Shoppers were evacuated from Tesco in Accrington town centre last night because a pipe was leaking carbon dioxide.
Fire chiefs said the pipe which was linked to a refrigeration unit had burst.
Crews were at the store on Eagle Street from around 11.40pm to 2am this morning.
John Taylor, of Lancashire Fire and Rescue Service, said: "People were evacuated as a precaution. Maintenance staff from Tesco fixed the pipe and we just provided security at the scene."