Specialist hazardous materials firefighters went to the Sainsbury's Superstore in Bridgnorth in the early hours of Wednesday when the alarm was raised at 1.20am.
Four fire crews including the environmental protection unit were joined by police and ambulance officers.
The firefighters wore protective breathing apparatus to isolate the gas supply in the store and then vent the building in Whitburn Street.
The incident was under control by 3am.
Meanwhile fire crews in Shrewsbury were called to recycling bags on fire in Pride Hill in the town.
The fire, next to a shop window, was quickly extinguished. Police were also on the scene and have appealed for anyone who knows how the fire was started to contact them on 101.