People living near a burning social club in Sheffield were advised to stay indoors after chemicals were found in the building.
The derelict St Phillips Social Club, on Daisy Walk, off the inner ring road, caught fire at 0330 BST on Monday.
Crews found hydrochloric acid and other chemicals when they entered the building at about 0800 BST.
The fire sent a plume of smoke, which could contain toxic fumes, over the city centre.
People were advised to stay indoors and keep doors and windows closed.
Residents of some nearby flats were evacuated from their homes for several hours but have now returned.
The cause of the fire is being investigated.