Fire Causes $500,000 Damage to Building : Disaster: Putting out the flames in Mission Viejo offices took three hours. The cause remained unknown.

A three-alarm fire early Monday caused more than $500,000 damage to a 20-unit office building, fire officials said. Orange County had planned to locate local counseling offices for alcohol abuse and mental health services in the building later this week.

It took more than 70 firefighters three hours to put out the blaze, which began just before midnight Sunday at the north end of the second story at 28261 Marguerite Parkway, according to Orange County Battalion Chief Marc Hawkins. The entire second floor was gutted, and there was significant fire damage as well as serious flooding throughout the first-floor offices, Hawkins said.

Investigators believe the fire was accidental, but they had not determined its exact cause Monday afternoon, fire officials said.

Tenants in the building, which is managed by D.W.A. Smith of Newport Beach, include a family planning center, the anti-abortion group Birthright, a dental laboratory, an advertising agency and several private doctors and therapists. Most are looking for temporary space until the building can be refurbished.

A county drug abuse counseling clinic occupied one of the first-floor offices, and the agencies providing alcohol abuse and mental health counseling were scheduled to move into adjacent suites Friday. Mike Hansen of the county Health Care Agency’s management services department had planned a final walk-through of the facility for Monday morning.

“It looks like it won’t be ready for a while now,” Hansen said as he stared at piles of ash at the side of the building.

Many who worked in the building were alerted in Monday’s wee hours by alarms or colleagues who called after seeing the flames. Several kept a vigil through the early hours as 11 fire engines and three ladder units struggled to control the fire; others who wanted to enter the building returned with lawn chairs to wait.

“After watching the inferno for two hours--the smoke billowing, the flames--it’s just amazing that anything is left,” said Family Planning Assn. manager Ginny Dean, peering through the blown-out windows of her first-floor office at a lampshade and two wall hangings still intact. “I thought for sure the ceiling would have caved in.”

Just before 11 a.m., firefighters removed file cabinets filled with the drug clinic’s patient records. Other offices’ paperwork and computer equipment were salvaged later Monday afternoon, but much of the building’s contents were burned beyond recovery.

“It’s pretty much gone,” dental technician Larry Weinberger said of the more than 200 teeth impressions stored in his second-floor lab.

When Andrea Nishihara of Santa Ana arrived for her morning appointment with Weinberger, she found him in the parking lot, wearing jeans rather than his white coat.

“The doctor has been waiting two years to fix my front teeth,” a disappointed Nishihara said. “I guess we’ll have to wait some more.”

Two survivors of the fire, goldfish that lived atop a drug abuse counselor’s desk, swam calmly in their tank among the beach-chair crowd.

“Lives were saved,” said Brett O’Brien, owner of the fish, Flotsam and Jetsam. He praised the firefighters for grabbing the fish food along with the tank.