FIREFIGHTERS rush to the scene of a massive bomb that reduces buildings to rubble, overturns passenger buses and injures 200 people. Horrified, they detect radiation and confirm that terrorists have unleashed a “dirty bomb” in Seattle.

A deadly biological agent creeps undetected through the air in Chicago, 1,700 miles away. Over five days it will infect people across the United States and Canada with pneumonic plague.

This is how the biggest mock terrorist assault in US history began to unfold yesterday, a nightmare scenario dreamt up to reflect what experts say is the real threat facing Americans in the post- September 11 era.

The drill, involving 8,500 people in 19 federal agencies, the American Red Cross and Canada, cost $16 million (£10 million) and is packed with realistic touches, not the least of which is one that the scriptwriters did not have to invent.

An al-Qaeda member told an Arabic magazine this month that the group had re-organised and was planning an operation similar to the hijacked aircraft assaults of September 11, 20 months ago.

Planners have prepared a few surprises, including an aircraft crash in Chicago on Thursday. Communications will be put to the test.

Leading officials with expertise in terrorism and attacks with unconventional weapons are participating.

Today a few people will start showing up in local hospitals with mysterious flu-like symptoms, “but nothing that would lead us to believe that something has gone wrong”, the Chicago spokeswoman said.

Soon the trickle will turn into a flood. Pneumonic plague creates far more victims than the anthrax letters that killed five people in the United States in late 2001.

Investigators are still baffled by that — genuine — case. They are considering dragging a pond in Maryland where they suspect that the attacker may have hidden a chamber to pack safely the envelopes used in the terror campaign.

Pneumonic plague is curable if diagnosed quickly. However, the bioterrorism victims of the fictional Glodo group will turn up not only in the United States but also in Vancouver, British Columbia, sparking a response from health authorities that echoes the real-life outbreak of Sars in the area. Glodo will claim responsibility for the attacks tomorrow. A raid in the Chicago area on Thursday will uncover its bio-laboratory.

Hospitals in the United States would be unable to handle a biological attack of the type envisaged in the scenario, according to the new Department of Homeland Security’s website, which is spearheading the drill. It describes communications between hospital emergency departments and public health officials as “antiquated and inadequate” and the training for medical staff as “infrequent”. However, the 2003 budget includes $1.6 billion to help to address these problems. Another $2.4 billion is to be spent updating healthworkers’ toolkits for tackling biological agents, which were devised for the Cold War era. The attack agents were chosen because they are considered real threats. US authorities are holding Jose Padilla, a former Chicago gang member, alleging that he plotted to unleash a real dirty bomb for al-Qaeda.

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