Fictional bomb to test disaster response in Tempe

Arizona authorities will set off a fictional "dirty bomb" in Tempe next week.

But as high-profile as that sounds, they hope the terrorism exercise goes entirely unnoticed by the public.

That's because nothing actually will be detonated, and no actual emergency responders will be deployed.

The Top Officials exercise -- dubbed TOPOFF 4 -- is part of what will be the nation's largest terrorism drill ever and is the fourth in a series of exercises mandated by Congress.

The exercise begins Tuesday and is designed to test officials' response to hypothetical mass casualties and widespread radiological contamination.

In addition to the "attack" in Tempe at the Loop 101 and 202 freeways, "dirty bombs" will go off at a Cabras power plant in Guam and on the Steel Bridge in Portland, Oregon.

Loops 101 and 202 will remain open during the exercise. →