'Evacuation plans for office blocks must be tightened'

Regulations governing how long it takes to evacuate tall buildings in an emergency should be tightened, construction experts said yesterday.

They believe architects and engineers will have to "think the unthinkable" when designing tall office blocks such as the Canary Wharf tower in London, because existing safety measures fail to take into account how long it takes to get everyone out of a burning building.

John Roberts, a fellow of the Royal Academy of Engineering and director of the Babtie Group construction company, told the British Association's Science Festival that buildings should be given safety licences similar to those issued to football grounds, which depend on annual inspections and a time-limit for evacuation.

"We now have to think the unthinkable at the design stage in a way we've never had to do before. There are some quite simple things that we can do without increasing the cost of new buildings too much, and some we can do with existing buildings as well," he said.

One idea was to end the ban on using lifts in a fire because lifts were far more effective than stairs at getting people out of large buildings quickly. Lifts would be essential to remove thousands of people from a large office block.

"One of the most important considerations is how to get everyone out of a very tall or large building simultaneously. In the past, we've planned mainly for phased evacuations," he said. "If we made sure lifts were fire and impact-proof we could use them for rapid evacuation, instead of the conventional wisdom that you should use only stairs in an emergency. We need to plan and site stairwells to minimise the chance of them becoming impassable," Dr Roberts said.

A report last week by a Commons select committee recommended setting a time-limit within which large offices could be evacuated and introducing regular inspections for fire certificates.

Dr Roberts said modern office blocks were vulnerable to fire because a principal construction material – structural steel – lost half its strength at 600C, easily reached in a burning building. "The key to avoiding progressive collapse is to design robust, ductile [non-brittle] buildings. That means they can deform to absorb an impact without fracturing."