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BRUSSELS (Reuters) - Toxic fumes from kitchen drains forced the European Union on Wednesday to switch the venue of its summit in Brussels less than 24 hours before leaders were due to begin the two-day meeting.

The Europa Building, also known as “The Egg” and opened only in January amid controversy over its cost, was evacuated for the second time in a week on Wednesday after catering staff were taken ill due to fumes suspected to be leaking from the drains.

As a “precautionary measure”, the summit will now take place next door in the Justus Lipsius Building, an anonymous 1990s glass and stone-clad structure, which housed Europe’s councils until the opening of the 321-million-euro ($378 million) Europa.

The new building incorporates an exterior of jumbled salvaged window frames, a summit chamber painted a psychedelic patchwork, and an illuminated “lantern” containing several stories of offices that is visible from the street and known to locals as “Van Rompuy’s Egg” after the Belgian former summit chair.

About 20 kitchen staff were treated in hospital on Friday and an EU official said the Council and Belgian safety bodies were working on the assumption that Wednesday’s incident was due to the same source.

It was unclear how many staff were made ill on Wednesday.

Highlights of the summit are likely include an address by British Prime Minister Theresa May to the other 27 on her Brexit plans over dinner on Thursday and a statement to be agreed by the 27 on Friday that will demand London offer tens of billions of euros more on its withdrawal in 2019 if it wants to start negotiating a future relationship based on a free trade pact.