US authorities began a simulated "dirty bomb" attack on Seattle yesterday in a major test of disaster relief workers.
A similar mock biological attack was scheduled to test Chicago emergency crews today in a week-long exercise in disaster management.
The simulations, organised by the Department of Homeland Security, will cost $16 million and run until Friday in Seattle and Chicago - which will be hit by a pneumonic plague outbreak - before shifting to Vancouver, Canada. A total of 8,500 people will join the exercise.
The Seattle "attack" began just after noon in an open gravel pit across the street from a coffee roasting plant and about a mile to the south of the city.
Three minutes later, the first of dozens of fire and emergency vehicles arrived. Firefighters doused the flames within 22 minutes although the smoke, bearing simulated radioactive material, was carried for miles on a brisk wind.
Emergency personnel scoured the wreckage but pulled back to don shiny chemical protection suits, temporarily abandoning scores of "victims", when their equipment indicated low-level radiation from a simulated "dirty bomb".
Some 200 firefighters took part in the exercise, though a fire official said he would have needed "a great deal more" in a real disaster.
If the fictitious disaster had been real, two people would have died and 150 would have been injured, officials said.