Mumbai

‘Sustainable Fire Engineering for All’ – SDI’s Professional Service

2012-12-14 & 2012-12-30:  Further to this distressing incident … which exposed a profound lack of awareness, care and competence within the general fire safety industrial sector …

Recent Fatal Fire at a Disabled Workshop in SW Germany

… this is how we would like to help you … whether you are an individual, or an organization … whether you are located in Ireland, Italy or Turkey … some other part of Europe, the Arab Gulf Region, India, Japan, China … or wherever !

And … we can, if requested or necessary, work in collaboration with local partners in those different geographical regions.

– FireOx International is the Fire Engineering Division of Sustainable Design International Ltd. (SDI) –

.

Colour photograph showing the 2 World Trade Center Towers, in New York City, immediately after the second plane impact. The mechanical damage arising from such a plane impact had been considered in the Initial Building Design Process; incredibly, any type of Fire Incident had not ! In the case of both towers and within a short period of time, Fire-Induced Progressive Damage resulted in Disproportionate Damage, and eventual Total Building Collapse. The horror and carnage at the World Trade Center Complex, and the extensive collateral damage to everywhere south of Canal Street, caused enormous long-term damage to the economy of Manhattan ... and had a very significant adverse impact on Global Financial Markets. Click to enlarge.

Colour photograph showing the 2 World Trade Center Towers, in New York City, immediately after the second plane impact. The mechanical damage arising from such a plane impact had been considered in the Initial Building Design Process; incredibly, any type of Fire Incident had not ! In the case of both towers and within a short period of time, Fire-Induced Progressive Damage resulted in Disproportionate Damage, and eventual Total Building Collapse. The horror and carnage at the World Trade Center Complex also caused enormous long-term damage to the economy of Manhattan … and had a very significant adverse impact on Global Financial Markets. Click to enlarge.

.

Introduction

Fundamentally, the 9-11 World Trade Center Incident in New York (2001) was an Extreme ‘Real’ Fire Event.  It presented the International Fire Engineering Community with a catastrophic failure in conventional practices and procedures related to:

  • Fire Engineering, Structural Engineering, and Architectural Design ;
  • Human Building Management Systems ;
  • Emergency Response by Firefighters, Rescue Teams, and Medical Personnel ;
  • National and Local Organizations Having Authority or Jurisdiction (AHJ’s) ;

… and with the serious problem of entirely inadequate Fire Safety Objectives in the building legislation, model codes and design standards of the most economically advanced countries in the world.

Those people who understand the building design process, and have experience as construction practitioners, have long realised that the lessons from 9-11 must be applied across the full spectrum of building types … not just to tall buildings.  Right up to the present day, unfortunately, many people in the International Fire Engineering Community are either unwilling, or unable, to do this.

Furthermore … Fire Engineering, Architectural Design and Structural Engineering must, of urgent necessity, be seamlessly conjoined … with the aim of removing misunderstandings and the wide gaps in client service delivery between the different disciplines.

In 2002, a series of Long-Term 9-11 Survivor Health Studies commenced in the USA … and in 2005 and 2008, the U.S. National Institute of Standards and Technology (NIST) issued a series of Post 9-11 Critical Recommendations concerning the design, construction, management and operation of buildings.

At FireOx International … we have fully integrated this essential design guidance into our frontline fire engineering and architectural practice … we have developed unique and practical solutions for worldwide application, some of which appear in International Standard ISO 21542: ‘Building Construction – Accessibility & Usability of the Built Environment’, published in December 2011.

.

Colour photograph showing an armed assailant during the November 2008 'Hive-Attack' on Mumbai ... an extraordinarily violent, co-ordinated assault on the largest (and wealthiest) city in India, which involved the strategic targeting of built environment Places of Public Resort, Iconic Buildings, High-Rise Buildings, Buildings having a Critical Function, Transport Infrastructure and Service Utilities ... with the aim of causing widespread terror among the general population, including tourists, and disruption to the city’s important economic environment. Click to enlarge.

Colour photograph showing an armed assailant during the November 2008 ‘Hive-Attack’ on Mumbai … an extraordinarily violent, co-ordinated assault on the largest (and wealthiest) city in India, which involved the strategic targeting of built environment Places of Public Resort, Iconic Buildings, High-Rise Buildings, Buildings having a Critical Function, Transport Infrastructure and Service Utilities … with the aim of causing widespread terror among the general population, including tourists, and disruption to the city’s important economic environment. Click to enlarge.

.

FireOx International’s Commitment to You

As a necessary response to the New 21st Century Paradigm of Real Extreme Event in a Built Environment which is becoming more and more complex … is subject to climate change and severe weather events … and is vulnerable to malign and malevolent disruption –

WE are committed to … the implementation of a Sustainable Human Environment which is Fire Safe and Secure for All, meaning that an ‘appropriate project-specific fire safety level’ is our fire engineering objective, with ‘human health protection’ targeted as a priority … through the use of innovative, reliability-based and person-centred sustainable design practices and procedures.

.

What is an ‘Appropriate Fire Safety Level’ in Your Building or Facility ?

It is rarely, if ever, explained to clients/client organizations that the Minimal Fire Safety Objectives in building legislation are focused solely on protecting the ‘interests’ of society, not those of the individual …  are, quite often, inadequate and/or flawed … and are, always, revised only after the latest tragedy !

To properly protect Your Interests as a client/client organization … we strongly advise that the Appropriate Level of Fire Safety in Your Building or Facility should exceed the minimal level of safety required by building legislation.  We would also caution that, in many jurisdictions (e.g. India), compliance with national building legislation is voluntary.

Which raises the issues of whether or not you will actually get what you pay for, and whether or not the Fire Protection Measures in Your Building or Facility are reliable (in other words, will they perform as intended at the time of a ‘real’ fire, which may occur at any time in a building’s long life cycle) !?!   Competent Technical Control of Design and Construction, independent of the design and construction organization(s), is essential.

You should carefully consider the following spectrum of issues which may be directly relevant to Your Project.  Following a process of consultation with you, we then develop Project-Specific Fire Engineering Design Objectives … bearing in mind that you must also comply with safety at work, anti-discrimination, and environmental legislation, etc … maintain business continuity, etc … be energy efficient, etc … and be socially responsible, etc …

–     Protection of the Health of All Building Users … including People with Activity Limitations (2001 WHO ICF), Visitors to the building or facility who may be unfamiliar with its layout, and Contractors or Product/Service Suppliers temporarily engaged in work or business transactions on site ;

–     Protection of Property from Loss or Damage … including the Building or Facility, its Contents, and Adjoining or Adjacent Properties ;

–     Safety of Firefighters, Rescue Teams and Other Emergency Response Personnel ;

–     Ease and Reasonable Cost of ‘Effective’ Reconstruction, Refurbishment or Repair Works after a Fire ;

–     Sustainability of the Human Environment (social – built – virtual – economic) … including Fitness for Intended Use and Life Cycle Costing of fire engineering related products and systems, etc … fixed, installed or otherwise incorporated in the building or facility ;

–     Protection of the Natural Environment from Harm, i.e. Adverse or Damaging Impacts.

.

FireOx International – Our Fire Engineering Services

  • WE  will advise you on Fire Safety Policy, Fire Safety Strategy Development, Fire Safety Implementation … and, whether you are within or from outside the European Union, on CE Marking of Fire Protection Related Construction Products

  • WE  understand the process of Design, particularly the new language of Sustainable Design … and we will produce Creative Fire Engineering Solutions for Your Project

  • WE  are thoroughly familiar with the intricacies of Building Sites … and we will verify and/or validate Design Compliance during construction, and at project completion … and, if requested or necessary, as a completely Independent Technical Controller ; 

  • WE  communicate easily and effectively with other Professional Design Disciplines, including architects and structural engineers … and we will act as fully participating members of Your Project Design & Construction Team … and, if requested or necessary, as the Design Professional in Responsible Charge **

  • WE  practice in accordance with a comprehensive Professional Code of Ethics

.

Sustainable Fire Engineering Solutions ?

  1. Are adapted to Local Geography, Climate/Climate Change, Social Need, Culture, Economy … and Severe Events (e.g. earthquakes, flooding) ;
  2. Are ‘Reliability-Based’, i.e. that design process based on practical experience, competence and an examination of real extreme events, e.g. 2001 WTC 9-11 & 2008 Mumbai Attacks, and 2011 Fukushima Nuclear Incident … rather than theory alone ;
  3. Are ‘Person-Centred’, i.e. that design process which places ‘real’ people at the centre of creative endeavours and gives due consideration to their responsible needs, and their health, safety, welfare and security in the Human Environment.

.

FireOx International’s Contact Information

E-Mail:  cjwalsh@sustainable-design.ie

International Phone:  +353 1 8386078   /   National Phone:  (01) 8386078

.

.

Important Note:  This Post should be read in conjunction with an earlier Post …

Sustainable Design International Ltd. – Our Practice Philosophy

It is there, not here, that we define Sustainable Human & Social Development … and describe how our Practice is responding to this open, intricate, dynamic, and still evolving concept.  The resulting transformation in how frontline services are provided to our Clients/Client Organizations ensures a much more comfortable ‘fit’ to their needs … and a greater level of protection, safety and security for society !

.

[ ** 2005 NIST(USA) Final Report on 9-11 World Trade Center 1 & 2 Tower Collapses

– Footnote 49 –

… the Design Professional in Responsible Chargeusually the lead architect – ensures that the (Design) Team Members use consistent design data and assumptions, co-ordinates overlapping specifications, and serves as the liaison with enforcement and review officials, and with the client or client organization. ]

.

.

END

Enhanced by Zemanta

Tags: , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , ,

Progressive Collapse of WTC 7 – 2008 NIST Recommendations – Part 1 of 2

See the 1st Series of Posts on the 2005 NIST WTC 1 & 2 Collapse Recommendations … which began, here, towards the end of 2011 …

2011-10-25:  NIST’s Recommendations on the 9-11 WTC Building Collapses … GROUP 1. Increased Structural Integrity – Recommendations 1, 2 & 3 (out of 30)

.

Colour plan showing the World Trade Center Complex in New York City, and its surrounding neighbourhood in Manhattan. By means of yellow shading and annotation in red text, the extent of direct damage caused by the collapse of the 2 WTC Towers on 11 September 2001 is shown. Not shown is the much greater extent of indirect damage caused, e.g. dust and debris from the collapses clogged up and destroyed air conditioning systems and ductwork in buildings. Everywhere south of Canal Street was a disaster zone. Also not shown is the damage caused by WTC 7, at the north-eastern tip of the Complex, which collapsed late on the afternoon of 9-11. Click to enlarge.

Colour plan showing the World Trade Center Complex in New York City, and its surrounding neighbourhood in Manhattan. By means of yellow shading and annotation in red text, the extent of direct damage caused by the collapse of the 2 WTC Towers on 11 September 2001 is shown. Not shown is the much greater extent of indirect damage caused, e.g. dust and debris from the collapses clogged up and destroyed air conditioning systems and ductwork in buildings. Everywhere south of Canal Street was a disaster zone. Also not shown is the damage caused by WTC 7, at the north-eastern tip of the Complex, which collapsed late on the afternoon of 9-11. Click to enlarge.

.

2012-01-18:  SOME PRELIMINARY COMMENTS …

  1.     World Trade Center Building 7 was a 47 Storey Office Building located at the north -eastern tip of the WTC Complex in Lower Manhattan, New York City.  It had been built on top of an existing Consolidated Edison of New York electric power substation, on land owned by the Port Authority of New York and New Jersey.

On Tuesday, 11 September 2001 … WTC Building 7 was on fire for almost seven hours … from the time of the collapse of WTC Tower 1 – North Tower, just before 10.30 hrs (local time), until 17.21 hrs … when WTC 7 failed completely, collapsing progressively as a result of ‘real’ fires – as distinct from ‘standard test’ fires – on many floors. 

There were only two certainties on that fateful day (9-11) … the Fire-Induced Progressive Collapse of WTC Building 7 could no longer be ignored by the International Fire Science and Engineering Community … and the ‘reality’, which Modern Fire Engineering must now confront, was significantly altered.  Secondly, it is NEVER acceptable to a general population for buildings to collapse !

Later in 2008, the Mumbai ‘Hive’ Attacks would add a sinister new ingredient to the standard threat profile for buildings, their occupants, and emergency services.

However, long before 9-11 and Mumbai, the growing complexity of modern communities and their rapidly evolving architectural forms had left the Fire Engineer far behind, unable to respond to the new fire safety challenges posed.

.

  2.     The second of the NIST Publications being referenced in this New Series of Posts is as follows …

NIST (National Institute of Standards and Technology).  August 2008.  Federal Building and Fire Safety Investigation of the World Trade Center Disaster: Final Report on the Collapse of World Trade Center Building 7.  NIST NCSTAR 1A.  Gaithersburg, MD, USA.

This 2008 NIST Report contains, in Chapter 5, a list of 13 Recommendations for Action (A-M), grouped together under the same 8 Subject Headings used in the 2005 NIST Report (NCSTAR 1) …

     i)       Increased structural integrity … Recommendation A ;

     ii)      Enhanced fire endurance of structures … Recommendations B, C, D & E ;

     iii)     New methods for fire resisting design of structures … Recommendations F & G ;

     iv)     Improved active fire protection … Recommendation H ;

     v)      Improved building evacuation … Long before its collapse, all occupants/users had evacuated WTC 7 … No Recommendation ;

     vi)     Improved emergency response … Recommendation I ;

     vii)    Improved procedures and practices … Recommendations J & K ;   and

     viii)   Education and training … Recommendations L & M.

NIST has clearly stated that “the urgency of these Recommendations is substantially reinforced by their pertinence to the collapse of a tall building that was based on a structural system design that is in widespread use”.

.

  3.     The Colour Coding of Texts which I am using in this new series of posts … where NIST has presented new texts relating to WTC Building 7, these are shown in blue … where NIST has chosen to reinforce earlier texts from the 2005 Report on the WTC Towers 1 & 2 Collapses, these are shown in black.  The important new paragraphs describing the critical relevance of WTC Building 7 are shown in red.

Please pay particular attention to these Red Paragraphs.  Having carefully digested their contents … then if, by any chance, you happen to encounter somebody who still insists that the NIST 9-11 WTC Recommendations have no relevance to the design, construction, management and operation of ALL Buildings … that person is either living in Alice’s Wonderland … or he/she has never bothered to read the NIST Recommendations in the first place !!

.

  4.     While it is still essential to distinguish clearly between the two closely related structural concepts below … I would like to take this opportunity to bring to your attention a necessary and important modification … more, a refinement … to the definition of Fire-Induced Progressive Collapse

Disproportionate Damage

The failure of a building’s structural system  (i) remote from the scene of an isolated overloading action;  and (ii) to an extent which is not in reasonable proportion to that action.

Fire-Induced Progressive Collapse

The sequential growth and intensification of structural distortion and displacement, beyond fire engineering design parameters, and the eventual failure of elements of construction in a building – during a fire and the ‘cooling phase’ afterwards – which, if unchecked, will result in disproportionate damage, and may lead to total building collapse.

This modification/refinement recognizes the following … that Fire-Induced Progressive Collapse may commence long before any breach occurs in a Fire Compartment Boundary … that, as a result of rampant commercial pressures in our societies, the tendency is for Compartment Volumes to become far too large to be any longer effective … and in the case of a Sustainable Building, for example, where natural patterns of air movement in buildings are used for either heating or cooling purposes, there may be no Compartments at all !

Restricting the application of one or both of these structural concepts, in law, to Multi-Storey Buildings, i.e. in many jurisdictions, those buildings having 5 or more storeys … is a purely arbitrary cut-off point.

CIB W14’s Research Working Group IV: ‘Structural Reliability & Fire-Induced Progressive Collapse’ would argue, rationally, that both of these concepts are fundamental to all structural fire engineering design.

.

  5.     Structural Fire Engineering is concerned with those aspects of fire engineering which relate to structural design for fire, and the complex architectural interaction between a building’s structure and fabric, i.e. non-structure, under conditions of fire and its immediate aftermath.

As Chair of CIB W14’s Research Working Group IV … I will shortly be making a Workshop Presentation in Europe, the aim of which will be to set the scene for the launch of an International CIB W14 Research WG IV Reflection Document;  the specific objective of the Presentation, however, will be to accurately describe the phenomenon that is Fire-Induced Progressive Collapse … and to outline a necessary new design approach which will fulfil future requirements, legal and otherwise, concerning adequate resistance to this phenomenon.

It will be shown that the new design approach is fully compatible with the Recommendations contained in the 2005 and 2008 NIST Reports on the 9-11 World Trade Center Buildings 1, 2 & 7 Collapses – NCSTAR 1 & NCSTAR 1A.

.

2008 NIST WTC 7 RECOMMENDATIONS  (Final Report NCSTAR 1A)

5.1  GENERAL

In its final report on the collapse of the World Trade Center Towers (NIST NCSTAR 1), NIST made 30 Recommendations for improving the safety of buildings, occupants, and emergency responders.  These encompass increased structural integrity, enhanced fire endurance of structures, new methods for fire resisting design of structures, improved active fire protection, improved building evacuation, improved emergency response, improved procedures and practices, and education and training.

WTC 7 was unlike the WTC Towers in many respects.  It was a more typical tall building in the design of its structural system.  It was not struck by an airplane.  The fires in WTC 7 were quite different from those in the Towers.  Since WTC 7 was not doused with thousands of litres of jet fuel, large areas of any floor were not ignited simultaneously.  Instead, the fires in WTC 7 were similar to those that have occurred previously in several tall buildings where the sprinklers did not function or were not present.  These other buildings did not succumb to their fires and collapse, because they were of structural designs that differed from that of WTC 7.

The Investigation Team has compiled a list of key factors that enabled ordinary fires to result in an extraordinary outcome.  In so doing, the Team recognized that there were additional aspects to be included in the content of some of the earlier 30 Recommendations.

Based on the findings of this Investigation, NIST has identified 1 New Recommendation and has reiterated 12 Recommendations from the Investigation of the WTC Towers.

The urgency of the Prior Recommendations is substantially reinforced by their pertinence to the collapse of a tall building that is based on a structural system design that is in widespread use.  A few of the Prior Recommendations have been modified to reflect the findings of this Investigation.

The partial or total collapse of a building due to fires is an infrequent event.  This is particularly true for buildings with a reliably operating active fire protection system, such as an automatic fire sprinkler system.  A properly designed and operating automatic sprinkler system will contain fires while they are small and, in most instances, prevent them from growing and spreading to threaten structural integrity.

The intent of current practice, based on prescriptive standards and codes, is to achieve life safety, not collapse prevention.  However, the key premise of NIST’s Recommendations is that buildings should not collapse in infrequent (worst-case) fires that may occur when active fire protection systems are rendered ineffective, e.g. when sprinklers do not exist, are not functional, or are overwhelmed by the fire.

Fire scenarios for structural design based on single compartment or single floor fires are not appropriate representations of infrequent fire events.  Such events have occurred in several tall buildings resulting in unexpected substantial losses.  Instead, historical data suggests that infrequent fires which should be considered in structural design have characteristics that include:  ordinary combustibles and combustible load levels, local fire origin on any given floor, no widespread use of accelerants, consecutive fire spread from combustible to combustible, fire-induced window breakage providing ventilation for continued fire spread and accelerated fire growth, concurrent fires on multiple floors, and active fire protection systems rendered ineffective.  The fires in WTC 7 had all of these characteristics.

NIST believes the Recommendations are realistic, appropriate, and achievable within a reasonable period of time.  NIST strongly urges that immediate and serious consideration be given to these Recommendations by the building and fire safety communities in order to achieve appropriate improvements in the way buildings are designed, constructed, maintained, and used – with the goal of making buildings safer in future emergencies.

A complete listing of all 13 Recommendations (Recommendations A through L) based on this Investigation follows.  Under a few of the Recommendations, the pertinent lesson from the reconstruction of the WTC 7 Collapse is reflected in the form of a modification.   For the 12 Reiterated Recommendations, the pertinent codes, standards, and organizations were listed in Table 9-1, and Tables 9-2a through 9-2c of NIST NCSTAR 1 and are not repeated here.  For the 1 New Recommendation, B, this information is provided in the text.

.

5.1.1     GROUP 1.  Increased Structural Integrity

The standards for estimating the load effects of potential hazards (e.g. progressive collapse, wind) and the design of structural systems to mitigate the effects of those hazards should be improved to enhance structural integrity.

NIST WTC 7 Recommendation A  (NCSTAR 1  Recommendation 1).

NIST recommends that:  (1) progressive collapse be prevented in buildings through the development and nationwide adoption of consensus standards and code provisions, along with the tools and guidelines needed for their use in practice;  and (2) a standard methodology be developed – supported by analytical design tools and practical design guidance – to reliably predict the potential for complex failures in structural systems subjected to multiple hazards.

Relevance to WTC 7:  Had WTC 7 been expressly designed for prevention of fire-induced progressive collapse, it would have been sufficiently robust to withstand local failure due to the fires without suffering total collapse.

.

5.1.2     GROUP 2.  Enhanced Fire Endurance of Structures

The procedures and practices used to ensure the fire endurance of structures should be enhanced by improving the technical basis for construction classifications and fire resistance ratings, improving the technical basis for standard fire resistance testing methods, use of the ‘structural frame’ approach to fire resistance ratings, and developing in-service performance requirements and conformance criteria for sprayed fire resisting materials.

NIST WTC 7 Recommendation B  (New)

NIST recommends that buildings be explicitly evaluated to ensure the adequate performance of the structural system under worst-case design fires with any active fire protection system rendered ineffective.  Of particular concern are the effects of thermal expansion in buildings with one or more of the following features:  (1) long-span floor systems* which experience significant thermal expansion and sagging effects;  (2) connection designs (especially shear connections) that cannot accommodate thermal effects;  (3) floor framing that induces asymmetric thermally-induced (i.e. net lateral) forces on girders;  (4) shear studs that could fail due to differential thermal expansion in composite floor systems;  and (5) lack of shear studs on girders.  Careful consideration should also be given to the possibility of other design features that may adversely affect the performance of the structural system under fire conditions.

[ * F-6   Typical floor span lengths in tall office buildings are in the range of 12-15 metres;  this range is considered to represent long-span systems.  Thermal effects (e.g. thermal expansion) that may be significant in long-span buildings may also be present in buildings with shorter span lengths, depending on the design of the structural system.]

Building owners, operators, and designers are strongly urged to act upon this Recommendation.  Engineers should be able to design cost-effective fixes to address any areas of concern that are identified by these evaluations.  Several existing, emerging, or even anticipated capabilities could have helped prevent the collapse of WTC 7.  The degree to which these capabilities improve performance remains to be evaluated.  Possible options for developing cost-effective fixes include:

  • More robust connections and framing systems to better resist the effects of thermal expansion on the structural system ;
  • Structural systems expressly designed to prevent progressive collapse.  The current model building codes do not require that buildings be designed to resist progressive collapse ;
  • Better thermal insulation (i.e. reduced conductivity and/or increased thickness) to limit heating of structural steel and to minimize both thermal expansion and weakening effects.  Currently, insulation is used to protect steel strength, but it could also be used to maintain a lower temperature in the steel framing to limit thermal expansion ;
  • Improved compartmentation in tenant areas to limit spread of fires ;
  • Thermally resisting window assemblies which limit breakage, reduce air supply, and retard fire growth.

Industry should partner with the research community to fill critical gaps in knowledge about how structures perform in real fires, particularly considering:  the effects of fire on the entire structural system; the interactions between sub-systems, elements, and connections; and scaling of fire test results to full-scale structures, especially for structures with long-span floor systems.

Affected Standards:  ASCE 7, ASCE/SFPE 29, AISC Specifications, and ACI 318.  Development of performance objectives, design criteria, evaluation methods, design guidance, and computational tools should begin promptly, leading to new standards.

Model Building Codes:  The new standard should be adopted in model building codes (IBC, NFPA 5000) by mandatory reference to, or incorporation of, the latest edition of the standard.

Relevance to WTC 7:  The effects of restraint of free thermal expansion on the steel framing systems, especially for the long spans on the east side of WTC 7, were not considered in the structural design and led to the initiation of the building collapse.

.

NIST WTC 7 Recommendation C  (NCSTAR 1  Recommendation 4).

NIST recommends evaluating, and where needed improving, the technical basis for determining appropriate construction classifications and fire rating requirements (especially for tall buildings) – and making related code changes now, as much as possible – by explicitly considering factors including:*

[ * F-7  The construction classification and fire rating requirements should be risk-consistent with respect to the design-basis hazards and the consequences of those hazards.  The fire rating requirements, which were originally developed based on experience with buildings less than 20 storeys in height, have generally decreased over the past 80 years since historical fire data for buildings suggest considerable conservatism in those requirements.  For tall buildings, the likely consequences of a given threat to an occupant on the upper floors are more severe than the consequences to an occupant on the first floor or the lower floors.  For example, with non-functioning elevators, both of the time requirements are much greater for full building evacuation from upper floors and emergency responder access to those floors.  The current height and areas tables in building codes do not provide the technical basis for the progressively increasing risk to an occupant on the upper floors of tall buildings that are much greater than 20 storeys in height.]

  • timely access by emergency responders and full evacuation of occupants, or the time required for burnout without partial collapse ;
  • the extent to which redundancy in active fire protection systems (sprinklers and standpipe, fire alarm, and smoke management) should be credited for occupant life safety ;*

[ * F-8  Occupant life safety, prevention of fire spread, and structural integrity are considered separate safety objectives.]

  • the need for redundancy in fire protection systems that are critical to structural integrity ;*

[ * F-9  The passive fire protection system (including the application of fire protection insulation, compartmentation, and fire stopping) and the active sprinkler system each provide redundancy for maintaining structural integrity in a building fire, should one of the systems fail to perform its intended function.]

  • the ability of the structure and local floor systems to withstand a maximum credible fire scenario* without collapse, recognizing that sprinklers could be compromised, not operational, or non-existent ;

[ * F-10  A maximum credible fire scenario includes conditions that are severe, but reasonable to anticipate, conditions related to building construction, occupancy, fire loads, ignition sources, compartment geometry, fire control methods, etc., as well as adverse, but reasonable to anticipate operating conditions.]

  • compartmentation requirements (e.g. 1,200 sq.m*) to protect the structure, including fire rated doorsets and automatic enclosures, and limiting air supply (e.g. thermally resisting window assemblies) to retard fire spread in buildings with large, open floor plans ;

[ * F-11  Or a more appropriate limit, which represents a reasonable area for active fire fighting operations.]

  • the effect of spaces containing unusually large fuel concentrations for the expected occupancy of the building ;   and
  • the extent to which fire control systems, including suppression by automatic or manual means, should be credited as part of the prevention of fire spread.

Relevance to WTC 7:  The floor systems in WTC 7 failed at lower temperatures because thermal effects within the structural system, especially thermal expansion, were not considered in setting the fire rating requirements in the construction classification, which are determined using the ASTM E 119 or equivalent testing standard.

.

NIST WTC 7 Recommendation D  (NCSTAR 1  Recommendation 5).

NIST recommends that the technical basis for the century-old standard for fire resistance testing of components, assemblies and systems be improved through a national effort.  Necessary guidance also should be developed for extrapolating the results of tested assemblies to prototypical building systems.  A key step in fulfilling this Recommendation is to establish a capability for studying and testing components, assemblies, and systems under realistic fire and load conditions.

Of particular concern is that the Standard Fire Resistance Test does not adequately capture important thermally-induced interactions between structural sub-systems, elements, and connections that are critical to structural integrity.  System-level interactions, especially due to thermal expansion, are not considered in the standard test method since columns, girders, and floor sub-assemblies are tested separately.  Also, the performance of connections under both gravity and thermal effects is not considered.  The United States currently does not have the capability for studying and testing these important fire-induced phenomena critical to structural safety.

Relevance to WTC 7:  The floor systems failed in WTC 7 at shorter fire exposure times than the specified fire rating (two hours) and at lower temperatures because thermal effects within the structural system, especially thermal expansion, were not considered in setting the endpoint criteria when using the ASTM E 110 or equivalent testing standard.  The structural breakdowns that led to the initiating event, and the eventual collapse of WTC 7, occurred at temperatures that were hundreds of degrees below the criteria that determine structural fire resistance ratings.

.

NIST WTC 7 Recommendation E  (NCSTAR 1  Recommendation 7).

NIST recommends the adoption and use of the ‘structural frame’ approach to fire resistance ratings.  This approach requires all members that comprise the primary structural frame (such as columns, girders, beams, trusses, and spandrels) be fire protected to the higher fire resistance rating required for the columns.  The definition of the primary structural frame should be expanded to include bracing members that are essential to the vertical stability of the primary structural frame under gravity loading (e.g. girders, diagonal bracing, composite floor systems that provide lateral bracing to the girders) whether or not the bracing members carry gravity loads.  Some of these bracing members may not have direct connections to the columns, but provide stability to those members directly connected to the columns.  This Recommendation modifies the definition of the primary structural frame adopted in the 2007 supplement to the International Building Code (IBC).  The IBC considers members of floor or roof construction that are not connected to the columns not to be part of the primary structural frame.  This Recommendation ensures consistency in the fire protection provided to all of the structural elements that contribute to overall structural stability.  State and local jurisdictions should adopt and enforce this requirement.

Relevance to WTC 7:  Thermally-induced breakdown of the floor system in WTC 7 was a determining step in causing failure initiation and progressive collapse.  Therefore, the floor system should be considered as an integral part of the primary structural frame.

.

.

END

Enhanced by Zemanta

Tags: , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , ,

Search

 

Follow SFE2016Dublin on Twitter

October 2019
S M T W T F S
« Jul    
 12345
6789101112
13141516171819
20212223242526
2728293031  

Links