Iano's backfill

Standards: New (costly?), New (better?), and Needed(?)

ENR's Third Exit Stair Could Make Highrises Too Costly to Build (June 4, 2007) reports on the adoption of more stringent life safety requirements for tall buildings in the 2007 Supplement to the International Building Code. Both the Building Owners and Managers Association International and the American Institute of Architects oppose as too costly a new requirement for buildings taller than 420 feet to have at least 3 independent exit stairs. Other changes to tall building requirements in the 2007 Supplement, all coming in the aftermath of the 9/11 attacks on the World Trade Center Buildings in New York City, include:

• protected fire service elevators and lobbies
• photoluminescent pathway markings in exit stairwells
• inspection and greater strength requirements for spray-applied fireproofing.

Proposals for progressive collapse resistance, increased  exit stairway enclosure integrity, and requirements for a a building's ability to burn without collapse were rejected. See the ICC's Code Development page for more information about that organization's code development process and the adoption of these new requirements.

In the same issue, Energy-Efficiency Guidelines Would Be National Model reports on the American Society of Heating, Refrigerating and Air Conditioning Engineer's (ASHRAE) ongoing development of Standard 89, an enhanced building energy efficiency guideline. Standard 89, now open for comments, is intended to reduce building energy consumption by 30% in comparison to ASHRAE's long-recognized Standard 90, and is being touted as a national standard for achieving LEED certified optimized energy performance. See ASHRAE's Advanced Energy Design Guides page for more about this organization's enhanced energy performance guidelines.

Lastly, Innovative Mix with Fly Ash is Still Not Widely Used describes a concrete mix composed of lime, portland cement, and fly ash developed by Nai C. Yang of the New Port Authority 38 years ago for use in airport runway construction. The mix is claimed to provide superior concrete and a reduction in environmental impact (due to reduction in cement content and, consequently, reductions in C02 emissions). However its broader use in airport construction has been hampered by unfamiliarity and a lack of standards for its production.

NIST Continues Progress on WTC Report

Report on Trade Center Collapses Emphasizes Damage to Fireproofing (April 5, 2005, New York Times) reports on the National Institute of Science and Technology's (NIST) April 5, 2005 public progress briefing. Some of the Institutes's findings include:

• Structural damage caused by the impacts of the airplanes in and of themselves was not sufficient to have caused the tower collapses.
• The towers collapsed when the structural frames were further weakened by the fires that followed the plane impacts.
• The structures were rendered more vulnerable to fire when fireproofing was dislodged from the structural steel members by the plane impacts.
• Though jet fuel contributed to the initial fires, the fires were mainly fueled by building contents, and to a lesser extent by aircraft contents.

The article also states that had the towers been full at the time of the attacks (they were each only about 1/3 occupied) roughly 14,000 persons could have died due to the greater time required to evacuate the larger numbers of occupants from the buildings.

Critics Blast Findings of Federal 9/11 Study (April 18, 2005, Engineering News Record) reports on critics who characterize the NIST study as expensive ($16 million) and misguided.

Jon D. Magnusson of Magnusson Klemencic Associates, Seattle, is quoted criticizing NIST for proposing building code changes based on the study of "one building that was unlike any other, for a single vent that had never happened before." Magnusson does not believe the NIST recommendations will lead to actual increases in public safety. Others echo similar concerns, citing a lack of analysis to determine the degree to which recommended safety enhancements can save lives, or characterizing recommendations as based on speculation.

Additional related articles available from ENR include:

• WTC Report Triggers Debate Over Safety (ENR 7/4/2005)
• Recommendations Gain Qualified Support (ENR 7/25/05)
• A New Era for Fire Protection and Life Safety (Architecture Record, 8/2005)

NIST will be publicly releasing its Draft Report and Recommendations on June 23.

More Info:

• Previous articles on Iano's Backfill related to building safety in general and the World Trade Center disaster in particular
• NIST's WTC web site

More WTC Findings

WTC wind load findings (Structural Engineer, November 2004) reports that additional analysis of the original wind load design for the World Trade Center towers has lead to a revision of the National Institute of Standards and Technology's previous findings. According to the revised analysis, the wind loads used in the design of the two towers exceeded code requirements throughout the life of the structures, starting with New York City's pre-1968 code requirements in effect when the buildings were constructed, and including subsequent updated code requirements through 2001, when the buildings were destroyed.

According to the brief article, the new analysis is based on original source documents including wind tunnel testing and wind load estimation methods, as well a revised interpretation of the application of this information. This has lead to an upward revision of the original design loads from earlier preliminary estimates.

Design Flaws did not lead to WTC collapse (Structural Engineer, December 2004) reports on additional NIST interim findings released in late October. Of particular note is a lead investigator S.Shyman Sunder's statement regarding the overall performance of the towers:

The buildings performed as they should have considering the airplane impact and extreme fires to which they were subjected. There is nothing there that stands out as abnormal.

Additional findings included in this NIST report address hypotheses for the causes of the tower collapses, explanation of the differences in survival time between the two towers, assessment of the post-impact capabilities of the towers, the role of fireproofing, the effects of fire on the tower structures, the quality of the structural steel itself, and factors related to occupant egress prior to the collapses.

More info:
NIST's WTC web site

Interim WTC Investigation Findings

The National Institute of Standards and Technology (NIST) has issued its second major progress report and interim findings related to the WTC disaster of 9/11/2001. The report discusses, in part:

• Working hypotheses for the collapses of the towers, as well as for the 47-story WTC 7 building.
• Factors contributing to the building collapses including the impacting aircraft, building structural systems, fireproofing, active fire protection systems, structural materials, and failure mechanisms.
• Emergency response, command and control, and communications during the disaster
• Applicable building codes at the time of the buildings' construction
• Design practices related to fire- and structural-safety, performance-based fire safety design, and the roles of building standards, codes, and regulations in such design
• Issues meriting further consideration

A few of the more interesting findings in the report include the following:

NIST's working hypothesis is that the towers failed due to column instability caused by the airplane impacts and subsequent fires. One question concerns why WTC 1 stood for nearly twice as long after plane impact as WTC 2. Though the report draws no inference, it notes separately that affected floors in WTC 1 had significantly upgraded amounts of fireproofing in comparison to affected floors in WTC 2.

The role of spray-on fireproofing in protecting the building frames from the heat of fire continues to receive considerable attention. Fireproofing thicknesses applied to the long-span floor trusses ranged from 1/2-inch to 1 1/2-inches. Separately, an unrelated 2001 model code report recommended 2-inch thickness for a similar floor system. These large discrepancies indicate a lack of technical basis for the fireproofing thicknesses used in the towers.

More than 99 percent of the tower occupants below the impact floors were able to evacuate safely prior to building collapse. Significant drops in evacuation rates prior to the collapses suggest that there was sufficient egress capacity to accommodate these building occupants. However, on the day of the attacks, both buildings were each occupied at approximately only 1/3 of full capacity. Estimates indicate that evacuation of either tower at full capacity would have required significantly more time, approximately 4 hours.

The towers were not constructed to meet requirements of the building code in effect at the time that they were built, the 1938 New York City Building Code. Rather, the Port Authority opted to conform to requirements of the upcoming 1968 Code, even though this new code was three years away from going into effect. As a result, significant reductions in life-safety requirements were applied, such as reduction in number of required stairwells, reduction in levels of fire-resistance ratings, and reduction in partition structural load requirements.

The Institute's Key Findings document is especially recommended for further reading.

More Info
NIST News Release
NIST Progress Report
Columns Likely Failed First in Terrorist-Triggered WTC Fires, ENR, June 28, 2004

Fire-Safe Debate Continues

Issues related to building fire-safety continue to receive attention both in the technical and mainstream press.

Fire Prevention and Protection: The Big Picture, Building Safety Journal, May-June 2004, offers another perspective on the ongoing fire-safety debates.

Author, Mike Slaughter, fire-safety specialist, and former firefighter and code official, addresses the question of the connection between modern building construction systems and reductions in in firefighter safety. Key points raised include:

• Slaughter cites as "common knowledge" that modern construction systems rely on lighter materials that are more vulnerable to fire.
• Between 1978 and 1999, the rate of firefighter deaths from traumatic causes inside structure fires increased by 60%.
• Other aspects of fire-safety, including building code requirements, firefighting equipment, and firefighting tactics, have undergone significant improvements during this same period.

Slaughter concludes that trends toward lighter-weight construction systems have likely reduced firefighter safety, while other improvements in code requirements, firefighting equipment and tactics have probably to some extent counteracted this negative trend.

Skyscapers' Supporters Infuriated by Fire Fearmongers, Engineering News Record, June 7, 2004, discusses the increased controversy surrounding fire safety in tall buildings in the aftermath of the collapse of the World Trade Center towers. Some interesting facts and perspectives presented in the article:

• Between 1997 and 2001, and excluding the 9/11 events, sixty-eight percent of civilian fire deaths occurred in one- and two-family dwellings, 14 percent in other residential building types, 13 percent in road vehicles. Only 3 percent of civilian fire deaths occurred in nonresidential structures.
• According to NFPA statistics, between 1985 and 1995, seven civilians died in office tower fires. During the same period there were over 57,000 civilian deaths from all kinds of building fires combined.
• W. Gene Corely, of Construction Technology Laboratories argues that buildings should be designed to withstand a full "burnout" without collapse. In the case of 9/11, the WTC 5 and 7 buildings did collapse due to fire (without the addition of large quantities of jet fuel as occurred in the two main towers).
• An article sidebar makes the case that structural steel and cast-in-place concrete are both approximately equally vulnerable to the effects of fire.
• Last month the ICC (authors of the International Building Code) voted to eliminate allowable tradeoffs for passive containment and sprinklers in buildings greater than 420 feet tall.

More Articles
Fire Codes Spur Debate, Architecture, 06/2004
New York's Building Code Reflects High-Rise Concerns, ENR Construction, Spring 2004
A Myriad of Issues, Newsweek, 6/10/2004

Defensive Design Guidelines

DHS Announces New Building Safety Guidelines, Building Safety Bulletin, May 2004, describes new publications developed by the Federal Emergency Management Agency (FEMA) and released by the Department of Homeland Security related to the design and construction of buildings for resistance to terrorist attack. Documents available on FEMA's web site include:

• FEMA 426 - Reference Manual to Mitigate Potential Terrorist Attacks Against Buildings
• FEMA 427 - Primer for Design of Commercial Buildings to Mitigate Terrorist Attacks
• FEMA 428 - Primer for Design Safe School Projects in Case of Terrorist Attacks
• FEMA 429 - Insurance, Finance, and Regulation Primer for Terrorism Risk Management in Buildings
• E155 - Building Design for Homeland Security

Elevators and Emergency Egress

Industry group proposes use of elevators during fires, Building Design & Construction, 05-04, reports on plans by the elevator industry and standards organizations to develop elevator systems suitable for occupant egress and firefighter access during building emergencies.

According to the article, benefits of such "protected" elevator systems include reduction in building evacuation times by as much as 50%, and delivery of firefighters to upper floors in high-rises up to six times faster than possible by use of stairs. These plans took a significant step forward with a March workshop sponsored by the National Institute of Standards and Technology, attended by various stakeholders including the American Society of Mechanical Engineers, International Code Council, National Fire Protection Agency, Americans with Disabilities Act board members, elevator manufacturers, and industry consultants and experts.

According to the article, in twelve countries outside the US, lifts dedicated solely to firefighter access are required in buildings 30 meters or taller. In contrast, the plans being developed here in the US will rely on normal service elevators, and will provide not only firefighter access but also occupant evacuation capabilities. The basic operational strategy works as follows:

• When any detector in the building signals a fire alarm, one designated elevator is recalled to the ground floor and taken out of service, where it can be put back into service under manual control by emergency personnel.
• As long as smoke or heat detectors in elevator lobbies and hoistways do not signal alarms, other elevators would continue to operate normally.
• If lobby or hoistway detectors do signal, then all affected elevators would be similarly recalled.
• Advanced sensing and communications systems would allow emergency personnel to gauge occupant loads and fire conditions on individual floors. Using this information, occupants could be directed to wait for elevators at their current location, proceed to elevator lobbies on other floors, or exit the building by stairway.
• Elevators themselves would be protected from smoke and fire by 1-hour rated, pressurized lobbies and pressurized hoistways.
• Proposals for integrating elevator control and communications with HVAC and fire protection systems are also part of the planning.

More Information:
Conference Proceedings: Workshop On Use of Elevators In Fires And Other Emergenices

Height & Area Requirements In The IBC

As noted in the textbook, the three previous US model code organizations have consolidated themselves into the International Code Council, and merged their model codes into the International Building Code. Recently, this author had reason to compare height and area limitations between one of the "legacy" model codes and the new International Building Code. It's no secret that the new code is at times less restrictive than its predecessors, but even knowing this in advance, the results were eye opening.

The following two charts are adapted from our design handbook, The Architect's Studio Companion. One portion of this book deals with the effects of the building code on building form by providing a series of charts that allow the designer to quickly determine allowable height and area for a project under consideration depending on such factors as applicable code, construction type, and related considerations. By comparing tables from an earlier edition of the Companion, that compiled results for the previous codes, with information from the latest edition, which refers to the new International Building Code, easy comparisons can be made.

Combustible Construction, UBC vs IBC
This first chart compares height and area limits for two codes, the "legacy" Uniform Building Code (UBC) and the International Building Code (IBC), for buildings with Occupancy Group B (Business) and constructed of combustible construction. The base chart (rendered in grey scale) represents data for the UBC. Information overlaid in blue represents data from the IBC.

Read the chart as follows:

• Various construction types and their level of fire protection are listed across the top rows of the chart. For example, "Wood light frame, 1-Hour" refers to stick built construction with 1-hour fire protection applied to the framing (typically in the form of fire-rated gypsum wallboard). Mill construction refers to buildings with noncombustible exterior wall construction and heavy timber framing for the interior structure. Noncombustible structures made from concrete or steel (included in the chart below) are listed simply according to the level of fire protection applied.
• Below the construction types, columns are further divided to distinguish between sprinklered ("Spr") and unsprinklered ("Unspr") buildings.
• Once a construction type, level of fire protection, and sprinkler condition have been established, allowable height and area can be read as follows. For maximum height in feet, read from the row directly below the sprinkler designation row. ("UH" on the chart below refers to unlimited height.)
• For maximum height in stories, proceed down a column until arriving at the solid horizontal line. Read across to the side of the chart to find the allowable stories permitted.
• To determine the maximum permitted area for the building, read the number directly below (or above, where space was limited) the solid line. This is the maximum allowable area for all floors of the building. ("UA" refers to unlimited area.)

Keeping in mind that data for the IBC is rendered in blue, a few facts are readily apparent:

1. For the cases illustrated here, more often than not, the IBC is moderately more generous in its allowable building height than the UBC.
2. In these cases the IBC is significantly more generous in its allowable building area than the UBC. This is particularly true for sprinklered buildings, where on average, the allowable area for all floors has increased by a factor of 7 times in comparison to allowable area for the UBC.

Noncombustible Construction, UBC vs IBC
This second example continues the comparison for noncombustible construction types, for the same Occupancy Group B.

The results are similar: The IBC is more often than notgenerous in allowable height than the UBC. But the IBC is significantly more generous in its allowable area than the UBC, particularly for cases where the building is sprinklered. (Though not illustrated here, the same trends are true for most other occupancy groups as well.)

Comments
Reportedly, at the time of the creation of the IBC, the approach taken to establishing height and area limitations was to take the least restrictive requirements from any of the three legacy codes and apply those requirements to the new code. As it was explained to this author by one representative of the International Code Council, this decision was based on the absence of any data indicating any one of the legacy code's limits was technically superior to the others.

For any design and construction professional interested in the topic of building safety, these are interesting times. A confluence of events have brought new attention to a number of questions that have always been part of this profession, but that often may be taken for granted by many of us. To name just a few: How is building safety measured? Who decides what constitutes a reasonably safe building? Who should be responsible for ensuring the safety of buildings? This site will continue to report on developments in these areas as they arise.

More Information
Category 01 Making Buildings on this site includes articles related to regulation of construction, building codes, and the general considerations of how buildings get built. Category wtc on this site includes articles related to building safety and in particular issues arising out of the collapse of the World Trade Center towers. Many of the articles in both of the categories link to other Web resources for further coverage of these topics.

For an introduction to building codes, Occupancy Groups, Construction Types, Height and Area restrictions, and related topics, see pages 4 - 10 of the textbook.

More On Highrise Safety

The debate on building safety continues...

Building Safety Journal
Fire Protection - The Fire Service Viewpoint?, Building Safety Journal, January-February 2004, (available online at the time of this writing) rebuts charges that current building standards allow construction of buildings that are unsafe for firefighters during building fires. This article, authored by fire protection engineer Richard C. Schulte, is perhaps most noteworthy for the prominence granted to it by its publication in the International Code Council's flagship journal. This author found the arguments put forth in the article less than compelling.

Metropolis Magazine
Shortcuts to Safety, Metropolis Magazine, March 2004, takes the position that "Two and a half years after the worst tragedy in skyscraper history, highrises are no safer." This is an informative article offering insights this author has not encountered elsewhere on this topic. Whether or not one agrees with its premise, this article is worth the attention of those concerned with the topic.

Some of the key points raised in this article include:

• The Skyscraper Safety Campaign, founded by the family of a firefighter lost in the disaster, has played a prominent role in raising issues of building safety and pushing for investigation into the causes of the building collapses. According to the article, this group was partially responsible for the creation of the ongoing investigation by the National Institute of Standards and Technology.
• Though building safety standards are enforced through public regulation, the standards themselves are crafted in the private sector, and to a significant extent by the same parties with an interest in minimizing building costs. As an example, the article cites New York City's own building regulation department, the Department of Building, that has a dual mission of maintaining building safety while also "streamlining the occupancy of new and existing office space".
• According to sources quoted in the article, the standards of safety applied to the World Trade Center towers were sufficiently lax that these buildings could not have been built in Germany, the United Kingdom, Japan, or even possibly in any American city--including New York City--if they had had to meet local building code requirements. (The developer of the towers, the Port Authority of New York is exempt from City building and fire department regulation.)
• Trends in construction since World War II toward lighter construction materials and assemblies have resulted in building systems that some argue are less resistant to fire and that are less safe for building occupants and fire fighters.

The article also discusses the reconstruction of Seven WTC, the 47-story highrise that collapsed due to fire some hours after the two main towers. The new building, dubbed "Seven II", is being built to standards significantly in excess of current code requirements including a reinforced concrete core, fire sprinklers with double the required supply capacity, exit stairs 20 percent wider than required, and other safety features. The article also notes that these enhancements may reflect both the developer's good intentions and/or economic realities of insuring a building in this sensitive location.

For more on this topic, see the previous articles on this site:
Fire-Safe Debate
The Current State of Fire Protection Design
Debate Over Fire Testing

Fire-Safe Debate

With the World Trade Center collapses, several recent catastrophic building fires, and the publication of two new model building codes, fire safety in buildings is getting more than its usual share of attention. Two recent opinion articles take the position that current trends toward relaxing building fire safety requirements are ill advised and should be reconsidered.

Reliance on sprinklers a mistake, Building Design & Construction, 01.04, takes the position that "building codes...are based on the mistaken assumption that sprinklers virtually never fail and that fire-resistant construction materials can, therefore, be minimized or eliminated". This guest commentary piece is authored by W. Gene Corley, PhD, Senior VP, Construction Technology Laboratories, and team leader for FEMA's WTC Building Performance Study.

Some of Sorley's assertions include:

• Sprinkler failure rates may be as high as 16%.
• The trend in the model codes is toward increasing reliance on sprinklers, while reducing requirements for fireproofing, fire-barriers, and smoke-barriers.
• Fire-barriers and smoke-barriers are considered "life savers" by fire fighting personnel, and they reduce the risk of building collapse.

Sorley continues with examples gleaned from his his experience as a lead investigator of the WTC disaster. He then offers more criticism for the International Building Code (IBC), which he claims has "drastically lowered" requirements for fire-resistant construction in comparison to older model codes. Sorely concludes with the advice that building fire safety requires both sprinkers and fire-resistant construction to best ensure the safety of building occupants and emergency responders.

Fire-Safe Buildings and Masonry Codes, Masonry Today, Winter 2003/2004, takes a similar position, stating "Today's building code officials should be encouraged to develop code provisions that provide an improved level of redundancy for life safety, property proteciton, and welfare of the general public". This article is written by Stephen Szoke, Director of Codes and Standards, Portland Cement Association.

Szoke states that in the process of merging the three previous model building codes, the least restrictive passive fire protection requirements from these codes were used as the basis for the requirements in the new IBC. Furthermore, new code change proposals seek to reduce even further the IBC's passive fire protection requirements.

Szoke goes on to make a number of arguments for reconsidering an overreliance on fire sprinklers in buidings, including considerations of:

• Aging population
• Risk of malicious disabling of fire sprinkler systems
• Trends in other aspects of the building code toward more stringent safety requirements
• Increased construction of multi-family building types
• Sprinkler system effectiveness
• Sprinkler malfunctions
• Reliable water supply for sprinklers

Szoke advocates a "balanced design" approach to fire-safe construction that relies on both sprinkler systems and the redundancy of passive fire-resistant construction. He further recommends building designers consider in some circumstances exceeding current code fire-separation requirements.

This Author's Comments
Readers should take note that both authors cited above are associated with construction trade groups that have an ecomonic interest in promoting non-combustible construction methods. Construction Technology Laboratories, of which Sorley is a Senior Vice President, is closely associated with the American Institute for Concrete Construction. Szoke's organization, PCA, is a promoter of concrete and masonry materials and construction. (Szoke is quite forthright in his article concerning his association and interests in this matter. He states "PCA and allied industry groups advocate changes to increase passive fire protection for buildings...")

Despite these authors' perhaps vested interests, it is this author's opinion that their points are well founded and worthy of serious consideration.