Research carried out by the Universities of Greenwich, Ulster and Liverpool found even though the buildings were only one third occupied on the day of the attacks staff were delayed on the stairs with 82% saying they stopped more than 20 times during their descent - because of ascending fire fighters, or injured people. And almost one in 10 (9.7%) had to rest.
Ed Galea, project director at the University of Greenwich, said: "Providing people with good information about what is happening and what to do can significantly reduce occupant response times and lead to safer evacuation."
He added: "These results quantify the benefits that can be derived from providing hardened emergency communications systems"
