SCOTLAND'S largest and most important library is to shut for a year from September for essential fire safety works.

The move, which has been well publicised to regular users of the National Library, yesterday attracted criticism for its impact on scholarship at a time when interest in Scottish history and culture is increasing.

Closure of the main building on Edinburgh's George IV Bridge will mean no access for those wishing to read its 100,000 manuscripts. A limited service for other readers will be offered at a newer library outpost in Causewayside.

The reason for the disruption is a five-year project, costing #13m, to upgrade the fire protection system and other renovations to safeguard its priceless collections.

However, the net result is that Scotland's greatest literary and historical treasures will be effectively hidden from public gaze just when greater attention is focussing on them with the advent of home rule.

Medieval historian, Professor Emeritus Geoffrey Barrow, of Edinburgh University, said: ''It is a very worrying situation, particularly for those postgraduate students just embarking on serious research and also for other working scholars and those travelling from overseas. The library is normally a very busy place. There simply is not going to be access to the manuscripts and that is a terrible blow.''

The library, which has a total of seven million items, attracts 70,000 reader visits a year. As one of the five legal deposit libraries it can request of a copy of any title published in Britain.

The library has been giving advance notices of the changes in letters, on the Internet and through other libraries.

The 1956 building has a windowless frontage and drops 11 storeys at the rear into the Cowgate, making fire brigade access very difficult.

A new system will be installed, allowing sprinklers to work individually to contain local outbreaks. Other libraries have made similar investments on the grounds that limited water damage is better than total loss through fire.

The director of the library's public services, Dr Alan Marchbank, said there would be inevitable inconvenience but every effort was being made to keep this to a minimum.

He said shutting the whole building was the only option because of the scale and complexity of the project.

''The simplest way is to close for a year, bite the bullet and get on with it. When we re-open we hope to provide a much better service with refurbished reading rooms and improved access,'' he added.

Professor Christopher Smout, Scotland's Historiographer Royal, said: '' Some scholars were rather indignant when they first heard about it, but this may well be the only option the National Library has.''