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Conservation and fire science: a delicate balance

By Daniel J. Lemieux AIA posted 05-06-2019 11:18

  


Conservation and fire science: a delicate balance


By Daniel J. Lemieux, AIA, RIBA and Nicholas E. Ozog, PE


Energy efficiency and conservation of our natural resources have arguably become two of the most significant influences on the design and construction of our built environment. The demand for deep-energy retrofits and adaptive reuse of post-war and more recently constructed modern and post-modern built assets is a reflection of this trend. In the wrong hands, this demand can create fertile ground for the introduction of exterior wall components and materials that may increase the risk for fire, particularly when regulatory enforcement is weak, product substitutions are not fully vetted and untested products are allowed to reach the marketplace. As designers and stewards of our built environment, the public trust is safeguarded when we take the time to investigate what past mistakes taught us and apply those lessons to advance our own understanding of building science and the physics of building enclosure performance, both in the context of heat, air and moisture transport and in the broader context of fire science and engineering.

Energy costs drive product development and innovation

Since about 1970, new drivers have emerged in both product development and the evolution of building codes and standards, most notably energy use in our existing building stock - increasingly seen as built rather than disposable assets - and the steadily increasing demand for conservation of our natural resources. Of these, the rising cost of energy has arguably had the single most significant and quantifiable influence on design and construction. Beginning with the Oil Embargo of 1973, rising energy costs - in particular fossil fuels - led directly to the development and introduction of new guidelines and standards to assess the thermal performance of buildings and a corresponding advancement in the development of new products, materials and technologies to optimize and improve whole building performance. When measured today simply by comparing the published cost of electricity in the UK and a handful of other countries in the EU vs. the same costs in the continental U.S., Canada and other nations (setting aside taxes, subsidies and other factors that may influence these figures), we find that, by some estimates, the cost of energy in the UK and Western Europe can be as much as 12-15 cents higher per kilowatt hour (kWh) than in the U.S. and other nations.1

It should come as no surprise, then, that the trend-line in the construction products industry in the UK and elsewhere has been toward thinner, lighter, more cost-effective and energy efficient products and materials, including exterior cladding and insulation. Product development in this space increased dramatically during the 1980s and 1990s, resulting in the introduction and more widespread acceptance and use of exterior cladding and insulation products that included rigid and semi-rigid foam, foam- insulated “sandwich” panels and lightweight exterior cladding products with metal facer-sheets and core materials that included thermoset and thermoplastic materials. These included polyurethanes (PUR), polyisocyanurate (PIR), expanded polystyrene (EPS), extruded polystyrene (XPS), polyethylene (PE) and similar products - all derived from or otherwise refined and formulated in part from petroleum-based products.

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ACM panel with Polyethylene (PE) Core; Image: Courtesy WJE
As designers, we are drawn to these new products and materials not just for the range of options they offer aesthetically, but also for all of the performance attributes cited by industry: thinner, lighter, more cost-effective and energy efficient. This is particularly true when we are faced with the challenge of improving energy performance in existing buildings and an aging building stock. In fact, when we consider the effects of climate-specific heat, air and moisture transport across a building envelope, the fundamentals of building science and the physics of building envelope performance often tell us to insulate outboard of the primary air barrier in an exterior wall system to optimize thermal performance and minimize the risk for direct rainwater penetration and condensation within the envelope of the building.

This, of course, results in wall sections that include a layer of insulation located directly behind the exterior cladding in both new construction, refurbishment, and adaptive re-use of existing buildings. Good intentions with a noble purpose and a change in design and construction philosophy that has been incentivized in recent years through the efforts of the United States Green Building Council (USGBC) and parallel efforts such as the Building Research Establishment Environmental Assessment Method (BREAMM) in the UK; the European Commission Joint Research Centre on Sustainability; ESTIDAMA, Green Emirates Dubai and similar efforts across the UAE, and; various other voluntary guidelines and standards published around the world.

In the US, concerns regarding the horizontal and vertical spread of fire associated with these products resulted in the development of a full-scale fire testing program that began in 1980 and ultimately led to a first draft in 1985 of what would later become NFPA 285 and publication of Test Standard 17-6 in the 1988 edition of the Uniform Building Code (UBC). Since that time, this standard has undergone several changes and exists today as NFPA 285, Standard Fire Test Method for Evaluation of Fire Propagation Characteristics of Exterior Non-Load-Bearing Wall Assemblies Containing Combustible Components. In the UK, concerns associated with this trend lead to the publication in 1988 of the first edition of BRE 135, Fire Performance of External Thermal Insulation for Walls of Multi-Storey Building.

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This NFPA 285 test by BAMCO evaluated the FABLOGIC D-500 Rainscreen Panels’ exterior, non-load bearing wall assemblies and panels as components of curtain wall assemblies and measured fire propagation characteristics for post-flashover fires of interior origin. Image: Courtesy of BAMCO

Grenfell Tower

Originally constructed in 1972 and refurbished in 2016, the tragedy at Grenfell Tower in the summer of 2017 was, quite literally, a wake-up call for all of us who gathered early that morning at Southbank Centre in London for a symposium on building physics and conservation. What we saw unfolding before us was, sadly, immediately recognizable - another building engulfed in flames in a pattern all too reminiscent of The Address hotel fire in Dubai and so many other high-rise buildings around the world over the past ten to fifteen years.

Public outcry was understandable and swift: Why did this happen? Who is responsible? What can be done?

As human beings, we mourn those who were lost and feel deeply for those left behind who continue to grieve and now turn to us for answers. As architects and engineers, problem-solving is familiar territory for us. Solving for ‘Why?’ is the assignment we have been given: A first-principles approach to safeguard lives and to restore the public trust.

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Tragedy at Grenfell Tower; Images: courtesy of WJE
Unlike the exterior cladding fires we witnessed in Dubai where occupancies are often seasonal and buildings, therefore, may be lightly occupied, the fire at Grenfell Tower was particularly tragic both for the number of casualties and the time at which it occurred - overnight, a time when much of the building was occupied and many of its occupants may have been asleep. For that reason, reaction from the manufacturer of the cladding panels supplied for the refurbishment of Grenfell Tower and the response from the government came quickly:

Manufacturer’s Statement (June 26, 2017)
“The loss of lives, injuries and destruction following the Grenfell Tower fire are devastating, and our deepest condolences are with everyone affected by this tragedy. While the official inquiry is continuing and all the facts concerning the causes of the fire are not yet known, we want to make sure that certain information is clear… We sold our products with the expectation that they would be used in compliance with the various and different local building codes and regulations. Current regulations within the United States, Europe, and the UK permit the use of aluminum composite material in various architectural applications, including in high-rise buildings depending on the cladding system and overall building design. Nevertheless, in light of this tragedy, we have taken the decision to no longer provide this product in any high-rise applications, regardless of local codes and regulations.”3

Regulatory Response (June 15, 2017, and June 29, 2017)
“Following the Grenfell Tower tragedy, the government has established a Building Safety Programmed with the aim of ensuring high rise residential buildings are safe, and residents feel safe in them...” “Screening tests at the Building Research Establishment (BRE) have been identifying whether Aluminum Composite Material (ACM) cladding samples from buildings meet the limited combustibility requirements of current Building Regulations guidance.”4

The position taken by the manufacturer is understandable. Current building codes governing the use of combustible materials in high rise construction, while not strictly prohibited in many jurisdictions, are typically governed by combustibility of the product or material itself in addition to building height, use and occupancy. It is not surprising at all, therefore, to see both the industry and regulatory response focus first on combustibility of the cladding material itself before focusing more closely on the fire risk posed by the entire exterior wall assembly and its interaction with other building features.

When past is prologue

In the UK, the Great Fires of London (c. 1666) and Warwick (c. 1694) taught us long ago that “… old paper buildings and the most combustible matter of tar, pitch, hemp, rosen and flax…”5 were undesirable cladding materials at any height, and that “… the close-packed nature of the environment and amount of combustible building material all lead to the fire’s start and spread…”6

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Image of Triangle Shirtwaist Factory fire on March 25, 1911

In the US, the Triangle Shirtwaist (c. 1911) and subsequent fires during the first half of the twentieth century7 also taught us a great deal and began to shift our focus to include combustibility of interior finishes and a more holistic approach to fire protection that included fire separation, egress requirements and a “shift in emphasis in building design and construction from the protection of property to the protection of lives.”8 Over time, lessons regarding combustible building materials would result in the development of British Standard (BS) 476, Fire Test to Measure Surface Spread of Flame, first published in 1932, and ASTM E84/NFPA 255, Standard Test Method for Surface Burning Characteristics of Building Materials, first published in 1944 and often referred to less formally as the “Steiner Tunnel Test” after its inventor, Al Steiner of Underwriter’s Laboratories. For code developers and the authorities having jurisdiction over the adoption and enforcement of those codes, these tests were a step toward protecting property and saving lives. For manufacturers, they also represented a new threshold to be met for the same reasons, and to ensure access-to-market for their products and materials.

Déjà Vu (All over again)

Fire as a principal driver in the development of building codes and standards resurfaced again at the turn of the last century and continued during the first two decades of the 21st century. In the UK, three fires, in particular, gained public notice both for the materials associated with each fire and the challenges faced by Fire Services in fighting those fires.

The first, at Knowsley Heights in Liverpool (1991), included a rainscreen exterior cladding system over an existing building façade and saw rapid propagation of fire inside the cavity space behind the exterior cladding. The regulatory response included a new requirement for horizontal fire stops at each floor level inside the cavity space behind the exterior cladding and, perhaps more noteworthy, the start of a discussion about large-scale assembly testing in addition to small-scale product testing to assess both combustibility and reaction-to-fire.9

The second, at the Sun Valley Poultry cold storage facility in Herefordshire (1993), included foam-insulated sandwich panels on both the walls and ceilings that, in the aftermath of that event, spurred further discussion about the combustibility of the core material used in the manufacture of those panels (EPS and PUR). This discussion was spurred by concern for the challenges faced by firefighters who entered the facility to fight a fire below ceiling panels with a core material that had begun to melt and fall into that space.

The third, at Garnock Court in Scotland (1999), included glass-fiber reinforced plastic exterior cladding installed in a rainscreen configuration over exterior insulation and an existing building façade. Once again, rapid-fire propagation inside the rainscreen cavity space at this property occurred, reigniting several of the same concerns raised following the Knowsley Heights fire and accelerated the discussion regarding the need for large-scale assembly testing in addition to small-scale product testing to more fully understand reaction-to-fire.

Each of these fires and the discussions that followed would lead ultimately to the development by the BRE of BS 8414, Fire Performance of External Cladding Systems, first published in 2002 and republished today to include BS 8414-1 for cladding systems applied to the masonry face of a building and BS 8414-2 for cladding systems fixed to and supported by a structural steel frame.

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At left above, assemblies with fire-resistant core ACM on non-combustible gypsum and a 2-in. (51 mm) air cavity are tested in the 16-ft. high parallel panel test method of ANSI/FM 4880. At right, the peak flame height reached was approximately 8 ft. (2.4 m). This ACM sample performed well and passed ANSI/FM 4880 for unlimited height. Image: © 2018 FM Approvals. All rights reserved. Used with permission.

Exterior cladding fires are not limited to countries outside the United States. In the US, a fire at the Monte Carlo Casino and Resort (2008) was notable for its use of an Exterior Insulation and Finish System (EIFS) as exterior cladding. In this case, the insulation below the exterior finish was combustible, unlike much of the External Thermal Insulation Composite Systems (ETICS) more commonly found in Europe, where the exterior finish is over a layer of mineral wool fiber insulation.

Around the globe—and as building codes and standards struggled to keep pace—fires associated with exterior cladding continued to occur. Perhaps the most notable of these was the widely publicized series of fires in the UAE that began with Tamweel Tower in Dubai (2012) and were followed soon thereafter by The Address Hotel, Al Haffeez Regal Tower and Torch Apartment fires in Dubai (2015). During the same period, we also witnessed similar events across Europe, including the fires at Mermoz in Roubaix, France and Polat Tower in Istanbul, Turkey (2012), Grozny City Tower in Chechnya (2013) and Grenfell Tower (2017).

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Smoke billows from the Address Downtown Hotel, after it caught on fire hours earlier.

Evolution and progress

Returning to the tragedy at Grenfell Tower, we now recognize and perhaps understand more clearly the evolution in thought that has occurred relative to exterior cladding and fire protection. In the UK, this evolution has been informed in large part through the wisdom and experience of practicing design professionals, fire services personnel, and an Expert Panel convened by the BRE in the aftermath of Grenfell Tower. The advice given today by BRE to building owners and investors goes on to state:

“Large scale tests10 have been undertaken to understand whether and when it may be safe to use ACM as part of a wall system in high rise buildings…”11

“The Expert Panel’s advice following these tests is that ACM with an unmodified polyethylene filler with any type of insulation (behind the cladding panels) presents a significant hazard on buildings over 18 metres…”

“It is possible ACM with a fire-retardant filler could be used safely with non-combustible insulation (behind the cladding panels) but this is highly dependent on the insulation used and how it is fitted…”12

In the UAE, we see a similar trend. The UAE Fire and Life Safety Code of Practice, first published in 2011, has recently undergone a thorough review in response to exterior cladding-related fires in that region and, when adopted, will no longer allow small-scale product testing for combustibility alone to satisfy code requirements for fire and life safety. Beginning in 2017, the updated code will require (in addition to small-scale product testing for combustibility) large-scale assembly testing and pass/fail criteria as described in BRE 135, Fire Performance of External Thermal Insulation for Walls of Multi-Storey Buildings when tested in accordance with BS 8414-1 or -2, or; NFPA 285, or; ISO 13785-2. Today, full-scale assembly tests very similar to BS 8414 are reflected in ISO 13785-2 and a variety of other test standards currently under development or already adopted and enforced in countries from Europe to Australia.

Where do we go from here?

Future stewardship and the physical conservation of modern buildings can and should build on lessons learned from the past. This is particularly true when we seek to reconcile the demands of energy use and conservation with fire and life safety. If past is prologue, then a more integrated, cross-disciplined approach that includes an increased technical understanding of building science, construction materials and assemblies and their behavior both with regard to the effective management of heat, air and moisture transport as well as combustibility and reaction to fire is critical. While we have witnessed a significant increase in our knowledge and understanding of these principles over the past 25 years, we continue to struggle with the dissemination of that knowledge to both practicing and future generations of design professionals. Overcoming this challenge will be fundamental to our on-going effort to meet the demands of the marketplace that we will continue to face and to the development of the next generation of design and construction professional.

References

  1. Eurostat 2013
  2. Building Physics and the Conservation of Modern Architecture, 17 June 2017, Southbank Centre, London
  3. Public statement by ‘Arconic’ in the aftermath of Grenfell Tower and reported by Reuters on June 26, 2017
  4. BRE DCLG Government Building Safety Programme - Advice for Building Owners
  5. The Diary of John Evelyn, Great Fire of London, 16
  6. Ibid
  7. Cocoanut Grove, New York City (1942); LaSalle Street Hotel, Chicago (1946); Winecoff Hotel, Atlanta (1946)
  8. Geisler, M.P.; NFPA; Fire Engineering News
  9. BRE 135, Fire Performance of External Thermal Insulation for Walls of Multi-Storey Buildings, Fire Note 9, “Assessing the Fire Performance of External Cladding Systems - A Test Method” (1999), a precursor to the development of BS 8414, Fire Performance of External Cladding Systems (2002).
  10. BS 8414, Fire Performance of External Cladding Systems
  11. Visit www.bre.co.uk/regulatory-testing for a complete listing of products and assemblies tested and test results
  12. Duval, Bob, NFPA Journal®, May/June 2008 “Monte Carlo Hotel Casino Fire’

Acknowledgments

The authors wish to gratefully acknowledge the following organizations for their permission to re-publish portions of the following: “Exterior Cladding and Fire Protection: More Than Skin-Deep”, SFPE Viewpoint, Q2 2018, Lemieux, D. and Nicholas Ozog

About the authors

Mr. Lemieux is a Principal and Director of International Operations for Wiss, Janney, Elstner Associates, Inc. and a Director of Wiss, Janney, Elstner Limited in London. He is a registered architect in five jurisdictions in the US and listed architect in the UK, Ontario Province in Canada and New South Wales Province in Australia. He currently serves as Chair of ASTM Subcommittee E06.55, Performance of Building Enclosures and Vice-Chair of ASTM Committee E06, Performance of Buildings. His experience includes over 25 years of professional practice in assessment, repair design, and performance testing and overseas supply-chain technical support for building enclosure systems and assemblies in the US, UK, EU, UAE, and China.

Mr. Ozog is a Senior Associate in the Fire Protection practice for Wiss, Janney, Elstner Associates, Inc. He is a registered Fire Protection Engineer and consultant with over 10 years of professional experience in the application of performance-based design, and building and fire code consulting for a wide range of occupancy types and uses including hospitality, office, assembly and industrial occupancies located around the world. Nick’s global experience includes evaluation of cladding materials, façade designs, and fire protection-based risk assessment of buildings and structures with potentially combustible exterior cladding and underlying wall assemblies.
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