Stockholm Public Library includes more than 2 million volumes and 2.4 million audio tapes, CDs and audio books but are now in surplus. The library is waiting for an extension but it was put on hold in late 02009 due to a change in city government. The air in the basements of the library are polluted by Radon, a radioactive, colorless, odorless, tasteless noble gas, occurring naturally as an indirect decay product of uranium or thorium. In an amount 100 times more than normal, a regular and prolonged presence may cause lung cancer. The makeshift ventilators aim to renew the air.