NASA (via Flickr) European astronaut Samantha Cristoforetti and NASA's Terry Virts participate in an emergency exercise training drill on Dec. 1, 2014.

Crewmembers on the International Space Station have now been allowed into the U.S. segment of the orbiting outpost, after a false alarm caused astronauts to evacuate that part of the station early Wednesday (Jan. 14).

The alarm could have indicated a possible leak of toxic ammonia into the station's cabin; however, NASA has found no evidence of a leak. NASA astronauts Terry Virts, Barry "Butch" Wilmore and European Space Agency astronaut Samantha Cristoforetti re-entered the U.S. side which include the European, Japanese and U.S. station modules wearing masks at about 3:05 p.m. EST (2005 GMT). Cristoforetti and Virts took samples of the station's air and found no ammonia, according to NASA.

"The crew is in good condition, was never in any danger and no ammonia leak has been detected on the orbital laboratory," NASA officials wrote in an update.

NASA Crewmembers were forced to evacuate the U.S. segment of the International Space Station on Jan. 14, 2015 due to a possible ammonia leak.

NASA officials were worried that the space station's cooling system which uses ammonia to help regulate temperatures on the station could have been leaking the noxious gas into the station's atmosphere. [Inside the International Space Station (Infographic)]

Virts, Cristoforetti and Wilmore joined cosmonauts Elena Serova, Alexander Samokutyaev and Anton Shkaplerov in the Russian segment for much of the day after the alarm sounded at about 4 a.m. EST (0900 GMT). Because there is no sign of ammonia in the cabin, the crewmembers should be allowed to take of their masks and roam freely through all parts of the station, according to NASA.

Officials now think that the false alarm may have been caused by an error in a computer used to beam information to and from the space station. The computer, called a multiplexer-demultiplexer, now seems to be in good shape after officials turned the device off and on again, NASA officials said.

Mission Controllers are still working to understand exactly what set off the alarm, but work for the astronauts should continue as normal on Thursday (Jan. 15). NASA officials will now take steps to re-activate a cooling loop powered down because of the alarm.

NASA officials do not think that the research on the station was negatively impacted because of the evacuation.

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Space Station Ammonia Leak Scare Likely a False Alarm, NASA Says