Arwel Jones from the National Library of Wales told ITV News that he is hoping that the damage will be limited - "the most valuable stuff is housed in purpose-built cells at the very bottom of the library, and this fire is at the very top."
He admitted to concern that the damage from water pumped onto the building by firefighters would be as bad as the fire damage.
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Low cloud will bring murky conditions with extensive hill fog.
The team, which is manned by volunteers, will operate out of Pontardawe Fire Station in partnership with Mid and West Wales Fire Service.
Dan Biggar has no doubt that Wales remain flrmly in the Six Nations title mix ahead of next Saturday's clash against Scotland.