Ground Zero buildings must not exceed 60 storeys - experts

Skyscrapers built on Ground Zero to replace the World Trade Centre in New York should be no more than 60 storeys high, engineers said today.

The structures should also be secure against sophisticated bioterrorism attacks, the study by the American Society of Civil Engineers found.

It advises that buildings on the site should be designed to allow for mass evacuations, which would require any structure similar in size to the 1,378ft (420m) World Trade Centre to be fitted with extra-wide stairwells.

The subsequent loss in floor space would make the buildings unprofitable, details of the report published in the New York Times concluded.

‘‘We contractors and engineers are going to be practising our profession differently now, based on what we’ve learned from the World Trade Centre,’’ said the study’s author Robert Borg.

He said excessive heights may no longer be worth achieving, even though they might be technically possible.

The report, entitled ‘‘Rebuilding the World Trade Centre’’, said biological and chemical attacks were the main threat that new buildings must be protected against.

It comes after experts warned that the anthrax attacks sent through the post last year would have been more deadly if the spores had been put directly into a buildings’ ventilation system.

Filters in current ventilators used in large buildings are not equipped to stop the minute particles that carry the disease.