The crews of the shuttle Atlantis and the International Space Station were awakened Thursday night by what flight controllers quickly concluded was a false alarm indicating a sudden depressurization. That false alarm caused ventilation fans to shut down, resulting in a fire alarm tripping in the European Space Agency's Columbus laboratory module.

But after checks on the ground and in orbit, flight controllers concluded the station was safe. While the cause of the initial false depressurization alarm was not immediately clear, officials said the crews were in no danger.

"It appears a false indication of a rapid depressurization led to the automatic shutdown of ventilation fans through the station, which in turn led to a false smoke detection in the Columbus laboratory," said mission control commentator Kelly Humphries. "The crew is in no danger, there is no rapid depressurization, there appears to be no smoke, just some dust that got into one of the smoke detectors in the Columbus lab as a result of the ventilation fans being shut off.

"Everything is looking good on board the station so far, but the team is continuing to step through their emergency procedures just as a precaution."

The initial depressurization alarm tripped at 8:36 p.m. EST, waking the astronauts and kicking off a flurry of calm-but-hurried troubleshooting. It was quickly apparent the station's internal pressure was stable, but flight controllers in the United States, Europe and Russian worked through a series of checks to make sure there was no threat to the station.

"Station, Houston, on the big loop. So Frank, with those readings we concur with you, atmosphere is good," Ryan Lien radioed from mission control at the Johnson Space Center in Houston.

"We believe this was a false fire (alarm) due to the lack of ventilation in Columbus as well as lack of ventilation throughout the stack that was probably caused by that false rapid depress indication. We did not see a depress event on the ground, we just started seeing caution-and-warning events. So we're going to stand down from the emergency at this point and work on recovery and examination of that depress event. Believed to be a false alarm at this point."

Lien later told station commander Frank De Winne the initial alarm might have originated with a new Russian docking module that was attached to the station earlier this month.

"Everything we're seeing right now, ISS, the whole stack is in a stable and safe config first and foremost," he said. "Everything is shut down, the vehicle followed its depress response based on what we think was maybe the MRM-2 (mini-research module). Telemetry to confirm that source being MRM-2 is a little hazy right now, we're trying to get those words."

Lein said it would take another hour or so to reactivate the ventilation system.

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