NFPA 5000

NIST WTC Recommendations 25-28 > Improved Practices

Previous Posts in This Series …

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)

2011-11-18:  NIST WTC Recommendations 4-7 > Structural Fire EnduranceGROUP 2.  Enhanced Fire Endurance of Structures – Recommendations 4, 5, 6 & 7

2011-11-24:  NIST WTC Recommendations 8-11 > New Design of StructuresGROUP 3.  New Methods for Fire Resisting Design of Structures – Recommendations 8, 9, 10 & 11

2011-11-25:  NIST WTC Recommendations 12-15 > Improved Active ProtectionGROUP 4.  Improved Active Fire Protection – Recommendations 12, 13, 14 & 15

2011-11-30:  NIST Recommendations 16-20 > Improved People EvacuationGROUP 5.  Improved Building Evacuation – Recommendations 16, 17, 18, 19 & 20

2011-12-04:  NIST WTC Recommendations 21-24 > Improved FirefightingGROUP 6.  Improved Emergency Response – Recommendations 21, 22, 23 & 24

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2011-12-07:  SOME PRELIMINARY COMMENTS …

  1.     Concerning Recommendation 25 below … yes, this Recommendation applies to the types of organizations identified in the text, but it should also be understood as applying to ALL Organizations … public or private, governmental or non-governmental or quasi-governmental, whatever, etc … ‘supported’ (see the text further down in Recommendation 25) with rigorous enforcement, in all cases, by publically appointed building control officials and/or by private, independent, competent technical control professionals.

Once more … and again and again (!) … confirmed by the sort of debacle seen at the Priory Hall Apartment Complex, in Dublin … Self-Certification / Self-Approval, i.e. ‘lite’ regulation, does not work.  For National Authorities Having Jurisdiction (AHJ’s), however, it is a cheap solution to a difficult, resource-devouring issue, i.e. protecting society and the consumer … in that order.

  2.     Concerning the Footnote to Recommendation 26 below … the choice should never be between either Fire Compartmentation or Sprinklers … or the other way around, whichever you prefer.  Neither is 100% reliable !

Fire Compartmentation

The division of a building into fire-tight compartments, by fire and smoke resisting elements of construction, in order …

  • to contain an outbreak of fire, and to facilitate effective firefighting ;
  • to prevent damage, within the building, to other adjoining compartments and/or spaces ;
  • to protect a compartment interior from external fire attack, e.g. fire spread across the building’s facade or from an adjacent building ;
  • to minimize adverse, or harmful, environmental impacts outside the building.

As developed as that definition is above, Fire Compartmentation should be regarded as just one Fire Safety Strategy / Fire Engineering Strategy … not the only strategy, and certainly not the main strategy.

Here are two reasons why not …

a)   The connection between compartment size and the ability to effectively fight a fire within a space of limited volume has been lost … so more and more, commercial pressure is being exerted on national authorities to expand the acceptable compartment sizes in buildings … which significantly increases the fire hazard ;

[ Remembering the difference between the limited Fire Safety Objectives of Building Codes/Regulations and the much broader Project-Specific Fire Engineering Objectives of Ethical Fire Engineering required to protect society and the full interests of our clients … it is easy to understand why national authorities feel that they can respond positively to such commercial pressures.]

b)   In a Sustainable Building … it is a very common design strategy to take advantage of the natural patterns of air movement in a building, for either cooling or heating purposes, depending on local climate conditions.  So there is simply no compartmentation, as understood in conventional fire engineering terms … and this throws up a fundamental conflict between the two.  To be discussed in another post !

  3.     Concerning the 2nd Footnote to Recommendation 28 below … in the very same New York City … at 09.40 hrs on a Saturday morning, 28 July 1945 … lost in fog, a B-25 Bomber slammed head-on into the 79th Floor of the Empire State Building … and caused enormous damage.  That building is still standing today … and surprise, surprise … there was aviation fuel in the B-25 !

In a similar vein … Fire-Induced Progressive Collapse was not observed for the first time, in New York, on 11 September 2001 !

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2005 NIST WTC RECOMMENDATIONS

GROUP 7.  Improved Procedures and Practices

The procedures and practices used in the design, construction, maintenance, and operation of buildings should be improved to include encouraging code compliance by non-governmental and quasi-governmental entities, adoption and application of egress and sprinkler requirements in codes for existing buildings, and retention and availability of building documents over the life of a building.

NIST WTC Recommendation 25.

Non-governmental and quasi-governmental entities that own or lease buildings and are not subject to building and fire safety code requirements of any governmental jurisdiction are nevertheless concerned about the safety of building occupants and responding emergency personnel.  NIST recommends that such entities be encouraged to provide a level of safety that equals or exceeds the level of safety that would be provided by strict compliance with the code requirements of an appropriate governmental jurisdiction.  NIST further recommends that as-designed and as-built safety be certified by a qualified third party, independent of the building owner(s).  The process should not use self-approval for code enforcement in areas including interpretation of code provisions, design approval, product acceptance, certification of the final construction, and post-occupancy inspections over the life of the buildings.*

[ * F-46  The long-standing stated policy of the Port Authority of New York & New Jersey (PANYNJ) was to meet and, where appropriate, exceed the requirements of local building and fire codes, and it entered into agreements with the New York City Department of Buildings and the Fire Department of the City of New York in accordance with that policy.  Although the PANYNJ sought review and concurrence from New York City in the areas listed in the Recommendation, the PANYNJ was not required to yield, and appears not to have yielded, approval authority to New York City.  The PANYNJ was created as an interstate entity, a ‘body corporate and politic’, under its charter, pursuant to Article 1, Section 10 of the United States Constitution permitting compacts between states.  Further, there are many other similar non-governmental and quasi-governmental entities in the U.S.  A comprehensive review of documents conducted as part of this Investigation suggests that the WTC towers generally were designed and maintained consistent with the requirements of the 1968 New York City Building Code.  Areas of concern included fireproofing of the WTC floor system, height of tenant separation walls, and egress requirements for the assembly use spaces of ‘Windows of the World’ in WTC Tower 1 and the ‘Top of the World’ Observation Deck in WTC Tower 2.  These areas of concern did not play a significant role in determining the outcomes related to the events on 11th September 2001.]

NIST WTC Recommendation 26.

NIST recommends that state and local jurisdictions adopt and aggressively enforce available provisions in building codes to ensure that egress and sprinkler requirements are met by existing buildings.*  Further, occupancy requirements should be modified where needed (such as when there are assembly use spaces within an office building) to meet the requirements in model building codes.  Provisions related to egress and sprinkler requirements in existing buildings are available in such codes as the International Existing Building Code (IEBC), International Fire Code, NFPA 1, NFPA 101, and ASME A 17.3.  For example, the IEBC defines three levels of building alteration (removal and replacement or covering of existing materials and equipment, reconfiguration of space or system or installation of new equipment, and extending the work area in excess of 50% of the aggregate area of the building).  At the lowest level, there are no upgrade implications for sprinklers and the egress system.  At the next level, sprinklers are required in work areas serving greater than 30 people if certain other conditions related to building height and use such as shared exits also are met.  There are numerous requirements for means of egress, including number of exits, specification of doorsets, dead-end corridors and travel distances, lighting, signage, and handrails.  At the highest level, the sprinkler and egress requirements are identical to the second level without the minimum 30-person restriction and the other conditions related to building height and use.  The Life Safety Code (NFPA 101) applies retroactively to all buildings, independent of whether any work is currently being done on the building, and ASME A 17.3 applies retroactively to all elevators as a minimum set of requirements.

[ * F-47  The WTC towers were unsprinklered when built.  It took nearly 28 years after passage of New York City Local Law 5 in 1973, which required either compartmentation or sprinklering, for the buildings to be fully sprinklered (the Port Authority chose not to use the compartmentation option in Local Law 5).  This was about 13 years more than the 15-year period for full compliance with Local Law 5 that was set by Local Law 84 of 1979.]

NIST WTC Recommendation 27.

NIST recommends that building codes incorporate a provision that requires building owners to retain documents, including supporting calculations and test data, related to building design, construction, maintenance, and modifications over the entire life of the building.*  Means should be developed for off-site storage and maintenance of the documents.  In addition, NIST recommends that relevant information be made available in suitably designed hard copy or electronic formats for use by emergency responders.  Such information should be easily accessible by responders during emergencies.  Model Building Codes:  Model building codes should incorporate this Recommendation.  State and local jurisdictions should adopt and enforce these requirements.

[ * F-48  The availability of inexpensive electronic storage media and tools for creating large searchable databases makes this feasible.]

NIST WTC Recommendation 28.

NIST recommends that the role of the ‘Design Professional in Responsible Charge’* be clarified to ensure that:  (1) all appropriate design professionals (including, e.g. the fire protection engineer) are part of the design team providing the highest standard of care when designing buildings employing innovative or unusual fire safety systems;**  and (2) all appropriate design professionals (including, e.g. the structural engineer and the fire protection engineer) are part of the design team providing the highest standard of care when designing the structure to resist fires, in buildings that employ innovative or unusual structural and fire safety systems.  Affected Standards:  AIA Practice Guidelines.  Model Building Codes:  The International Building Code (IBC), which already defines ‘Design Professional in Responsible Charge’, should be clarified to address this Recommendation.  NFPA 5000 should incorporate the ‘Design Professional in Responsible Charge’ concept, and address this Recommendation.

[ * F-49  In projects involving a design team, the ‘Design Professional in Responsible Charge’ – usually the lead architect – ensures that the team members use consistent design data and assumptions, co-ordinates overlapping specifications, and serves as the liaison between the enforcement and reviewing officials and the owner.  This term is defined in the International Building Code (IBC) and in the International Code Council’s Performance Code for Buildings and Facilities (where it is the Principal Design Professional).]

[ ** F-50  If the fire safety concepts in tall buildings had been sufficiently mature in the 1960’s, it is possible that the risks associated with jet-fuel ignited multi-floor fires might have been recognized and taken into account when the impact of a Boeing 707 aircraft was considered by the structural engineer during the design of the WTC towers.]

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NIST’s Recommendations on the 9-11 WTC Building Collapses

2011-10-25:  Since shortly after my visit to Lower Manhattan in mid-October 2001 … we have maintained an Archive Page on Structural Fire Engineering, World Trade Center Incident (9-11) & Fire Serviceability Limit States … at SDI’s Corporate WebSite.  And I have referenced here … many, many times … the Recommendations contained in the 2005 & 2008 Final Reports of the U.S. National Institute of Standards & Technology (NIST) on the 9-11 World Trade Center Building 1, 2 & 7 Collapses.

In this post (and a series of future posts) … I find it most necessary that the 2005 & 2008 NIST Recommendations now be presented for everyone to read.  Yes, some of Recommendations apply specifically to Tall and Very Tall Buildings … and Building Designers in India, China, Brazil, Russia & South Africa (BRICS), the Arab Gulf RegionEurope and North America, etc., should be fully aware of their contents.

BUT … I am also strongly convinced … precisely because I am an Architect, a Fire Engineer and a Technical Controller … that most of the NIST Recommendations apply to ALL Buildings … so catastrophic was the failure exposed on that fateful day (11 September 2001) … in all of our common design and construction practices … and our operation, maintenance and emergency response procedures !

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PRELIMINARY COMMENTS

  1.     Extract from Paragraph #9.2, Chapter 9, NIST Final Report on the Collapse of the World Trade Center Towers – Report Reference NIST NCSTAR 1 (2005) …

  • NIST believes  that these Recommendations are both realistic and achievable within a reasonable period of time, and that their implementation would make buildings safer for occupants and emergency responders in future emergencies.
  • NIST strongly urges  that immediate and serious consideration be given to these Recommendations by the building and fire safety communities – especially designers, owners, developers, codes and standards development organizations, regulators, fire safety professionals, and emergency responders.
  • NIST also strongly urges  building owners and public officials to:  (i) evaluate the safety implications of these Recommendations for their existing inventory of buildings;  and (ii) take the steps necessary to mitigate any unwarranted risks without waiting for changes to occur in codes, standards, and practices.

  2.     At the time of writing … it is important to point out that although they are related Structural Concepts … and there is still, to this day, a lot of confusion about these concepts in the USA … it is important to clearly distinguish between …

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 distortion, displacement and 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.

  3.     Recommendation 2, below, would certainly need to be understood and implemented within today’s additional design constraints of Sustainable Climate Change Adaptation and Resilience to Severe Weather Events.  Therefore … Design Wind Speeds must be increased, accordingly, for ALL Buildings.

  4.     As such a high level of performance is expected … indeed demanded … of a Sustainable BuildingSustainable Fire Engineering must be ‘reliability-based’.  In other words, it must have a rational, empirical and scientifically robust basis … unlike conventional fire engineering, which is yet aimlessly wandering around in pre-historic caves !

  5.     Finally … there is no use trying to hide the fact that progress on implementing the NIST Recommendations, within the USA, has been lamentably slow.  Outside that jurisdiction, the response has ranged from mild interest, to complete apathy, and even to vehement antipathy.  The implications arising from implementation are much too hard to digest … for long established fire safety professionals and researchers who are unswervingly committed to the flawed and out-of-date practices and procedures of conventional fire engineering and, especially, for vested interests !

However … is it either in society’s interest, or in the interests of our clients/client organizations … that, to give you a simple example which is relevant close to home, British Standard 9999 (published on 31 October 2008): ‘Code of Practice for Fire Safety in the Design, Management and Use of Buildings’ takes absolutely no account of any of the NIST Recommendations ?   As far as the British Standards Institution is concerned … 9-11 never happened … which I think is an inexcusable and unforgivable technical oversight !

For this reason, the General Public in ALL of our societies and Clients/Client Organizations in ALL countries should also be fully aware of the contents of these Recommendations …

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Colour photograph showing the two World Trade Center Towers immediately after the impact of the second plane. At a fundamental level, this was a very serious 'real' fire incident ... which was extensively, and very thoroughly, investigated by the U.S. National Institute of Standards & Technology (NIST) ... and resulted in the important 2005 & 2008 NIST Recommendations. Click to enlarge.

Colour photograph showing the two World Trade Center Towers immediately after the impact of the second plane. At a fundamental level, this was a very serious 'real' fire incident ... which was extensively, and very thoroughly, investigated by the U.S. National Institute of Standards & Technology (NIST) ... and resulted in the important 2005 & 2008 NIST Recommendations. Click to enlarge.

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2005 NIST WTC RECOMMENDATIONS

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 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.

a.   Progressive collapse* should be prevented in buildings.

[ * F-19  Progressive collapse (or disproportionate damage) occurs when an initial local failure spreads from structural element to structural element resulting in the collapse of an entire structure or a disproportionately large part of it.]

The primary structural systems should provide alternate paths for carrying loads in case certain components fail (e.g. transfer girders or columns).  This is especially important in buildings where structural components (e.g. columns, girders) support unusually large floor areas.*

[ * F-20  While the WTC towers eventually collapsed, they had the capacity to redistribute loads from impact and fire damaged structural components and sub-systems to undamaged components and sub-systems.  However, the core columns in the WTC towers lacked sufficient redundant (alternative) paths for carrying gravity loads.]

Progressive collapse is addressed only in a very limited way in practice and by codes and standards.  For example, the initiating event in design to prevent progressive collapse may be removal of one or two columns at the bottom of the structure.  Initiating events at multiple locations within the structure, or involving other key components and sub-systems, should be analyzed commensurate with the risks considered in the design.  The effectiveness of mitigation approaches involving new system and sub-system design concepts should be evaluated with conventional approaches based on indirect design (continuity, strength and ductility of connections), direct design (local hardening), and redundant (alternate) load paths.  The capability to prevent progressive collapse due to abnormal loads should include:  (i) comprehensive design rules and practice guides;  (ii) evaluation criteria, methodology, and tools for assessing the vulnerability of structures to progressive collapse;  (iii) performance-based criteria for abnormal loads and load combinations;  (iv) analytical tools to predict potential collapse mechanisms;  and (v) computer models and analysis procedures for use in routine design practice.  The federal government should co-ordinate the existing programmes that address this need:  those in the Department of Defence;  the General Services Administration;  the Defence Threat Reduction Agency;  and NIST.  Affected Standards:  ASCE-7, AISC Specifications, and ACI 318.  These standards and other relevant committees should draw on expertise from ASCE/SFPE 29 for issues concerning progressive collapse under fire conditions.  Model Building Codes:  The consensus standards should be adopted in model building codes (i.e. the International Building Code and NFPA 5000) by mandatory reference to, or incorporation of, the latest edition of the standard.  State and local jurisdictions should adopt and enforce the improved model building codes and national standards based on all 30 WTC Recommendations (2005).  The codes and standards may vary from the WTC Recommendations, but satisfy their intent.

b.   A robust, integrated predictive capability should be developed, validated, and maintained to routinely assess the vulnerability of whole structures to the effects of credible hazards.  This capability to evaluate the performance and reserve capacity of structures does not exist and is a significant cause for concern.  This capability would also assist in investigations of building failure – as demonstrated by the analyses of the WTC building collapses carried out in this Investigation.  The failure analysis capability should include all possible complex failure phenomena that may occur under multiple hazards (e.g. bomb blasts, fires, impacts, gas explosions, earthquakes, and hurricane winds), experimentally validated models, and robust tools for routine analysis to predict such failures and their consequences.  This capability should be developed via a co-ordinated effort involving federal, private sector, and academic research organizations in close partnership with practicing engineers.

NIST WTC Recommendation 2.

NIST recommends that nationally accepted performance standards be developed for:  (1) conducting wind tunnel testing of prototype structures based on sound technical methods that result in repeatable and reproducible results among testing laboratories;  and (2) estimating wind loads and their effects on tall buildings for use in design, based on wind tunnel testing data and directional wind speed data.  Wind loads specified in current prescriptive codes may not be appropriate for the design of very tall buildings since they do not account for building-specific aerodynamic effects.  Further, a review of wind load estimates for the WTC towers indicated differences by as much as 40 % from wind tunnel studies conducted in 2002 by two independent commercial laboratories.  Major sources of differences in estimation methods currently used in practice occur in the selection of design wind speeds and directionality, the nature of hurricane wind profiles, the estimation of ‘component’ wind effects by integrating wind tunnel data with wind speed and direction information, and the estimation of ‘resultant’ wind effects using load combination methods.  Wind loads were a major factor in the design of the WTC tower structures and were relevant to evaluating the baseline capacity of the structures to withstand abnormal events such as major fires or impact damage.  Yet, there is lack of consensus on how to evaluate and estimate winds and their load effects on buildings.

a.   Nationally accepted standards should be developed and implemented for conducting wind tunnel tests, estimating site-specific wind speed and directionality based on available data, and estimating wind loads associated with specific design probabilities from wind tunnel test results and directional wind speed data.

b.   Nationally accepted standards should be developed for estimating wind loads in the design of tall buildings.  The development of performance standards for estimating wind loads should consider:  (1) appropriate load combinations and load factors, including performance criteria for static and dynamic behaviour, based on both ultimate and serviceability limit states;  and (2) validation of wind load provisions in prescriptive design standards for tall buildings, given the universally acknowledged use of wind tunnel testing and associated performance criteria.  Limitations to the use of prescriptive wind load provisions should be clearly identified in codes and standards.

The standards development work can begin immediately to address many of the above needs.  The results of those efforts should be adopted in practice as soon as they become available.  The research that will be required to address the remaining needs also should begin immediately and results should be made available for standards development and use in practice.  Affected National Standard:  ASCE-7.  Model Building Codes:  The standard should be adopted in model building codes by mandatory reference to, or incorporation of, the latest edition of the standard.

NIST WTC Recommendation 3.

NIST recommends that an appropriate criterion be developed and implemented to enhance the performance of tall buildings by limiting how much they sway under lateral load design conditions (e.g. winds and earthquakes).  The stability and safety of tall buildings depend upon, among other factors, the magnitude of building sway or deflection, which tends to increase with building height.  Conventional strength-based methods, such as those used in the design of the WTC towers, do not limit deflections.  The deflection limit state criterion, which is proposed here is in addition to the stress limit state and serviceability requirement;  it should be adopted either to complement the safety provided by conventional strength-based design or independently as an alternate deflection-based approach to the design of tall buildings for life safety.  The recommended deflection limit state criterion is independent of the criterion used to ensure occupant comfort, which is met in current practice by limiting accelerations (e.g. in the 15 to 20 milli-g range). Lateral deflections, which already are limited in the design of tall buildings to control damage in earthquake-prone regions, should also be limited in non-seismic areas.*

[ * F-22  Analysis of baseline performance under the original design wind loads indicated that the WTC towers would need to have been between 50 % and 90 % stiffer to achieve a typical drift ratio used in current practice for non-seismic regions, though not required by building codes.  Limiting drift would have required increasing exterior column areas in lower stories and/or significant additional damping.]

Affected National standards:  ASCE-7, AISC Specifications, and ACI 318.  Model Building Codes:  The standard should be adopted in model building codes by mandatory reference to, or incorporation of, the latest edition of the standard.

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