FIRE LOSS STATISTICAL CONSIDERATIONS IN RELATING FAILURE AND BUILDING DAMAGE TO THE BUILDING CODE OBJECTIVES

Transcription

1 FIRE LOSS STATISTICAL CONSIDERATIONS IN RELATING FAILURE AND BUILDING DAMAGE TO THE BUILDING CODE OBJECTIVES P.L. Senez*, K.D. Calder, Hsing H (Isabella) Li Sereca Fire Consulting Ltd., Canada INTRODUCTION Recent efforts to increase the height and area limits for buildings of combustible construction in Canadian building codes have prompted an examination of fire loss statistics with the intention of quantifying the fire risk associated with these changes. However, most of the existing fire loss statistics have been collected in a manner that does not directly correlate with the principles upon which building codes are based, and since the existing statistics favour lower buildings of smaller area, their suitability was found to be unreliable in extrapolating to higher buildings. This paper outlines a framework for the collection of fire loss statistics that can better align with the fundamental fire safety principles within the Canadian building code system. A sample data set collected over a 10 year period is used to illustrate the effectiveness of this framework relative to informing users on the risk associated with increasing the building height and area limits in the Canadian Codes. OBJECTIVES OF THE NATIONAL BUILDING CODE OF CANADA The National Building Code of Canada ( Building Code ) 1 is an objective-based code with a framework of objectives, sub-objectives and functional statements, developed through a bottom-up analysis of the existing requirements called acceptable solutions. The objectives are high level and qualitative, covering general concepts of the Building Code such as Fire Safety. The sub-objectives and functional statements provide an additional level of detail that can be used as the basis of a framework in establishing what the Building Code is trying to achieve. An example is the set of subobjectives for fire protection of the building, specific to fire spread. These are the limitations of the risks of injuries and property damage caused by: OP/OS1.2 - fire or explosion impacting areas beyond its point of origin OP/OS1.3 - collapse of physical elements due to a fire or explosion The associated functional statements, which indicate the performance of the design, are: F02 - To limit the severity and effects of fire or explosions. F03 - To retard the effects of fire on areas beyond its point of origin. F04 - To retard failure or collapse due to the effects of fire. In addition, the Building Code also has intent statements associated with the requirements that provide a plain-language explanation of the requirement to assist in the interpretation of the acceptable solution requirement. For example, the following intent statement is provided relative to fire spread: To limit the probability that floor assemblies exposed to fire will prematurely fail or collapse, which could lead to the spread of fire from a lower storey of a building to an upper storey or to the exterior of the building during the time required to achieve occupant safety and for emergency responders to perform their duties, which could lead to harm to persons.

2 The acceptable solution requirements in the Building Code target to achieve the objectives through a combination of compartmentation, limits on building size and type of construction, provision of firefighting access and sprinklering. These requirements define an acceptable solution to limiting fire spread. However, the acceptable solutions can be, or are sometimes perceived to be, ineffective in achieving the objectives of the Building Code. Often these concerns manifest themselves following the occurrence of fires resulting in significant injury, life loss or substantial property damage. Contemplating changes to the existing acceptable solution requirements is disconcerting where knowledge of the potential safety impact of those changes can not be formalized and is established based on perceived levels of safety rather than measurable ones. It is also frequently complicated by the differing professional viewpoints of the causation and spread mechanisms that can occur between respected parties. This constitutes one of the challenges in evaluating differing viewpoints in recent Canadian efforts to increase combustible construction building height and area limits. Since there are few buildings of dimensions, other than some historic buildings, there is little data available relative to their performance. The corresponding discussions are frequently polarized by advocacy on one front, and concern for safety on the other. A more balanced measuring stick could be available with relatively minor adjustments to the statistics gathering framework which could significantly contribute to the National knowledge and understanding of building fire performance in alignment with fire engineering principles. EXISTING FIRE LOSS STATISTICS The current fire loss statistics in Canada are collected within a framework that includes five main categories: key building characteristics, fire detection and protection systems, notification and response, fire development, and injuries and losses (life and material); however, the focus is on fire initiation and frequency; alarm and sprinkler operation; injuries and deaths. Information on building characteristics and fire development are included in the framework, but only limited fire development data can be related back to the building design and construction. Yearly reports based on these statistics are in some cases used to support changes to the Building Code. The Building Code is developed Nationally but empowerment for control over construction is a Provincial mandate as is the gathering of statistics. Consequently, the Canadian system encompasses numerous Provincial codes that are based on model National codes but are different depending on the degree of Provincial variation that is incorporated in the acceptable solutions. This variability between the codes and statistical data further complicates the alignment of the codes and the statistics. Better alignment and a National database could allow for a broader distribution of fire and building types. However, there is sufficient similarity for purposes of the discussion on how best to gather statistics. Within the current statistical framework, fire spread is currently categorized as: a function of object, part of room/area, room, storey, building, beyond property, and roof/attic. These descriptors cover a progressive degree of compartmentation, but the degree of compartmentation does not directly align with the fire compartmentation in the Building Code or with

3 the degree of fire separation rating contained within the building code. It also does not cover fire initiation and development in concealed spaces or at the building exterior, both of which have been found to be significant contributors to fire spread through our forensic investigation work. Further, despite being significant factors in the acceptable solutions, the following key aspects are not accounted for in the current fire loss statistics framework: interior finish of materials used on walls and ceilings, fire compartment fire-resistance ratings, fire stopping systems, and fire separation continuity, fuel load or density of occupancy type contents, use of masonry or other types of firewalls, the existing of concealed spaces and the extent of fire spread in the concealed spaces, and the method of construction of the building s exterior façade and extent of spread from the exterior. The interior finish and compartment ratings are aspects regulated by the Building Code that are related to the development and spread of fire. The density of building contents is not regulated by the Building Code, but is fundamental in the development of the occupancy classifications. The identification of firewalls affects the determination of the building area, which dictates the design criteria for a building. For example, a large complex may be designed with a firewall in place to reduce the building area to permit less restrictive construction requirements. If firewalls are not identified, the building area may not be correctly identified, in turn affecting the accuracy of the data. The fire development in a compartment, concealed space, and building exterior are very different based on the difference in fuel configuration and compartmentation, or lack thereof. Acceptable solution requirements in the Building Code are different depending on the assumed point of development of fire. For example, there have been many large-loss fires originating at roof level in buildings with both combustible and noncombustible construction. The current framework for the fire statistics collection does not identify these environments in a manner that can be correlated with the Building Code. Therefore, assessing and improving the effectiveness of the fire protection provisions for these environments will be difficult based on the existing data. All of the above were identified as issues in the examination of existing data as it limited the potential to derive directly comparable and building code specific data from within the existing statistics. Correlating the statistical framework with the objectives of the Building Code and associated fire engineering principles would establish a more congruent framework for data collection that would be more functional in gauging historical risk and the effectiveness of changes to the code. PROPOSED FRAMEWORK FOR FIRE LOSS STATISTICS The effectiveness of the building code provisions can be examined based on the analysis of data framed around compartmentation and subsequent degree of fire and smoke containment. This can be achieved through damage indexing relative to the degree of fire and smoke spread, and parallel examination of the design conditions that accelerate the growth and spread of fire beyond the limits intended by the Building Code. The proposed framework for collecting fire loss statistics includes four areas of interest: key building characteristics, hazard contributing factors, fire protection features, and fire development. The fire development information is collected based on an indexing system established for three potential fire environments: a compartment, a concealed space, and at the building exterior. For purposes of this study, residential apartment fire loss data was collected within the the proposed

4 framework to determine its effectiveness in establishing whether the acceptable solutions achieve the objectives of the Building Code, and where they don t, the reasons why. Data was collected from 120 fire investigations conducted over a 10 year period in the Province of British Columbia. The fires occurred in multi-family residential apartment buildings, constructed between 1912 and The buildings ranged in area from 150 to 5,000 m 2 and were 2 to 25 storeys in building height. The data from these fires was collected based on the criteria outlined in the following sections. Building Characteristics The building characteristics used for establishing the design criteria required by the Building Code are year of construction, occupancy, building height, and building area. These characteristics are key elements required to categorize the building based on the definitions provided in the Building Code. Some of the buildings in the data set had extensive repairs and/or renovations that significantly changed the building s characteristics. Therefore, the year of construction identified for a building is the year of original construction or the year the building was substantially repaired or renovated. The year of construction or significant alteration is used to establish the Building Code applicable at that time. Fire Hazard Contributing Factors Contributing factors to the fire hazard of a building include the type of construction, interior finish material, fire load, and occupant load. The fire load in a compartment was identified by an indexing system over a range of no contents to extensive furniture and storage, but also included an option for a N/A classification for a fire originating in a concealed space or at the building s exterior wall. Fire Protection Features Fire protection features consider both passive and active systems including compartmentation, detection, alarm and sprinkler systems. Compartmentation is characterized by the fire-resistance rating of the floor and wall assemblies including the suite separation, public corridor, and shafts. Fire alarm and sprinkler systems were identified for each fire incident and whether these systems were operational at the time of the fire, including the number of sprinkler heads that operated during the fire. Fire Development Information The fire development information includes the material first ignited, ignition source, ignition circumstances, storey on which the fire originated, fire ignition environment and fire development. The fire development data consists of information from a combination of fire scene observations relative to fire spread supported by witness statements. The fire ignition environment is classified as either a compartment, concealed space, or at the building exterior. The fire dynamics differ depending on which environment the fire develops in. A compartment, concealed space, and building exterior are addressed differently by the Building Code as the hazards associated with these environments differ. Identifying the key modes of fire spread associated with each of these environments will identify the effectiveness of the existing acceptable solution requirements relative to achieving the objectives of the Building Code to contain the fire. The intent of compartmentation is to limit the spread of fire from an area of greater hazard to an area of lesser hazard, as well as limiting the overall extent of building involvement. This is achieved through provision of fire-rated assemblies, building height and area limits. However, there are incidents where fire has spread beyond these limits and in some cases, to involve the entire building. The mechanism resulting in the extent of spread is important to measuring the effectiveness of the

5 acceptable solution requirements, and can be characterized through documentation and grading the associated fire damage. The level of fire damage for each incident is quantified based on an indexing system that considers the extent of fire and smoke damage. A set of fire damage indices is developed for each environment. The fire damage indices used for compartment, concealed space, and building exterior fires are summarized in Table Fire and Smoke Damage Indices for Compartment, Concealed, and Exterior fires. "Compartment" Index Nature Degree of Damage 1 Burn: Damage limited to item first ignited Smoke: Light smoke staining to contents and room lining in proximity to item first ignited Burn: Damage limited to item first ignited and damage to adjacent item/building component 2 Smoke: Smoke staining of contents throughout room of fire origin with indication of smoke layer line Burn: Damage to lining of entire compartment (post flashover) 3 Smoke: Smoke staining to all room contents and heavy smoke layer line with smoke staining to adjacent room(s) or exterior Burn: Extension of damage to compartments bordering the compartment of origin or exterior 4 Smoke: Smoke staining to room of fire origin and remainder of rooms on the same level and above the room of fire origin 5 Burn: Extension of damage to entire storey of origin Smoke: Smoke staining evident in entire building 6 Burn: Extension of damage to storeys beyond story of origin Smoke: Heavy smoke staining throughout building Burn: Entire building significantly damaged with damage to adjacent building or spatially 7 separated building Smoke: Heavy throughout building with staining to adjacent building or spatially separated structure 8 Burn: Multi building damage with collapse of structure of origin Smoke: Heavy smoke to building of fire origin and adjacent building "Concealed" 1 Burn: Damage limited to item first ignited Smoke: Light smoke staining to concealed space boundaries 2 Burn: Damage limited to item first ignited and adjacent building component Smoke: Heavy smoke staining to concealed space Burn: Burn damage to most of the lining materials in concealed space 3 Smoke: Heavy smoke staining to concealed space ad light smoke staining to adjacent concealed spaces or rooms Burn: Burn damage to most of the lining materials in concealed space and damage to adjacent 4 concealed spaces/rooms Smoke: Heavy smoke staining to concealed space and adjacent concealed spaces, medium smoke staining to adjacent rooms 5 Burn: Damage to concealed spaces on multiple levels with extension to rooms Smoke: Smoke damage to multiple levels and extension to rooms

6 "Exterior" Burn: 1 Smoke: Burn: 2 Smoke: Burn: 3 Smoke: Burn: 4 Smoke: Damage limited to item first ignited Light smoke staining to adjacent items Damage limited to item first ignited and adjacent building component Smoke staining to adjacent building component Burn damage to multiple levels or to roof level of building exterior Heavy smoke staining to exterior wall Burn damage to exterior wall with extension to interior room or roof Heavy smoke staining to exterior wall and extension to interior room or roof space The fire damage indices are intended to characterize the level of fire damage without requiring extensive analysis to quantify the degree of damage in isolation. Since the damage indices are qualitative and not absolute, their application may require some degree of interpretation and results vary as a function of the individual using them. To reduce this variance, the damage indices are applied to each fire incident by two individuals in isolation and where the index assigned for an incident differs between the two individuals, a review is performed to determine the source of discrepancy and the indexing system is revised accordingly if possible. RESULTS The 120 apartment fire incidents were examined based on the fire damage index framework outlined above, indicating the following relative to the effectiveness of the acceptable solution requirements in achieving the objectives of the Building Code: 90 percent of the fires originating in fire rated compartments, regardless of building size and construction type, were contained to the compartment of origin (i.e., damage index of 3 or less). The remaining 10% had spread beyond the fire rated compartment to adjacent compartments or the exterior of the building as a result of unintended human intervention and exterior openings. 44 percent of fires originating in concealed spaces were contained to the space of origin. The remaining 56 percent spread to adjacent concealed spaces or compartments through membrane failure or inadequate fire stopping/blocking. 8 percent of exterior fires were limited to a single storey of exterior damage. The remaining 92 percent of fires spread to involve more than 1 storey, but in many cases resulted in significant damage to the entire roof of the building. This occurred as a result of combustible content on exterior balconies, combustible exterior cladding, combustible and open soffits, and combustible unsprinklered concealed roof spaces. This information on fire containment and propagation from one environment to another is summarized in Figure 1, and provides a good indication of which aspects of the building design for a residential occupancy are effective at preventing fire spread and which require improvement relative to the objectives of the Building Code. The extent of damage increased as a function of originating environment with fires originating in fire rated compartments resulting in the least damage to fires originating on building exteriors resulting in the greatest damage. One of the key results of the analysis was that fire-rated compartments perform as intended by the Building Code, limiting the growth and spread of fire to the compartment of origin regardless of

7 building size or structure construction type. In some cases fire was observed to spread to firewall separated buildings, but primarily where: fire stopping was not installed or where the building did not otherwise comply with the acceptable solution requirements, or the roof became fully involved as a result of spread from the building exterior. In all of the fires reviewed, fire spread to spatially separated buildings either did not occur or was limited to radiant heat damage to the exterior façade with no extension to the interior of the building. Figure 1: Analysis results from the proposed framework. 25 Compartment Concealed Exterior Number of Fires Compartment Concealed Exterior Building Code Objective 57% 43% 5 0 Increasing Damage FIRE LOSS STATISTICS COMPARISON The fire loss database from the Fire Commissioner s Office in British Columbia was provided to assist the evaluation of the current framework for data collection by the public system. A fire incident common to the Fire Commissioner dataset and the set of 120 fires was examined to illustrate the limits of the framework by which the Fire Commissioner data is collected. The fire loss incident selected for comparison is a three storey apartment building of wood frame construction. The information in the public database for the sample incident is extracted for the four areas of interest addressed by the proposed framework and compared. The information is summarized in Table 2.

8 2. Current and Proposed Fire Data Comparison. Key Building Characteristics Current Data Proposed Data Year of Construction Occupancy Residential Residential Building Height 4 storeys 3 storeys with basement Building Area m 2 Approx. 553 m 2 Hazard Contribution Construction Type Protected combustible construction Combustible construction Interior Finish - Noncombustible Contents in Compartment - Index 3 - Average furniture and contents Occupant Load of Compartment 20 1 Fire Protection Features Compartmentation - Floor assembly 45 min. FRR Roof assembly 45 min. FRR Public corridor 45 min. FRR Service shaft 45 min. FRR Fire Alarm System Fire alarm system local Activation not reported Sprinklers No sprinkler protection Not installed Fire Development Ignition Source Not Determined Appliance failure or smoking materials Level of Fire Origin 4 th Storey 3 rd Storey Initial Fire Environment - Compartment Environment of Dominant Fire - Compartment Damage Extent of Fire and Damage Confined to building of origin Index 6 for Compartment Fire damage to the entire floor with some damage to upper floor and structural failure. Index 4 for Exterior Burn damage to exterior wall with extension to interior room or roof. The sample incident was a fire that initiated in the vicinity of the kitchen and propagated throughout the floor, to the exterior, and into the roof space. The above example illustrates that the framework for the current data collection system provides only limited information for the fire development relative to its associated environment. The data does not provide any indication of the extent of fire damage that resulted. The information provided by the current method could be applicable to a compartment, concealed space, or exterior fire ranging in magnitude. This example demonstrates only one aspect of the gap in the information collected for fire incidents.

9 Figure 2: Exterior of building during the fire. Figure 3: Exterior of building after suppression.

10 Figure 4: Fire damage to the compartment. CONCLUSION The fire loss statistics collected within the current framework used by the public sector is difficult to interpret and accurately assess in a manner that can inform on defining appropriate design criteria in the Building Code. A proposed framework for collecting fire loss statistics outlined in this paper focuses on key building characteristics, hazard contributing factors, fire protection features, and fire development in a manner that is more reflective of building code objectives. Application of the proposed framework on a sample set of residential apartment fire data, collected over a period of ten years, provided insight on the effectiveness of the acceptable solution requirements in achieving their objective. This information will permit a more detailed evaluation of the fire protection provisions in place to permit revision and advancement of the Building Code based on the risk associated with the key building characteristics. The current framework for fire loss statistics includes a substantial amount of information; however, the information that specifically relates back to the building design criteria is limited. It is recognized that expanding the forms for data collecting purposes may not be practical; therefore, the intent of the proposed framework is not to substantially increase the effort required for data collection but to modify the information currently being collected to improve its applicability in the Building Code development process. ACKNOWLEDGEMENT The authors thank the Fire Commissioner s Office of British Columbia for providing their database to assist the evaluation of the current fire loss data collection framework and development of the proposed framework. REFERENCES 1 National Building Code of Canada 2010.