An unknown explosion rips out the side of a two-story apartment building, collapsing the floors. Many residents are injured; some are missing, possibly trapped inside. Local first responders recover the people they can reach, but the rubble is rickety and the clock ticking. They decide to call in state resources, and a short time later, a small army of specially trained search and rescue teams, K-9 teams and other squads roll in and begin the search for the living and the dead.

 This is the scenario that played out in Covington this weekend during a large-scale, 36-hour search and rescue exercise that drew about 40 agencies and 140 participants from across the state to Willow Bend Apartments, which are scheduled for demolition and have been donated to the Covington Fire Department for training.

 The exercise was designed to put the Georgia Emergency Management Agency, the Georgia Search and Rescue teams, K-9 teams, Georgia Mutual Aid Group and other state agencies through their paces in a mass casualty and collapse situation, said GEMA spokesperson Buzz Weiss.

 "These exercises are a critical part of their experience to maintain their skills and all the possibilities they may encounter," Weiss said. "This is when you want to find out what the problems are so you can correct them before the real thing happens."

 The exercise also tested the command structure set up to handle disasters and events under the federally and state mandated National Incident Management System (NIMS).

 "That way you nave all these multiple agencies operating under a unified command, so there's no question as to who's answerable to whom, how to hand off the command," Weiss said.

 The teams, which have over 300 hours of training in specialties such as heavy rescue and extrication, confined space rescue, collapsed building rescue, swift water rescue, and more, were established with Homeland Security funds but are now used for a variety of situations from "terrorism to tornados," Weiss said. Many of the teams were deployed after tornadoes ripped through downtown Atlanta earlier this year, after the sugar refinery explosion, the Georgia and Florida forest fires last year and in Mississippi after Hurricane Katrina.

 A CFD crew was on site with a fire engine and ambulance to respond to any actual fires or injuries and to play the role of the local first responders, said Deputy Chief David Gunter.

 Though this is part of a series of drills with different scenarios held each year, this was one of the first drills to bring together the metro-Atlanta, Coastal, and Central GSAR teams in an actually collapsed building, according to Ronnie Register, fire services coordinator for the Georgia Emergency Management Agency.

 "This is about as real as it gets," said Register. Previous exercises would only simulate a collapsed building, he explained, but with an actual building, teams have to take into account shifting and unsteady rubble and the challenge of propping collapsed floors.

 Search dogs also climbed methodically and purposefully through the twisted wood, metal and glass debris, searching for scents from bed sheets soaked in cadaver fluid and scents of people deliberately scattered in the structures.

 "It's essentially a hide and go seek game for them," said handler Tracy Sargent. "They already have a natural drive to hunt something down. We simply direct that drive."

 Only about one dog out of every 10 they evaluate makes the cut to a full-fledged rescue dog, said Sargent, and the canines also go through constant training and annual certification of their skills.

 "Dogs are the perfect tool to find people dead or alive," she said, pointing out that they help humans focus their resources on areas with possible survivors or cadavers.

 Students from University of Georgia's College of Veterinary Medicine and College of Agricultural and Environmental Science were also on hand to monitor the search dogs and observe their working conditions.

 The Willow Bend Apartments was also the site of an Alcohol, Tobacco and Firearms training exercise in May and is scheduled to be demolished after this exercise, which ends today.