Using the CATS (Consequences Assessment Tool Set) software created by the US Federal Emergency Management Agency (FEMA) and the Defense Threat Reduction Agency (DTRA), the authors have calculated the numbers of dead and wounded to be expected from a 12.5 kiloton nuclear explosion at ground level in New York City. The casualty model used assumed a cloudless day and a 100% fatality rate for people in the firestorm area, which extends out to 2.4 km (1.5 mi) for a blast of this size. To calculate the effects of direct radiation exposure from the explosion, it assumed a 100% fatality rate for people beyond the firestorm who are exposed to 600 cGY, and a 50% fatality rate for people exposed to 450 to 599 cGy. It also assumed that people with exposures in the range of 50 to 449 cGy would develop radiation sickness. To calculate the effects of local fallout beyond the zone of firestorm and direct radiation exposure, we assumed an attack in September, and the model examined a fallout footprint extending 113 km (70 mi) to the East from the explosion. The size and shape of the fallout footprint were calculated from the most probable prevailing wind direction and speed at that time of the year. The model used residential demographic data and thus predicted casualties for an attack at night. An attack during the day when large numbers of people come into Manhattan from outlying areas would produce substantially higher casualty figures. For purposes of this study, the explosion was placed in New York Harbor between lower Manhattan and Brooklyn to reflect concerns that a nuclear device could most easily enter a US city smuggled in a cargo container on board a commercial ship.
A 12.5 kiloton nuclear explosion in New York Harbor produce casualties more than one order of magnitude greater than those inflicted at the World Trade Center. Blast and thermal effects would kill 52,000 people immediately. Another 238,000 would be exposed to direct radiation from the blast, and of these 44,000 would suffer radiation sickness and more than 10,000 of these would receive lethal doses. In addition to this direct radiation from the explosion, fallout would expose another million and a half people. For this group, the 24 hour cumulative dose would be high enough to kill another 200,000 and cause several hundred thousand cases of radiation sickness. In addition there would be many thousands of people with mechanical and thermal injuries.
Casualties on this scale would immediately overwhelm medical facilities leading to a high mortality rate among those injured but not killed by the initial blast and thermal effects. Over 1000 hospital beds would be destroyed by blast, and 8700 beds would be in areas with radiation exposures high enough to cause radiation sickness.