Issue 97: Fire Hazards of Exterior Wall Assemblies Containing Combustible Components
By Amanda Kimball, P.E., Fire Protection Research Foundation
Many combustible materials are used today in commercial exterior wall
assemblies to improve energy performance, reduce water and air
infiltration, and allow for aesthetic design flexibility. These
assemblies include Exterior Insulation Finish Systems (EIFS or ETICS),
Metal Composite Material (MCM) claddings, high-pressure laminates, foam
plastic in cavity walls, and water-resistive barriers (WRB). The
combustibility of the assembly components directly impacts the fire
hazard. For example, the insulation component of EIFS and MCM claddings
is combustible foam which exhibits rapid flame spread upon fire
exposure. There have been a number of documented fire incidents
involving combustible exterior walls, but a better understanding is
needed for the specific scenarios leading to these incidents to inform
current test methods and potential mitigating strategies.
The Fire Protection Research Foundation undertook an international
project with CSIRO (Commonwealth Scientific and Industrial Research
Organization, Australia's national science agency) and FireSERT, the
Institute for Fire Safety Engineering Research and Technology at the
University of Ulster, to gather information on fire incidents involving
combustible exterior walls, compile relevant test methods and
regulations globally on the use of combustible materials in exterior
walls, and identify the knowledge gaps for future work that would
develop guidance on evaluation, testing, and fire mitigation strategies
for these wall assemblies. A full report was published in June 2014
entitled Fire Hazards of Exterior Wall Assemblies Containing Combustible Components (White and Delichatsios, 2014).
Available statistics were compiled to determine the extent of fires
that involve exterior walls. The statistics for the United States were
based on information from the National Fire Incident Reporting System
Version 5.0 (NFIRS 5.0) for 2007-2011 as well as the findings of the
NFPA’s annual survey of fire department experience. The building types
included in the analysis were assembly, educational, health care,
residential (excluding one-or two-family homes), mercantile, offices,
laboratories and data centers, manufacturing, and selected storage
properties. For all building types analyzed, exterior wall fires
accounted for 3% of all structure fires, 3% of civilian deaths and
injuries, and 8% of property damage (White and Delichatsios, 2014).
The majority of exterior wall fires in the U.S. during the period
studied were in low rise buildings. Of all building types, 79% of fires
were in buildings one to two stories (White and Delichatsios, 2014).
In addition, it was found that while sprinkler systems provide
protection, there are still a significant number of fires occurring in
buildings protected by sprinklers. For example, in 39% of exterior wall
fires in buildings six to ten stories, an automatic extinguishing
system was present (White and Delichatsios, 2014).
Statistics from other countries were also examined to determine the
extent of fires involving exterior walls. For example, annual fire
statistics from New South Wales Fire Brigade, one of the largest fire
brigades in Australia, indicate that fires starting in wall
assemblies/concealed wall spaces make up 0.5% of total fires and fires
starting on exterior wall surfaces make up 1.3% of total fires (White
and Delichatsios, 2014).
One issue identified from the examination of available statistics was
that there was limited information on the types of exterior walls
involved in fires, ignition details, and mechanisms of fire spread.
Therefore, the study included a literature review of incident case
studies. While few documents with detailed investigations of fire
incidents were found, information presented in journals, newspaper
articles, and from other sources were examined.
Based on the statistics, exterior wall fires are low frequency
events, but the potential for loss can be high. The major fire
incidents outlined in the case studies appear to have predominantly
occurred in countries with poor regulatory controls on combustible
exterior walls at the time of building construction or where the
construction was not in accordance with regulations. The most common
ignition scenarios are internal fires that then spread to the exterior
wall. And it was found that exterior wall configurations with re-entrant
corners and/or vertical channels may increase fire spread.
One of the other major components of the project was a review of
current regulations and test methods globally. The regulations vary
greatly between countries. While many require exterior wall assemblies
to pass a full-scale test for buildings of a certain height and/or close
to a property boundary, in some cases exceptions allow the use of
materials based on results from small scale tests.
In addition, quite a large variation between the full scale tests was
noted. Most simulate the scenario of an internal post-flashover fire
that spreads via openings (i.e. windows), but the configurations can
vary from a single wall surface to a re-entrant corner "L” arrangement,
and the fire sizes and test durations are not constant.
Based on the research, the fire safety issues relating to exterior
wall assemblies with combustible components can be summarized into four
parts (White and Delichatsios, 2014):
- "Specification of fire exposure scenario and the heat flux
distribution both inside the enclosure and from the façade flames
originating from the fire in the enclosure. This requirement is
prerequisite for the following parts.
- Fire resistance of the façade assembly and façade-floor slab
junction including structural failure for non-combustible and
combustible façade assemblies.
- Fire spread on the external surface of the façade assembly if combustible due to the flames from the enclosure fire.
- Fire spread and propagation inside the façade insulation, if combustible, due to the enclosure fire.”
To address these fire safety issues, the recommendations for future
work are not to develop a new full-scale test, but to instead conduct
further research to validate the existing full-scale and small-scale
tests, develop a more affordable and dependable intermediate-scale test,
investigate the effect of vertical channels on fire spread, and
development of façade flame spread models. The specific recommendations
for future work can be found in the full research report.
White, Nathan and Delichatsio, Michael. "Fire Hazards of Exterior
Wall Assemblies Containing Combustible Components”. Fire Protection
Research Foundation, June 2014.
4th Quarter 2011 – The Monte Carlo Exterior Façade Fire – Jesse J. Beitel, Hughes Associates, Inc., and Douglas H. Evans, P.E., FSFPE, Clark County, Nevada
On January 25, 2008, fire spread along the upper portions of the
southwest facing exterior façade(s) of the 32-story Monte Carlo Hotel
and Casino in Las Vegas, Nevada. The flames and heat caused several
windows to break, but automatic sprinklers kept the fire from entering
the building. It took approximately 100 determined suppression personnel
to stop the fire’s progression. This article addresses the ensuing
forensics investigation, contributing aspects, lessons learned, and
whether combustible exterior facades should continue to be allowed. READ MORE
4th Quarter 2011 – Complex Curtain Wall Geometry and Material Selection for Passive Fire Protection – Ajla Aksamija, PhD, and Bruce Toman, Perkins + Will
Curtain wall systems have evolved to more complex and customized
solutions, driven by architectural design aspirations and technical
capabilities. Innovative building forms are imposing new challenges in
terms of facade structural stability, fire protection, and material
selection compared to traditional flat facades and standard curtain
walls. This article uses examples of actual buildings to show how
challenges were overcome. READ MORE
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