GOLDEN, Colorado (AP) Demolition began on what has been called "the most dangerous building in America," where workers at the Rocky Flats nuclear plant once handled highly radioactive plutonium used in triggers for nuclear weapons.

Leaks, spills and a 1957 fire plagued the building, and part of it was closed 30 years ago because radiation levels were off the charts.

The building was called the workhorse of the weapons factory 16 miles northwest of Denver. The Department of Energy also called the building its "greatest vulnerability" in 1994 because of the buildup of contamination over five decades.

"This [building] was the bad actor and that’s really what made it so notorious," said Nancy Tuor, president and chief executive of Kaiser-Hill Co., in charge of the roughly $7 billion cleanup.

The jaws of excavators chewed through the north face of Building 771 on Thursday, ripping through corrugated metal and sheetrock of a section that was once a cafeteria. Workers who fashioned plutonium triggers in the building were among those who watched it come down.

"It’s awesome," said Chris Gilbreath, a Kaiser-Hill manager who gave the signal for demolition to start. "Any time something disappears around here, it’s awesome."

Rocky Flats started producing plutonium triggers in the 1950s and was closed in 1989 when chronic safety violations led to a raid by federal agents. The end of the Cold War scuttled plans to reopen the plant.

Work began in 1994 on decommissioning Rocky Flats, which will eventually be turned over to the U.S. Fish and Wildlife Service to manage as a wildlife refuge. The core, 385-acre (154 ha) industrial area is surrounded by 6,000 acres (2,400 ha) of open space stretching over rolling hills of long-grass prairie beneath the craggy foothills of the Rockies.

Half of the roughly 800 buildings that made up the sprawling complex have been dismantled. Completion is expected by December 2006.

Energy Department officials originally estimated the cleanup would take 60 years and cost up to $36 billion. The final cost will likely be less than $7 billion.

The faster-than-expected pace has led critics to question whether proper precautions are being taken and if Kaiser-Hill is more interested in earning hundreds of millions of dollars in bonuses for finishing ahead of schedule. The company also has been fined for safety violations.

Kaiser-Hill has defended its safety record, and state and federal officials said they are confident proper procedures are being followed.

Cleanup crews were faced with 251 tanks and 11 mi. (17.7 km) of pipes containing plutonium-contaminated liquid. The so-called "infinity room" had been boarded-up since the 1970s. Radiation levels in the room were so high that monitors couldn’t register them; workers said they went to infinity.

Mike Beranek said he felt proud as he stood with a crowd of about 100 behind a chain-link fence Thursday. He worked for 28 and a half years in Building 771 and is on a cleanup crew.

"Getting to this point has been an incredible accomplishment for everybody involved," the 52-year-old Beranek said.

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