The shock wave of a blast centred in the Fort area would destroy more or less completely a circle with a 1.1-kilometre radius. Most of the buildings from Colaba to Victoria Terminus, along the entire width of the island, would be destroyed. All kuchha houses up to 1.7 km from the point of explosion would be destroyed. The winds accompanying the shock wave, reaching speeds of over 110 km/h to a distance of 3 km or more, would destroy many more buildings. One has to remember that many of the city’s buildings, especially older ones, are poorly constructed and are liable to collapse due to the shock wave and the hurricane-speed winds even if they are far from the epicentre.
Within a few minutes the fires ignited by the flash of light and heat would start to coalesce into super-fires, engulfing an area within a radius of up to 2 km. The temperatures in the fire zone could reach several hundred degrees. The high heat covering such a large area would act like a large pump sucking in air from surrounding areas. The inward winds would reach speeds of 50-80 km/h.
The combination of high winds, thick smoke, destruction of water mains, debris blocking access routes, as well as destruction of men and materials would make effective fire-fighting impossible. The chance of citizens in the blast area escaping the firestorm would be slim.
Unlike the cities that suffered firestorms during World War II due to aerial bombings, the fires in Bombay would be much worse because of the many secondary explosion which would take place in the wake of the heat and fire of the nuclear blast. These would include explosions of gas cylinders in household kitchens, diesel and gasoline tanks of motor vehicles, pump stations, as well as industrial neighbourhoods full of flammable and toxic materials. India’s highest concentration of chemical industries is in the trans-Thane creek area, which has over 2000 factories. Central Bombay itself is home to several mills.
Besides chemical industries, India’s largest nuclear laboratory, the Bhabha Atomic Research Centre, is in Trombay, just outside Bombay. A nuclear explosion in the vicinity of the reactors or the reprocessing plant or radioactive waste/spent fuel storage facilities could lead to the release of a large amount of radioactivity in addition to the quantities resulting from the explosion itself. This would increase the amounts of fallout tremendously.
In Hiroshima and Nagasaki, black rain carrying radioactive fallout descended after the explosion. Bombay, being close to the sea, has high levels of water vapour in the atmosphere. This could lead to water droplets condensing around radioactive particles and descending as rain soon after the blast.
Since the direction of wind is variable, it is not easy to predict which areas would be subject to high levels of radioactivity. The regions subject to high levels of fallout would have high levels of casualties and radiation sickness. But, even people who live in areas subject to lower levels of radiation, unless they are immediately evacuated, would be victims of radiation sickness. Given the large population of Bombay and the likely damage to transportation infrastructure (train stations and tracks, roads, petrol stations, dockyards, airports, etc), the evacuation of all inhabitants would be nearly impossible.
According to the 1991 census, the population of Greater Bombay is 9.9 million. If the satellite city of Thane is also included, the population goes up to 12.6 million. Since the growth of Bombay’s population in the preceding decade was a little over 20 percent, it is safe to assume that these numbers are significantly conservative.
The Corporation of Bombay lists the area of the city as 438 square kilometres, which leads to an average population density of about 23,000 people per square kilometre. However, there are areas where the population density exceeds 100,000 people per square kilometre. These figures, however, do not take into account the commuters who flood in and out of Bombay every day, from as far away as Pune. A daytime attack (which is more likely than a nighttime one) would, therefore, trap tens of thousands more in the blast and fireball.
Assuming these population densities, one would conservatively expect somewhere between 150,000 to 800,000 deaths within a few weeks of the explosion, resulting from just one small 15-kiloton nuclear device. If the weapon used had a yield of 150 kilotons, then the immediate deaths would go up to anywhere between two to six million. These would be the “prompt” casualties (those who die within a few weeks of the explosion). Many more would die of long-term effects, especially of radiation-related causes leading to leukemia, thyroid cancer, breast cancer, lung cancer and so on. There would also be numerous non-fatal health effects such as growth of keloids, cataracts, malformations and other birth defects, mental retardation in young children, and so on.
It is important to understand that the medical facilities of Bombay, extremely inadequate in the best of circumstances, would be mostly dysfunctional due to the attack. It is extremely unlikely that those injured in the nuclear attack would find medical treatment to help them survive.
The immense catastrophe which would result from a nuclear blast over Bombay, that too resulting from just a single-fission weapon of a low yield, should give pause to those who contemplate use of such weapons in warfare in South Asia.