About 50 people were evacuated briefly from the Recreation Centre on Monday evening after a chlorine warning was triggered in a mechanical room.
Red Deer Emergency Services personnel were called about 8:25 p.m. after higher-than-normal chlorine levels were detected in a stand-alone chlorine room on the outside of the centre.
As a precaution, the building and pool were cleared and people were mustered in front of the nearby museum.
A transit bus was called in so people, some still in their bathing suits, could warm up until the all-clear was given, which came about 9 p.m.
City recreation superintendent Kay Kenny said earlier in the day staff had been working in the chlorine room, which can only be accessed from outside the Rec Centre by staffing wearing protective equipment, to prepare for opening the outdoor pool and a fan had been turned off.
Chlorine levels rose and a warning light was activated.
No chlorine gas got into the public part of the building.
Kenny said procedures are being reviewed to prevent future issues.