 The Unchahar boiler explosion is the biggest of its kind that NTPC has faced in its entire history. 33 people have died already, 80 people are seriously injured. We are going to examine how did such a big explosion take place. Was it due to negligence, were the design flaws? This is the question we need to answer. The first thing to note is this is a boiler that both BHL and NTPC are very well acquainted with. This boiler or this design of boilers has been in operation for more than 40 years. It is said that the accident took place because various safety measures were being bypassed because NTPC was in a hurry to complete the full commissioning of the plant which had not yet been done so that Prime Minister could inaugurate this unit number 6 of the Unchahar plant. In the midst of this, it is argued that various safety precautions were not taken and various safety measures bypassed. Let us look at how this could have happened and let us look at how a boiler operates and the scenario that could have unfolded leading to such a severe accident. This is what a boiler is and if you see it, that it in fact takes coal. It is burnt at this level in the furnace in the boiler. Hot flue gases flow down and escape to the atmosphere to the chimney and hot ash. Lot of it comes down at this level to what is called the bottom ash system and some of it also goes out from what is called the fly ash collection system. This case, the issue was really in the bottom ash system where the problem took place. This is a schematic of the boiler and we can understand what happens in the boiler a little better with the schematic. This is where coal comes in and is fired. This is the firmness and here is the bottom ash system which was apparently the guilty party. Here are the hot flue gases that go over. These are the super heater regions and then here is the economizer. This is where water boils, comes in, boils and then is going out as super heated steam out of the boiler. So what went wrong on that day? The argument again we have information from various people who are connected with operating design or operations of such boilers which seems to indicate that this plant or this particular unit had a lot of problems with regard to what is called clinkering of the plant. Clinkering of the unit means that inside the boiler the ash becomes sort of solidified and becomes like blocks of cement and they therefore are difficult to bring down from the bottom ash system. They sort of stick over there and they may even block the bottom ash system. Apparently such clinker formation was taking place in this unit. The attempt by NTPC officials, the people responsible was to bring down the load of the unit while trying to manually see whether they could actually stop the clinkering or they could remove the clinkers from the bottom side of the boiler. Now when you bring down the load clinkering may reduce but if already clinkering has taken place and there is a lot of ash build up in the system then removing it is not easy. NTPC in this case tried to do two things. One is use long rods to try and poke it from the bottom as well as used at 10 meter elevation. There are what are called manholes. Also try to use rods to poke them. So this is what is called a double poke system and they were doing it while the plant was in operation. Now this is a risky proposition not really recommended. Unfortunately this has become something which most plants tend to do because they did not want to shut off the boiler. They try to manually see if they can actually sort of help the bottom ash system to take out the clinkers in this manual through this manual process. This is normally supposed to be completely automatic process. So while they were doing it two things happened. It appears because of the ash build up and the clinker formation the pressure in the boiler started rising. One of the most dangerous things that happened was NTPC seems to have bypassed what is called the master fuel relay trip which is actuated by high pressure. This is a boiler protection that if the pressure goes high the furnace pressure goes high the boiler should trip which means all fuel should stop coming to the boiler. In this particular case it appears that this protection the boiler protection was actually disabled manually so that it would not trip automatically with high furnace pressure. Normally the furnace is really under vacuum. It is under less than atmospheric pressure. So once the bypass of the protection took place we are already entering into a dangerous zone that something can go wrong and the protection automatic protection of the boiler would not be there. When this double poking was taking place it appeared large amount of clinkers and ash fell down at the bottom. Once a large amount of ash and clinkers fell down with this double poking of the furnace. What seems to have happened is that the boiler became unstable. This led to boiler fluctuations pressure fluctuations in the boiler. Please note that as we have already said the protection of the boiler due to high furnace pressure has been bypassed. So this pressure fluctuations did not trip the fuel. So fuel was still entering the boiler that led at some point to an explosion in the boiler. And at one point this seems to have one elevation corner seems to have actually cracked leading to furnace gases exiting into that atmosphere and obviously causing a lot of damage. Second part that happened was that a lot of unfired fuel was getting now carried over into this what is called the second pass. This is the second pass of the boiler and in this pass of the boiler once this lot of unfired coal particles were carried over they caught fire over here and it appears there was an explosion here which led to the economizer flue gas escaping into that atmosphere. So we have two things one is an explosion which caused a crack and furnace duct to really come apart. Large amount of flue gas and ash escaping from this region including steam as well as we had a lot of ash coming out from this region and also it appears a crack somewhere in this region of the boiler. So we had multiple things that happened in the boiler and this whole area around the boiler was then covered in hot ash, flue gas and steam and this is what has given rise to the various burn injuries that people have suffered and killing a number of people. The question to ask is should this have happened? The answer is clearly no that if these safety precautions had not been bypassed there is no way such an accident could have happened. First should this boiler have been maintained under such conditions where it was clinkering? Should manual attempts of double poke which is known to be dangerous? Should it have been a part of the procedure? Should the bypass have taken place of vital protections of the boiler? Should such a thing have been allowed to happen and why was NTPC in such a hurry when already they have at the moment surplus capacity to supply the grid? Why was there such a pressure on NTPC to bring this unit into full commissioning when there was no pressure on the NTPC to produce more electricity? Already NTPC has a surplus of electricity production at the moment. So what was the pressure? Was the pressure only because they wanted to have everything under automatic controls for PM's visit? Was that one of the reasons that NTPC bypassed protection and various security and safety measures? This is a question that we need to ask NTPC. Unfortunately we have no answer from NTPC as yet why this accident happened? Let us see what are the kind of enquiries that take place and whether an independent enquiry really takes place to establish the cause of the accident.