Select Committee on Transport, Local Government and the Regions Minutes of Evidence


Examination of Witnesses (Questions 392 - 399)

TUESDAY 5 FEBRUARY 2002

MR ANDREW ALLSOP, MR PETER BRESSINGTON AND DR JOHN ROBERTS

Chairman

  392. Can I welcome you this morning, and ask you to introduce yourselves?

  (Dr Roberts) I am a consulting engineer, a director with a firm called Babtie Group. I live in Manchester but I do a lot of work in London as well. I am here because I am the chairman of a committee which has been set up by the Institution of Structural Engineers; it includes members from most of the professions in the built environment, and it is going to provide advice to designers relating to tall building design, the safety of people in tall buildings, following the 11 September events in America.
  (Mr Bressington) I am a director of Ove Arup & Partners. I am responsible for its fire engineering group. I am particularly interested in the events of 11 September. I chair Arup's extreme events task force, and we were set up to look at what happened and perhaps where the future takes us in terms of design of tall buildings.
  (Mr Allsop) I am from Arup and am head of the wind engineering work that Arup is involved with.

  393. Are you happy for us to go straight to questions?
  (Mr Bressington) In terms of safety, we have heard talk and obviously most of the discussion has been around the feasibility and the desirability of tall buildings. From a technical point of view we are just talking about safety, and I do not think there are any reasons from a safety point of view that tall buildings should not be built; we just need to look at some of the issues.

Christine Russell

  394. Could you tell the Committee whether you believe the collapse of the World Trade Center was effected by its structural design?
  (Dr Roberts) The story on why it collapsed is not yet fully understood by the people who have been appointed in America to investigate it. The head of that team of investigators is a Fellow of the Institution of Structural Engineers of the UK, because it is a worldwide organisation, and he is a member of our committee, so we are getting some direct feedback from the investigations. All the signs are as you might expect that it is quite complex and there is not one single factor that caused the collapse of the buildings themselves. It is related to a combination of physical damage by the plane impact which did remove a portion of the structure; very severe fire—and most buildings, as Peter will explain in more detail, certainly buildings in the UK, are designed for fire from normal occupational hazards which are essentially burning paper and wood and other cellulose materials, and here a fire was delivered into the buildings from hydrocarbons which burn a lot hotter, so there was very severe fire going on in the building and buildings have fire resistance. This building had a defined fire resistance but against a cellulose type of fire, and the final collapse occurred by something that structural engineers would call progressive collapse, which is where a part of the building collapsing on to the part below it can trigger what you would call a pack of cards, in loose terms, type of collapse. We would call that a progressive collapse, where one or more floors falling on to a floor below can trigger an almost immediate chain-reaction collapse down to the ground, and that appears to be what happened

  395. Is it true that our safety regulations, certainly after Roman Point and the disaster there, in the UK are already more stringent than in the States?
  (Dr Roberts) I am very reluctant to say that. What is true is that, post the collapse of Roman Point in 1968—which, as I am sure people will remember, was triggered by a gas explosion in a very particular type of building, and that was a system-built block of flats which had on the evidence afterwards quite weak connections between all the pieces and which progressively collapsed down through about 22 storeys from an explosion quite near the top—that triggered a change in the UK building regulations which came in in the early 70s. There were a couple more collapses in 1973 and 1974 of some school roofs in the London area, in Camden and Stepney, and those regulations have been with us since that time and they serve to limit the effect of what is called disproportionate collapse from an accident. You have to guess what the accident might be. It is not just to protect against a gas explosion or a fire; it aims at producing robust buildings that will tolerate some quite unusual accident happening in them. Those regulations are in place for all buildings in Britain and have been since that time but I think it is a huge step to jump from that and say, "Oh, had this building been in Britain it would not have collapsed". I do not think that is a step you can take at all.

  396. Do you have concerns about existing buildings in the UK that may be vulnerable to what you described earlier as progressive collapse?
  (Dr Roberts) Yes, because buildings are not designed for an event of that magnitude or those sorts of events. We hope they will be robust to survive some of them or most of them, but I do not think there is any doubt that there are serious accidents that could affect some British buildings.

  397. And is it premature to say yet whether or not you believe it would be possible to strengthen further the existing regulations in the light of what happened on 11 September?
  (Mr Bressington) There are a few issues there. The structure robustness is one issue and the other, obviously, is fire and evacuation and management of those buildings. My feeling is that certainly people will look at the codes. The codes are really based on a fire which can happen in a building which you would associate with that occupancy, so it may well be there are more performance requirements in the codes. It therefore gives people the opportunity to look at specific buildings in different areas, whether structure or fire, and make decisions based on a performance criteria. For instance, if you need 45 minutes to clear a high rise building in terms of evacuation, you need to try to do that based on the tenability, so I think it will move that way. It may not be a prescriptive requirement but more of a guidance.
  (Dr Roberts) Looking back, which is very easy to do with hindsight, is that in the UK buildings are required to have defined periods of fire resistance, as you have no doubt heard from some other evidence, (probably from manufacturers of fire resistant materials), and typically in the UK large buildings would be required to have two hours' fire resistance for the above-ground structures. First of all, it does not mean that the building will stand there for two hours in a very serious fire—it is a sort of guide as to how long it will last but it is not absolutely for sure that that will happen—and the other link that is missing is that there is not any requirement in the UK to ensure that you can get everybody out in two hours in a building with a two-hour fire resistance, and that missing link is rather worrying when you think about it.

Chris Grayling

  398. If an aircraft hits the side of a tall building, as happened in New York, you get a catastrophic impact and fire but in the case of the World Trade Center buildings, given the number of people who worked in those buildings, a very large proportion of those in the building did get out. When the planes hit the building, a lot of the impact burst out beyond the buildings rather than being contained within it. If a plane were to hit a medium-rise building with much greater density within a geographical area, is there an argument for saying that an aircraft landing in a 20-storey building with a larger number of workers could have a greater impact on that building than a high-rise building?
  (Mr Bressington) Potentially, the World Trade Center I would suggest was picked out because it was a symbol and they decided they would attack that. They could have chosen to attack a sports stadium where, in terms of trying to achieve their objective which is to kill as many people as you can, they would have achieved that end using that. So it is not just tall buildings with these incidents because a lot of this is to do with security, politics, and all sorts of other issues rather than design. Certain aspects have come out of the World Trade Center and obviously more will in terms of what happened there, and we just need to build on some of those points and perhaps use them in the future. I do not think it is to say that, because a plane flew into the World Trade Center it is the sort of thing that is going to happen every day of the week. Certainly a plane was also flown into the Pentagon and that building was quite resilient in terms of attack but it still did kill quite a few people.

  399. So there is a danger that safety restrictions around tall buildings become focused entirely on September 11?
  (Mr Bressington) Yes.


 
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