Physicist Dr M V Ramana works at the programme of science and global security at Princeton, and is the author of a unique study on the effects of a nuclear attack on a South Asian city like Mumbai. His paper, entitled 'Bombing Bombay? Effects of nuclear weapons and a case study of a hypothetical explosion', was researched at the Massachusetts Institute of Technology in 1996. The study concluded that a single nuclear bomb attack could result in up to 860,000 deaths.

In an interview with Shyam Bhatia, Dr Ramana says the conclusions he drew are as valid today as they were six years ago.

Why did you choose Mumbai for your study?

For two reasons. One is that I started looking at this as an exercise in a course I sat through given by Dr Ted Postol, professor of science, technology and national security policy at MIT, in 1996. He's done similar work, for example on the mass fires started after a nuclear attack in the case of the US and the Soviet Union.

My initial expectation was that everyone knows nuclear weapons are very destructive, lots of people are going to die, and stuff like that. But what I found while doing this was that the graphic details were so graphic that it shook me up to know the exact ways by which people die.

So l thought it was important to write about it in detail and do this analysis in as much detail as possible.

Why did you base your study on the likely impact of a 15 kiloton explosion? Is that the size of the average Pakistani nuclear warhead?

I actually didn't want to talk about whether the bomb would come from Pakistan or China, or any other place. What I thought I would use as my basis was the oldest and first bomb that was ever used, which was Hiroshima. One could assume that any modern weapon would be at least that much and probably larger.

The reason is that it was not actually the Pakistani bomb at the time, but this work was before much of the nuclear tests of 1998 and suddenly it became relevant. It was not something I had planned. The only thing that was in existence at that time in South Asia was the 1974 nuclear test by India and that was of a 12 kiloton weapon. They had talked a lot about weaponising it and there was talk about making it into a usable nuclear weapon.

Indeed when the later tests happened, the one test of what they called of a weaponising configuration was of the 12 kiloton weapon. It was the same order of magnitude as Hiroshima.

Could you list the causes of death caused by a nuclear attack?

The first thing you will experience is the light and heat that comes out of the fireball. When the bomb explodes, a huge amount of energy is created very locally and that heats up the air around the point of explosion so much that it starts radiating enormous amounts of heat and light. Your skin just starts to burn.

The fireball would be like a thousand suns. So what you would first experience is this very large amount of heat and light coming out of there, so people's skin would burn, their clothes would catch fire.

The nuclear reaction that caused this energy to be produced also produces neutrons and gamma rays and these would emanate from the point of explosion, coming outwards. If you're exposed to them and if you are not shielded you could get a lethal radiation dose. You would not die immediately from it, but it would start manifesting itself in a matter of a few days -- the vast majority of deaths happen within a few weeks.

It depends on the level of radiation dose that you get. At lower doses you get cancers, but what happens at high doses is that you start throwing up, there is body hemorrhage, bloody diarrhoea and so on. Essentially there is a complex of symptoms that goes under the name radiation sickness.

The third type of exposure from standing near the bomb is the blast, which is like from any explosion, like from a car bomb, for example. There is a small portion of the atmosphere that's compressed and expands out from the point of explosion. Your lungs could collapse, your ears could collapse, you could be thrown against a wall, various objects that are in the region, a piece of furniture, could be picked up by the blast and could hit you.

A little later you get the start of delayed effects. The immense amount of heat will set many things on fire, like bits of paper, wood, anything that's combustible. Initially there are only localised fires, but soon the fire region starts coalescing and you have this whole region on fire.

How hot does it get?

The temperatures that are generated go up 700 to 800 degrees. Anyone who is in that region will be trapped. It's very difficult to run out of that part because what happens is that the heat is so high all the air starts to rise like from a chimney and then to replace the air, more air comes from the outside. It's like a circle with wind coming from the outside everywhere, like a suction pump. When you try to leave the circle, you won't be safe because there's a very stiff wind and the wind blows at 50 to 60 kilometres per hour and you're like trying to escape in the face of a cyclone or something like that.

In some of the pictures that one sees from Hamburg or Dresden or so on, people who are trying to leave essentially have to crawl out of the fire. You can't walk because the wind is so intense and you can't crawl very fast so you're pretty much going to be caught there.

Finally, if the explosion happens sufficiently close to the earth then the initial fireball sucks up huge amounts of soil, all kinds of things on the ground and these things mix with the radioactive materials created during the explosion and go up initially with the famous mushroom cloud, but eventually they come down to the ground.

This is all part of the radioactive fallout and exposure to that gives you a radiation dose. Depending on how much, the symptoms you will have range from radiation sickness mentioned earlier to an increased risk of cancer.

How long do the overall effects last?

The people who were exposed to the bomb in Hiroshima and Nagasaki, some of the survivors are still living. But among them you do see an increased incidence of cancer, especially leukaemia and various solid cancers. It essentially goes on for at least 50 years and then the area itself is contaminated. So to live there would be difficult unless you mount a vast clean-up operation. Finally, the nuclear radiation can cause genetic defects that go through generations. We have seen what happened after Chernobyl and at the old Soviet nuclear testing grounds in Kazakhstan. Even in India, for example, one sees evidence of genetic birth defects in high radiation areas like the uranium mining area of Jaduguda.

Has the international community learned any lessons from Hiroshima and Nagasaki?

I would say that we have seen how nuclear weapons are hugely destructive, they are nothing like what we have seen before. By no means should one think of them as glorified large firecrackers. Unfortunately, that's the view many people have of these things. So I'm not sure that a lesson has been learned, but its certainly one that ought to be learned.

In terms of the damage that radiation causes to human health, the vast majority of our knowledge about what happens when people are exposed to radiation still comes from Hiroshima and Nagasaki and these include cancers, birth defects and so on. As for the physical effects, more of the knowledge comes from the tests that were conducted at Nevada and Kazakhstan. These were much more like well-studied experiments. The US actually built houses which they tried to knock down from a nuclear blast, just to see how far these effects go. A lot of technical knowledge came from that. But a lot of the knowledge about fires still comes from Hiroshima and Nagasaki.

Is there any conceivable protection from a nuclear attack?

Not really. There are three possible ways of protection. The first is prevention, to prevent the bomb from exploding by deploying ABM systems. Those things really don't work. The other thing we know is that defence is much more expensive than offence.

Second, both the US and the Soviet Union did build a large number of bomb shelters. What these shelters could do -- provided you had sufficient warning -- is that they could protect you from the blast effect and they could prevent the initial radiation from hitting you. However, the shelters cannot withstand these mass fires. During the height of the Second World War in Germany the population of Hamburg and Dresden used to hide in bomb shelters, but after some of the mass fire attacks people just got charred inside. The temperatures inside were so high that they either asphyxiated to death or just got charred. It was like an oven. There was one memorable picture of how a bomb shelter was opened in Germany and all they found was ash on the ground.

Then again there is the whole question of what happens when you do come out. You'll come out into extremely radioactive surroundings and you cannot escape that.

Finally, some people, including personnel at the Bhabha Atomic Research Centre at Trombay, have said they will distribute iodine tablets, which are supposed to protect your thyroid, but that's such a small part of the damage that its ridiculous to think of that as a solution. It would be laughable if it were not so tragic. I don't think there is any protection whatsoever.

Are buildings in Mumbai more vulnerable for some reason?

It's not so much Mumbai that is unique as the typical South Asian city. The most important characteristic is high population density. Several million people in a hundred odd square kilometres. Any region that's destroyed will kill a huge number of people. Then there are large number of shacks, gas cylinders, automobiles that will add to the fire.

Some parts of Mumbai have a large number of industries, for example the whole Chembur/Trombay area is home to a large number of chemical industries. Trombay has BARC, which is India's nuclear weapons laboratory and a likely target and explosions could result in either toxic chemicals or radioactive material adding to the mixture.

In your study you estimate the number of deaths in Mumbai resulting from a nuclear attack at anything from 160,000 to 860,000. Isn't that a huge number?

The initial comments I had from everyone was that this was too small and wasn't I underestimating it. To some extent the answer is yes, because I wanted to be as conservative as possible. The larger figure is entirely possible because the population density in some parts of the city is so high. Think of the morning rush at Churchgate or Victoria terminus and you'll see that if something goes off there it will instantly kill huge numbers of people.

Therefore, I have good reason to believe that the final count could be at the higher end of the estimates. But I also think there is no need to exaggerate. There's no need to talk about millions dying, this is shocking enough as it is.

Do we assume that if there is a counter attack from India, the same devastation would be visited on Karachi or Lahore?

Right, although one of the reasons I used Mumbai is that it's close enough to the border with Pakistan and it's a city I am roughly familiar with, whereas I'm not so familiar with Calcutta or Lahore or Karachi. But I think Mumbai is fairy typical of a lot of cities on the subcontinent.

What would happen if the bomb were bigger than 15 kilotons? Does that mean the casualties in somewhere like Mumbai would be twice as large?

Yes, to give you a technical answer, the area that is exposed to the vast fires would be proportional to the size of the bomb. So if it's a 150 kiloton bomb, the area affected increases by a factor of 10. That means if the population density was exactly the same it would mean that many more deaths. In a place like Mumbai that may not be the extent because it's an area jutting out into the sea. So a lot of the area is sea and there probably wouldn't be the number of deaths proportionally. But in a place like Delhi, for example, it would be the case.

From what you know is there any specialist medical training available in India for victims of a nuclear attack?

No, not to my knowledge. What you would probably require in the nuclear aftermath is the expertise to deal with the victims of fires, burn injuries and so on. Off the top of my head I don't have the numbers, but I remember the number of fire beds in hospitals is less than one per 10,000 on average in India. In any area hit by the bomb you are already going to be destroying the hospitals, not to mention the transport infrastructure so that people can't come in and go out so easily. It will be a big mess.

The one hospital that deals with radiation is the Tata Memorial Hospital in Mumbai, which is associated with the BARC. If it's Mumbai that's going to be hit that will also be out.

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