CombustionGases, page 1-240 @ Normalize

Development of Novel Techniques Based on Sorptive Extraction for the Analysis of Combustion Gases

Desmet Koen Thesis submitted to the Faculty of Science in fulfilment of the requirements to obtain the degree of Doctor in Science (Chemistry)

Promotor: Prof. Dr. P. Sandra

January 2005

Faculteit Wetenschappen Vakgroep Organische Chemie

TABLE OF CONTENTS

Chapter 1 General Introduction and Scope

1 10

References

Chapter 2 General Insights in Combustion Gas Analysis 1. The basics of fire 2. Methodology of combustion gas research 2.1 Box furnace models 2.2 Tubular furnace models 2.3 Radiative heating 2.4 Medium to large scale test facilities 2.5 Other methods in combustion gas analysis 3. Analytical techniques employed 4. References

11 12 14 15 17 19 20 22 23 27

Chapter 3 A Simple Approach to Oxidative Pyrolysis 1. Introduction 2. Fire gas analysis using pyrolysis CGC-MS 3. Experimental 3.1 Instrumental set-up 3.2 Sample handling 3.3 Instrumental conditions 4. Results and discussion 4.1 Optimization of pyrolysate transfer 4.2 Instrumental robustness 4.3 OxPYR- and PYR-CGC-MS analysis of polymers 5. Conclusion 6. References

i

29 30 31 33 33 34 34 35 35 35 39 43 44

Chapter 4 Analysis of Combustion Gases of Selected Materials upon Bunsen Exposure 1. Introduction 2. Experimental 2.1 Indoor fire simulation 2.2 Sorptive sampling 2.3 Thermal desorption and analysis 3. Results and discussion 3.1 Natural wood and synthetic wood materials 3.2 Polyvinylchloride (PVC) 3.3 Expanded polystyrene and extruded fire-retarded polystyrene 3.4 Polyurethane foam 4. Conclusion 5. References

45 46 48 48 49 49 50 50 59 63 68 72 73

Chapter 5 Evaluation of the Use of Sorptive Sampling for the Analysis of Combustion Gases 1. Introduction 2. Experimental 2.1 Chemicals 2.2 Sampling 2.3 Thermal desorption and analysis 3. Evaluation of sorbent tubes using a surrogate standard mixture 4. Evaluation of sorbents for the sampling of combustion gases 5. Analysis of bromophenol and isocyanate standards 6. Conclusion 7. References

75 76 78 78 78 79 80 83 88 90 91

Chapter 6 Tubular Furnace Experiments 1. Introduction 2. Experimental 2.1 Construction of a tubular furnace combustion apparatus 2.2 Sorptive sampling 2.3 Thermal desorption- GC-MS 3. Results and discussion 3.1 Analysis of the combustion products of creosote treated railroad ties 3.2 Analysis of the combustion products of polyamide 3.3 Analysis of the combustion products of polymethylmethacrylate 4. Conclusion 5. References

ii

93 94 97 97 98 98 99 99 104 107 112 113

Chapter 7 Determination of Bromophenols in Combustion Gases of Fire-Retarded Extruded Polystyrene 1. Introduction 2. Experimental 2.1 Sampling 2.2 Thermal desorption- GC-MS 3. Results and discussion 4. Conclusion 5. References

115 116 119 119 120 121 126 127

Chapter 8 Investigations into the Formation of Polyhalogenated Dibenzofurans and Dioxins in Combustion Processes 1. Introduction 2. Dioxin formation mechanisms 3. Dichlorobenzene combustion in an adapted DIN furnace set-up 3.1 Introduction 3.2 Experimental 3.3 Results and discussion 4. Study of possible interferences in on-line precursor monitoring using non-selective REMPI-MS 4.1 Resonance-enhanced multiphoton ionization in PCDD/F emission monitoring 4.2 Relative correlation of JET-REMPI monitoring with adsorption tube sampling 4.3 Experimental 4.4 Results and discussion 5. Conclusion 6. References

129 130 134 139 139 140 141 144 144 148 149 151 157 158

Chapter 9 Analysis of Smoke Gases Released at Fire Incidents 1. Introduction 2. Experimental 2.1 Sorptive sampling 2.2 Thermal desorption and analysis 3. Results and discussion 3.1 Analysis of smoke gases released at a fire training centre 3.2 Analysis of combustion gases present at house fires 3.3 Analysis of the combustion gases emitted during an industrial fire 3.3.1 Introduction 3.3.2 History of the Carcoke Marly - fire 3.3.3 Discussion 4. Conclusion 5. References

iii

161 162 163 163 164 165 165 169 176 176 177 178 183 184

Chapter 10 Biomonitoring Smoke Gas Exposure 1. Biomonitoring smoke gas exposure 2. Biological monitoring of PAH exposure 3. Analysis of hydroxylated-PAH 3.1 Experimental 3.1.1 Chemicals 3.1.2 Sample preparation 3.1.3 Stir bar sorptive extraction (SBSE) 3.1.4 Instrumental conditions 3.2 Results and discussion 3.2.1 In-situ derivatisation-SBSE optimization 3.2.2 Validation of the in-situ derivatisation-SBSE-TD-CGC-MS procedure 3.2.3 Analysis of real-life samples 4. Conclusion 5. References

185 186 192 197 198 198 198 199 200 200 200 201 203 206 207

Chapter 11 General Conclusion

209

Summary

211

Samenvatting

215

List of Abbreviations

219

Dankwoord

223

Curriculum Vitae

225 227 229

Scientific Publications Scientific Presentations

iv

CHAPTER 1

GENERAL INTRODUCTION AND SCOPE

The story of combustion gas research is ascribed to have commenced with John Zapp who in 1951 reported in ‘The toxicology of fire’, that fire fatalities were often caused by smoke inhalation and thermal damage of the respiratory tract [1]. Although other scientists became interested in the toxicity of smoke during the next twenty years, it was only during the early 1970s that research in the area of smoke toxicity expanded rapidly. There were two reasons which caused this impetus. The first was the Federal Trade Commission (FTC, US) complaint, who announced in October 1972 its inquiry into the flammability of plastics. As a result, the Society of Plastic Industry (SPI) formed a Urethane Safety Group to ‘foster intelligent regulations, meaningful standards, and truthful communications looking toward consumer safety’. This group comprised of high-level executives quickly raised a fair budget for research and large scale tests. Next to this, the group began aggressive efforts to discourage practices contributing to fires and it hired a public relations firm to promote the industry’s image. In May 1973, the FTC proposed a complaint that ‘certain plastic products used in construction and furnishing of buildings and homes may constitute serious fire hazards’. The plastics involved were cellular polyurethane and all forms of polystyrene and its copolymers. The commission alleged that the Society of the Plastic Industry, the American Society of Testing and Materials (ASTM) and 26 producers and marketers either directly or indirectly withheld information to users on the serious fire hazard their products formed. The complaint also alleged that invalid testing standards enabled these plastics to be classified as non-combustible in numerous building codes throughout the country. The complaint suspected that these plastics, once ignited, frequently produce greater fire hazards than traditional materials. Specifically, it was claimed that these 1

General Introduction and Scope

products, compared to materials being displaced, contributed to the likelihood of flashover, produced more dense smoke and released toxic or flammable gases more quickly. As might be expected, there were considerable comments on the FTC action. Both SPI and ASTM claimed that the FTC had no reason to name them in the complaint and pointed out that they started working to upgrade the testing methods and standards even before the FTC complaint. The second impetus behind the intensified interest in, and concern over the toxicity of smoke was the finding in 1974 of a neuro-toxic organophosphate ester in the smoke produced by the combustion of non-commercial polyurethane foam by Petajan et al. [2]. As consequence of this finding, the Products Research Committee (PRC) was formed in 1974, with substantial resources provided by the industry for support of research in the behaviour of cellular plastics in fire. With funding by this committee as well as by government agencies, numerous laboratories became involved in various areas of fire research. The Products Research Committee was also organized as a result of the Consent Agreement entered into by the FTC and the respondents. In this action, the committee was created to coordinate and manage a scientific research program on the combustibility of cellular plastics for a period of five years, with as main focus the minimization of fire hazards and the development of tests which would produce an index of the behaviour of cellular plastics in various burning conditions. The PRC completed its work in April 1980 and issued a progress report in which 17 recommendations were made, some of which called for action by the ASTM for greater speed in study of deficiencies in existing tests and the adoption of new ones developed, while others called on industry to continue active research in developing test methods for smoldering and toxicity of combustion gases. As a result the ASTM abandoned the ASTM D 1692-74 Test for the Rate or Extent of Burning of Cellular Plastics. A test in which e.g. 20 to 30% of ordinary expanded polystyrene samples passed because of rapid shrinkage of the thermoplastic foam away from the flame which resulted in a failure to ignite adequately for continued burning. The suppliers of plastics, on the other hand, have been much more careful in describing the flammability of their products, following the FTC complaint [3]. 2

Chapter 1

One of the unfortunate consequences of the sudden availability of research funds was the evolution of a plethora of laboratory test methods for assessing the toxicity of smoke produced by the combustion of materials. The various methods that evolved during this period utilized different combustion devices and conditions, different animal exposure chambers, in some cases different indices of toxicity and even different test animals. Because of these marked differences, data obtained with one laboratory test method generally had little relevance to data obtained with a different method. A few investigators who appreciated the complexity of smoke atmospheres developed test methods to enable the comprehensive evaluation of the toxicity of combustion products and to understand the mechanisms of their toxicity. Papers presented at the ‘International Symposium on Toxicology of Combustion Products’ held at the University of Utah in 1976 emphasized the dual objectives of that time namely to understand the fire threat and to develop methods to test materials [4]. During the 1980s, emphasis in combustion toxicology moved from development of test methods to the promulgation of standardised toxicity tests. This came forward from the review published by Birky in 1976 [5]. As example, in 1980 the Center for Fire Research of the National Bureau of Standards (NBS) published the NBS test method [6]. The method was developed by the NBS, with the assistance of an ad hoc working group composed of members of academia, industry and government, for the purpose of establishing a standardized procedure for evaluating toxicity of combustion products. In Europe, the DIN 53436, ‘Erzeugung Thermisher Zetsetzungsprodukte von Werkstoffen unter Luftzufuhr und ihre Toxicologishe Prüfung’ a different standard test method was published in 1981 by the Deutsches Institut für Normung [7]. These and some other accepted normalized methods were rapidly used to compare and rank materials according to the toxicity of their combustion products; a use that was vehemently opposed by the plastic industries. On the other hand, independent assessments, including one by the US National Academy of Sciences, pointed out that any projected use of the tests should be consistent with an understanding of the shortcomings and limitations of this type of testing [8]. Furthermore increasing emphasis was put on the role of toxicological testing as a contributor to hazard analysis and risk assessment for materials rather than as a direct decision making fire standard.

3

General Introduction and Scope

An extensive review, titled ‘Combustion Toxicology-Principles and Test Methods’ published in 1983, by Kaplan et al. [9], formed the basis for reports by ASTM and ISO. Next to these reports another study of similar scope and depth entitled ‘An Analysis of Current Knowledge in Toxicity of the Products of Combustion’ was published by the National Fire Protection Association (NFPA) [10]. Both studies concurred in the conclusion that ‘the current tests for toxicity of products are inadequate for regulatory purposes’ and that ‘toxicity should be a part of the general fire hazard assessment’. At the end of 1982, a consensus was reached within the concerned workgroup at the ISO. The workgroup concluded that a standard based on the integration of toxicity and combustibility information was needed, but no consensus was reached with regard to the timing. Between 1989 and 1993, first attempts to realize this were made by publishing technical reports on ‘Toxicity Testing of Fire Effluents’ describing the accepted scientific basis in the field [4]. Next to the lack of consensus, the lack of support by the general public on animal testing emphasized the need for analytical techniques and models to determine the lethal toxic potency of fire effluents. Most recent developments are found in the incorporation of parameters concerning the toxic potency of a material in computer modelling. Many applications remain, however, solely as research due to the lack of official standards and legislation. The field of research into combustion gases was at this point in time, however, about to be drastically broadened due to historical events.

4

Chapter 1

On the first of November 1986, a fire started at the Sandoz industrial area near Basel, Switzerland. The fire took place in a warehouse containing 1250 tons of chemicals and packaging materials. The chemicals stored, consisted mainly of pesticides, herbicides and highly flammable liquids. The fire caused considerable discomfort to people in the surrounding areas and severe damage to the environment, mainly to the river, where contaminated water from fire-fighting operations and residual chemicals from the warehouse collected. The fire plume, containing sulphur and other organic and inorganic substances, spread over the Basel area, causing anxiety and discomfort among the inhabitants. This and other major fires at the end of the twentieth century in Europe like the Protex, pesticide factory, fire in Antwerp (Belgium, 1991) which caused serious discomfort to intervening crews and the Thetford plastic fire (UK, 1991) concerning 1000 tonnes of plastic mostly polyvinylchloride that endured for 72 hours [11], caused public awareness to the problem of toxic compounds released in large fires, which led to new legalisation and guidelines. Probably most noted is the Seveso directive introduced in Europe during 1987. A lack of knowledge was, however, identified concerning substances produced in fires involving chemical substances. This prompted the European environment program to start several research programs of which e.g. the STEP program which investigated ‘Combustion of Chemical Substances and the Impact on the Environment of the Fire Products’ initiated in 1991 [12] and followed in 1993 by the TOXFIRE project which titled ‘Guidelines for Management of Fires in Chemical Warehouses’ [13], next to other programmes such as the MISTRAL I & II which researched ‘Modelling of Transport and Environmental Impact of Fires’ [14]. The research into toxic combustion gases related to industrial or chemical fires renewed interest in research on the toxic combustion gases from building and other household materials. Combustion devices and methodologies were adapted and analytical detection of species evolved, prevailed over the use of animals in the laboratory tests. Studies on ‘scaling mall scale experiments’ to ‘real life scale fire’ were conducted, using a DIN 53436 furnace as micro-scale, moving onto cone-calorimeter measurements and large scale indoor fire tests, hence combining test methods from other fields in fire research [13]. Analytical methodology, however, remained largely uniform and was mainly based

5

General Introduction and Scope

on simple techniques such as Fourier Transform Infrared which was e.g. thoroughly evaluated in the SAFIR project concerning the analysis of various textile products [15]. Incidents continued in the twenty first century, a few examples of serious fire incidents in Europe are given. On the 12th of May 2000 a fire broke out at the ATF in Drachten (The Netherlands), a hazardous waste treatment facility dealing with pesticides, polychlorobiphenyls, batteries and paint, causing heavy metal and dioxin contamination up to 1 km downwind from the site and inciting preventive measures towards cattle and grassland [16]. The 21st of September 2001 the AZF fertilizer factory in Toulouse (France) exploded releasing a cloud of acrid smoke. In Tyneside (UK) a fire broke out in the night of 12th of April 2002 at the Distillex chemical factory that recycled solvents, causing the evacuation of several hundred of residents. The Marly fire, which broke out the 10th of December 2003 during sanitation of an abandoned coal tar distillation factory near Brussels (Belgium), released large amounts of polycyclic aromatic compounds for several days causing discomfort as far as Düsseldorf (Germany), and demonstrated the lack of knowledge and analytical technology to tackle such event. Because of the risen general concern, various research groups and governmental institutes started to focus on the analysis of combustion gases or related topics e.g. Prof. Bahadir and Prof. Lorenz of the Institute of Ecological Chemistry and Waste Analysis of the Technical University of Braunschweig (Germany) [17,18]; Prof. Kettrup and Dr. Matushek related to the Institut für ökologische chemie des GSF-forshungszentrums für Umwelt un Gesundheit (Germany) [19], the Department of Fire Safety Engineering of the Lund University (Sweden)[20]; the Health and Safety executive (UK) [21], and the Rijksinstituut voor Volksgezondheid en Milieu (RIVM, The Netherlands) [22]. Developments have also been made to provide on-site analytical instrumentation for example by Prof. Matz of the Technical University of Hamburg (Germany), who developed a portable thermal desorption gas chromatography based analysis system [23]. As in most scientific research coordination of data is rather scarce, resulting in few practical guidelines on compounds evolved.

6

Chapter 1

In this framework, the current work aims to add some pieces to the large puzzle of combustion gas chemistry with regard to the organic decomposition products formed. Next to this general goal, this work mostly focuses on the development and evaluation of novel sorptive sample preparation techniques for volatile and semi-volatile organic compounds useful for combustion gas laboratory testing as well as for real fires analysis. Sorptive sampling, based on the dissolution of the chemical of interest in a gum-like sorbent material, has been pioneered recently by Baltussen et al. [24]. This principle is possible because the polymer material utilised is above its glass transition point at room temperature. The polymer material consequently acts as an organic solvent from which the compounds can be liberated via liquid or thermal desorption. Of the materials exhibiting these characteristics polydimethylsiloxane (PDMS), commonly employed in capillary gas chromatography as one of the most popular stationary phases, was selected as the material of choice because of its high inertness, thermal stability and readily identifiable decomposition products. The use of sorptive sampling opens new possibilities in gas sampling as more polar compounds can be analysed without sample degradation while more strongly retained compounds, with higher boiling points, are released in more favourable conditions due to the weak interactions. Water vapour interference, of concern in combustion gas analysis, does not affect retention due to the inherent aversion to water of the sorbent material [24-27]. Hence, strong indications of sorptive sampling being able to provide benefits in combustion gas analysis are at the basis of this study. To evaluate the use of polydimethylsiloxane sampling, various small scale tests were designed and evaluated next to field analytical tests at fire incidents. Chapter 2 aims to provide a general insight in combustion gas analysis. It discusses the basics of fire next to providing an overview of laboratory scale combustion devices and a brief overview of analytical methodologies applied. In Chapter 3 a small scale screening method based on oxidative pyrolysis was developed and discussed for the analysis of polyethylene and polystyrene samples. Using air as oxidative medium during pyrolysis, additional oxygenated decomposition products were formed compared to the decomposition products commonly formed during inert gas pyrolysis.

7

General Introduction and Scope

In Chapter 4 a sampling methodology based on sorptive enrichment of volatile and semivolatile combustion gases released upon Bunsen exposure of various polymers such as polystyrene, polyvinylchloride, polyurethane, and selected wood based materials such as regular pine and particle board is described. The tests provided insights in the combustion products formed and allowed the selection of target compounds, namely bromine and nitrogen containing organics, used in Chapter 5 for the evaluation of polydimethylsiloxane sampling of combustion gases compared to common adsorption based sampling media, indicating the advantages of the inertness of the polydimethylsiloxane material. Chapter 6 discusses the development and preliminary combustion gas screenings, conducted with a tubular furnace combustion apparatus constructed according to the DIN 53436 standard. Samples under study were creosote treated railroad sleepers, a polyamide (nylon-6) and polymethylmethacrylate proving the sensitivity and the wide range of applicability of the polydimethylsiloxane sampling coupled to thermal desorption and gas chromatographic analysis. Based on the detection of brominated decomposition products during preliminary combustion tests of fire-retared extruded polystyrene panels, the presence of bromophenols as dioxin precursors in the combustion gases was investigated in Chapter 7 employing sorptive sampling and tubular furnace combustion. Chapter 8 discusses the formation of polyhalogenated dibenzofurans and dioxins in combustion and thermal processes as investigated using an adapted version of the tubular furnace for the combustion of 1, 2-dichlorobenzene and employing thermal desorption gas chromatography to aid in the identification of interferences during nonselective resonance-enhanced multiphoton ionization experiments. Chapter 9 focuses on the application of the developed methodology to real fire incidents. This evaluation aptly proved the flexible and versatile sampling methodology developed. Biomonitoring smoke gas exposure is discussed in Chapter 10 with the development of a sorptive extraction based analytical routine for the analysis of 1-hydroxypyrene in urine, as biomarker for polycyclic aromatic hydrocarbon exposure. 8

Chapter 1

Although this work merely tips the iceberg with regard to providing total insight in combustion gas chemistry, it aims to present the reader a broad overview of combustion gas research based upon the selected materials analysed and an illustration of the benefits of the use of sorptive sampling in combustion gas research. Furthermore, this work aims at inciting others and the government to continue research in this area, as large deficits remain especially with regard to environmental and public safety, for example, in the event of large industrial fires. Small scale combustion gas research could not only aid in risk assessment of industrial installations or warehouses, it could provide insights in combustion gases evolved at large fires allowing adequate measures to be taken next to providing target compounds for analytical follow-up during and after the incident.

9

General Introduction and Scope

References [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14] [15] [16] [17] [18] [19] [20] [21] [22] [23] [24] [25] [26] [27]

J. Zapp, The Toxicology of Fire, Medical Division Special Report N°4, US Army Chemical Centre, Maryland, (1951) 92. J. H. Petajan, K. J. Voorhees, S.C. Baldwin, M.M. Birky, Science, 187 (1975) 742. G. Shayne, R. Anderson, Combustion Toxicology, CRC Press, Boca Raton, Florida US, (1990). Toxicity Testing of Fire Effluents: Part 1 General, ISO/TR 9122-1 (1989). M.M. Birky, J. Combustion Toxicology, 3 (1976) 5. M.M. Birky, M. Paabo, B. Levin, C. Womble, D. Malek, Development of Recommended Test Method for Toxicological Assessment of Inhalated Combustion Products, NBSIR 80-2077, National Bureau of Standards, Washington DC, (1980). Erzeugung Thermisher Zetsetzungsprodukte von Werkstoffen unter Luftzufuhr und ihre Toxicologishe Prüfung, DIN 53 436, (1981). Smoke and Toxicity, National Materials Advisory Board, NMAB 318-3, National Academy of Sciences, Washington DC, (1978). H.L. Kaplan, A.F. Grand, G.E. Hartzell, Combustion Toxicology- Principles and Test Methods, Technomic Publishing Co., Lancaster, Pensylvania, US, (1983). F.B. Clarke, I.A. Benjamin, J.W. Clayton, An Analysis of Current Knowledge in Toxicity of the Products of Combustion, NFPA , Morgan Technical Library, Quincy, Massachusetts (1982). P.J. Baxter, B.J. Heap, M.G.M. Roland, Occup. Environ. Med., 52 (1995) 694. L. Smithansen, Combustion of Chemical Substances and the Impact on the Environment of the Fire Products, Risö-R-765, (1994). K.E. Petersen, F. Markert, Assessment of Fires in Chemical Warehouses- An Overview of the TOXFIRE Project (1999). J-C. Malet, MISTRAL I & II, Modelling of Transport and Environmental Impact of Fires, IPSN Cadarache, France. T. Hakkarainen, E. Mikkola, J. Laperre, F. Gensous, P. Fardell, Y. Le Tallec, Baiocchi, K. Paul, M. Simonson, C. Deleu, E. Metcalf, Fire. Mater., 24 (2000) 101. Onderzoek naar de brand bij ATF in Drachten, RIVM rapport 609022 011, www.rivm.nl (2001) T. Dettmer, dissertation, Universität Carolo-Wilhelmina, Braunschweig (2001). H. Richter, dissertation, Universität Carolo-Wilhelmina, Braunschweig (1999). M. Herrera, dissertation, T.U. München (2001). www.brand.lth.se/english. www.hse.uk. Resultaten van metingen door de Milieuongevallendienst bij branden, MG Mennen, RIVM rapport 609100002 www.rivm.nl (2002). G. Matz, W. Schröder, A. Harder, P. Rechenbach, Field Anal. Chem. Tech., 1 (1997) 181. E. Baltussen, P. Sandra, C. A. Cramers, J. High Resol. Chromatogr., 20 (1997) 385. E. Baltussen, F. David, P. Sandra, C. A. Cramers, J. High Resol. Chromatogr., 21 (1998) 332. E. Baltussen, F. David, P. Sandra, C. A. Cramers, J. Chromatogr. A, 864 (1999) 345. E. Baltussen, C. A. Cramers, P. Sandra, Anal. Bioanal. Chem., 373 (2002) 3.

10

CHAPTER 2

GENERAL INSIGHTS ANALYSIS

IN

COMBUSTION GAS

Fire gas analysis can be considered an a-typical field in air analysis requiring additional insights as it combines facets from various fields of science. This chapter aims to introduce the reader to the basic aspects of fire, pointing to its multiple stages influencing the decomposition products formed. Due to this multiplicity, various types of laboratory combustion devices have been developed and refined throughout time to allow to re-create the various combustion processes, of which a selection, based on box-furnaces, tubular furnaces and radiative heating, are discussed next to other off-line and on-line techniques commonly employed in the investigation of thermal degradation products. Finally, an overview of analytical methodologies commonly employed, is discussed, focusing on the determination of organic volatile and semi-volatile decomposition products of interest from environmental and medium to long-term toxicological points of view. Based on the presumption that the methodology developed within this work should be applicable for both laboratory and field purposes, sorptive based sampling is discussed more in depth.

11

General Insights in Combustion Gas Analysis

1. The basics of fire Combustion processes are rapid exothermal reactions of the combustible substance and an oxidative medium. Characteristic to fires is the energy release in forms of heat and light. The visible light given of at fires is, however, linked to the material burned. Commonly glowing carbon particles in a flame cause the well known yellowish glow. The heat release not only heats the combustible and the surrounding materials, it also displaces the air present, causing combustion gases to rise, creating a depression in which fresh air is transported to the base of the fire. To start a fire, sufficient activation energy needs to be provided once, after which the reaction can sustain itself when all parameters are favourable. The activation energy needed depends on the combustible and the general circumstances. Gasoline e.g. can be lit with a simple match while the same amount of energy is not sufficient to light diesel fuel. If the surrounding temperature or oxygen level increases, fewer amounts of energy are needed to start the combustion reaction. The energy radiated back to the combustible substrate causes its pyrolysis or evaporation. Pyrolysis, or thermal decomposition of a material, causes the chemical structure of the fuel source to breakdown releasing smaller molecules, which in turn evaporate and combust with the oxygen present in the gas phase. These pyrolysis reactions can continue in the gas phase if sufficient energy is present. The fire development depends on various parameters of which the most important are the fire load, i.e. the amount of combustible materials present, the geometrical distribution of the fire load, the ventilation and the thermal properties of the surrounding walls. In general, a confined fire will develop in three distinct phases namely (Figure 2.1) the initial phase, the fully developed or steady state phase and the decay phase. The early stage of a fire, during which oxygen and fuel concentrations are virtually unlimited compared to the small seat of the starting fire, is called the growth or initial phase. This phase is characterised by an exponentially increasing heat release. The middle stage of a fire is referred to as the steady state phase. At this moment the fire is fully developed and the heat release rate is relatively unchanging. The final stage of a fire is

12

Chapter 2

the decay phase, which is characterised by a deceleration of heat release leading to fire extinguishment due to oxygen or fuel depletion. Flashover is defined as the culmination of the fire growth phase. Flashover is a heat induced transition, occurring when temperatures approach 500-600°C. At these temperatures all pyrolysis gases collected in the room ignite, causing rapid fire spread, engulfing the compartment. The temperature consequently rises rapidly to attain final temperatures close to 900-1000°C [1]. T (°C) 1000

Initial phase

Steady state phase

Decay phase

800 600 400 200

Time

Figure 2.1 Phases in fire development.

In each of these phases, a different mixture of decomposition products will be obtained. In order to study a material’s contribution to the fire atmosphere, consideration of decomposition products under different conditions of both temperature and ventilation is necessary. For research purposes, fire classes have been defined based on the carbon dioxide and monoxide ratio (CO2/CO), the oxygen concentration and the expected fire severity based on expected temperatures or irradiance. The resulting six fire types, according to the International Organisation for Standardisation (ISO), are a smouldering fire, a non-flaming oxidative decomposition, a non-flaming pyrolytic decomposition, a developing flaming fire, a fully developed flaming fire with limited ventilation and a fully developed well ventilated fire [2].

13

General Insights in Combustion Gas Analysis

2. Methodology of combustion gas research In order to study a material’s contribution to a fire atmosphere, consideration of the production of fire effluents from the material under different conditions of both temperature and ventilation are necessary. Small or developing fires are characterised by a minor release of carbon monoxide and hydrogen cyanide, in relation to the complex mixture of pyrolysis and oxidized organic products that are formed. Fully developed fires, on the other hand, generally release toxic compounds of smaller molecular mass due to the high temperatures reached. A schematic overview of the general classification of fires can be found in Table 2.1. Fire type Oxygen (%) Ratio CO2/CO1 Temperature (°C)2 Irradiance (kW/m2)3 1. Decomposition - Smouldering 21 < 100 - Non-flaming (oxidative) 5-21 < 500 < 25 - Non-flaming (pyrolytic) 400

2 2 2 2 3

graphitised carbon black graphitised carbon black carbon molecular sieve carbon molecular sieve styrene-divinylbenzene resin ethylvinylbenzenedivinylbenzene styrene-divinylbenzene

> 400 > 400 > 400 > 400 200

Adsorbent

Type

3

Chromosorb 102 Chromosorb 104 Tenax TA

3

PDMS

4

3 3

Composition

acrylonitriledivinylbenzene poly-2,6-diphenyl-pphenylene oxide polydimethylsiloxane

Application range

Remarks

polar compounds polar compounds amines, alcohols high volatiles, CO

seldom used hygroscopic

irreversible adsorption displacement hydrophobic, nonporous slight H2O retention very hydrophobic -

180

non-polar compounds C3AC20 C5AC20 C2-C5 C2-C5 > C12, nitro compounds -

180

e.g. Cl-pesticides

180

polar compounds e.g. mercaptans C5-C26 e.g PAH, PCBs -

350 350

irreversible adsorption

apolar-polar Q