The mystery of the cylinder was discovered on the 7th floor of the new Carpthorne Hotel at Bramall Lane.
Bramall Lane and Cherry Street had to be closed due to this operation. 150 staff and customers at the ground had to be evacuated while the cylinder was cooling down after it set alight at 8:50am yesterday morning.
The main offices, ticket office and the superstore will all be open for business at 9:00am.