S. Doroudiani and B. Doroudiani,     University of Toronto, Canada

Z. Doroudiani,     Building Housing Research Centre, Iran

9.1 Introduction

Fire has always been a major hazard to cities, buildings and transport facilities through accidents, arson or war. There have been numerous fires throughout history that resulted in many casualties and great damage. Notable among these were the great fires of Rome (64), Amsterdam (1452), London (1666), New York (1776), Toronto (1849, 1904 and 1940), San Francisco (1906), Tokyo (1923) and many other major cities on several occasions, with thousands dead and numerous buildings and infrastructures destroyed (Arnold, 2005).

The primary causes of home fires are cooking (40%), heating systems (18%) and intentional (8%) (Diekman et al., 2011). In 2008, approximately 54,500 people suffered fatal unintentional injuries in homes in the USA, in which fire events were the third leading cause of these deaths. During the period 2003–2007, more than 1000 home fires were reported each day. These home fires resulted in a civilian injury every 40 minutes and a civilian death about every three hours (Ahrens, 2010).

Fire protection and behaviour of materials used in construction have long been a serious concern. People spend most of their time inside buildings; therefore, buildings play a crucial role in their safety and lifestyle. In spite of significant progress in the science and technology of materials, we still observe that in the event of fire, buildings or vehicles often burn to the end with huge damage.

An estimated 1800 fatal residential building fires are reported to US fire departments each year, causing an estimated 4000 deaths, 25,000 injuries, and $196 million in property loss (Karter, 2003). According to the figures published by World Fire Statistics (Woodrow, 2010), the direct cost of fire, about 1% of GDP in most developed countries, has received much less attention than the cost of crime and road accidents. The fire deaths figures (deaths only in buildings, excluding firefighters and deaths in hospital) in the past decade show a decreasing trend. The figures for deaths in fire range from 1.2 people per million population in Singapore to 19.3 in Finland. Fume toxicity has been found to be the most critical factor for fatal casualties in building fires (Gann et al., 1994). The heat and flames from fires are obvious risks; however, the effect of toxic smoke may actually be the greatest danger in fire (Richardson, 2007). Approximately half of the fatalities and a third of all injuries in buildings fires are caused by exposure to toxic products and fumes (Purser, 2002). With improved building design, materials quality and better regulations, the fire death rate in the USA fell by 46.3%, from 36.3 fire deaths per million population in 1979 to 19.5 fire deaths per million population in 1992 (FEMA, 1997).

Fire is a chemical reaction in which a material reacts with an oxidant and releases heat. Fuel, an oxidizer, and an ignition source are three essential elements for combustion. Fire is rapid oxidation of ignited materials, which always occurs in the vapour phase. The high temperature of fire thermally decomposes the materials and converts them to vapours before burning. The presence of all three elements is necessary in order for burning to happen. Fire is an exothermic (heat-producing) and irreversible process involving flame, heat and oxygen depletion, and releasing fumes, toxic gases and light energy. Despite the fatal incidents in fire, a larger number of people experience non-fatal fire injuries, including various degrees of burns and internal (lung) damage. According to some studies (Zhang, 2004), about 20% of those who die in airplane crashes are killed by fire, most often because several polymers that are used in seat fabrics, overhead bins, wall and windows will burn, leaving passengers limited time to escape.

Smoke is a mixture of various combustion products of gases, vapours and aerosols. Smoke properties are the particle yield and size, and the type and amount of toxic gases adsorbed on the particulate. Factors affecting smoke transport allow one to estimate the smoke exposure of a person at a target location in a building and to give information about the distribution of the smoke in different places in the building (Butler & Mulholland, 2004).

The chain reactions between combustible substances and the oxidizing agent during combustion complete the conditions of a sustainable fire. Oxygen is the most common oxidizing agent present in fire events, constituting approximately 21% of the air and being available everywhere. Oxygen plays a major role in the spread of fire. In general, when the concentration of oxygen in the air reduces to less than 10%, combustion with flame will fade away (Mahoney et al., 2007). Smouldering, the combustion process without flame, might take place at oxygen concentrations of less than 10%. Fire can be ignited by various sources of thermal energy: mechanical, chemical, electrical, biological and nuclear (Martin & Pepler, 2000). Ordinary individuals may be exposed to fire by chance, but fire fighters and emergency personnel are always in contact with fire products.

Many different materials are used in the construction of buildings. In general, they can be classified as inorganic and organic based materials. Inorganic materials, such as concrete, glass, and metals, are usually nonflammable and do not burn but require special design considerations (Levesque, 2006; Phan & Carino, 2000). However, organic materials, like polymers and wood products, are mostly flammable and burn readily in air. The flammability of organic materials and polymers is a serious concern and rigorously limits their applications. Recent fire safety concerns put more stringent requirements for the materials used in enclosed and escape-proof areas, such as electronic enclosures, high-rise buildings, submarines, ships, and aircraft cabins.

The toxicity of fumes generated in fire has been studied for more than six decades (Zapp, 1951). Toxicity is a property that affects organisms. Toxic hazard is the chance of damage to organisms based on exposure resulting from usage and transport of substances. Although the toxicity of substances cannot be changed, the toxic hazard of a substance can be reduced by application of appropriate methods (Crowl & Louvar, 2002).

After the toxic substance enters the body, it moves into the bloodstream. It may be eliminated from the body or transported to the target organ, where the damage is done. The toxic substance may enter the body in various ways. When exposed to toxic fire fumes, entry to the body can be controlled by application of methods and equipment, like using masks. Ventilation, proper masks and other means of personal protection can be used to control entry of fumes by inhalation through the mouth and nose. The respiratory system plays an important role in the entry of toxic substances through inhalation in fire events. The main function of the respiratory system is to exchange oxygen and CO₂ between blood and the inhaled air. A normal person at rest uses about 250 millilitres of oxygen and expels approximately 200 millilitres of CO₂ in one minute. The need for oxygen significantly increases with physical activity (Davies & Moores, 2010).

Toxic substances are classified and compared for relative toxicity based on their LD₅₀ values (Lethality Dose 50), which is the dose that results in 50% lethality (Derelanko & Hollinger, 2002). Other values, like LD₁₀ or LD₉₀, are also reported for substances. Another value representing toxicity, commonly used for gases, is LC (Lethal Concentration). Threshold limit values (TLV) of toxicants evaluate the lowest value below which the body can detoxify and eliminate the toxic agent without any detectable adverse effects. There are three types of TLVs. Time-weighted average TLV (TLV-TWA) represents what people can be exposed to for a normal working day without adverse effects (Derelanko & Hollinger, 2002).

Concrete provides the best fire resistance of building materials and does not burn. It does not emit any toxic fumes, smoke or drip molten particles when exposed to fire. This excellent fire performance is mainly because of its constituent materials that, when chemically combined, form a material that is essentially inert and has good thermal insulation. The slow rate of heat transfer enables concrete to act as an effective fire shield not only between adjacent spaces but also to protect itself from fire damage (Milner, 2007).

The chance of incapacitation and lethality from the inhalation of toxic gases was studied and a mathematical model for estimating the lethality was presented (Stuhmiller & Stuhmiller, 2005). The model finds an internal dose that is used to extrapolate results across species. The internal dose is correlated with each result that allows estimating the tolerances of any population incidence. The model compares favourably to the combined gas and large animal data.

The present knowledge about the relationships between materials and fire is insufficient and research should be focused on fundamental studies. New and more reliable experimental techniques to characterize the thermal decomposition and flammability of materials need to be developed and relationships between materials structure, composition and their macroscopic flammability should be established. Moreover, we need to have better understanding about the effects of various flame-retardant additives on material flammability and the toxicity of fumes. A deep knowledge about the mechanisms of the thermal decomposition and fire resistance of materials is necessary for improving the safety of buildings. Knowledge about the health effects of fire is insufficient and more research on the effects of fire fumes on the organs and on the toxicity level of building materials is necessary.

9.2 Fire behaviour of building materials

In this section, building materials, their combustibility and behaviour in fire and the chemical composition of toxic fumes and particles they release are reviewed. A correlation between polymer structure, material composition and flammability is established and experimental techniques to characterize the thermal decomposition and flammability of polymers are discussed.

A large number of researches have been conducted on the flammability of polymers. All flammable materials have minimum ignition energy (MIE) values, which is the lowest amount of energy required to initiate combustion. The value of MIE depends on factors including the chemical structure of the material, pressure and temperature. An increase in pressure decreases the MIE value. Methane has an MIE value of 0.28 mJ; therefore, a static discharge of 22 mJ energy generated by walking on a rug can ignite a fire in an atmosphere containing methane (Glassman & Yetter, 2008). Many fire incidents are initiated because of the heat produced from slow oxidation of materials (autoxidation). Materials such as oils and cottons are susceptible to oxidation when stored in warm and humid storage rooms.

Fire behaviour of materials is a critical factor in their selection. The materials selected for use in the building must obey certain standards of fire performance appropriate for the application. The fire performance of materials is determined through flammability tests. When exposed to heat, materials are thermally degraded, mainly in three ways: oxidative pyrolysis, anaerobic pyrolysis and combustion with flame. Most fire events occur in aerobic conditions. Many materials, particularly polymers, thermally degrade below 400 °C and release flammable gases, and likely toxic compounds.

The ratio of the heat release and the time response parameters (HRP/ TRP) provides an estimation of how fast fire would spread on a material. A combination of the HRP, TRP and heat flux values is related to the flame spread behaviour of materials and is expressed as the fire propagation index (FPI). These properties and parameters are taken from the flammability diagrams.

Light and high-performance organic materials offer many advantages in buildings over conventional metal and ceramic materials, but they greatly increase the fire risk because of their flammability and potential release of toxic fumes. Polymers, because of their versatility, ease of forming and good performance to cost ratio, have grown into many applications, including building materials. However, their high flammability greatly increases fire risk, particularly in buildings.

Chemical structures of polymers mainly consist of carbon and hydrogen atoms that make them combustible. Many polymers, when subjected to some ignition sources, will undergo self-sustained combustion in air. Chemical reactions may take place in three interdependent regions: within the condensed phase, at the interface between the condensed phase and the gas phase, and in the gas phase.

Polymers can be classified in a variety of ways: as natural or synthetic materials, based on their physical and mechanical properties (elastomers, plastics and fibres), and in terms of their chemical structures. Polymers are often further subdivided into thermoplastics (whose softening at elevated temperature is reversible) and thermosets (which undergo irreversible changes when heated). Polymers behave differently in production of smoke and fume when they burn. All these types of classifications of polymers are useful and, depending on the situation, a particular type may be selected. For instance, classification of polymers based on chemical structure is more useful when dealing with their reactivity and role in chemical reactions. When the response of the polymer to heat is under consideration, the classification of polymers as thermoplastics and thermosets may be selected.

Polymer combustion occurs in a few steps: heating, pyrolysis (decomposition), ignition and combustion. The material is first heated to pyrolysis temperature, producing bubbles and releasing usually combustible gaseous products. On most occasions, the pyrolysis process is necessary for the combustion. Pyrolysis is a chemical reaction that usually occurs in three main mechanisms, producing many products that diffuse into the flame. Some polymers undergo crosslinking reactions during pyrolysis, producing a solid char that does not spread fire. The presence of contaminations, such as oils and water, may direct the pyrolysis to the production of some other substances. For instance, pyrolysis of polyesters in the presence of water directs the process to the hydrolysis reaction and production of oligomers (shorter-chain polymers) (Moldoveanu, 2005).

The fire point (or flame point) of a substance is the lowest temperature at which it produces sufficient amounts of vapours to form an ignitable mixture that will sustain combustion. When a liquid reaches its fire point and is ignited, combustion will be sustained until the material is totally consumed or other extinguishing action is taken (Davletshina, 1998; Davletshina & Cheremisinoff, 1998). If there is an ignition source, the pyrolysis products will undergo combustion in the gas phase and produce more heat. Under steady-state burning conditions, some of the heat is transferred back to the material surface, producing more volatile polymer fragments to sustain the combustion cycle.

Flames are self-propagating combustion reactions in which both the fuel and the oxidant are present in the gas phase. Because the majority of polymers are hydrocarbon based, the flame above burning polymers is usually a hydrocarbon flame. Smoke formation in flames is highly dependent on the structure of the gaseous fuel and on the fuel-to-air ratio. In general, polymers containing purely aliphatic structural units produce relatively little smoke, while polymers with aromatic groups in the main chain produce larger amounts of black smoke (Gallo, 2009).

A variety of physical changes result from pyrolysis, including char development, intumescences, melting and vaporization. Char is a black and porous residue of burning of some organic materials. Thermoplastic polymers tend to soften when exposed to heat and melt without forming char. For example, poly(methyl methacrylate) (PMMA) burns with very little melt and leaves no residue. However, rigid poly(vinyl chloride) (PVC) and polyurethane (PU) foams char when burned. The char layer may act as an insulating barrier between the external heat source and the rest of the material. This will slow the pyrolysis rate unless the external heat flux increases to compensate for the insulating char layer.

Intumescence is defined as the process of swelling up or bubbling up. There are many coatings on the market for fire protection purposes. The intumescent coatings, when heated, expand, similar to the development of a char layer. When the intumescent char layer is formed, a blowing agent is released, creating a low-density, relatively thick carbonaceous layer. As the material expands, the water is released, maintaining the surface temperature. The char can expand to 50 to 100 times the original thickness of the intumescent coating (Troitzsch, 2004).

A large number of toxic compounds are present in fire smoke with a highly variable composition that depends on the composition of the materials and the temperature of the fire. Respiratory irritant compounds (including ammonia, acrolein, SO₂ and formaldehyde), by causing chemical tracheobronchitis, pulmonary oedema, upper airway obstruction, or pneumonia, produce shortage of oxygen supply and hypoxia. The asphyxiant compounds (such as CO₂, methane and CO), by displacing oxygen from the surroundings, cause hypoxia too.

The behaviours of a large number of polymers in flame have been studied (Panagiotou, 2004). When exposed to an external heat flux, the polymer surface begins to produce small bubbles that start to break and release fuel vapour. The burning process continues along the same lines with an increased rate of bubbling. The bubbling covers the entire surface of the sample and resembles a boiling liquid. No residue is left over after burnout. Some polymers (like styrene polymers) produce a lot of soot on burning (see Fig. 9.1).

Furniture is part of the building that makes it more vulnerable to fire and plays a major role in fatal fires. The fire safety aspect of furniture has been studied by several researchers (Sundstrom, 1995, 1996; Fowell, 1994; Krasny et al., 2001). Recently, Shousuo (2006) carried out an in-depth study of fire safety of furniture. Ignitability, flammability of the volatiles, total heat and its release rate, flame spread, smoke obscuration and fume toxicity are the main hazardous factors of fire. Furniture is usually made of polymers, textiles and wood. The fire behaviour of some major materials used in buildings is reviewed below.

9.3 The effects of conditions on the initiation and propagation of fire

The materials and conditions essentially determine the initiation and spread of fire, and the composition of the combustion products. Temperature, pressure, water, oxygen content, and ventilation are major factors affecting fire. As stated, inhalation of toxic fumes is a major cause of death or permanent injury in fire events. The products of the combustion of the materials are highly dependent on the fire conditions; therefore, it is necessary to evaluate the combustion products of the material under various conditions to understand the effects of conditions on the toxicity of the fumes. As the fire develops, the conditions change; the temperature increases, oxygen concentration decreases and the concentrations of combustion products increase.

The toxicity of fire fume depends on both the material and the fire environment and conditions. There are a number of methods to determine the toxicity of fire effluents. These methods yield apparently contradictory information and confusing results (Hull & Paul, 2007). The need for international harmonization of toxicity testing has been emphasized. The fire fume toxicity is essentially determined by CO levels, and to a lesser extent by other toxicants (Purser, 2002), particularly HCN. A chemical kinetics model for calculation of the formation of HCN showed that recycling of the combustion products to the fire increases the formation of HCN and CO, and less ventilated conditions increase the formation of these toxic substances, which is in good agreement with the experimental measurements (Tuovinen et al., 2004).

Fires may occur in various stages and conditions, from smouldering to completely ventilated flaming. In all fires, the combustible gases produced from the thermal decomposition of the materials react with oxygen. Solid fuels are converted to gas, through the pyrolysis process, prior to the combustion reaction. In the smouldering process (similar to glow on charcoal), combustion occurs on the surface of the solid fuel, which needs less oxygen than flame combustion. The fume products comprise complex mixtures of fully oxidized products, such as CO₂, partially oxidized products (for instance CO or aldehydes), fuel or fuel degradation products (such as aliphatic or aromatic hydrocarbons), and other stable gas molecules (like nitrogen and hydrogen halides). Stec et al. (2008) studied the relationships between the ventilation conditions and product yields at different temperatures using online Fourier transform infrared spectroscopy (FTIR) for identification and quantification of the products.

The British Standards Institution has divided fires into a number of stages, from smouldering combustion and partly ventilated flaming through to completely developed under-ventilated flaming (BS, 2003). The flaming stages are strongly dependent on the fuel-to-oxygen ratios, which are controlled by the air supply (Hull et al., 2000). In stoichiometric conditions, the amount of available oxygen equals the required oxygen as fuel for complete combustion. In the event that less oxygen than the stoichiometric amount is available, it is vitiated, and if the available air requirement is exceeded, then the conditions are ventilated. The yields of at least two major toxicants, CO and HCN, are critically dependent on the degree of ventilation. The CO/CO₂ (v/v) ratio in the ventilated conditions has been approximately 0.01, whereas in vitiated conditions the ratio was approximately 0.24 (Blomqvist et al., 2007).

The values of yields obtained from combustion of various polymers have been shown to be highly dependent on the fuel to oxygen ratio and on the nature of the material. It is therefore vital that in any standard method for determination of toxic product yields, the relationships of products yields with the variables affecting the decomposition conditions are established. The PE, PS and nylon 66 results clearly showed similarities in behaviour for yields of CO, HCN and hydrocarbons at various temperatures studied, which were independent of the temperature over the range of 650–850 °C. The combustion behaviour of PVC was different from that of the other polymers, and the toxic product yields for PVC were almost independent of the fire conditions (Stec et al., 2008).

9.4 Health effects and analysis of combustion products

In most countries, pathology information and data from fires are usually not published. There are a large number of substances known to be products of materials combustion, but what substances produced in fire events may be considered toxic? According to Swiss physician and father of toxicology, Paracelsus: ‘All substances are poisons: there is none which is not a poison. The right dose differentiates a poison and a remedy’ (Paracelsus, 1493–1541), in other words, dose makes the poison. Dose is the amount of the substance entering the body.

Smoke inhalation injury is a major effect of fire on human beings, in addition to direct burn, which increases the mortality of patients with thermal injury (Cancio, 2005). Care of patients with smoke inhalation injury, and of patients with similar injuries secondary to the inhalation of toxic industrial chemicals, should be conducted in burn centres with a multidisciplinary, research-oriented focus. In a recent fire event in a residential building under construction (1 May 2011), the fumes produced from burning of the EPS blocks used in the ceilings incapacitated the workers, causing the death of at least six workers (ISNA, May 2011). The images in Fig. 9.1 show thick fume produced from burning of EPS. According to the regulations, only flame-retarded EPS with specific mechanical performance is permissible in buildings. The core EPS must be completely covered and protected by a non-flammable skin, such as cement-based sheets, and the use of open fires in construction sites is strictly prohibited. In the said fire event, regular EPS was used and there had been an open fire in the construction site (BHRC, 2010). Recently, the US Department of Health and Human Services (June 2011) reported a new list of carcinogenic substances, including styrene. Animal studies indicated that styrene caused lung tumours in several strains of mice.

Chemicals are potentially harmful to biological tissues and human health. In the event of fire, significant amounts of substances are produced from materials combustion. The effects of these substances depend mainly on the quantity of the compounds, the time of exposure and the closeness of the exposed organs to the fire. Smoke is considered as an opaque cloud of small, individually invisible particles. Fumes are less opaque forms of smoke. Combustion gases and smoke are different because they can have different effects, and different methods are used for their measurement (Price et al., 2001).

Gases and fumes can easily diffuse into rooms from adjacent exterior space. In the interior space of the building, high airflow and ventilation with an open inside door significantly decreases the dangerous conditions. While high airflow dilutes the concentration of CO gas in the interior space, in the event of fire more airflow extends the flame by making more oxygen available for combustion. Therefore, ventilation plays two contradictory roles in reducing fire casualties.

Trauma, respiratory disease, cardiovascular illness, reproductive hazards, toxic substances, and carcinogenic hazards are some of the important health concerns for people in fire areas, especially firefighters. In fire events, only a minority of deaths and injuries are due to the heat and flames, while many victims die from the effects of poisonous fire effluents (Stefanidou et al., 2008). It has been estimated that more than 50% of fire-related deaths occurring each year in the USA can be attributed to inhalation-related injuries (Locatelli et al., 1994).

The most common source of CN poisoning occurs from exposure to fires (Walsh & Eckstein, 2004). In fire events, CN is produced when the temperature reaches approximately 315 °C and is released from the toxic fumes in gaseous form that may then be inhaled by the victim. HCN is developed from incomplete combustion of any N-containing material, such as polyamides, wool or silk (Gracia & Shepherd, 2004). Cyanide can also be a product of burning of materials without nitrogen. For instance, burning cotton develops 130 μg HCN/g and burning paper makes 1100 μg HCN/g, while burning wool produces 6300 μg HCN/g (Lawson-Smith & Hyldegaard, 2011).

Nitric oxide (NO), as one of the toxic gases in fire events, has a very different toxic effect from that produced by NO₂. Formation of NO and NO₂ in fire fume, their potential toxic effects and the need to reconsider the methods of calculating toxic potency values have been investigated (Paul et al., 2008). The authors recommended that the complex chemical reactions and the toxicity of NO should be studied to improve the accuracy and reliability of the methods used to calculate the toxicity of the fire fumes.

Information about the production of toxic gases is important in order to estimate the time for evacuation in fire events. Quantitative information on toxic gases for an evacuation scenario has been determined in real-scale fire experiments (Blomqvist, 2005). The study showed that the gases produced are the greatest danger and that HCN, in particular, had a major impact on the fire casualties.

Blomqvist (2005) studied some important components that typically are found in fire fumes, including CO, HCN, HCl, polycyclic aromatic hydrocarbons (PAH), furans, isocyanates and particulate matter. PAH and dioxins have important sublethal effects on humans and emissions of these types of compounds are of potential environmental concern. Isocyanates are potent irritants and are known to cause hypersensitivity from exposure, which is of particular concern to firefighters and others who are exposed to fire fumes. The small particles and soot in fire fumes are of concern as they have a tendency to penetrate deep into the lungs.

The total time of exposure to fumes is a key factor on health that must be considered in fire events. Many people are trapped at an early stage of fire by relatively thin smoke, and loss of visibility is often an indirect cause of death.

Exposure to wood smoke is associated with a variety of adverse health effects in humans. However, there is much to learn about the relationship between wood smoke exposure and disease. Most available animal studies indicate that exposure to wood combustion fume results in significant impacts on the respiratory immune system and at high doses can produce long-term or permanent lesions in lung tissues. Wood smoke is also mutagenic and possibly carcinogenic, but less so than coal smoke.

Insufficient information about the toxicological effects of various types of biomass smoke (e.g., smoke from combustion of wood versus agricultural wastes) is available. More work in this area is needed for better understanding the mechanisms by which adverse effects observed in exposed individuals might occur. Because wood smoke is made up of such a large mixture of various substances, it is hard to attempt to accurately assess its health impacts by simply summing the potential effects of individual constituents. Particularly, in high exposure situations with fresh wood smoke, as with occupational exposures or vegetation fire episodes, there may be a need to derive indices of exposure that take into account a range of toxic endpoints because of the wood smoke, for instance including acute acting and chronic toxicants, so that appropriate protective actions can be taken (Naeher et al, 2007).

Fire in buildings usually consists of generation of heat, reduction of available air and production of various substances, including CO. Combustion of materials yields heat, smoke and different amounts and types of toxic agents, such as HCl, HCN, CO_x, SO_x and NO_x. This mainly depends on the flammability of the material and the conditions, such as temperature, ventilation level, and available fuel. Fire-retardant additives may affect the amount and type of fumes released in the fire. Combustion of the materials under poorly ventilated conditions results in less heat and more CO and other toxic products of incomplete combustion.

The toxicity test of the inhaled fumes and compounds consists of measuring the biological response of the subject, which usually falls into three categories: mortality, incapacitance and sensory irritation. CO often acts synergistically with CN and other compounds released through combustion of various materials. Life-threatening complications, such as pulmonary oedema, may suddenly develop up to several days after exposure to the smoke.

Estrellan and Iino (2010) reviewed the toxic emissions from fire and concluded that combustion involving traditional and recreational practices, such as incense burning, firework displays and grilling over charcoal are sources of hazardous emissions. Considerable levels of soot, gaseous PAH, inorganic gases and aldehydes were detected in ambient air in temples burning incense. Fireworks contribute significantly to ambient air metal concentrations during detonation episodes, while charcoal was found to emit mercury and benzene during grilling.

Various analytical techniques are used to evaluate the flammability and to analyse thermal decomposition products of materials. Gas chromatography (GC) and mass spectrometry (MS) are two main techniques that are comprehensively used to analyse the composition of smoke and other fire products (de Hoffmann & Stroobant, 2007; McMaster, 2008). Pyrolysis gas chromatography/mass spectrometry (PGC/MS), simultaneous thermal analysis (STA) and pyrolysis–combustion flow calorimetry (PCFC) are three common methods that need only a very small amount of sample. These methods are efficient screening tools for newly synthesized fire-safe materials. They consist of submitting a sample to GC to separate the components of the mixture based on different properties, such as boiling point and polarity.

Infrared polarization spectroscopy (IRPS) has been used to detect HCl in situ in the combustion test. The method allows one to obtain valuable information that could not be extracted from sampling methods, for instance from GC/MS or FTIR. The method is in the development stage and is predicted to be able to detect toxic gases in the fire fume other than HCl, like HCN, NO₂, and HF (Sun et al., 2011). Moreover, the FTIR technique was used to determine the toxic components of combustion gases in fire events (Hakkarainen et al., 2000; Bulien, 1996; Pottel, 1996).

The fire behaviour of materials has been investigated at bench scale under laboratory conditions, which are somewhat different from the conditions in real fire events. Hull et al. (2008) compared the toxic product yields of burning electric cables in bench and large-scale experiments and found only minor differences in toxic product yield between the methods and conditions of the test.

Toxicity of CO and other toxic gases increases in the presence of CO₂. For inhalation experiments, the concentration of the chemicals in air that kills 50% of the test animals in a given time (usually four hours) is the LC₅₀ value. For instance, the LC₅₀ value of CO as a single gas was measured as 7560 mg/m³, while in the presence of 5% CO₂ the lethal concentration decreased to 4470 mg/m³. For NO₂ gas in the absence and presence of 5% CO₂, the values of LC₅₀ were 376 mg/m³ and 169 mg/m³, respectively (Levin & Kuligowski, 2005).

Flammable furnishing and decorative materials (particularly textiles) are among the main fire hazards in buildings. Textiles, as the first ignited material, cause about 20% of fires of houses in the UK (Horrocks & Price, 2001). These textiles are responsible for about 50% of deaths in these fire events. Toxicity index values (W_LC50) have been introduced as the minimum mass of fabric, in a proportionate volume of air, that produces limiting toxic concentrations of individual gases evolved at various combustions. Analyses of W_LC50 showed that the largest toxic hazard for the majority of the fabrics investigated occurred at 550 °C (emissions of CO and HCN) and at 750 °C (emissions of CO₂ and NO_x). In fabrics containing flame retardants, the toxic hazard created by CO was reduced at 450 °C and 550 °C and increased at 750 °C (Wesolek & Kozlowski, 2002). Products are ranked as very toxic, relatively toxic and moderately toxic when W_LC50 ≤ 15, 15 < W_LC50 ≤ 40, and W_LC50 > 40, respectively.

Liang and Ho (2007) used a toxicity index (TI) to compare the toxic products resulting from four different thermal insulation materials. TI values were then used to evaluate the combustion characteristic of the toxic gas of fibreglass, rock wool, PE foam and PU foam. Figure 9.2 reveals the TI of these building materials.

Most of the knowledge related to the behaviour of materials in fire comes from standards and product examinations. There are only a few compulsory standards that address the toxicity of fumes. While these standards classify the materials and products based on their fire properties, they usually do not include any requirement on combustion products toxicity. Most of the existing studies of fume toxicity have solely relied on data from small-scale physical fire models. It is, however, generally not straightforward to interpret such data in terms of fume composition in real-scale fires. There is generally a lack of quantitative chemical data concerning fire effluents from real-scale fires.

Carbon monoxide (CO), a major source of poisoning deaths in fire events, is colourless, tasteless, odourless and non-irritating; thus, it is hard to detect by an exposed person. When inhaled, CO is readily absorbed from the lungs into the bloodstream, where it forms COHb, a tight but slowly reversible complex with haemoglobin. The presence of COHb in the blood decreases the oxygen-carrying capacity, reducing the availability of oxygen to body tissues and resulting in tissue hypoxia. A reduction in oxygen delivery, because of the elevated COHb level, will potentially impair the cellular oxidative metabolism (Doroudiani & Omidian, 2010; Raub et al., 2000).

Sulphur oxides (SO_x) are produced during the burning of wool and other sulphur-containing materials, such as S-vulcanized rubbers. SO₂ is a moderate to strong acidic irritant. Most of the inhaled SO₂ only penetrates as far as the nose and throat, with minimal amounts reaching the lungs unless the person is breathing heavily or breathing only through the mouth or the concentration of SO₂ is high. The liver metabolizes SO₂ via a molybdenum-dependent SO_x pathway. The subsequent metabolites, sulphate esters and sulphate, are eliminated through the urine (Miller, 2004).

Clinical examinations of individuals rescued from fire events have provided valuable information. Firefighters are usually exposed to various kinds of toxic fumes; therefore, useful information can be found through their clinical examination and biochemical measurements. In clinical examinations, the delay between the initial exposure to the fire fumes and the clinical examination significantly affects the results. The concentrations of most toxicants in blood decrease rapidly at the beginning and gradually level up (Zikiria et al., 1976).

The degree of toxicity depends on the phase of burning of the fire, including oxidative pre-ignition, flaming combustion or fully developed combustion, and the level of the ventilation. Smoke toxicity plays an important role during fire events in buildings, where the majority of people die from smoke inhalation. Lestari et al. (2006) have studied an alternative method for in vitro fume toxicity assessment of materials using human lung cells, which can be used to screen the toxicity of materials and select the appropriate materials.

A range of building materials, including PE, PP, PC, PMMA, PVC, FRP, and melamine–plywood laminates (MPL) were examined. The results revealed that fume from PVC combustion was the most toxic, followed in toxicity by the combustion fumes from PE, PP, FRP, PC, PMMA, and MFP. Some materials exhibited more toxicity under flaming combustion (PP, PC, and FRP), while others (PVC, PMMA, PE, and MPL) appeared to be more toxic under non-flaming combustion (Lestari et al., 2011).

Research results have revealed that both styrene and styrene oxide, products of PS thermal degradation, are toxic substances (Vainio et al., 1977). The effects of styrene on the variation of apoptotic proteins and gene expression in the cord blood cells were studied to understand the toxicological mechanism (Diodovich et al., 2004). The findings supported the classification of styrene as a group 2B carcinogen to humans (possibly carcinogenic) by the International Agency for Research on Cancer (IARC).

Fire hazard and risk analyses establish the basis for providing useful information, including about the people who are more sensitive to fire smoke than others. In an interesting piece of research, Gann (2004) developed a method to estimate the safety conditions, to translate the database on lethal and incapacitating exposures for rats to the incapacitation of human beings. In another study, a mathematical model to estimate the chance of incapacitation and lethality from the inhalation of toxic gases was presented, comparing favourably to the combined gas and large animal data (Stuhmiller et al., 2006).

Most toxic smoke fatalities are found in areas remote from the fire epicentre (Gann et al., 1994). The results of the combustion examination of materials and the toxicity of the fumes are usually considered at locations immediately adjacent to the fire source. It is useful and necessary to estimate the concentrations of the gaseous fire products in areas far from the fire source. Various toxicity models to predict toxic gas concentrations within fire enclosures have been developed (Lattimer et al., 2005; Hyde, 2000; Wang et al., 2011a).

CO and HCN are found in the fumes of burning materials containing nitrogen, like wool, PU and polyamides. Correlations between the yields of CO and HCN resulting from the combustion of N-containing materials have been formulated, and are in good agreement with the corresponding measured data (Wang et al., 2011b). The relationship is useful in fire engineering assessments of toxicity in which only one of the two species, CO or HCN, is measured in the fire experiments.

The amount of atmospheric HCl produced from the combustion of some materials tends to decay because of mixing with the fresh air and absorption by surrounding solids. A model has been developed to describe and predict the HCl decay trend (Wang et al., 2007b). HCl is released from burning PVC as a dense white smoke, followed by dense soot with a very high CO content (Caldwell & Alarie, 1991). It is a much more potent and a faster incapacitating chemical than CO but less potent than HCN (Alarie, 2002).

Polymeric foams and non-woven fabrics are widely used as insulators in buildings and appliances. The toxicity of various kinds of insulation materials has been investigated (Liang & Ho, 2007). The toxicity indices of the examined materials were found to be in the range 5.386–18.239, and ranked as PE (18.239) > PU (12.35) > rock wool (6.949) > fibreglass (5.386). It appeared that the toxicity of these materials was greater than those of the untreated wood and the organic foams, like PE and PU foams, which did not meet the requirements of the low fire hazard material. The relationships between exposure concentration, death, LT₅₀, and COHb or blood cyanide concentrations are summarized in Table 9.1 (Alarie, 2002).

The respiratory system plays a major role in injuries during fire. The system consists of upper and lower parts. The functions of the upper part, consisting of the nose, sinuses, mouth, pharynx, larynx (voice box) and trachea (windpipe), are filtering, heating, and humidifying the inhaled air (NIH, 2011; Rogers, 2010). Toxic substances are treated differently in the upper and lower parts of the respiratory system. Water-soluble toxic substances in the fume usually affect the upper respiratory tract by reacting or dissolving to form acids or bases. Some toxic substances affect the lower respiratory system by blocking the transfer of fumes or reacting to produce other corrosive and toxic agents. The lower part of the respiratory tract is mainly affected by organic agents (such as halides, monomers, phosgene and methyl cyanide), dusts (silica, asbestos) and soot produced in fire.

Dusts, depending on their particle size, can penetrate to different parts of the respiratory system; the smaller particles can penetrate further and deeper into the system. In general, particles larger than 5 micrometres are filtered in the upper respiratory system and smaller ones can reach bronchial and alveolar areas. The alveoli are small air sacs, consisting of small capillaries, where gas is exchanged with blood (NIH, 2011).

Van Belle et al. (2010) investigated the health risk of fumes emitted from burning polyamide chairs when fire broke out on a grandstand in a stadium. The authors identified HCN, CO, NO_x, NH₃, and volatile organic substances among the emitted compounds. Simulation of the fire under controlled laboratory conditions confirmed the emission of a wide variety of substances in the fume. In the simulation, the concentrations of CO and NO_x were found to be high, while emissions of HCN and NH₃ were less than expected.

The effects of toxicants on body organisms may be reversible or irreversible (Derelanko & Hollinger, 2002). They may also be local or systemic and could be immediate or delayed. Some effects, like dermatoxicity, could be reversible and recoverable (Crowl & Louvar, 2002). Toxic substances that cause cancer, chromosome damage and birth defects are irreversible. In this regard, the chemical composition of fume is very important; therefore, when exposed to fumes, the physical state and composition of the fume should be identified.

Carson (1988) developed a method for measuring the effects of inhaling the fumes from burning plastics on the lungs. The products of burning materials in fire also include solid particles, in addition to gaseous products, which, depending on their amount and size, may carry a health risk. The maximum quantities of particles were found to come from materials that did not burn well (for example FRP, PS, PVC and flame-retarded materials), while well-burning materials, like wood, tend to fully oxidize and thus minimize the amount of particles in the fire fume (Hertzberg & Blomqvist, 2003). Very small fibrous particles resembling asbestos could be produced from underventilated combustion of composite materials. It is possible to inhale particles having a diameter of less than 10 μm; the smaller the particle, the less probable it is that the defence system of the body (nose and throat) can prevent the material from reaching deep into the lungs (Fig. 9.3).

In addition to the toxicity of the combustion products, the emotional conditions (stress) and other factors of human behaviour play a crucial role in the health effects of fire events. Studies from the World Trade Center incidents in New York in 1993 and, particularly, the 11 September 2001 disaster revealed the importance of human factors in fire events (Kobes et al., 2010). Stress has a significant effect on the lethality of toxic substances of combustion fume (Larsen et al., 2000).

9.5 Remedial actions

In this section, improvements in fire safety of materials and remedial actions in terms of combustion toxicity are discussed. Minimizing use of materials with significant health risk in fire and replacing them with alternative materials, fire-resistant materials and flame-retardant additives are reviewed. Understanding the effects of various flame-retardant additives on polymer flammability and on combustion products are crucial issues that will be addressed.

Therapeutic measures of intoxication by CO and other toxic fume gases include general supportive care as well as the treatment of burns and related toxicity. Arterial blood gases, COHb and CN levels should be monitored. Patients exposed to significant concentrations of CO require hyper-baric oxygen therapy. Suspected cyanide poisoning must be treated without waiting for laboratory confirmation. Untimely or incorrect intervention may compromise the chances of survival and seriously affect the future health status of fire victims (Locatelli et al., 1994).

The most efficient way to prevent polymer combustion is to design inherently fire-resistant polymers that offer high thermal stability, resistance to the spread of flame and low burning rate. The heat-resistance property of polymers can be improved by increasing the interactions between polymer chains (increasing the crystallinity and the hydrogen bonding) or by chain stiffening through inclusion of aromatic or heterocyclic structures in the polymer backbone. Polymers consisting of aromatic groups have a strong tendency to condense into chars on heating. Therefore, they produce less flammable gaseous products in a fire event. In general, polymers with high thermal stability that generate less flammable volatiles on decomposition are the most desired fire-resistant polymers (Frazer, 1968). For instance, polymers based on bisphenol-C (BPC) and dichlorodiphenylethene offer an exceptional combination of good properties, processability and extreme fire resistance (Lyon et al., 2006b). Polymers with better fire resistance include the engineering thermoplastics polycarbonate, polyarylate, polysulfone and thermoset resins. Semi-inorganic fire-resistance polymers have also been produced based on polysilphenylene–siloxane and polyphosphazene elastomers, with comparable fire safety to heat-resistant engineering plastics (Lyon et al., 2003).

Another strategy to slow down the combustion of polymers is to use flame-retardant additives, especially for the commodity polymers. Demands for better fire safety of buildings have led to greater interest in fire-retardant materials (Horrocks & Price, 2001). Horrocks et al. (2007) investigated the feasibility of creating fire-retardant PP nanocomposite fibres comprising dispersed nanoclay. In nanoclay composites of EVA, the production of CO in fire increased because of the presence of nanoclay filler. The increased yield of CO under stoichiometric conditions is attributed to the reduction in access to oxygen caused by the presence of a protective layer of nanoclay particles (Hull et al., 2003). The assessments of fire hazard and fire risk of polymers containing fire retardants have been studied in detail (Hall & Bukowski, 2000). Use of fire-resistant materials in buildings delays the extension of flame and significantly decreases casualties and damage.

Polybrominated diphenyl ethers (PBDE) are used as flame retardants in polymeric materials, such as furnishing foams, rigid plastics and textiles, to make these materials less flammable. There are, however, environmental pollution concerns about PBDEs because they have the potential for environmental consequences and to remain in the environment for years (Yogui & Sericano, 2009).

Various methods are used to reduce the hazards and casualties in fire events. Positive pressure ventilation is an approach in which a fan is used to force flammable gaseous products of combustion out and to spread the fume (Beal et al., 2009; Lin et al., 2008). To use this method, the driving forces behind the movement of smoke in buildings, like fire-induced buoyancy and expansion, wind effect and mechanical ventilation should be considered (Mowrer, 2009).

In addition to houses, fire events in large atria of airport terminals, shopping malls and railway stations occur, usually endangering large numbers of occupants. In fire events, the smoke can affect human health seriously and people may be unable to reach a safe place. On the other hand, the conventional facilities and methods used in smaller buildings, like sprinklers, usually do not work in large buildings. Computer modelling, simulation and analytical methods provide invaluable information about the smoke distribution pattern and evacuation strategy (Capote et al., 2009). The spread of fire and smoke in atria has also been investigated in practice, leading to the installation of a smoke management system to keep the smoke layer at higher levels (Huo et al., 2005; Chow & Chow, 2005).

In designing safer furniture, electronics and appliances in fire, both thermal resistance and fume toxicity and opacity should be considered (Shousuo, 2006; Blomqvist et al., 2004). To have useful information about the behaviour of furniture in fire, it is necessary to perform full-scale burning tests on material components of the furniture (foams, wood, plastics, and wood panels). Based on the results, a fire safety ranking system can be established that would be useful for measuring the degree of fire safety of furniture.

The safety of materials used in furniture is classified based on the behaviour of various materials in different burning conditions. Shousuo (2006) recommended establishing a fire risk diagram combining key factors influencing the fire safety of furniture as a unique criterion of ranking furniture materials. The factors might be based on the thermal properties of the materials (such as ignition temperature, time to ignite, heat of combustion, heat release rate and mass loss rate) and amount and toxicity of the fumes.

Reduction of the fire risks in buildings is a very crucial issue. Fundamental understanding of the thermal decomposition and fire-resistant mechanisms of materials must be thoroughly investigated. There are still many issues that need to be addressed. Mineral fillers have been used for a long time to enhance the fire retardancy of polymers (Le Bras et al., 2005). Flame-retardant chemicals significantly improve the thermal resistance of materials, increase their ignition temperature, reduce the combustion rate and decrease the amount of heat released. While most flame-retardant materials are quite non-reactive and have low toxicity, their presence in the environment could threaten their future use. The amounts of substances entering the air, water and land should be evaluated and the amount used should be reduced. While flame-retardant materials are commonly added to polymers, there are some restrictions, such as poor compatibility with the polymer, high volatility, adverse effects on the properties of the polymers, and increase of the production of CO and smoke in fire events.

Flame-retardant systems can perform either physically (by cooling, forming a protective layer or through fuel dilution) or chemically by reacting in the condensed or gas phase (Horrocks & Price, 2001). All flame retardants act either in the vapour phase or in the condensed phase through a chemical or physical mechanism to interfere with the combustion process during heating, pyrolysis, ignition, or flame spread.

Alkali earth carbonates (BeCO₃, MgCO₃, CaCO₃, and BaCO₃) are widely used as polymer fillers. All of the carbonates release CO₂ at elevated temperatures to form an oxide, which can perform as a flame retardant to prevent fire extension. Carbonates decrease flammability by replacing fuel (polymer) with a non-combustible inorganic mass. Calcium carbonate is commonly used in this way as a filler in commodity plastics, such as PVC and PE (Bellayer et al., 2010). Metal hydrates (like aluminium and magnesium hydroxides) are efficient and effective flame retardants in a wide range of polyolefins, EVE, and EEA applications. The relative yields of CO from the fire-retardant EVA composite samples showed very similar yields of CO under ventilated conditions to the pure EVA, but they generally yield more CO than the base polymer under the most toxic fuel-rich conditions (Hull et al., 2002). Some magnesium carbonate-based substances provide effective flame retardancy in EVA and EEA (Morgan et al., 2007). On exposure to fire, PVC-sheathed electrical cables containing flame-retardant intumescent smoke suppressant, did not show any surface spread of flame and production of smoke was very small (Sharma & Saxena, 2004).

PE and EVA are widely used in various applications, for example in cable sheathing. Both polymers have poor fire resistance. The use of halogen compounds as fire-retardant additives releases toxic fumes in fire events (Delfosse et al., 1989). Halogen-free fire-retardant compounds containing aluminium oxide trihydrate (ATH) or magnesium hydroxide alone (McGarry et al., 2000) or combined with clay nanofillers (Beyer, 2001) have been investigated as a more viable and safer alternative strategy, which protects the polymer by the formation of a layer at temperatures up to 450 °C. There have been attempts to develop new fire retardants based on the esterification of melamine phosphate and pentaerythritol (Wang et al., 2007a).

PP has a wide range of applications, including as a building material, because of its versatility and a good performance to cost ratio. In such applications, the occurrence of fire is very likely; therefore, it is required to be flame retarded. PP is generally used for wire sheathing and consumer electronics products. Usually, a bromide-based compound is added to PP as a flame retardant, but toxic fumes are released in the event of a fire. Some flame retardants, like metal hydroxides, degrade the properties of PP. The effects of lanthanum oxide as a synergistic agent on the flame retardancy of intumescent flame-retardant PP composites have been investigated (Li & Xu, 2006; Li et al., 2008). Effects of organo-bentonite, as a non-halogenated flame retardant, on the flame retardancy and properties of intumescent flame retardant (IFR) PP were investigated. The presence of organo-clay enhanced the flame retardancy and strength of PP/IFR composites, but larger organo-clay amounts degraded the mechanical properties (Du et al., 2009).

Yu et al. (2010) have compared the combustibility performance of five main thermoplastics (PC, PP, HIPS, ABS and PVC) and analysed the results. They found that fire hazards of HIPS-phosphate fire retardant (PFR), PVC-non-flame retardant, ABS-brominated flame retardant (BFR) and PC/ ABS-PFR were larger than hazards of PC-BFR and PP-non-halogenated flame retardant.

PC, ABS and their blends are generally used in appliances, electronics, compact discs (Chow & Han, 2004) and furniture and can be found all around buildings. PC, ABS and PC/ABS blends, like other thermoplastics, are combustible; therefore, to reduce the flammability in a fire event, flame-retarding additives are added. Commercially available flame retardants for PC are usually halogen-based and phosphorus-containing compounds, while commercially available flame retardants for ABS are mostly halogen-containing and silicon-containing substances (Lu & Hamerton, 2002). The thermal stability and flame retardancy of PC/ABS alloy have been improved by incorporation of a flame retardant containing silicon, phosphorus and nitrogen (Zhong et al., 2007).

As stated in the previous section, wood is one of the most common structural materials used in buildings. Wood is combustible and there have been numerous efforts to make it inflammable. The treatment of spruce wood boards with Na₂S₂O₃ and Na₂S₂O₅ resulted in a decrease of heat release rate. The total amounts of CO and CO₂ production were reduced by this treatment and the specific extinction area and mass loss rate decreased too (Simkovic et al., 2007). Wood panels, made of urea-formaldehyde as binder, are widely used in buildings and are highly combustible. It was found that the addition of fly ash to these composites, as a replacement for mineral and organic flame retarders, effectively enhances the fire resistance of particle boards (Guru et al., 2009).

Coating flammable fabrics with flame-resistant materials is a viable strategy to enhance the fire safety of fabrics. PU resins are usually used as coatings for textiles in order to improve some properties, for instance water repellency. Similar to fabric, these resins are flammable, releasing highly toxic fumes in fire events. Montmorillonite clay and polyhedral oligomeric silsesquioxanes (POSS) additives have been added to the coating resin to provide flame retardancy to the coated textile structure (Devaux et al., 2002).

Thermoplastic polyesters are used as insulating parts in electrical devices, where they compete with polyamides. Poly(butylene terephthalate) (PBT) is growing more rapidly than PET, mainly because of its processing advantages. Phosphorus–nitrogen containing intumescent was developed as a flame retardant of PBT to obtain halogen-free flame-retarded polyester (Gao et al., 2006). Recycled PET has been flame retarded using red phosphorus combined with metallic oxides Fe₂O₃ and MgO. The use of mineral oxides in combination with red phosphorus leads to synergistic effects on fire performance (Laoutid et al., 2006).

The increasing need to develop more environmentally friendly additives and to abandon halogenated additives has led to the introduction of new flame-retardant additives to minimize smoke density and toxicity of fumes in fire events. Organically modified clays have provided satisfactory fire behaviour to polyester matrices with the possibility of avoiding the addition of conventional flame-retardant additives with detrimental effects in producing toxic fumes in fire (Gianelli et al., 2006).

PMMA has been flame retarded by adding phosphorus-containing compounds (Price et al., 2002). The method was found to be unfavourable because of the high loadings required to achieve a sufficient level of flame retardancy. There were negative effects on the polymer’s physical and mechanical properties and leaching of the flame-retardant additive. The authors recommended copolymerization of MMA with phosphorus-containing monomers as an alternative method to reduce significantly the flammability of PMMA without the potential problems related to the flame-retardant additive.

Epoxy resins offer good performance in many industrial applications, but their flammability restricts their usage in cases requiring fire resistance. Addition of flame-retardant additives may adversely affect the performance of products made of epoxy resin. It was found that mixtures of epoxy and phenolic resins provide improved fire retardancy compared with the epoxy resin alone because of the thermal stability of phenolic resin (Laza et al., 2008).

Combustion of polyester resin generates dense smoke, which greatly reduces visibility. Halogenated flame-retardant additives used for polyester composites reduce flammability but increase the corrosiveness, toxicity and smoke content of the resultant combustion products. Inorganic tin compounds performed as smoke suppressants and as an effective synergist for flame retardants (Nazare et al., 2008). Recently, a model was developed to predict thermal and mechanical responses of polymer composites subjected to fire (Bai et al., 2010).

There is a wide variety of materials and procedures, combustible and non-combustible, for thermal insulation of buildings (Stec & Hull, 2011). Polymeric foams are used in sandwich panels as core filler and as thermal insulator. The skins are made of composites, cement-based sheets, or metallic sheets. As was explained earlier, despite the inflammable skins, the panels are major sources of fuel to extend fire and generate huge quantities of fume and soot. Polymers commonly used as the core of sandwich composites are PVC, PS, and PU. Nanocomposites offer a potential solution to improve both the fire retardancy and mechanical performance of foams in sandwich panels (Wang & Chow, 2005).

Despite some advantages of using flame-retardant additives and methods, various risks are linked to their use. Exposure and contact of people during manufacture and use, emission of toxic gases (CO, CO₂, NO_x, HCl, HBr, HCN and SO₂) during use or in the event of fire, in addition to the costs, are some of the concerns related to application of fire retardants (Chivas et al., 2009). Therefore, in using fire retardants, all of the important factors should be thoroughly investigated. Nanocomposites could avoid the disadvantages associated with conventional fire-retardant systems, of course at a higher cost (Fu et al., 2010; Beyer, 2002; Kashiwagia et al., 2005).

Training in fire safety and regular emergency exercises can lead to significant reductions in casualties in the event of fire (Huseyin & Satyen, 2006), which is related to the human factor. The toxic hazards accumulate mainly in a layer just below the ceiling, including hot smoke, organic and inorganic irritants, CO, HCN, HCl and other toxicants. The occupants can minimize their effects by dropping to the floor, also minimizing hyperthermia from radiant heat from the flames, and crawling out of the room (Alarie, 2002).

9.6 Future trends for reducing toxic substances in fire and related resources

Standards and building codes play crucial roles in the regulation of building materials and enhance safety and protection conditions against fire. Researchers at Forintek Canada have compared fire losses in selected wooden buildings with losses in similar buildings made of non-combustible materials to evaluate the adequacy of building code requirements (Richardson, 2007). Based on these investigations, approximately three of every five fires in hotels, motels and care homes for the elderly could be prevented by improving housekeeping and maintenance practices and security. It was found that the type of construction has no significant effect on the safety of the occupants in hotels and motels, though the use of non-combustible materials reduced property losses in unsprinklered structures.

Adequate fire safety in the design of electrical appliances is extremely important. Some fires start from the malfunction of an electrical appliance and extend flame to the appliance body. Therefore, in designing appliances, manufacturers must not only ensure the safety of the electrical system, but also consider the fire behaviour of the materials used in the body of the appliance (Babrauskas & Simonson, 2007).

There are a fair number of references providing information about performance of materials in fire. In addition to national standards of various countries, there are handbooks that cover the subject thoroughly and are frequently updated based on the recent findings and changes in standards and regulations. The subject of fire and combustion of materials in general has received extensive attention. Combustion is an important chemical reaction producing different chemicals and release of energy. Combustion may occur under close control in a boiler and heat-generating equipment or in uncontrolled conditions in the event of fire. Research on the debris of fire is common practice in forensic investigations. Forensic fire experts and scientists have produced a significant part of the information and knowledge about fire and combustion. There is an extensive literature on the analysis and investigation of fire debris and products from the forensic view (e.g., Stauffer et al., 2007; De Haan, 2006; Quintiere, 1997).

Several research and technical service institutions around the world are involved in fire studies; only a few are named here. The Center for Fire Research at the National Institute of Standards and Technology (NIST) in the USA is involved in the measurements, standards and technology needs of buildings and fire safety, sustainable materials, innovative fire protection and disaster-resilient structures. In Canada, the fire research programme of the NRC Institute for Research in Construction develops methods and technologies for improving the fire safety design of buildings and transportation systems, enhancing fire detection and suppression systems, and reducing the risks and costs of fire. The Building and Housing Research Centre in Iran is involved in research, standards and regulations related to fire in buildings and the behaviour of materials in fire, and issues licences for fire safety of building materials. The Fire Technology Department of the SP Technical Research Institute in Sweden offers a wide range of services for evaluation and investigation of the fire performance and behaviour of materials and products, testing fire-fighting equipment and carrying out theoretical studies on the growth of fires and the spread of smoke. The Building Research Establishment’s Fire Research Department (UK) is the largest set of fire research facilities in Europe, offering research, testing and technical services on all fire issues concerning buildings, infrastructure and transport.

In some universities, there are centres with activities focused on fire, such as the Center for Fire Research and Outreach of the University of California at Berkeley. The Department of Fire Protection Engineering at Worcester Polytechnic Institute (DFPE-WPI) is one of the institutions that offers a comprehensive fire protection engineering programme, leading to Master and Doctorate degrees and other advanced certificates. Victoria University, in Melbourne, Australia is also offering comprehensive programmes in fire engineering. The Department of Fire Protection Engineering in the University of Maryland (DFPE-UM) provides advanced research, undergraduate and graduate degree programmes in fire engineering. There are useful lists of more educational, research and industrial institutions and consulting firms with their URL links at the websites of DFPE-WPI and DFPE-UM. There is useful information and literature on the websites of these institutions. Moreover, there are several journals focusing on fire in buildings or publishing articles related to the subject, which have been cited widely in this chapter.

9.7 Conclusion

Fire is a potential hazard for human life, especially in an enclosed and escape-proof area, such as in buildings. Fire in buildings consists of many different aspects of which materials comprise only one. Lightweight, highperformance polymers offer many advantages in buildings, but their inherent flammability greatly increases the fire risk. The intrinsic relationships between the structure, composition and fire behaviour of materials, and understanding the thermal decomposition and fire-resistant mechanisms of polymers, are essential issues that help to identify and design new fire-safe materials.

The current knowledge about the relationships between materials and fire is insufficient and research should be focused on fundamental studies. The present environmental regulations require the development of new environmentally friendly flame retardants to replace the halogenated ones, which are the most efficient and are used in the largest volume but release toxic and corrosive gases in fire. Some new phosphorus-or silicon-based additives have been developed as substitutes, but they are not as efficient as the halogenated flame retardants. Therefore, searching for both environmentally friendly and efficient flame retardants is still a very demanding research direction. To achieve the maximum efficiency and reduce the amount of addition, a combination of different additives needs consideration. Because various additives act in different mechanisms and have diverse effects on various polymer systems, some fundamental understanding of the flame retardancy mechanisms of these additives needs to be applied. Additionally, the mechanism of polymer crosslinking and char formation by special chemical reactions is another possible way to reduce polymer flammability.

The twin buildings of the World Trade Center could sustain and survive the impact of the airplanes on 11 September 2001, but they collapsed because of the fire, and the majority of the victims died from incapacitation and toxication by fire fume. Review of the fire events reveals that the available information and knowledge about fire are not sufficient and generally we are not prepared to act properly and efficiently with fires.

The standards and methods of measurement and analysis of fire products and fire safety regulations are mostly at the national level of countries and currently there are no international and harmonized protocols related to fire. Better and more accurate and dynamic computer simulations of fire are needed to enable us to have a clear view about the concentrations and composition of fire fumes in various situations. These simulation programmes should provide invaluable tools to designers of buildings concerning safety in fire in order to give better protection.

Fire usually leads to a large number of casualties and damage in high-rise buildings. It is necessary to develop better technologies of fire-fighting and to perform more studies on the behaviour of occupants. It is also crucial to train occupants to behave properly in fire events and to enhance evacuation techniques and practices.>

9.8 References