Fire Hazards of Exterior Wall Assemblies Containing Combustible Components

The Fire Protection Research Foundation has funded a research project on "fire hazards of exterior wall assemblies containing combustible composites". This paper presents preliminary findings from the project. In particular, statistics relating to exterior wall fires have been reviewed. Exterior wall fires appear to account for somewhere between 1.3% and 3% of structure fires in the selected property types investigated. Fires involving combustible exterior wall assemblies are low frequency events however the resulting consequences in terms of extent of fire spread and injuries and fatalities can be large as demonstrated by selected fire incident case studies. An overview of this project and it's further work is provided.


INTRODUCTION
Many combustible materials are used today in commercial wall assemblies to improve energy performance, reduce water and air infiltration, and allow for aesthetic design flexibility. There have been a number of documented fire incidents involving combustible exterior walls but a better understanding is needed of the specific scenarios leading to these incidents to inform current test methods and potential mitigating strategies. This paper presents preliminary findings from the Fire Protection Research Foundation project on 'fire hazards of exterior wall assemblies containing combustible composites'. At the time this paper was written this project is at a preliminary, information gathering stage.

FIRE PROTECTION RESEARCH FOUNDATION PROJECT
The Fire Protection Research Foundation has initiated a research project on 'fire hazards of exterior wall assemblies containing combustible components'. The project objective is to develop the technical basis for evaluation, testing and fire mitigation strategies for fire hazards of exterior wall systems with combustible components. This research project is split into two phases.
Phase 1 of the project includes review of available fire statistics, fire incidents, literature and test methods relating to combustible external wall assemblies including those assemblies listed below.
 Exterior Insulation Finish Systems (EIFS) or synthetic stucco  Metal composite claddings such as Alucabond and Alpolic  High-pressure laminates  Structural Insulation Finish Systems (SIFS) and insulated sandwich panel systems  Weather-resistive barriers (WRB).  External timber panelling and facades including cross laminated timber (CLT).
The scope of the current effort, which is summarized in this paper, only covers Phase 1. A possible Phase 2 effort would include experiments to evaluate performance of exterior walls with combustible materials.

U.S. FIRE STATISTICS 2007-2011 3.1 Methodology
A preliminary statistical analysis of building fires reported to U.S. municipal fire departments has been completed for fire incidents relating to exterior walls.
The 2007-2011 statistics in this analysis are projections based on the detailed coded information collected in Version 5.0 of the U.S. Fire Administration's (USFA's) National Fire Incident Reporting System (NFIRS 5.0) and the findings of the National Fire Protection Association's (NFPA's) annual survey of local or municipal fire department experience [1,2] The number of NFIRS code choices relating to exterior wall fires is very limited and does not capture information such as the type of exterior wall material (combustible or non-combustible), the extent of fire spread, or the mechanism of fire spread (external surface or within cavity).
Except for property use and incident type, fires with unknown or unreported data were allocated proportionally in all calculations. Casualty and loss projections can be heavily influenced by the inclusion or exclusion of one or more unusually serious fires. Property damage has not been adjusted for inflation. Fires, civilian deaths and injuries are rounded to the nearest one and direct property damage is rounded to the nearest hundred thousand dollars (US).
Fires involving structures other than buildings (incident type 112), and fires in mobile property or portable buildings used as a fixed structure (incident type 120-123) were also excluded.
The following property type use codes were included:  Public assembly (100-199)  Educational (200-299)  Health care, nursing homes, detention and correction (300-399)  Residential, excluding unclassified (other residential) and one-or two-family homes (420-499). This includes hotels and motels, dormitories, residential board and care or assisted living, and rooming or boarding houses. Fires involving structures other than buildings (incident type 112), and fires in mobile property or portable buildings used as a fixed structure (incident type 120-123) were also excluded.
Separate queries were performed for:  Fires starting in or the exterior wall surface area (area of origin code76),  Fires that did not start on the exterior wall area but the item first ignited was an exterior sidewall covering, surface or finish, including eaves, (item first ignited code 12); and for  Fires which did not start in the exterior wall or area or with the ignition of exterior sidewall covering but fire spread beyond the object of origin (fire spread codes 2-5) and the item contributing most to fire spread was the exterior sidewall covering (item contributing to flame spread code 12).
Results were summed after unknown or missing data, including extent of fire spread for the last condition, were allocated. This summed result is taken to represent the total number of exterior wall fires.
Separate queries were performed for four above ground height groupings:  one to two stories,  three to five stories,  six to ten stories, and  11 to 100 stories.   Separate queries were performed for four categories of automatic extinguishing system (AES) presence: 

Results
Table 1shows the total number of "structure fires" in the selected property types overall, regardless of the area of origin or item first ignited. This includes fires with confined fire incident types (incident type 113-118), including cooking fires confined to the vessel of origin, confined chimney or flue fires, confined incinerator fires, confined compactor fires, confined fuel burner or boiler fires, and trash or rubbish fires inside a structure with no damage to the structure or its contents. Table 2 shows the total shows the building fires in selected properties that began on, at or with an exterior wall, by property use. These exclude the confined fire incident types listed above.
For all building types, Exterior wall fires accounted for 3% of all structure fires. Exterior wall fires also accounted for 3% of civilian deaths and injuries and 8% of property damage. The highest number exterior wall fires occurred in residential buildings, and was 2% of the total residential structure fires. However, the percentage of residential structure exterior wall fires was lower than the percentage of selected storage properties, public assembly, office buildings, and mercantile properties, with exterior wall fires being 10% of storage occupancy structure fires.
For exterior wall fires in the selected occupancies  42% were fires starting on the exterior wall surface,  32% were fires where the area of origin was not exterior wall, but item first ignited was exterior sidewall covering, and  26% were fires where area of origin or item first ignited were not an exterior wall but the item contributing most to fire spread was an exterior wall.
Inclusion of the exterior wall as the area of origin or item first ignited may be capturing scenarios such as fires in external fuel loads located against external walls or exposure of external walls to fires from adjacent buildings where the fire spreads to the interior of the building but the external (combustible or non-combustible) wall does not play a significant role in the fire spread.
The percentage of exterior wall fires within buildings of different height categories is shown in Figure 1. This indicates that the vast majority of exterior wall fires occur within low rise (5 stories or less) buildings. This may be due to two reasons:  The majority of the building stock is low rise.  Sprinklers are more likely to be installed in high rise buildings and reduce the risk of internal fires spreading via openings to the external facade.
As a sensitivity study, the percentage of exterior fires by building height has been plotted for only residential, office and institutional type buildings as these are expected to have a larger proportion of high rise building stock compared with other building types such as storage, manufacturing, mercantile and educational. A slightly increased percentage of exterior wall fires occur in three to five stories buildings compared to the other building types. Figure 2 shows the percentage of exterior wall fires by presence of automatic extinguishing system within the different building height categories. Figure 2 indicates that the majority of exterior wall fires occur in buildings with no automatic suppression system or no automatic suppression system installed in the fire area. Two points need to be considered when examining this data. The NFIRS data element "presence of automatic extinguishing system" is intended to document "the existence of an AES within the AES's designed range of a fire. NFPA added the category "present, but not in fire area, when an AES was coded as present, but the reason for a failure to operate was "Fire not in area protected."  Although it is expected that the majority of high-rise buildings (6 stories or more) would have at least internal sprinkler systems, the majority of exterior wall fires for high rise buildings occur in buildings where no suppression system is installed. It is concluded that sprinkler systems are likely to have a significant effect on the risk of exterior wall fires. For example internal sprinklers reduce the risk of spread from an internal fire to the exterior facade.
The data presented in Figure 2 provides no information regarding failure of automatic suppression systems where installed. However, previous NFPA reports address sprinkler effectiveness in general. The data also does not enable analysis of the effectiveness of internal sprinklers vs external facade sprinklers in preventing exterior wall fire spread.

OTHER FIRE STATISTICS 4.1 New South Wales Fire Brigade statistics, Australia
The Australian Incident Reporting System (AIRS) is an Australian national database framework for incidents reported to emergency services. Unfortunately not all Australian fire brigades actively report to AIRS and it is currently not well maintained or easy to retrieve data from. New South Wales Fire Brigade (NSWFB) is one of the largest fire brigades in Australia. NSWFB publish annual fire statistics which represent a selection of the NSWFB AIRS data. The only information relating to exterior wall fires is the "area of fire origin" as shown in Table 3   Table 3. NSWFB building fire statistics for area of fire origin [5] Area of fire origin This indicates fires starting in wall assembly/concealed wall space are 0.5% of the total fires and fires starting on exterior wall surfaces are 1.3 % of total fires. NSWFB statistics provide no information relating to the number of fires where the main area or fire spread was the exterior wall assembly or the types of exterior wall assemblies involved.

New Zealand Fire Service Emergency Incident Statistics
The New Zealand Fire Service (NZFS) publish annual fire statistics in a similar format to NSWFB. Again, the only information relating to exterior wall fires is the "area of fire origin" as shown in table This indicates that fires starting in wall assembly/concealed wall space are 1.7 % of the total fires and fires starting on exterior wall surfaces are 5.0 % of total fires. Fire statistics in the UK and Europe are currently being collected.

SELECTED FIRE INCIDENTS
Although the rate of fires resulting in extensive fire spread involving combustible exterior wall systems is low, the consequences of such fires is potentially very large. Examples of incidents on various different types of combustible wall systems from around the world are presented.

Fires involving aluminium composite panels
A spate of recent facade fires in the United Arab Emirates has involved aluminium composite panels with polyethylene cores. On 18 November 2012 a fire started at the top of the 34-storey Tamweel Tower, Dubai resulting in rapid fire spread down the external facade to ground level [7,8] . This was accompanied by a significant amount of falling flaming debris. In October 2012 a fire started in the fourth floor of the 13 storey residential building in Dubais's Tecom area [9,10] . The fire rapidly spread upwards on the aluminium composite facade to all floors above. A similar fire occurred in April 2012 in a 14 storey residential building, Al Tayer Tower in Sharjah with the fire starting on the second floor and spreading to all floors via the aluminium composite facade [11] . A change to the UAE Building code has been drafted to address fire safety requirements for facades [12] however it is estimated that non-fire resistant aluminium composite panels are currently installed on around 70% of high rise building facades in the UAE.
A similar fire occurred on 14, May 2012 at the Mermoz Tower, Roubaix, France [13][14][15][16] . The fire started on a second storey balcony of the 18 storey residential building. Flames spread upwards on the facade reaching the top of the building and resulting in one fatality. Fire spread up through external balcony channel which was lined with 3 mm thick aluminium composite cladding.  Factors contributing to the fire spread were the use of EPS insulation, inadequate installation of insulation and protective render and no use of mineral wool fire propagation barriers , particularly around window reveals [18] .

Fires involving other combustible wall materials
There has been some very large façade fire incidents reported in China. Unfortunately, detailed information on these incidents or any regulatory changes in China has not been available. One example is the Shanghai 28-storey residential building fire on 15 November 2010, believed to be caused by welding resulting fire spread on polyurethane insulation to external walls. This resulted in 58 fatalities [19] . Another example is the China Central Television headquarters (CCTV Tower). A 44 storey tower nearing completion of construction. The facade at the top of the building was ignited by illegal fireworks. The fire spread to involve the majority of the facade over the entire height of building. The façade is believed to have included a polystyrene insulation [20]