Priceless books and manuscripts were undamaged after a fire broke out at the British Library.
The British Library was opened five years ago
An electrical fault is believed to have caused the fire which began in a basement at 2330 BST on Tuesday.
It was brought under control before fire crews arrived.
A contractor was taken to hospital after it was feared he had been electrocuted, but was found to have fallen off a ladder.
The library at St Pancras contains rare and important artefacts such as copies of the Magna Carta and the Lindisfarne Gospels.
The British Library building was opened five years ago and has six storeys above ground and eight underground.