on the ground let us say I have the ground over here LNG is let's say leaking from from a reservoir here it falls on the ground cools the ground and therefore when the ground gets cold the the liquid natural gas does not increase in temperature and mix with air but supposing the same leakage happens from the ship and there are special ships available for LNG transport we have all all over the world including the Atlantic Ocean Indian Ocean we have births for ship even in India and therefore whenever you have LNG spill over water the turbulence in the water may sort of allow the mixing with air and therefore the transport of LNG has to be done with caution based on this particular example and the possibility of an LNG explosion in all these three case studies which I have done which I have just now gone through what is it we find let us quickly put things together in proper perspective we talked of the case over Port Hudson where in you had liquid propane from a pipeline we talked in terms of the UL mountains at Ufa wherein you had the natural gas C3H8 as a liquid you have natural gas and in Cleveland Ohio wherein we talk of liquid natural gas and all all these three apparently caused a detonation which caused caused lot of damage around including even to the extent of pushing up the manhole covers making them fly like rockets as it were therefore having seen these three cases it's now time we we focus on one or two let's let's take one more example let's take the example of a hydrogen air explosion you know I deliberately take this example because it's not very sure whether in this particular case we had a detonation or just something like a pseudo detonation or a fast deflagration therefore let's take a look at this hydrogen air explosion this happened in downtown Stockholm in Sweden this happened on March 3, 1983 the incident was the following there was this particular truck which was carrying the cylinders different cylinders containing different gases and in this particular accident the truck was was parked in downtown area or downtown in Stockholm and you know the this truck you know was stopped there to supply gas to different establishments around the particular place and what was there you had in the truck in addition to other gases you had something like 18 cylinders of hydrogen at 200 bar and all these things were interconnected together something like 18 of them and along with hydrogen gas in the cylinder there were other gases and the operator was shifting the other cylinders for supply he found that there is something like a hissing noise which he hears coming from the from the from from the cylinders therefore he wants to investigate it the moment he hears it he goes down but within 10 seconds he hears some there is an explosion and what happens is maybe at a distance of something like 90 meters away based on the breakages of glass from a building we say as 5 kPa over pressure was created we have studied different over pressures what causes glass to break we say 5 kPa over pressure can cause it apparently what has happened is there has been a leakage and the amount of leakage was something like totally 13.5 kg of hydrogen got leaked out of which when the explosion started at 10 seconds apparently something like 4.5 kilogram of hydrogen was was available in a cloud of something like 600 meter cube you know let's let's take a scenario you have something like several cylinders which are available a leakage of hydrogen takes place something like over an area of 600 meter cube it it it is possible this cloud gets ignited perhaps a flame got formed when the flame gets formed it meets the blockages it accelerates because we saw whenever you have a high speed flow interaction of the high speed flow with blockages creates shock waves or creates expansion and compression waves which are weak shock waves and in that presence because of the turbulence associated with these wave processes may be the flame becomes turbulent the acceleration of the turbulent flame leads to something like a turbulent flame brush which is severe turbulence and it's quite possible that this turbulent flame brush traveling with high speeds could could also result in 5 kPa over pressure therefore the accidental leak of hydrogen from these cylinders in Stockholm does not necessarily say a detonation is formed therefore but it is also possible that a detonation of this cloud could have could have resulted in this over pressure but it is also quite probable that even if it was not a pure detonation it was a high speed flame we could still expect to get this type of over pressure therefore I think before we we put this example through we must be a little more clear what we mean by this let's say turbulent brush of flame highly moving at high velocity and what we mean by a detonation is a detonation formed in this case or not you know to be able to do that we should be able to understand the the acceleration of a flame to high speed and therefore let's let's spend some two or three minutes on on interaction of a flame with blockages all what I am trying to say is it is not necessary that you have these pressure waves and damages coming only from a detonation but we could also have the pressure waves and damages in this case you know what happened buildings got damaged and people were thrown off because of the waves created by the particular flame brush or a detonation therefore it is not that only a detonation can cause damage whereas in the other three case studies which we just now saw in all the cases a detonation was formed in this particular case even a turbulent brush or a flame brush could have caused such a problem therefore what is this turbulent flame brush under what conditions does it get formed let's spend a couple of minutes on this particular problem you have blockages which are there maybe in the truck in terms of cylinders maybe outside you have the blockages from buildings and all that and what happens if a flame is being if a flame is traveling well it initially travels at laminar velocity of flame is formed here depending on the conditions and this when it interacts over here maybe this is the zone of higher turbulence and whenever you have zone of turbulence the flame becomes wrinkled and when it wrinkles well it engulfs more gas it becomes more and more wrinkled if the status is such that you have the shock waves and or weak shock waves which are being formed in all particular direction you have slip streams you have vortex and all that therefore you have something like an intense turbulence over here you have something like a flame which is formed which is highly turbulent well we have seen we have distinguished between a detonation and a flame in the reaction hugonium let's plot that figure again we said well pressure versus 1 over density the initial pressure is let's say p1 the initial density is 1 over rho 1 therefore this is my initial point well I have the reaction hugonium over here and therefore we talk in terms of the upper the Chapman Juge points in the in the particular plot which I show over here we say well the Chapman Juge point is the tangent point from the initial point to the reaction hugonium over here therefore this is my Chapman Juge point which we say is upper Chapman Juge point this corresponds to a detonation if I were to extend my my hugonium and then I plot the tangent to it that is the Rayleigh line from here I get the lower point well we said you know the the region between this to this is somewhat stable is somewhat can be met in practice you have the lower Chapman Juge point here the velocity behind the flame is equal to the sound speed just like we have u is equal to a such that we had u1 is equal to a1 here therefore this corresponds to the lower Chapman Juge point but what was the characteristics of a flame the flame is always such that you have an expansion solution we cannot get compression solution if we talk in terms of a of a flame even if it is moving at high velocities when you have these blockages and you have the flame accelerating it has been observed that sometimes the flame is so turbulent that it almost travels at something like the sonic speed that means it travels at a speed corresponding to the to the sonic conditions behind it you know therefore you are having something like a choked flame or rather the chemical energy supplied to the flame is such that it almost choked chokes it and it travels at the sonic speed but how is it possible that is one question we have to ask but since we are talking of flame has an expansion solution how do we get pressure over here now when we say you know we are saying there are shocks ahead of it if there are shocks ahead of it the pressure increases and therefore in this high zone of pressure that means the pressure is no longer atmospheric pressure here it is high pressure and in this zone of pressure if a flame is traveling and it is traveling at the sonic speed well we still call it as something which is a turbulent flame brush but since a turbulent flame the common notion is the pressure should be less than the ambient pressure we also call this as something like a pseudo detonation in other words a pseudo detonation is a shock front behind which may be chemical reactions are taking place but the chemical reactions are such that it is not able to drive the shock front effectively to form a cj detonation and what happens is the net flame that is the net shock now travels at a speed which is around which is such that the speed corresponds to the sonic speed behind it which in effect corresponds to the velocity of cj detonation divided by 2 this is the typically the velocity of a pseudo detonation that means you whenever you have a shock which forms chemical reactions but these chemical reactions are decoupled from the shock you say well it is a it is a pseudo detonation you still have a compression solution over it and the compression solution corresponds to this particular l point and you call that as a pseudo detonation and whenever you have blockages what happens let us assume I have blockages and in these blockages let us say Chapman-Jugay detonation at vcj is traveling and when the diffraction takes place at the at the blockages well you know the gas expands and when the gas expands well I have the shock here well the the chemical reactions now the shock expands and therefore its velocity decreases when its velocity decreases the chemical reaction gets decoupled and therefore the effect of losses from the blockage are such that well I can have a pseudo detonation but we must also remember we had developed an equation for cj velocity vcj square is equal to 2 into gamma square minus 1 into the heat release therefore you know we cannot imagine that the heat loss due to blockages essentially cause the cj velocities to drop in drop to a value around half the value but it is effectively what is happening is the decoupling behind the shock and this decoupled chemical reactions from the shock is what we call as a pseudo detonation well it is also something like a highly turbulent flame brush which is being formed and the initiation of a detonation if we go back to what we discussed about initiation we always formed a shock wave and under critical conditions of initiation well the flame lagged behind or the zone of chemical reactions lagged behind the shock by a by a particular small distance which means in practice I could have a pseudo detonation if I have plot the distance over here I say I have something like a like the shock over here rs dot over here it it it decays in strength travels as a pseudo detonation and then becomes a detonation and we did discuss this earlier this is equal to rs dot as a function of distance therefore you know in in the case at Sweden perhaps in the example of Stockholm where in hydrogen league you form something like a highly turbulent flame brush or a pseudo detonation which created the waveform therefore it is not essential that you always get a get something like a like a detonation to damage buildings you could also get a highly turbulent flame brush which could cause havoc having said that let us take one or two small examples which relate to other substances let us take let us say solid substances solid fuels I will just concentrate on two typical examples the first example I take is terrorist attack and this terrorist attack happened at Oklahoma city you know in this Oklahoma city a nice posh building a nine-story building a federal building known known as Murray building nicely done with lot of glass front and all that was ever was there it was the pride of Oklahoma city and some disgruntled elements in society they they wanted to attack this building and what what they did was they got together on on April 16 1995 I take this example because we have lot of articles on the terrorist attack and Murray building it came in readers digest also a few years ago you know the what what was done was they took something like 2500 kg of ammonium nitrate NH4NO3 crystals ammonium nitrate NH4NO3 and mixed it with diesel oil and some nitromethane see nitromethane is a cleansing fluid it is also used as a fuel for sports car this is a fuel this is a fuel this is an oxidizer they mixed 2500 kilograms of this parked the truck just outside the Murray building and they made sure that it gets initiated into a detonation by by forming a strong shock using some other initiator that means they directly initiated a detonation initiated a detonation in the in the 2500 kg and this particular the detonation was so strong that it blew off about more than half of the Murray building totally it damaged something like 89 cars it killed something like 280 people who were in the building and around and it was the worst ever tragedy one could think of you know these are the type of things which have up which a detonation can do and we must remember that maybe we should we should take these things a little seriously and make sure that such terrorist strikes do not happen but getting getting back to this particular example this is a case of direct initiation of a detonation in this particular mixture of 2500 kg and the amount of substance was so large that it just blows off the the source was the source of this namely ammonium nitrate diesel oil and nitromethane was kept in a truck and it created it was forced to create a detonation by a by a strong initiator and that caused the damage as it were well we have such a number of explosions taking place and one of the recent ones which I want to just highlight before I stop here such that we can get started with confined explosions in the next class or confined and unconfined relates to the example at which happened last year namely the boston marathon this is on april 15 2013 you know here what happened is you had these pressure cookers that means you had cookers which can hold pressure and that is how we cook off hold in two pressure cookers combustible substances were kept and maybe some some energetic substances combustion or detonation was initiated and when high pressure gets developed in the cooker well the cooker just ruptures a blast wave is formed and this blast wave disrupted the the boston marathon last year and it result resulted in fatality being three but more than the fatality the type of damage and the type of people getting injured is something which is which which is very very undesirable therefore in this particular case you have a confined vessel of a given volume in which we start an explosion and in the next class what we do is we take a look at explosions in confined and also in unconfined geometries well thank you an announcement please we covered the subject of flames and detonations in as much as they influence the explosions in the lectures 20 to 27 additional reading material and a set of homework problems pertaining to these lectures are given in the 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