Fire Hazard in Buildings: Review, Assessment and Strategies for Improving Fire Safety
The current fire protection measures in buildings do not account for all contemporary fire hazard issues, which has made fire safety a growing concern. Therefore, this paper aims to present a critical review of current fire protection measures and their applicability to address current challenges relating to fire hazards in buildings.
To overcome fire hazards in buildings, impact of fire hazards is also reviewed to set the context for fire protection measures. Based on the review, an integrated framework for mitigation of fire hazards is proposed. The proposed framework involves enhancement of fire safety in four key areas: fire protection features in buildings, regulation and enforcement, consumer awareness and technology and resources advancement. Detailed strategies on improving fire safety in buildings in these four key areas are presented, and future research and training needs are identified.
Current fire protection measures lead to an unquantified level of fire safety in buildings, provide minimal strategies to mitigate fire hazard and do not account for contemporary fire hazard issues. Implementing key measures that include reliable fire protection systems, proper regulation and enforcement of building code provisions, enhancement of public awareness and proper use of technology and resources is key to mitigating fire hazard in buildings. Major research and training required to improve fire safety in buildings include developing cost-effective fire suppression systems and rational fire design approaches, characterizing new materials and developing performance-based codes.
The proposed framework encompasses both prevention and management of fire hazard. To demonstrate the applicability of this framework in improving fire safety in buildings, major limitations of current fire protection measures are identified, and detailed strategies are provided to address these limitations using proposed fire safety framework.
Fire represents a severe hazard in both developing and developed countries and poses significant threat to life, structure, property and environment. The proposed framework has social implications as it addresses some of the current challenges relating to fire hazard in buildings and will enhance overall fire safety.
The novelty of proposed framework lies in encompassing both prevention and management of fire hazard. This is unlike current fire safety improvement strategies, which focus only on improving fire protection features in buildings (i.e. managing impact of fire hazard) using performance-based codes. To demonstrate the applicability of this framework in improving fire safety in buildings, major limitations of current fire protection measures are identified and detailed strategies are provided to address these limitations using proposed fire safety framework. Special emphasis is given to cost-effectiveness of proposed strategies, and research and training needs for further enhancing building fire safety are identified.
Buildings constitute majority of built infrastructure and play a pivotal role in socio-economic development of a country. Most of the buildings are designed to last for several decades and provide residential and functional operations to large number of inhabitants throughout their design life. During this long time-span, buildings are subjected to several natural (earthquake, hurricane, tsunamis etc.) and manmade (fire, explosion etc.) hazards which can cause partial or complete collapse of the building, and incapacitation of building operations. Such destruction or incapacitation in the event of a hazard can jeopardize the life safety of inhabitants and can cause significant direct and indirect monetary losses. Hence, buildings are designed to withstand actions from numerous anticipated hazards to ensure life and structural safety during their design life, and fire represents one such extreme hazard that can occur in buildings.
Fire hazard in buildings can be defined as the potential of accidental or intentional fire to threaten life, structural, and property safety in a building. With rapid development across the globe, fire hazard in buildings have undergone significant transformation in terms of severity and versatility and have become a growing concern in recent years. In the past two decades (1993-2015), a total of 86.4 million fire incidents have caused more than one million fire deaths ( Brushlinskyet al., 2017), and total annual loss from global fire hazard accounts for about 1 per cent of the world GDP (Bulletin, 2014) (approximately US$857.9bn [GDP, 2018]). On an average, 3.8 million fires caused 44,300 fire deaths every year in both developed and developing countries across the globe ( Brushlinskyet al., 2017). Between 2010-2014, maximum number of fires (600,000-1,500,000 per year) and the second highest number of fire deaths (1,000-10,000 per year) in the world occurred in a developed country such as USA ( Brushlinskyet al., 2016). Whereas, developing countries such as India and Pakistan suffered highest number of fire causalities (10,000-25,000 per year) and second highest number of fires (100,000-600,000 per year) ( Brushlinskyet al., 2016). Therefore, to mitigate these adverse effects of fire hazard, it is important to provide necessary fire safety in buildings.
Fire safety can be defined as the set of practices to prevent or avert occurrence of fire and manage growth and effects of accidental or intentional fires while keeping resulting losses to an acceptable level. Currently, fire safety in buildings is provided through following provisions recommended by building codes of practice. While specifications and strategies for ensuring fire safety in buildings vary from one code of practice to other, most of them are based on prescriptive based approach and are derived from similar fire safety principles. In prescriptive based approaches, fire safety in buildings is provided using a combination of active and passive fire protection systems. Active fire protection systems (sprinklers, heat and smoke detectors etc.) are designed to detect and control or extinguish fire in its initial stage and are more important from life safety perspective. Whereas, passive fire protection systems (structural and non-structural building components) are designed to ensure structural stability during fire exposure and to contain fire spread. Their main goal is to allow ample time for firefighting and rescue operations, and to minimize monetary losses.
This traditional approach of ensuring fire safety have several limitations in addressing contemporary fire hazard challenges (discussed in detail in Section 4) and provide limited guidelines on prevention of fire hazard itself. Major limitations of active fire protection systems include poor performance and functional reliability, and high cost of installation and maintenance -which often becomes a big concern in developing countries with limited monetary resources. On the other hand, passive fire protection focusses on fire performance of individual structural members and building components instead of holistic fire safety in building; which leads to an unquantified fire safety in building. Moreover, prescriptive approach of ensuring fire safety is not well integrated with actual building design process, and often fire design is done with the main goal of obtaining approval from fire safety regulatory bodies ( Maluket al., 2017). Therefore, in developing countries with poor regulation and enforcement environments, often no or inadequate fire safety provisions are provided in buildings.
To address these challenges, this study proposes a new integrated framework (see Figure 1) of fire protection features in buildings, regulation and enforcement, consumer awareness, and technology and resources advancement to improve fire safety in buildings. Unlike current fire safety improvement strategies, which focus only on improving fire protection features in buildings (i.e. managing impact of fire hazard), the novelty of proposed framework lies in encompassing both prevention and management of fire hazard. To demonstrate the applicability of this framework in improving fire safety in buildings, major limitations of current fire protection measures are identified, and detailed strategies are provided to address these limitations using proposed fire safety framework.Special emphasis is given to cost-effectiveness of proposed strategies, and research and training needs to further enhance building fire safety are identified.
- Impact of fire hazard
Buildings contain several direct and indirect sources that contribute to fire hazard; and in the event of a fire there is significant risk to life, structure, property and environment from the initial development stages of fire itself.
2.1 Sources of fire hazard
Fire hazard constitute of all factors present in a building that can cause ignition (start fire), aggravate fire severity, incapacitate building fire safety provisions, and hinder escape or firefighting operations. Based on available statistics it is suggested that cooking is the leading cause of fire in both residential and non-residential buildings (USFA, 2016). Other sources of ignition in buildings include all live flames, heaters and hot surfaces, electrical malfunction, fireworks, and arson and vandalism. After ignition, fire severity can be aggravated by several factors such as large quantity of combustible household materials; improper storage of tools, rubbish, equipment, and volatile flammable materials (liquid petroleum gas, paints, ammunition etc.); materials producing toxic smoke on combustion; and combustible building components such as composite panels and timber. Also, use of open architecture (glass partitions, false ceiling etc.), large windows, and poor fire compartmentation design can cause rapid fire growth and spread by providing constant supply of oxygen to fire. All of the factors discussed above have a direct impact on starting fire or increasing its severity, and a comprehensive review of all such factors can be found in the literature (Buchanan and Abu, 2017; Drysdale, 2011).
On the other hand, fire safety in building can be threatened by indirect factors as well; which can incapacitate building fire protection measures, and hinder fire escape and firefighting operations. Some of these factors include poor regulation and enforcement of building codes (no or inadequate fire safety provisions in buildings), lack of common and civic sense (disabling or not using smoke detectors, ignoring fire alarm, vandalism etc.), lack of resources for maintenance of active fire systems (insufficient water for sprinklers, expired fire extinguishers etc.), and damage to fire safety provisions from other hazards (earthquakes, hurricanes etc.). These factors can lead to insufficient fire safety provisions within a building and significantly increase risk to life, structural, and property safety in the event of a fire; thus, contribute to fire hazard.
Another source of fire hazard, especially in populated areas close to wildlands, is one arising from forest fires (wildfires). Due to increase in human encroachment on the wildland urban interface, number of buildings and people living in the fire prone wildland is increasing significantly in recent years. This has made wildfires (resulting primarily from arson and lightning) a major source of fire hazard in wildland urban areas across the globe. In USA alone, an average of 66,903 wildfires occurred every between 2009-2018 which burned an average of 6.9 million acres and caused an average of US$1.8bn for firefighting costs (NICC, 2018; Cost, 2018). In 2018, a total of 25,790 structures were destroyed by wildfires including 18,137 residences, 6,927 minor structures, and 229 commercial/mixed residential structures; which is highest number of structures lost to wildfires since 1999, and almost double of previous highest of 12,306 in 2017 (NICC, 2018). In Canada, about 8,000 wildfires occur every year and are responsible for burning of 6.1 million acres per year (CWFIS, 2018). Similar trends in building fire hazard from wildfires can be found across the globe as well.
2.2 Development of building fire
The full uninterrupted development process of a building fire inside a typical room is illustrated in Figure 2 through temperature-time evolution. The temperature-time evolution depends on a wide range of variables (fuel load, ventilation, compartmentation characteristics etc.), therefore, there is significant variation in fire dynamics of each fire. A comprehensive discussion on fire development and its characterization can be found elsewhere in the literature (Buchanan and Abu, 2017). In general, growth of fire in a compartment is categorized into two distinct phases; namely pre-flashover fires and post-flashover fires (Figure 2). In pre-flashover phase, the duration from smoldering (flameless combustion) to ignition (combustion with flames) is defined as incipient stage, and duration from ignition to flashover (rapid increase in temperatures) is defined as growth stage of fire. Whereas, in post flashover phase, duration for which temperatures keep increasing from combustion is defined as burning stage, and subsequent cooling is defined as decay stage of fire. Pre-flashover phase is important from life safety perspective, and post-flashover phase is important from structural safety perspective. Detailed impact of fire hazard in pre and post-flashover phases is discussed below.
2.3 Impact on life safety
There is significant risk to life safety in both pre and post-flashover phases of building fires, and on an average about 44,300 fire deaths have occurred every year between 1993 and 2015 ( Brushlinskyet al., 2017). During pre-flashover phase of fire, combustion generates several toxic gases which are extremely deleterious to humans and inhalation (even in small quantities) can be fatal within minutes (Nelson, 1998; Alarie, 2002). Most common among these are carbon monoxide (generated from incomplete combustion), hydrogen cyanide (generated from burning plastics), and phosgene gas (generated from burning vinyl-based household materials). The smoke generated from combustion also contains small soot particles and toxic vapor which can cause irritation to eyes and digestive system. It is due to this high toxicity of smoke (toxic gases, soot particles and vapor) that more fire deaths occur from smoke than burning itself (NFPA, 2018). Also, smoke and hot gases obscure and hinder escape routes from building during fire, which further increases risk to life safety from inhalation of toxic gases and burning.
Other threats to life safety are from reducing oxygen levels in room from combustion and inhaling hot air. Humans undergo impaired judgement and coordination when oxygen levels in room fall to 17 per cent from normal 21 per cent; headache, dizziness, nausea, and fatigue at 12 per cent; unconsciousness at 9 per cent; and respiratory arrest, cardiac arrest, and even death when oxygen levels fall to 6 per cent (NFPA, 2018). Also, inhaling hot gases can burn respiratory tract, and one breath of hot air can even lead to death. During post-flashover phase, the concentration of toxic smoke is very high and fire temperatures are untenable for humans and can lead to certain death, thus, all life safety operations are usually targeted towards pre-flashover phase of fire. Apart from toxic smoke and burning, biggest risk to life safety during post-flashover phase is partial or complete collapse of structure which can inhibit firefighting operations and kill trapped inhabitants under collapsed debris. Therefore, fire represents significant threat to life safety even when it is not fully developed, and every minute is critical in evacuating inhabitants during building fires.
2.4 Impact on structural safety
During fully developed stage, fire temperatures can reach above 1,000°C which can cause significant degradation in strength and stiffness properties of structural materials (concrete, steel, wood, etc.) (Kodur, 2014). This material degradation can incapacitate structural members to carry designed structural loads, and lead to partial or complete collapse of building during or after fire. Also, material degradation has strong potential to cause permanent structural damage which can cause premature failure of building under other natural hazards for which it was originally designed for; thus, endangering structural safety. A detailed review on impact of fire on structural safety can be referred to literature (Buchanan and Abu, 2017).
2.5 Impact on property safety
One of the biggest impact of fire hazard is on property safety and it causes direct and indirect losses of billions of dollars in both developed and developing countries across the globe ( Brushlinskyet al., 2017). Even if building withstands fire without life losses, aftermath of almost every fire involves monetary losses magnitude of which depends on severity of fire. Direct losses from fire hazard include loss of property from burning, sprinkler operation, firefighting operations (damage to property from water of fire brigade, breaking of doors and windows etc.), falling debris from partial or complete collapse of structure; and structural damage and cost of repair. Whereas, indirect losses include loss of use during time required for repairs, loss from temporary or permanent relocation, loss from demolishing structure, increase in insurance costs, environmental contamination etc.
2.6 Impact on environmental safety
Fire hazard generates several environmental pollutants from combustion, firefighting operations, and spillage from containers of hazardous materials due to damage from fire. Most common fire pollutants include metals, particulates, polycyclic aromatic hydrocarbons, chlorinate dioxins and furans, and brominated dioxins and furans, polychlorinated biphenyls and polyfluorinated compounds ( Martinet al., 2016). During fire, transmission of these pollutants occurs to environment through fire plume (air contamination), from firefighting water runoff (water contamination), and deposited air and water contaminants (land contamination); thus, causing environmental pollution. The magnitude of environmental pollution depends on the exposure duration, transmission medium, and susceptibility of receiving atmospheric, aquatic and terrestrial environments; and a detailed study on effect of fire on environment can be referred to the literature ( Martinet al., 2016).
- Review of current fire protection measures
Most of the current fire protection measures are prescriptive and based on similar fire safety principles. Therefore, these provisions can be grouped under four generic categories as: general strategy for fire safety, building codes and standards, safety provisions within building, and firefighting operations.
3.1 General strategy for fire safety
The first line and foremost strategy to tackle fire hazards is prevention of fire occurrence. Because it is not always possible to prevent fire, impact of fire should be managed by either managing fire itself or by managing exposed persons and the property. The usual strategy for managing persons is to evacuate exposed persons from the building by causing movement of people through a safe fire escape route. For people to evacuate safely, it is important that these requirements are met simultaneously: fire is detected in incipient or growth stage (earlier the better), occupants are notified using fire alarm and a safe fire escape route exists in the building. However, in case of high rise buildings, it is not possible to evacuate people through a safe fire escape passage in the time bound. Therefore, defend-in-place strategy is adopted by providing safe refuge on certain levels of building, which are then evacuated by firefighting department. This allows firefighters to target evacuation operations to these specific refuge areas only and save precious time which can be a factor of life and death in fire situations.
To manage fire and its impact, general strategy is to control the available fuel for combustion and use suppression by using various fire protection features installed in a building. Many building codes and standards specify a permissible limit of the available fuel load in a building (given as energy floor density in MJ/m2), so that in case of ignition, fire growth is controlled by limited fuel supply. The fire severity corresponding to this limited fuel load is taken into consideration in the building design to withstand this certain level of fire severity. Therefore, the limit on the available combustible fuel load inside a building is dependent on the fire resistance requirement of the building and vice versa.
The other effective method of controlling fire is through suppression using automated or manual fire protection provisions. In case of automatic fire suppression systems, it is essential that both fire detection equipment and fire suppression equipment work simultaneously. The automatic provisions for fire suppression include automated sprinklers, condensed aerosol fire suppression systems, and gaseous fire suppression systems. On the other hand, manual fire suppression refers to manual fire extinguisher systems or standpipe systems. The suppression of fire depends upon early detection, functional reliability, and performance reliability of fire protection measures.
The last defense (for controlling fire and to manage its impact) is through compartmentation and structural stability. The structural stability is important as it helps in localizing fire, allows the firefighting operations to continue safely and prevent property losses arising from total collapse of structure. To ensure structural stability, it is important to control the fire spread inside building and to keep it to a localized zone only. This can be achieved by using fire compartmentation which contains the fire to a local area only and does not allow further movement of fire inside the building. Another possibility for controlling fire movement is by using fire venting which provides increased ventilation to fire affected zone only and exhausts the available fuel.