Safety in tall buildings

Safety in tall buildings In any subject area related to the provision of safety, failure is typically the most effective mechanism for evoking rapid reform and an introspective assessment of the accepted operating methods and standards within a professional body. In the realm of tall buildings the most notable failures in history, those of the WTC towers, widely accepted as fire induced failures, have not to any significant extent affected the way they are designed with respect to fire safety. This is clearly reflected in the surge in numbers of Tall Buildings being constructed since 2001. The combination of the magnitude and time-scale of the WTC investigation coupled with the absence of meaningful guidance resulting from it strongly hints at the outdatedness of current fire engineering practice as a discipline in the context of such advanced infrastructure. This is further reflected in the continual shift from prescriptive to performance based design in many parts of the world demonstrating an ever growing acceptance that these buildings are beyond the realm of applicability of prescriptive guidance. In order for true performance based engineering to occur however, specific performance goals need to be established for these structures. This work seeks to highlight the critical elements of a fire safety strategy for tall buildings and thus attempt to highlight some specific global performance objectives. A survey of tall building fire investigations is conducted in order to assess the effectiveness of current designs in meeting these objectives, and the current state-of-the-art of fire safety design guidance for tall structures is also analysed on these terms. The correct definition of the design fire for open plan compartments is identified as the critical knowledge gap that must be addressed in order to achieve tall building performance objectives and to provide truly innovative, robust fire safety for these unique structures.

July 2002 Safety in tall buildings and other buildings with large occupancy Prepared by an international working group convened by The Institution of Structural Engineers IStructE Safety in tall buildings and other buildings with large occupancy Published by The Institution of Structural Engineers 11 Upper Belgrave Street London SW1X 8BH United Kingdom Telephone: +44(0) 20 7235 4535 Fax: +44(0) 20 7235 4294 Email: mail@istructe.org.uk Website: http://www.istructe.org.uk ISBN 901297 24 © 2002 The Institution of Structural Engineers The Institution of Structural Engineers and those who served on the Working Group which produced this report have endeavoured to ensure the accuracy of its contents However, the guidance and recommendations given in the report should always be reviewed by those using the report in the light of the facts of their particular case and specialist advice obtained as necessary No liability for negligence or otherwise in relation to this report and its contents is accepted by the Institution, the members of the Working Group, its servants or agents No part of this publication may be reproduced, stored in a retrieval system or transmitted in any form or by any means without prior permission of the Institution of Structural Engineers who may be contacted at 11 Upper Belgrave Street, London SW1X 8BH, UK IStructE Safety in tall buildings and other buildings with large occupancy Constitution of Working Group John M Roberts, FREng BEng(Hons) PhD CEng FIStructE FICE, Babtie Group, Chairman John Ahern, AADIP RIBA, J Ahern Associates, representing The Royal Institution of British Architects Stuart J Alexander, MA CEng FIStructE FICE MIMgt, WSP Group W Gene Corley, PhD CEng FIStructE, CTL Group Keith J Eaton, BSc(Eng) PhD CEng FIStructE MIM, The Institution of Structural Engineers Paul F Everall, MA(Cantab) CEng MICE Hon RICS HonFIBC Hon FB Eng, Department for Transport, Local Government and the Regions, Observer Max Fordham, OBE FREng MA FCIBSE FConsE Hon FRIBA, Max Fordham LLP, representing The Chartered Institution of Building Services Engineers Craig Gibbons, BEng(Hons) PhD CEng MICE MHKIE, Arup, Hong Kong Peter R Head, OBE FREng CEng FIStructE FICE, FaberMaunsell Martin Kealy, BSc(Hons) CEng FIFireE MSFPE MCIBSE, WSP Fire, representing The Institution of Fire Engineers Gordon G T Masterton, BSc BA MSc DIC CEng FIStructE FICE FIES MCIWEM, Babtie Group, representing The Institution of Civil Engineers David McCullogh, FRICS PPIBC, Hartlepool Building Control, representing The Royal Institution of Chartered Surveyors John B Menzies, FREng BSc(Eng) PhD CEng FIStructE Dip CU, Standing Committee on Structural Safety David B Moore, BTech PhD CEng MIStructE, BRE Ltd H K Ng, MSc CEng FIStructE, J M K Consulting Engineers Hong Kong Alan Parnell, FRIBA PPIFireE, Fire Check Consultants, representing The Royal Institution of British Architects Ysrael A Seinuk, PE CEng FACI FICE FASCE, Cantor Seinuk Group Inc Faith H Wainwright, BA CEng FIStructE, Arup, London Corresponding members David I Blockley, FREng BEng PhD DSc CEng FIStructE FICE, University of Bristol Thomas J P Byrne, BSc MSc, WSP Group Charles Clifton, BE(Hons) ME(Civil) FIPENZ FNZSEE, HERA Ian P Firth, BSc MSc DIC CEng FIStructE FICE, Flint & Neill Partnership Graeme Forrest-Brown, MSc CEng MICE, Maunsell Structural Consultants Ltd Norman Glover, BSc CE FIStructE, Aegis Institute, Architectural Institute ASCE Mick G Green, BE CEng MIStructE MICE, Buro Happold John A Hill, FREng BSc CEng FIStructE FICE, Doran Consulting Alan P Jeary, PhD DSc CEng FIStructE MIEE FCIOB, University of Western Sydney Bob A McKittrick, BSc CEng FIStructE FICE, Scott Wilson Brian S Neale, AGCT CEng FIStructE MICE FIDE, Health and Safety Executive Graham Owens, MSc PhD CEng FIStructE MICE MWeldI, Steel Construction Institute Roger J Plank, BSc(Eng) PhD CEng MIStructE MICE, University of Sheffield Ian Thirwall, CEng FIStructE MICE, Cameron Taylor Bedford Martin J Wyatt, BSc MSc PhD CEng MIStructE MBCS, BRE Ltd Secretary Susan M Doran, BSc(Eng) AKC PhD CEng MICE ACIS, The Institution of Structural Engineers IStructE Safety in tall buildings and other buildings with large occupancy IStructE Safety in tall buildings and other buildings with large occupancy Contents Foreword Definitions for the purposes of this Report Summary Introduction 13 Objectives of the Working Group 14 The World Trade Center towers 15 The collapses of the World Trade Center towers 16 Safety issues raised by the collapses of the World Trade Center towers 18 5.1 Major safety issues 18 5.2 Vulnerability to progressive collapse 18 5.3 Passive and active fire protection 20 5.3.1 Passive fire protection, including compartmentation 20 5.3.2 Active fire protection 21 5.4 Escape, its management and the emergency services 22 5.4.1 Escape routes and emergency services access 22 5.4.2 Management of escape 23 5.4.3 Interaction with emergency services 25 5.5 Other issues 27 5.5.1 Security and safety of cladding, including glazing 27 5.5.2 Security and safety of building services 27 5.5.3 Security against unauthorised entry 27 5.5.4 Implementation of design and construction 27 The new situation post 11 September 2001 29 Initial recommendations 31 7.1 Introduction 31 7.2 Vulnerability to progressive collapse 31 7.3 Passive and active fire protection 32 7.3.1 Passive fire protection, including compartmentation 32 7.3.2 Active fire protection 32 7.4 Escape, its management and the emergency services 33 7.4.1 Escape routes and emergency services access 33 7.4.2 Management of escape 34 7.4.3 Interaction with emergency services 34 7.5 Other issues 36 7.5.1 Security and safety of cladding, including glazing 36 7.5.2 Security and safety of building services 36 7.5.3 Security against unauthorised entry 38 7.5.4 Implementation of design and construction 38 Development and research needs 40 Concluding remarks 42 10 References 43 IStructE Safety in tall buildings and other buildings with large occupancy Appendix A: Recent extreme event damage to tall/large buildings 44 Appendix B: Regulations and Codes of Practice 48 Appendix C: Use of risk management processes 54 IStructE Safety in tall buildings and other buildings with large occupancy Foreword The reality of threats to the safety of tall and large buildings was starkly demonstrated by the unprecedented events at the World Trade Center in New York on 11 September 2001 Had these events not occurred, the World Trade Center would no doubt have continued to give many years of excellent service The buildings were not unsafe by any criterion hitherto regarded as being credible in peacetime This Report examines what can be learned from the extreme events of 11 September 2001 for the future design of new buildings and the appraisal of existing ones The purpose is to assist owners and operators of tall/large buildings and their professional advisers to play their part in reacting to the new threats to the safety of building occupants The Report presents therefore initial recommendations by the Working Group on ‘Safety in Tall Buildings’following review of damage by extreme events to tall/large buildings at the World Trade Center and elsewhere world wide The Working Group has concentrated initially on gaining an overview of the safety issues arising from the events of 11 September 2001 The aim has been to point to directions for improving future provisions for occupant safety in tall/large buildings The resulting initial recommendations are in no way a panacea for dealing with threats to the building infrastructure Rather they indicate possibilities that require consideration and study There are many ways to inflict heavy blows of death and destruction in cities For society as a whole, the most effective measures that can be taken following the events of 11 September 2001 are those related to improving security in cities (especially around high ‘profile’ tall/large buildings, landmarks and infrastructure), preventing terrorists from gaining control of means to make attacks, and the deeper resolution of conflicts that breed resentment and create the environment in which terrorism flourishes The solutions to reducing the probability of a recurrence of extreme events, such as occurred on 11 September 2001, not lie within the gift of building owners and construction professionals This Report, nevertheless, seeks to contribute to public safety by providing recommendations to assist building owners and their professional advisers to provide buildings and infrastructure better able to sustain any future malicious attacks with a reduced risk of loss of life Much further work and international collaboration amongst construction professionals and others is needed to assist building owners and their professional advisers to optimise occupant safety in extreme events I would like to thank members of the Working Group and others, around the world, who have collaborated and contributed generously to the preparation of this Report I would also particularly like to thank John Menzies for preparing drafts of the report for the Working Group John Roberts Chairman July 2002 IStructE Safety in tall buildings and other buildings with large occupancy Definitions for the purposes of this Report Tall/large building A building of many storeys or of large size that may be occupied by significant numbers of people Hazard Anything that has potential to cause loss or damage (harm) Hazard (or emergency) scenario The total circumstances within or around a tall/large building arising due to an event that may place occupant health and safety in jeopardy Risk The combination of the likelihood of occurrence of a particular hazard and the consequences thereof Incident An abnormal event within or outside a tall/large building that requires investigation by the building management and may give rise to an emergency Extreme event A man-made or naturally-occurring abnormal event that may cause a major emergency in a tall/large building Emergency An incident outside or within a tall/large building that requires investigation or action by emergency services Major emergency An emergency caused by an extreme event outside or within a tall/large building that may place the safety of all occupants in jeopardy either by causing loss of stability of the whole building or by the environment in part or the whole of the building becoming harmful to health and safety due to fire gases or contaminants in the air, water or food supply Multi-occupancy The occupancy of a tall/large building by more than one organisation Robustness The ability of an engineered structure or system that enables it to survive a potentially damaging incident or extreme event without disproportionate loss of function Redundant structure A structure that possesses more load paths than required for equilibrium Fire compartment A part of a building, comprising one or more rooms, spaces or storeys, constructed to prevent the spread of fire to or from another part of the same building Ductility The ability of a structural material or element to deform without fracturing IStructE Safety in tall buildings and other buildings with large occupancy Summary Following the extreme events at the World Trade Center in New York on 11 September 2001, the Institution of Structural Engineers convened a Working Group on ‘Safety in Tall Buildings’, with the support of fellow professional bodies, industry and the United Kingdom government, to review and report on the safety issues The objective was to provide guidance and advice on the implications that follow the structural collapses and loss of life at the World Trade Center At the outset it was decided the Working Group would not undertake any independent investigation of the extreme events on 11 September 2001 Rather it would consider all relevant available information, in particular the papers submitted to the Group by its members and others and the large number of other papers recently published elsewhere The scope included buildings of large occupancy generally, since it was anticipated that the guidance produced would also be relevant to them The Group considered not only the collapses and damage to buildings at the World Trade Center, but also recent collapses and damage to other tall/large buildings due to extreme events in other parts of the world Review of available information on the collapse of the World Trade Center (WTC) towers identified several major safety questions: • What can be done to reduce the vulnerability of a tall/large building to collapsing progressively and totally? • Should provisions for the protection of occupants and the building itself in the event of fire be set at a higher standard? • Could escape routes and evacuation of building occupants and the linkage with the emergency services be better provided and managed to help save lives? Consideration of these questions focussed attention on key safety issues related to vulnerability to progressive collapse, to passive and active fire protection, and to escape, its management and the emergency services Other safety issues, i.e security and safety of cladding, security and safety of building services, security against unauthorised entry, and implementation of design and construction, were also found to be relevant The key issues as a whole are multi-disciplinary and strongly interrelated There was recognition that extreme man-made events that may cause a major emergency in a tall/large building can take many different forms Their nature and scale cannot be predicted precisely There was consensus that loss of life and damage caused can be limited in many extreme events by the use of broadly-based strategies involving design, construction and management of the building Key safety issues Vulnerability to progressive collapse • The redundancy of the structure and available alternative load paths • The strength, ductility and hence the energy absorption capacity of the structure (i.e structural elements and particularly the connections between them) • The retention of structural integrity in fire IStructE Safety in tall buildings and other buildings with large occupancy Passive and active fire protection • The real performance of buildings in fire compared to data from standard fire tests on components • The robustness of passive fire protection not only in extreme events but also over time in service • The effectiveness of compartments to prevent spread of fire and smoke • The survivability and functionality of active fire protection systems in extreme events • The desirability of a building being able to survive a full burn-out of its contents without collapse Escape, its management and the emergency services • The physical robustness, size and safety of escape routes and the diversity of vertical escape options • The use of occupant access/egress lifts and emergency services’ lifts for evacuation • Timely access for effective fire fighting and rescue, and provision of protected water mains • Provision for simultaneous evacuation in addition to phased evacuation • Management/emergency response plans for the evacuation of occupants depending on the nature and severity of the extreme event • Provision and use of communications and information systems during emergencies • Training of building management, emergency services and occupants in emergency management and response • Procedures for gathering relevant information when an extreme event occurs and for communication between building management, emergency services and occupants Other safety issues Security and safety of cladding, including glazing • Propensity to cause injury in the event of explosion, impact or fire outside or within the building Security and safety of building services • Design of services systems for robustness, redundancy, and with isolation provisions • Protection and sealing of systems • Security against unauthorised access to building services equipment, plant and control rooms Security against unauthorised entry • Prevention of approach and entry with malicious intent • Management and emergency services plans for response to potential extreme event scenarios Implementation of design and construction • Assurance of adequacy, including durability, of safety-critical elements • Quality of components and workmanship in life-safety installations 10 IStructE Safety in tall buildings and other buildings with large occupancy 8.5 8.5.1 Other issues Security and safety of cladding, including glazing (18) Cladding and glazing systems with minimum propensity to cause injuries following impact, fire or explosion 8.5.2 Security and safety of building services (19) Robust and protected building services systems, their performance and control (20) The location and protection of plant rooms, water and oil storage (21) The means of protecting against dispersion of airborne contaminants in and around tall/large buildings in major emergencies (22) The siting and number of air inlets for tall/large buildings 8.5.3 General (23) Risk management processes (24) Strategies for risk avoidance, reduction and acceptance IStructE Safety in tall buildings and other buildings with large occupancy 41 Concluding remarks 9.1 Current world wide social and political conditions suggest that it is now necessary explicitly to take account of risks arising from a wider range of extreme events than has been traditionally considered in the design, operation and management of tall/large buildings Consideration by the Working Group of recent extreme events causing danger to occupants and damage to tall/large buildings has identified a number of multi-disciplinary and interrelated safety issues 9.2 The safety of occupants in new and existing tall/large buildings can be enhanced in many extreme event scenarios by reductions in vulnerability to disproportionate damage and more effective protection through design, construction and building management measures The Working Group believes the key to minimising risks to occupants in extreme man-made events is to use overall strategies involving design, construction, maintenance, operation and management of the building The initial recommendations made in this Report indicate the main directions for reducing risks to occupants 9.3 The Working Group recognises that implementation of the recommendations in these directions will depend on the ‘profile’ of the building and the extreme man-made events considered in any particular case Development and research are required to provide the necessary tools and standards In this way the safety of occupants in new and existing tall/large buildings and the safety of the buildings themselves can be enhanced in the future 9.4 The Working Group benefited from drawing on a wide range of expertise across disciplines and from world-wide locations In itself this collaboration has proved fruitful and may serve as a model for future investigations/reports into other building/construction issues 9.5 The salutary reminders of the scale of loss of life and human tragedy at the World Trade Center have been at the forefront in discussions of the implications The Working Group acknowledges that 11 September 2001 will remain a defining moment in the history of building performance in the face of a malicious attack on civilised life 42 IStructE Safety in tall buildings and other buildings with large occupancy 10 References (1) Hart, F et al.: Multi-storey buildings in steel, 2nd edition London, Collins, 1985 (2) Federal Emergency Management Agency World Trade Center Building Performance Study: Data Collection, Preliminary Observations, and Recommendations FEMA 403, May 2002 (3) 11th September 2001, Supplement to High-rise Buildings, Munich Reinsurance Company, 2001 (4) Standing Committee on Structural Safety Structural Safety 1996-99 Twelfth Report, London, SETO, 1999 (5) American Society for Testing and Materials Standard Test Methods for Fire Tests of Building Construction and Materials ASTM E119-00 West Conshohocken, Pa, ASTM, 2000 (6) Steel Construction Industry Forum Investigation of Broadgate Phase Fire Ascot, Steel Construction Institute, 1991 (7) Bailey, C G., Lennon, T and Moore, D B.: ‘The behaviour of full-scale steel-framed buildings subjected to compartment fires’ The Structural Engineer, volume 77, no 8, pp 15-21, 20th April 1999 (8) Thomas, I R et al.: Fire Tests of the 140 William Street Office Building BHPR/ENG/R/92/043/SG2C Melbourne, Australia, BHP Research, 1992 (9) Chartered Institute of Building Services Engineers Fire Engineering, CIBSE Guide E London, CIBSE, 1998 (10) National Fire Protection Association Recommended Practice for Smoke Control Systems NFPA 92A Quincy, Mass., 1996 (11) Katzman, G M et al.: ‘Risk Assessment of Citicorp Center Original Design’ In: Safety, Risk and Reliability – Trends in Engineering, International Conference, Malta, 2001, p303-308 Zurich, IABSE, 2001 (12) Do Valle, G.: ‘Failure of a building in Rio de Janeiro’ In: Safety, Risk and Reliability – Trends in Engineering, International Conference, Malta, 2001, p699-704 Zurich, IABSE, 2001 (13) Nugent, W J and Schmidt, M K.: ‘Failures of Modern High-Rise Building Facades and Components’ In: Safety, Risk and Reliability – Trends in Engineering, International Conference, Malta, 2001, p711-716 Zurich, IABSE, 2001 (14) ‘Pirelli floor beams sag after Milan plane crash explosion’ New Civil Engineer, 25 April 2002, pp 6-7 (15) Standing Committee on Structural Safety Structural Safety 2000-01 Thirteenth Report London, SETO, 2001 IStructE Safety in tall buildings and other buildings with large occupancy 43 Appendix A: Recent extreme event damage to tall/large buildings A1 Damage caused by explosions Ronan Point, London 1968 A1.1 In the United Kingdom, the progressive collapse of part of the 22-storey Ronan Point flats following a gas explosion on the eighteenth floor is well known(A1) There were four fatalities Subsequently the phenomenon of progressive collapse was demonstrated in the laboratories of the Building Research Establishment in the United Kingdom A1.2 Following the Ronan Point collapse, the UK Building Regulations were revised to include a requirement for buildings of or more storeys to be designed with the aim that damage caused by an extreme event is not disproportionate to that event, see Appendix B World Trade Center, New York 1993 A1.3 A large car bomb was detonated against the south wall of the 110-storey north tower (WTC1) of the World Trade Center in an underground garage two levels below ground(A2) There were only six fatalities but over 1000 people were injured Electrical and water supplies were cut and sprinklers and standpipes were made inoperable The most severe structural damage occurred in the basement levels, creating extensive bomb craters on some of the levels A shock wave propagated throughout the basement structure, causing the slabs at parking levels to shear free from their supporting columns and other restraint locations In certain positions, the steel columns that were once braced at the parking levels had unbraced lengths as large as 21m after the explosion A1.4 The structural integrity of the tower was not threatened due to the ductility of the framed tube of structural steel and the provisions made in the design of the tower It was designed to resist a 240km/h wind storm, the loss of perimeter columns by sabotage, and the impact of a fullyloaded Boeing 707 aircraft at any height Although lateral horizontal pressures during the explosion were severe, the tower did not collapse because the magnitude was insufficient to cause the columns to fail in shear or in combined axial load and bending A1.5 Buildings adjacent to the WTC1 tower were designed to less onerous requirements and suffered extensive damage that threatened their structural integrity Murrah Federal Building, Oklahoma City 1995 A1.6 A large vehicle bomb was detonated approximately 5m from the north face of the Murrah Building(A3) The explosion and resulting collapse caused 168 fatalities and substantial damage to the Murrah Building and to other buildings in the vicinity of the blast The nine-storey Murrah Building of reinforced concrete slab and column construction was damaged severely at the north face where three of the four external columns and an internal column were destroyed causing a 3rd floor spandrel to give way As a result, eight of the ten bays along the northern half of the building collapsed progressively, together with two bays on the south side Surveys of the damaged building found that progressive collapse extended the damage beyond that caused directly by the blast St Mary Axe and Bishopsgate, London 1992/3 A1.7 Two separate incidents of detonation of relatively large bombs occurred in London(A2) Only one building suffered complete collapse, a 14th century church, but many suffered considerable damage to cladding and internal fixtures and fittings Only four buildings immediately adjacent to the explosions suffered severe local structural damage A1.8 The European Bank for Reconstruction and Development, approximately 150m from the bomb in St Mary Axe, suffered extensive glass damage The building was shielded from the blast by an adjacent building and so did not suffer structural damage A1.9 The glass damage to the European Bank building illustrated the influence of glass type, size, 44 IStructE Safety in tall buildings and other buildings with large occupancy strength, and orientation Nearly all windows on the upwind faces were shattered Large annealed glass windows were blown in and glass shards were projected well into adjacent offices Where blinds were drawn on windows, the projectile hazard was reduced noticeably It was also evident that blast effects of the explosion on the interior were of low intensity The only windows to survive on the upwind face of the building were double-glazed in toughened, 10mm-thick glass These windows were found to be crazed The 33mm-thick laminated glass windows at street level survived without crazing Manchester City Centre 1996 A1.10 A large bomb was detonated in the central shopping district of Manchester, England causing extensive damage(A2) There were no fatalities but many injuries were caused by flying glass Structural assessments found that the damage caused by the explosion was mainly to glazing and cladding panels Although glazing damage was extensive, it appeared to be randomly distributed Ground-floor windows relatively close to the blast remained intact, whilst windows much further away and at high elevation were shattered The worst case of structural damage occurred near to the heart of the explosion where the structural frame of a 200 tonne pedestrian bridge was twisted and lifted off its bearings A retail store immediately adjacent to the site of the explosion was subsequently demolished London Docklands 1996 A1.11 There were two fatalities and office buildings and nearby homes were damaged extensively when a home-made vehicle bomb was detonated in London Docklands(A2) There was little structural damage to nearby buildings However glazing and cladding damage was extensive No glazing within 50m of the blast survived A2 Damage caused by fire Seven World Trade Center 2001 A2.1 The 47-storey building known as Seven World Trade Center (WTC7) was set on fire by debris from the WTC towers (WTC1 and WTC2) when they collapsed on 11 September 2001 WTC7 collapsed totally about seven hours later The collapse appears to have been due primarily to the effects of fire, and not to impact damage from the collapsing WTC towers(2) The collapse may have been associated with the burning of a large quantity of diesel fuel stored in tanks on the 5th, 7th and 8th floors, and with nearby steel trusses used to bridge the building structure over electricity substations No other case of a fire-protected steel-framed building collapsing totally in fire is believed to have occurred in spite of there having been several cases world wide of large uncontrolled fires in tall buildings, even where the fire has burnt out all combustible materials inside The mechanisms causing the total collapse of WTC7 have not yet been confirmed Loss of structural integrity in one of the load transfer systems caused by fire has been suggested as the ‘trigger’ event Andraus Building, Sao Paulo 1972 A2.2 The fire developed on four floors of the 31-storey department store and office building It then spread externally up the side of the building involving another 24 floors Wind and combustible interior finishes and contents contributed to the fire spread The building was constructed of reinforced concrete Its faỗade had extensive floor to ceiling glazed areas, with a spandrel of only 350mm in height and projecting 305mm from the face of the building After the fire broke through the windows, three to four floors above the department store floors were exposed to a flame front The front increased in height as more floors became involved At its peak the mass of flame over the external faỗade was 40m wide and 100m high and projecting at least 15m over the street There were 16 fatalities Joelma Building, Sao Paulo 1974 A2.3 Fire started on the 12th floor near to a window of this 25-storey office building of reinforced concrete construction The in situ concrete floor slabs projected 900mm on the north wall and 600mm on the south wall The exterior facade was made of hollow tiles rendered with cement IStructE Safety in tall buildings and other buildings with large occupancy 45 plaster on both sides and aluminium-framed windows The fire spread externally up 13 storeys on two of the facades to the top of the building, readily igniting combustible finishes inside the windows of the floors above, enabling the vertical spread of the fire to continue There were 179 fatalities Las Vegas Hilton Hotel 1981 A2.4 This 30-storey hotel of reinforced concrete construction had windows between floors separated vertically by a prefabricated spandrel of masonry, plaster and plasterboard on steel studs The fire started on the 8th floor of the east tower lift lobby involving curtains, carpeting on the walls, ceiling and floor, and furniture An exterior plate glass window shattered allowing a flame front to extend upwards outside the building The fire spread from the 8th floor up 22 storeys to the top of the building in about 20 minutes A2.5 The vertical fire spread was facilitated mainly by two mechanisms Flames outside the upper windows radiated heat through the windows and ignited curtains and timber benches with polyurethane foam padding which then ignited carpeting on room surfaces The second mechanism involved the flames contacting the plate glass windows It is believed the triangular shape of the spandrels and recessed plate glass caused additional turbulence which rolled the flames onto the windows causing their early failure A2.6 There were fatalities The doors to the hotel rooms where four fatalities occurred were open or had been opened by the fire There were no fatalities in rooms where the doors had been kept closed First Interstate Bank Building, Los Angeles 1988 A2.7 This 62-storey building had sprinkler protection only in the basement, garage and underground pedestrian tunnel The building had a structural steel frame with sprayed fire protection and steel floor pans and lightweight concrete decking The exterior curtain walls were glass and aluminium with a 100mm gap between the curtain wall and the floor slab, fire stopped with 15mm gypsum board and fibreglass caulking A2.8 The fire started on the 12th floor and extended to the floors above primarily via the outer walls of the building Flames also penetrated behind the spandrel panels around the ends of the floor slab where there was sufficient deformation of the aluminium mullions to weaken the fire stopping allowing the flames to pass through, even before the windows and mullions had failed Flames were estimated to be lapping 10m up the face of the building The curtain walls including windows, spandrel panels and mullions were almost completely destroyed by the fire However, the building structure as a whole did not collapse There was one fatality One Meridian Plaza, Philadelphia 1991 A2.9 The construction of this 38-storey bank building used structural steel with concrete floors on metal decking and protected with spray-on fire protection The exterior of the building was covered by granite curtain wall panels with glass windows attached to perimeter floor girders and spandrels Only the below-ground services floors were fitted with sprinklers at the time of construction Subsequently sprinklers had been installed on the 30th, 31st, 34th, and 35th floors and to parts of the 11th to 15th floors Fire broke out on the 22nd floor, penetrated through the windows and heat exposure from the fire plumes ignited materials on the seven floors above The fire was stopped as it approached the 30th floor which had sprinklers Although the fire burned for 19 hours, the structure did not collapse Three firemen lost their lives President Tower, Bangkok 1997 A2.10 46 This 37-storey retail, commercial office and hotel development was under construction Interior fit-out was not fully completed and the sprinkler system was not yet operational An explosion and fire on level seven caused the destruction of the aluminium framed curtain walling The effectiveness of fire stopping at the floor edges was compromised by floor to IStructE Safety in tall buildings and other buildings with large occupancy floor cabling Window and spandrel glass shattered The fire spread up three floors to level ten There were three fatalities A3 References (A1) Ministry of Housing & Local Government Report of the inquiry into the collapse of flats at Ronan Point, Canning Town, London HMSO, 1968 (A2) Yandzio, E., and Gough, M.: Protection of buildings against explosions SCI Publication 244, Steel Construction Institute, 1999 (A3) Federal Emergency Management Agency The Oklahoma City Bombing: Improving building performance through multi-hazard mitigation FEMA 277 Reston, Pa., ASCE, 1996 IStructE Safety in tall buildings and other buildings with large occupancy 47 Appendix B: Regulations and codes of practice B1 General B1.1 The regulations and directives governing the construction of tall/large buildings generally cover a similar, but not always the same, scope in each country National and/or local regulations require application for permission, often in the form of a licence, to construct buildings Other regulations govern the form and detail of the building itself The latter are usually intended primarily to ensure personal safety and, as a requirement of lower importance, to protect the building against damage and defects There not appear to be regulations in any country requiring a licence to operate and use a tall/large building once built, although there are controls on some aspects of buildings such as emergency exits and fire escapes, e.g in hotels In comparison, licences to operate some other types of facility where large numbers of people are accommodated, e.g sports grounds, are required in some countries These licence systems are generally for the control of safety-related aspects of the facility and its operation B1.2 Regulations governing protection against natural hazards, such as wind and earthquake, are usually related to requirements for structural stability of the building The severity of the natural hazard that must be resisted is usually specified, sometimes via associated standards and codes These requirements usually also serve to protect people in the vicinity from falling parts of the building, especially parts of the faỗade In some cases regulations give specific requirements for the structure to be resistant to progressive collapse in the event of an accident Generally, man-made hazards to the structure are known as accidents, e.g impact and explosions Malicious acts are specifically excluded or are not specifically referred to Guidance on the magnitude of accidents to take into account in design is sometimes given in codes of practice B1.3 Regulations generally recognise fire as a major risk to buildings and require provisions for fire protection that cover fire resistance, compartmentation, sprinklers and escape routes The requirements may be more onerous for tall buildings than others The differences reflect the higher risk in tall/large buildings of spread of fire and smoke and the greater limitations in such buildings on escape and on the ability of emergency services to rescue people at height and to fight fires within the building B1.4 Regulatory requirements for operational security usually include the safety of lifts, stairs, guard rails and parapets, emergency lighting and non-slip floor coverings B1.5 In England and Wales, approved documents together with codes provide guidance on meeting the performance requirements of the Building Regulations(B1) They relate to performance on completion of construction Similar requirements apply in other parts of the United Kingdom National standards and codes in the United Kingdom are increasingly influenced by developing European codes that are expected to supersede the national standards in due course B1.6 In the United States, there is no national Building Code and most of the states have their own code Each community determines its own building code requirements(B2) There are, however, model building codes: • Uniform Building Code by the International Conference of Building Officials • National Basic Building Code by the Building Officials and Code Administrators • Standard Building Code by the Southern Building Code Congress • Codes relating to fire by the National Fire Protection Association B1.7 An International Building Code by the International Codes Council (applicable in United States only) also exists It is essentially a conventional prescriptive code obtained by merging the three United States model codes An alternative, the International Codes Council Performance Code, has recently become available B1.8 None of these codes is mandatory but many states adopt one of them, at least in part Others, 48 IStructE Safety in tall buildings and other buildings with large occupancy such as New York and Florida feel their specific needs are best met by a locally-developed code Some cities, such as New York, Chicago and Los Angeles, also have unique codes that not entirely conform to the local state codes Many codes in the United States, e.g New York City, provide exceptions/exemptions for government agencies and public utilities The New York City Building Code did not require detailing for seismic events when the WTC towers were designed and built Requirements for fire (covering compartmentation, fire resistance and escape routes) are quite detailed B1.9 The National Fire Protection Association in the United States has produced a ‘Life Safety Code’ that is specific to fire(B3) An NFPA task group has developed guidance on performancebased design B1.10 Many codes for design are largely prescriptive The relationship to life safety is not always clear However, performance-based guidance is becoming more widely established B1.11 This very brief review of some of the regulations that relate to the safety issues in tall/large buildings indicates that requirements are not consistent around the world The differences are due largely to independent development of regulations in each country and local experience and conditions Even where regulations are the same, important differences in the detailed code rules for implementation exist that may substantially influence the levels of safety achieved B1.12 Development work is needed in many areas of performance-based design covering the main safety issues Performance-based fire safety engineering design is perhaps the area where development is already well advanced and can be speeded up The approach has already been used in the design of tall/large buildings and other facilities with unique design features, e.g airport buildings, railway stations and tunnels Generally time, e.g time to escape, is likely to be the performance parameter of greatest relevance in many aspects of building design, operation and management for extreme events B1.13 The discussion below briefly describes some of the main requirements and provisions of Regulations and codes of practice in the United Kingdom, United States, Australia, Hong Kong and some other countries The discussion is not intended to be exhaustive but rather to illustrate the large number and different scope of regulations and code requirements that exist around the world relating to safety issues in tall/large buildings B2 Vulnerability to progressive collapse B2.1 Some regulations and codes of practice explicitly recognise the design principle for buildings that damage should not be disproportionate to the cause Currently, regulations and codes of practice for buildings in the United Kingdom, United States and elsewhere have different requirements for design against progressive collapse In the United Kingdom, there is a regulatory requirement, originally introduced following the progressive collapse of Ronan Point in 1968, to provide (in buildings over storeys tall) structural resistance with the aim of limiting damage caused by an accident so that it is not disproportionate to the cause Building Regulations Approved Document A and British Standard codes of practice give advice on meeting the requirement During 2001 the UK Department of Transport, Local Government and the Regions (DTLR) consulted on proposals to amend the Regulations to bring all buildings within the compass of the requirement The associated British Standard codes of practice provide guidance on designing the form and detail of structures for ductility and robustness Structural elements fundamental to the survival of the structure are recognised Effective vertical and horizontal tying forms the main thrust of the approved design rules B2.2 The Eurocode EN1990: Basis of design(B4) adopts, as a fundamental requirement, the principle that a structure shall be designed in such a way that it will not be damaged by events like fire, explosion, impact or consequences of human errors, to an extent disproportionate to the cause It gives strategies for avoiding or limiting damage along the lines of the recommendations in Section 7.2 Essentially, avoid or reduce hazards, select a redundant structural form with a low sensitivity to the hazards considered, and design and connect the structure together with strong ductile elements and connections so that it can absorb energy and survive removal of parts in an extreme event IStructE Safety in tall buildings and other buildings with large occupancy 49 B2.3 In the United States, whilst there is no explicit provision aimed at prevention of progressive collapse, current design guidance of cast in situ reinforced concrete structures and structural steel frames (with properly designed and constructed connections) generally produces structures with substantial ductility For zones of high seismicity, the model codes in the United States have detailing provisions that are intended to increase structural ductility and toughness, thereby reducing the risk of progressive collapse during earthquakes Following the explosion at the Murrah building in 1995, see Section A1.6, the potential of failure of key elements to trigger progressive collapse has been recognised(B5) B2.4 Australian requirements are given first as a functional statement of capability of the building to withstand combinations of loads and other actions to which a building may reasonably be subjected(B6) Associated performance requirements include resistance at an acceptable level of safety to the most adverse combinations of loads that might result in potential for progressive collapse B2.5 The Hong Kong Building Authority uses locally-developed codes of practice for the structural use of steel and concrete The approach to structural robustness, accidental damage and disproportionate collapse essentially follows the principles and methods adopted in the United Kingdom, although there is little specific reference to robustness in the Hong Kong Building (Construction) Regulations and Hong Kong codes of practice for structural design The code: Structural Use of Steel 1978 issued by the Building Authority gives no guidance on the issue, either in principle or prescriptive The code: The Structural Use of Concrete 1987 does however state the principle – ‘The structure should be designed to support loads caused by normal function, but there should be a reasonable probability that it will not collapse catastrophically under the effect of misuse or accident No structure can be expected to resist excessive loads or forces that could arise due to an extreme cause, but it should not be damaged to an extent disproportionate to the original cause.’ From time to time Practice Notes for Authorised Persons and Registered Structural Engineers (PNAPs) are issued by the Building Authority PNAP 140 gives a list of standards that are considered to satisfy the technical requirements of the Building Regulations This list includes British Standards BS 8110 and BS 5950 It is through these two particular codes that the conventional provisions for tying, localisation of damage, and key elements, as used in design in the United Kingdom, are applied B2.6 Overall therefore, regulatory and code requirements across the world differ in the extent to which they recognise vulnerability to progressive collapse There appear to be none that deal explicitly with the issues of weakening from impact or explosion combined with further weakening from a major fire B3 Passive and active fire resistance B3.1 There are regulatory requirements in the United Kingdom for inhibiting the spread of fire within a building through the use of linings that resist the spread of flame, and through fireresisting construction that sub-divides the building into fire compartments Overall, these requirements seek to prevent the premature failure of the building structure in a fire There are also requirements to restrict fire spread over external walls and roofs and from one building to another B3.2 Sprinklers are recommended in all buildings (except those for residential use) where they exceed 30m in height to the highest floor Under the Building Regulations, the sprinklers need to be designed to a higher specification of ‘life safety standard’ The higher specification includes additional measures that reduce the likelihood of sprinkler failure The regulations relating to fire work together as a package Compartmentation is required to contain the spread of a fire, sprinklers to stop the fire developing sufficiently to breach the compartmentation, and protected shafts to enable people to escape safely when, by necessity, they have to escape passed the fire B3.3 In the United States, many states and cities have fire codes that give building requirements Building code requirements for structural fire protection are based on laboratory tests, the ASTM E119 standard fire test on building components(5) This standard test provides comparisons between component behaviour under controlled conditions Similarly to the 50 IStructE Safety in tall buildings and other buildings with large occupancy BS 476 standard test used in the United Kingdom, the test is not intended to predict actual behaviour of the component in a building during a real fire A handbook of fire protection engineering has been published by the Society for Fire Protection Engineering(B7) B3.4 Australian building codes require fire-resisting construction according to building size, building over storeys being the highest category Load-bearing elements are required to maintain integrity and insulation for specified times Lightweight non-combustible materials, specified for protecting structure from heat, are required to meet prescribed mechanical tests Requirements for compartmentation are specified in terms of floor area and volume Fire stopping of services penetrations is required B3.5 In Hong Kong, the Building Code(B8) for fire resisting construction has been derived mainly from earlier British counterparts A barrier is required at openings in floors to prevent the spread of fire and smoke Curtain walls extending beyond one storey must be of noncombustible materials and have fire stops in any void between the wall and the building perimeter B3.6 Pressurisation methods required for the control of smoke from fire and prevention of its spread through a tall/large building differ across the world In the United Kingdom, positive pressurisation of stair wells and negative pressures on fire floors are required In Hong Kong, the fire floor does not have to be depressurised, whilst in Australia additionally the floors above and below the fire floor have to be positively pressurised B3.7 Overall, the requirements for the fire protection of building structures and smoke control vary significantly around the world In many countries, e.g United Kingdom, United States, Australia, Hong Kong, Sweden and Singapore, the requirements for fire protection are obtained from tabulated data of the performance of structural elements in standard laboratory tests There are anomalies in the ratings that are derived Other methods are available for deriving requirements, e.g the Eurocode method(B9) These methods are based on ‘real’ fire scenarios and provide more realistic gas-temperature/time curves that can then be used to input into structural fire analyses to give predictions of the behaviour of the load-bearing system as it is heated by the fire Proposals being considered by the ISO/TC92 Committee for a framework for long-term standardisation of fire safety in support of performance-based fire engineering design may provide an effective international forum B4 Escape, its management and the emergency services B4.1 The Building Regulations of the United Kingdom have requirements in Regulation B1 for means of escape in case of fire(B10) Provisions for early warning of fire and for means of escape to a place of safety outside the building are required The requirements for escape routes depend on the use, size and height of the building They cover number and capacity of routes, distance of travel, protection, lighting, signing and facilities to limit ingress of smoke or to restrict the fire and remove smoke There are also requirements for fire precautions that require a fire certificate for a tall/large building(B11) The precautions required, in addition to means of escape, include the provision of fire alarms and fire fighting equipment As a whole, the requirements for fire safety are designed to ensure the provision of adequate general fire safety, means of escape and related fire precautions B4.2 Phased evacuation is recognised in several countries, e.g United Kingdom(B10), United States(B3) and Australia(B6), as an appropriate way of evacuating tall buildings The Australian building code provisions for escape require at least two exits for tall buildings and they must be fire-isolated and exit within a certain distance to an open space There are limits to distances in the building from exits The size of the exits is related to the number of people accommodated in the building Barriers must be provided to prevent vehicles blocking exits B4.3 In Hong Kong, the Building Code is also prescriptive but well developed on the basis of the long history of tall buildings there Prescriptive measures include stair pressurisation of fire fighting lift and stair shafts, and provision of refuge floors Means of escape are defined using total evacuation as the escape strategy Escape stairs must lead directly to a street and exit doors must be easily operated from within The width of staircases depends on the number of occupants Refuge floors are required every 20 storeys, except for residential buildings where IStructE Safety in tall buildings and other buildings with large occupancy 51 the requirement is relaxed to 40 storeys In Germany, concrete shafts are required for escape stairs B4.4 The use of lifts for evacuation in emergencies in airport control towers is allowed in the American code NFPA 101(B3) and, in the United Kingdom, Part of BS 5588(B12) allows their use in buildings B4.5 Code requirements for fire detection systems vary significantly around the world For example, in Australia, both smoke detectors and sprinklers are required in tall office buildings whilst, in Hong Kong, only sprinklers are required for the detection and suppression of fire B4.6 Various standards exist for informative warning systems, including BS 5839: Part 8(B13), AS 2200(B14), and NFPA 72(B15) In many countries, only relatively simple alarm systems are required, e.g a bell B4.7 The provision of access and facilities for emergency fire services are required in the United Kingdom Designated fire fighting shafts (lift and stairs) are required that have additional fire protection measures to protect ‘emergency services’ personnel and to facilitate their fire fighting work, i.e the shafts may be pressurised or ventilated Similar requirements apply in Hong Kong Other countries, e.g Australia, not have this requirement B4.8 Overall current regulations and codes are focussed on emergencies and means of escape in case of fire Further research is needed not only on systems for escape and emergency services access in case of fire, but also on life safety in non-fire types of extreme event where different evacuation and rescue strategies may be needed B5 Other issues B5.1 Security and safety of cladding, including glazing B5.1.1 In the United Kingdom, cladding, including glazing, is considered in the Building Regulations to be ‘structure’ The regulatory requirements for safety of the structure and resistance against disproportionate collapse therefore apply Approved documents give guidance on design of cladding and fixings to meet the requirements Enhanced glazing is only required at locations where occupants may accidentally impact against it B5.2 Security and safety of building services B5.2.1 There are no regulations in the United Kingdom specifically covering the security and safety of services in buildings However there are regulations and standards controlling the supply of electricity and clean potable water B5.3 Security against unauthorised entry B5.3.1 The introduction of regulatory requirements for entrance security of buildings is being considered in the United Kingdom B6 References (B1) The Building Regulations 2000 London, TSO, 2000 (B2) Pachecano, R R., and Goldsmith, J.: ‘One Size Does Not Fit All’ Facilities Design and Management, April 2002, pp26-28 (B3) National Fire Protection Association Code for safety to life from fire in buildings and structures NFPA101A Quincy, Mass., NFPA, 2000 (B4) prEN1990, Basis of design, CEN, July 2001 (B5) Hinman, E E., and Hammond, D J.: Lessons from the Oklahoma City bombing: defensive design techniques New York, ASCE, 1997 (B6) Australian Building Codes Board Building Code of Australia, 1996 – Canberra ABCB, 1996 (B7) Society for Fire Protection Engineers Handbook of Fire Protection Engineering, 3rd edition Quincy, Mass., NFPA, 2002 (B8) Building Department, Hong Kong Hong Kong Building Code: Code of practice for the 52 IStructE Safety in tall buildings and other buildings with large occupancy provision of means of escape in case of fire, 1996; Minimum fire services installations and equipment, and inspection, testing and maintenance of installations and equipment Hong Kong, Fire Services Department, 1998 (B9) Draft prEN 1991-1-2, 2000 Actions on structures exposed to fire, CEN 2000 (B10) The Building Regulations 2000: Approved Document B: fire safety London, TSO, 2000 (B11) Fire Precautions Act 1971, London, HMSO, 1971 (B12) BS 5588 Fire precautions in the design, construction and use of buildings, Series, BSI, London (B13) BS 5839: Part 8: 1995 Code of practice for the design, installation and servicing of voice alarm systems, Fire detection and alarm systems for buildings, BSI, London (B14) Standards Australia Emergency warning and intercommunication systems in buildings Australian Standard 2220, Sydney, 1989 (B15) National Fire Protection Association National Fire Alarm Code Handbook Quincy, Mass., NFPA, 1999 IStructE Safety in tall buildings and other buildings with large occupancy 53 Appendix C: Use of risk management processes C1 Virtually all human activity involves risk Owners and occupiers should therefore appreciate that absolute safety in tall/large buildings is not achievable Design, operation and management can only seek to keep risks to occupants and the building itself at an acceptably low level C2 A practical overall aim of design of a tall/large building against extreme events with a low probability of occurrence is to make provisions, both in the building and in its operation and management, such that the damage caused is not disproportionate to the event The ‘damage’ of primary concern relates to the safety of people The physical damage to the building itself is also of concern, particularly since damage to the building usually places people at risk Minimising the damage to the building fabric and its services systems can minimise the ‘damage’ to people in many, but not all, cases C3 Codes and standards have evolved to enable provision of safe buildings They provide reasonable protection for the occupants of a building in ‘normal’ hazard events, e.g ‘conventional’ fire scenarios As a result, modern tall/large buildings designed using current good practice to resist normal loading conditions and recognised extreme events such as extreme winds, earthquakes, and road vehicle impacts, have performed well This success can be attributed to the provision of generally robust structures and systems, and of protective measures within and around buildings to protect the buildings and their occupants from such events Tragic incidents with loss of life often stimulate a re-evaluation of codes and standards and lead to changes in practice which improve levels of safety C4 Safety and the protection of occupants provided by design and by building management for normal circumstances may be strengthened and made more effective in extreme events by specifically identifying possible hazard scenarios, assessing the risks and improving robustness and/or protective measures and emergency response plans accordingly A rational structured consideration of the hazards and risks of extreme events that may occur during the life of a tall/large building can assist designers and building management to enhance protection and advise building owners and operators C5 Explicit processes for identifying potential hazard scenarios and for managing risks due to extreme events have not yet been generally adopted world wide in current regulations and codes relating to building design and management There is, however, a trend in this direction Use of explicit risk management processes in structural engineering has been advocated elsewhere(C1, C2, C3) Their use has been encouraged in some other industries, e.g offshore oil and railways, following reports on incidents of extreme event damage The reports on, for example, Flixborough oil refinery (1974), Seveso chemical plant (1976), Piper Alpha off-shore oil platform (1988), and King’s Cross Underground station (1987) strengthened the trend away from prescriptive design methods towards probabilistic analyses and performance-based design C6 In the United Kingdom, the use of risk-based scenarios as the basis of design of structures is becoming established practice Some relevant standards have been produced, e.g BS 7974(C4) This fire engineering standard recommends an initial qualitative design review by several experts to decide what are the realistic scenarios and the fire safety objectives The draft European standard for structural design against accidental impact and explosions(C5) uses the concept that some damage is acceptable and gives design guidance on measures for reducing the probability of the event and the consequences In other industries in the United Kingdom and elsewhere, e.g offshore oil, railway and nuclear power, explicit risk management processes are required by regulations and supported by codes C7 Well-developed techniques of hazard identification and risk assessment exist to inform risk management processes Their use can aid judgments by designers and building managers on the risks of man-made hazard scenarios for which it is appropriate to make provisions or enhanced provisions C8 Such processes usually begin during the early stages of feasibility and development of the clients’ requirements and brief They can enable more consistent implementation of the principle in design that damage should not be disproportionate to the cause Application of these processes to 54 IStructE Safety in tall buildings and other buildings with large occupancy tall/large buildings necessarily embraces consideration of the building as a whole, its design and construction, its protective systems, operation, management, and links to the emergency services The process typically includes identification of potential events/threats/hazards, assessment of the risks judged against acceptability criteria, and choices and decisions about how the risks will be managed A range of techniques is available to assist, see for example, reference (C6) Although there is no certain way of identifying all potential hazards and the judgment of what is acceptable is subjective, the process of thinking through different scenarios can be helpful in identifying those measures – whether simple or complex – that have the greatest potential within the constraints of the project to improve life safety C9 Specific consideration of risk in extreme event scenarios can play an important role in determining what ‘enhancements’ should be considered, for example, relating to provisions for fire: • The use of phased and simultaneous evacuation • Use of lifts for evacuation • Target time for building evacuation • Evacuation management regimes • Selection and training of fire marshalls • Increasing robustness of escape stairs • Robustness of fire protection C10 More explicit risk management processes along the above lines could become a wider part of the routine of the creation of tall/large buildings with potential benefit for occupant safety Development work is needed to transfer and develop the relevant risk management processes used in related industries for tall/large buildings C11 References (C1) Standing Committee on Structural Safety Thirteenth Report, 2000-01 London, SETO, 2001 (C2) Schneider, J.: Introduction to safety and reliability of structures IABSE Structural Engineering Document Zurich, International Association for Bridge and Structural Engineering, 1997 (C3) prEN1990, Basis of design CEN, July 2001 (C4) BS7974 Application of fire safety engineering principles to the design of buildings, Code of practice London, BSI, 2001 (C5) Draft prEN 1991-1-7 Accidental actions due to impact and explosions CEN, March 2002 (C6) Managing safety risk Guidance Note RT/LS/G/001 Railtrack plc, June 2000 IStructE Safety in tall buildings and other buildings with large occupancy 55 ... adequacy, including durability, of safety- critical elements • Quality of components and workmanship in life -safety installations 10 IStructE Safety in tall buildings and other buildings with... raised by the individual performance of these buildings are incorporated into the discussion in this Report IStructE Safety in tall buildings and other buildings with large occupancy 17 Safety issues... IStructE Safety in tall buildings and other buildings with large occupancy 5.5 Other issues 5.5.1 Security and safety of cladding, including glazing 5.5.1.1 Cladding, especially glazing, can