Authorities say 12 people needed treatment after a freon leak in the refrigerated section of a store in Glendale.
The leak forced the evacuation of the Costco near Arrowhead Towne Center around 12:30 p.m. Friday.
Authorities say three people were taken to a hospital for respiratory problems and the rest were treated at the scene.
Fire officials say the leak was caused by a serviceman working on a refrigerator unit. A compressor blew a gasket.
"We were in the store and all we really heard was a loud POP," said customer Raymond Crump. "It ended up being the freon line for the A/C that had exploded in the inside of the store."
The Costco was closed while the leak was contained. It was back open a few hours later and normal hours have resumed.
The Associated Press contributed to this report.