A laboratory building that contains a deadly strain of avian flu and other germs is among four that lost power for more than an hour Friday when a backup generator system failed again at the Centers for Disease Control and Prevention.

The outage affected air flow systems in labs that help contain such germs as the H5N1 flu virus, which some experts fear could cause a pandemic. But there were no exposures to infectious agents, and neither workers nor the public were at any risk, said CDC spokesman Tom Skinner.

The outage is the latest in a string of mechanical and construction incidents at labs on the agency's Clifton Road campus — many in new buildings that are part of a $1 billion construction plan.

Last summer, an hour-long power outage at a different CDC lab tower, called Building 18, resulted in a congressional hearing. The Government Accountability Office, the investigative arm of Congress, is still examining safety at CDC's high-containment laboratories and concerns raised years ago by agency engineers that CDC's backup power system was likely to fail.

"It's important for people to understand that even though we lose power to these facilities from time to time, worker safety and the public's safety is not in jeopardy because multiple, redundant systems are in place, separate from those that rely on power," Skinner said Saturday.

Around 5:40 p.m. Friday, a Georgia Power transformer failed, cutting off electricity to part of the CDC campus. CDC's backup generators initially came on, Skinner said. But then the system detected some sort of power anomaly and shut itself off, cutting off backup power to three buildings, he said.

The buildings affected were:

• Building 17, a newer infectious disease research lab building, where scientists work with rabies, HIV, influenza and tuberculosis, including extensively drug-resistant strains. The building has Biosafety Level 3 (BSL-3) labs, which need electricity to maintain negative airflow. This key safeguard helps contain germs by making sure air is always being drawn into the lab and through special HEPA filters before leaving the building. When power is lost, the lab has neutral air that neither flows in or out.

• Building 20, a newer office building that also houses the agency's fitness center.

• Building 1 and Building 3, antiquated attached office buildings from about 1959.

Information about whether any labs were in use at the time of the outage was not immediately available Saturday, Skinner said.

"This happened late in the day and there were not many employees still in the buildings," Skinner said. "Those in the buildings evacuated without incident."

The power was out for about 1 hour 15 minutes, Skinner said, and was restored when Georgia Power fixed the transformer problem.

A bird caused the blown Georgia Power transformer, said power company spokesman Jeff Wilson.

CDC officials did not attempt to override and restart the agency's backup generators because they didn't know what the anomaly was that shut them down, Skinner said.

Skinner also said there was no power disruption at Building 18, the $214 million Emerging Infectious Diseases Laboratory that suffered the hour-long outage last summer.

The AJC reported last summer that government construction engineers had warned since 2001 that CDC's planned design for its centralized backup power generation system would not keep crucial lab systems from failing in an outage.

"I've been saying this for over three years now, but having the generators in this configuration gives us no protection whatsoever from many types of failures," CDC mechanical engineer Johnnie West wrote in an August 2003 e-mail to agency officials, one of several reviewed by the AJC.

CDC officials have said that despite West's concerns, the consensus of experts was that a centralized generator farm was better than having individual units at buildings.

Skinner emphasized that the CDC has many other physical barriers to contain germs that don't require electricity. They include safety cabinets and layers of rooms, filters and corridors between the germs and the outdoors.

"I think people need to know we're talking about an enormous campus with complex systems, and we're never going to be able to fully eliminate power outages," Skinner said. "That's impossible. The key for us is to minimize the duration of the outage."

To reach staff writer Alison Young, call 404-526-7372.