EMERGING RISKS FROM SMOULDERING FIRES: INITIAL RESULTS FROM THE EMRIS PROJECT

Transcription

1 EMERGING RISKS FROM SMOULDERING FIRES: INITIAL RESULTS FROM THE EMRIS PROJECT Dan Madsen 1 *, Christoph Wanke 2, Ragni Fjellgaard Mikalsen 3,4, Ingunn Haraldseid 3, Edmundo Villacorta 3, Bjarne C Hagen 3, Ulrich Krause 2, Gisle Kleppe 3, Vidar Frette 3, Bjarne Husted 1 dan.madsen@brand.lth.se 1 Lund University, Sweden 2 Otto-von-Guericke-University Magdeburg, Germany 3 Stord/Haugesund University College, Norway 4 SP Fire Research, Norway ABSTRACT The increased use of biofuels in the recent years in northern Europe has led to a growing number of smouldering fires in storage facilities. Mechanisms of smouldering are not fully understood. Some of the unsolved issues related to the research field of smouldering fires will be investigated within the EMRIS project (Emerging Risks from Smouldering Fires). The work within EMRIS is structured into four work packages and the results from the initial activities are presented in this paper. Experimental work has been performed to determine if transition from smouldering to flaming fire is dependent on sample size. The results from these experiments, with cotton as base material, indicates that sample size does affects the transition to flaming. Low repeatability in transition to flaming fire was observed for sample sizes 15 x 15 x 15 cm, however using the same experiment method with sample size 40 x 60 x 15 cm showed a 100 % repeatability in transition from smouldering to flaming fire in the conducted tests. When inert materials are mixed with combustible dusts, the mixed material shows different properties during combustion. A number of hot storage tests have been conducted using lignite as the main component and with different amount of sand and magnesium oxide of different particle size distributions. The results from these experiments showed that an increased mass fraction of inert material lead to an increase in the self-ignition temperature. It was also observed that for mixtures with up to 50 % inert material, the sample temperatures could exceed the pure lignite sample temperature with up to 400 C. It was also shown that particle size of the inert materials is an influencing factor as they form pores in the mixed material when the lignite coal is combusted. The formation of pores and increased porosity and permeability of the material results in more favorable combustion conditions, hens higher sample temperatures. A sensitivity study on the conditions leading to an onset of self-sustained smouldering combustion of wood pellets has been conducted using a small-scale top-ventilated experimental setup. By varying the heating condition of the sample it was found when a self-sustained smouldering fire was initiated. It was found that the mass loss for both smouldering and non-smouldering cases was larger than the measured water content, and a study of the residue after test displayed that the whole sample was affected by the heating. A critical mass of black/charred pellets needed to obtain a self-sustained smouldering is suggested.

2 INTRODUCTION In northern Europe the use of biofuels (e.g. wood pellets) has increased in the recent years, replacing black coal 1. The increased use of biofuels has led to a growing number of smouldering fires in storage facilities 2 3. Research on smouldering fires show that mechanisms involved in smouldering are not fully understood 4. Combustion of solid materials can be divided into three forms, smouldering, glowing and flaming fires. The definition of smouldering is combustion of a solid material without the emittance of light 5. The area of smouldering fires requires further research to understand self-ignition and smouldering of different materials and to develop related numerical models from empirical work. The onset of self-sustained smouldering fires can be caused by different heating scenarios, such as heating by hot surfaces or objects, or as a result of biological and chemical reactions as observed in storage piles of biomass materials. Smouldering fires often occur in porous materials with fine particles or fibres. The porous nature of the fuel allows oxygen to interact with the solid fuel or pyrolysis gases resulting in smouldering or glowing fires without transitioning into flaming. Smouldering fires result in substantial economic losses due to loss of the actual biofuel. Combined Heat and Power plants (CHP-plants) have large economic losses when biofuels decompose before the controlled combustion for heat production at the site 6. Company guidelines are implemented to minimize both the loss of materials and risk of ignition of the material. However, sometimes the heatbuild-up in the storages becomes unmanageable and results in large fires with great costs to the company. This type of fire also affects the community s resources and environment as fire and rescue services are required to combat the fire and hazardous smoke is released into the environment. Smoke from fires consists of two parts, a vapour phase that is invisible and particles that are visible. Smouldering fires tend to produce a larger amount of small particles than flaming fires. The small particles from smouldering fires are of great toxicological importance since the particle size determines how deep the particles penetrate into the respiratory tract and the lungs. Particle sizes of less than 5 µm can pass through the respiratory tract and deposit into the lungs. Smouldering fires in general produce particles less than 1 µm 7 which pass through the natural filters in the respiratory tract. The vapour phase of fires contains different gases and at different concentrations. Well-ventilated fires produce water vapour and CO 2 in large concentrations, while under-ventilated fires and smouldering fires produce high concentrations of asphyxiating gases such as CO and HCN 8. Smouldering fires produce gaseous reaction products that represent hazard to life, both in homes where people sleep and in workplaces such as silos, freight ships and bulk trucks. Unsolved issues related to the research field of smouldering fires will be handled within the project called EMRIS project (Emerging Risks from Smouldering Fires). The project is financed by the Norwegian Research Council for strategic university projects (Forskningsrådets strategiske høgskoleprosjekter), by 80 % and the Stord Haugesund University College by 20 %. The total investment in the project is 22 Million Norwegian kroner or approximately 2.2 million Euro. EMRIS started in 2015 and ends in 2019 and will then have contributed to the understanding, predicting and combating smouldering fires. The project involves four educational institutions: Stord/Haugesund University College (Norway), Otto-von-Guericke-University in Magdeburg (Germany), Lund University (Sweden) and Imperial College London (UK). Participants consist of Master and Ph.D. students together with supervisors and other experts. Four Ph.D. grants are included in EMRIS, and are allocated as follows: two Ph.D. students in Haugesund, one Ph.D. student in Magdeburg and the last Ph.D. student in Lund. The postdoctoral position in numerical modelling is located at Imperial College London.

3 The work within the project is defined as work packages, WP, and presented in Figure 1. In WP1, the effects of variations in geometries and boundary conditions on the transition from smouldering to flaming fire will be investigated both experimentally and through modelling. WP2 will characterize and measure the physio-chemical properties with relevance for self-ignition and smouldering combustion for common biofuels and wastes. WP3 will focus on smouldering in biofuels and waste products from the wood industry. WP4 will focus on the emergency response arrangements that are prepared by industry and fire services to manage both smouldering fires and worst-case scenarios caused by smouldering. EMRIS WP1 Haugesund, Lund, London WP2 Magdeburg WP3 Haugesund WP4 Haugesund Activity A Transition to flaming Activity B Self ignition Activity C Biofuels Emergency response Figure 1. Overview of the EMRIS work packages and the activities presented in this paper. Contact with industrial partners and public institutions has been established to gain experience and be up to date about problem areas to do with self-ignition and smouldering fires within the field of biomasses to make the research work as close to industrial practice as possible. This paper presents the initial findings from some of the work packages within the EMRIS-project. The work and findings are presented as activities A-C. ACTIVITY A: TRANSITION FROM SMOULDERING TO FLAMING Transition from smouldering to flaming is an interesting phenomenon within fire, that requires further investigation. Previous research shows that the transition from a surface reaction (smouldering) to a gas phase burning reaction (flames) may be dependent on different mechanisms. Ohlemiller 9 reported that increased air flow in voids between cellulose insulation and a wood frame may cause glowing and transition to flaming. Tse et al. 10 found that increasing air flows would increase the smouldering rate and cause oxidation of char (secondary char oxidation) left by smouldering of the initial material. Hagen et al. 11 found that increasing density in cotton affects the possibility of transition to flaming. However, in only approximately 20 % of the cotton experiments a transition to flaming occurred. Part of WP1 is to investigate the conditions for transition from smouldering to flaming fire in cotton. Experiments were made to find a setup that performs repeatable successful results in transition from smouldering to flaming fires The transition to flaming is affected by the sample size and the effects of changes in width, height and length were investigated. Material and experimental setup The material used in these experiments is commercially available, unbleached cotton batting. Cotton was chosen since it represents a group of cellulose-based materials that are prone to smolder 12. In addition, cotton is easy to compact to a wanted density. In the current study the density of cotton is 80 kg/m³ since this density has given transition to flaming previously 11. Previous studies with cotton show that transition to flaming only occur as the smouldering front interacts with a denser boundary 11. The current study uses a light weight concrete block as such a boundary. Two ignition sources are used. The large ignition source is a 10 by 10 cm ceramic hotplate described in reference 11. The small ignition source consists of a piece of light weight concrete that is 0.5 cm thick, 1 cm wide and 4 cm long and is heated using electrical wire and with a power of 50 W.

4 The small ignition source was placed 2 cm from the bottom of the sample and 2 cm from the concrete block at the centerline of the sample (see Figure 2). The small ignition source will heat the cotton for 3 minutes causing a smouldering fire and then switched off. The ignition sources were assumed to have little effect on the transition from smouldering to flaming. Figure 2. Test setup Activity A with small ignition source Results The following sample size is tested with the large ignition source: 15 x 15 x 15 cm high and 15 x 15 x 30 cm high. The samples that were 15 cm high had a transition to flaming in one of five tests, while the 30 cm high sample had no transition to flaming. Increasing the sample width to 40 cm and the length to 60 cm and maintaining the sample height at 15 cm using the small ignition source, gave transition to flaming in five out of five tests. The current study will continue work on different sample size and repeat test with the 15 x 15 x 15 cm high and 15 x 15 x 30 cm high using the small ignition source. Concluding summary The current results indicate that the transition from smouldering to flaming fire is dependent on the sample size. The increased size of the sample from 15 x 15 x 15 cm to 40 x 60 x 15 cm gives a rate of transition to flaming from 20 to 100 % in conducted tests. This experimental setup performs repeatable successful results in transition smouldering to flaming fire. ACTIVITY B: INFLUENCE OF INERT MATERIAL ON SMOULDERING Inert particles have an influence on the maximum reaction temperature, the self-ignition behaviour and the reaction mechanism of combustible dusts 13. In Activity B, this was investigated for lignite mixed with different inert materials in varying mixtures, particle sizes and specific surface areas of the particles. Material and experimental setup These experiments took place in a laboratory oven with an internal volume of 64 liters and a natural air exchange rate of 30 times per hour (1/h). The sample baskets where equidistant cylinders, made of wired mesh, to ensure the oxygen diffusion. The experimental setup is shown in Figure 3. Figure 3. Experimental setup of the hot storage experiments.

5 q3 [%/mm] An experimental series was performed with different mixtures of combustible dusts and inert materials. The focus of this activity is on the mixtures of lignite coal (LC) with sand (S) and magnesiumoxide (MO) of different particle size distributions. The substance name in table 1 consist of a letter and a number. The letter refers to the material and the number too either maximum particle size or specific surface. For example, S032 is sand with maximum 32 µm in particle size and M150 is magnesiumoxide with specific surface of 150 m²/g. Mixture rates are given in mass percentage separated by a slash. These substances were chosen to differentiate, if the effect of the higher reaction temperature depends mainly on the particle size or if catalytic surface effects due to high specific surfaces have to be taken into account. The specific surface was measured with BET-Analysis 14. It was not possible to determine exact values for the sand due to the smooth surface, but it can be shown that the values differ by orders of magnitude (see Table 1). Regarding to the particle size S063, MO150 and MO130 are within the same range, however they have different size distributions, as shown in Figure 4. Table 1. Material properties Substance Particle size [µm] Specific surface [m²/g] Lignite <800 4,5 S032 <32 0,4 S063 <63 0,4 S200 63<x<200 0,4 S <x<700 0,4 MO150 < MO130 < d_particle [µm] MO130 MO150 S 63 Figure 4. Density distribution of the particle size based on the particle volume (q3) measured by dynamic image analysis (measured with CAMSIZER XT by Retsch Technology) in the dispersed dust. Results and discussion According to DIN EN the sample was placed in a preheated oven at a constant temperature. This procedure is repeated, always with new sample material, until an ignition and a non-ignition can be observed within a temperature difference of 2 K. The non-ignition with the highest temperature is labelled the self-ignition temperature (TSI). Table 2 shows the increase of the self-ignition temperatures for the investigated mixtures compared to the pure lignite for different sample sizes. It is shown, that the TSI increases by the addition of inert material. The additive dilutes the concentration of the combustible mass per volume and results in an additional heat sink. It has to be remarked that the experiments with sand and magnesium oxide are made in different ovens with different batches of lignite. Within the scope of measurement uncertainties, the increase of the TSI is independent of the inert material, the particle size and the specific surface and depends on the mass fraction of the inert material only. Table 2. Increase of the self-ignition temperature [K] 15 compared to pure lignite due to addition of inert material. Sample T SI 100cm³ T SI 200cm³ T SI 400cm³ LC-S063 80/ LC-S063 60/ LC-S200 80/ LC-S200 60/ LC-S700 80/ LC-S700 60/ LC-MO130 80/ LC-MO130 60/ LC-MO150 80/ LC-MO150 60/

6 ln (δc T_SI²/r²) ; [K²/m²] Plotting the self-ignition temperatures in an Arrhenius diagram (see Figure 5) shows that the apparent activation energy Ea (slope of the lines) is independent of presence, particle size and specific surface of inert particles. Therefore, it can be concluded, that the reaction mechanism is similar. The lines are shifted in parallel, due to the increase of the self-ignition temperature, TSI ,5 10 9,5 9 8,5 8 0,0024 0, ,0025 0, ,0026 0, ,0027 0, /T_SI [1/K] Figure 5. Arrhenius Diagram for different mixtures. LC(1) LC(1) 60 S LC(1) 60 S LC(2) BK(2) 50 S BK(2) 50 MO The influence of the mixing ratio on the maximum temperature of the combustion was already shown by Schossig 13. Schossig could not find an explanation for this effect. These experiments were repeated with the inert material given in Table 1. The mixtures with S200 and S700 show no influence of the maximum reaction temperature, whereas finer particles had an increasing effect. These results were previously published by Wanke 16. In Figure 6, the results for MO150 mixtures are exemplarily shown. The focus was especially on small mixture rates, to examine when the effect starts. All samples were investigated in the same oven, preheated to a temperature of 150 C. Mixtures with an amount of more than 60% MO150 have not ignited due to the raise of the TSI. The effect of higher temperatures starts already at a mixing rate of 2,5%, whereby the fifty-fifty mixture gains the maximum temperature. Adding more than 50% inert material leads to temperatures below the peak temperature. Figure 6. Temperature-Time curves of different lignite MO150 mixtures in a 100cm3 sample basket at 150 C.

7 Concluding summary These experiments show that the addition of inert materials has an influence on the self-ignition temperature, but especially inert material with a huge amount of fine particles show an effect on the maximum reaction temperature. The main difference between the experiments is the volume of ashes that remains in the basket after the experiment (see Figure 7). The lignite particles shrink through the burn away process. Bulk material consisting of pure lignite collapses due to the shrinking process. Fine inert particles form a supporting structure. Pores are kept open. Therefore, are the porosity and the permeability increased. This results in an enhancement of the gas exchange, especially oxygen supply, and therefore a higher reaction rate. Additionally, the heat conductivity decreased due to the insulation effect of the pores. Summarizing it could be said, that the reasons for the effect of higher maximum temperatures could be determined, but that there are still some parameters whose influence is still uncertain. The concluding sentence is that while the effect on the self-ignition temperature is quite small and predictive due to the heat sink character of the inert material, the maximum reaction temperature raised up to 500 K. Figure 7. Ash height of pure lignite, lignite sand mixtures and lignite magnesium oxide mixtures. ACTIVITY C: SELF-SUSTAINED SMOULDERING IN WOOD PELLETS The motivation for this study was to find the conditions necessary to obtain a self-sustained smouldering combustion in wood pellets. Material and experimental setup The materials used were two types of commercially available Class 1 (NS 3165) spruce/pine pellets. The wood pellets were 8 mm in diameter with 7-8 % moisture and a bulk density of 707 and 732 kg/m 3. A small-scale experimental setup was used (see Figure 8). The wood pellets sample was placed inside an insulated steel pipe. The top of the steel pipe was open, giving a top-ventilated system. The pellets were heated by a heating source from below, until a given temperature was reached 2 cm above the aluminum plate, within the sample, after which the heating source was turned off. Thermocouples located within the sample measured temperatures, and a scale measured the mass change during the experiment. Thermocouple and scale locations are shown in Figure 8. Sample heights of 6, 8, 10 and 12 cm were used. For each sample height, a series of tests were run. Each test series included both non-smouldering and smouldering tests. Figure 8. The setup used in the study. Dimensions are given in mm. x: Thermocouple locations. h: height of the sample.

8 Results and discussion Typical temperature evolutions are shown in Figure 9. During the heating period with the heating source on, increasing temperatures were observed in the sample. The increased temperatures were first observed in the lower part of the sample. Two different behaviors in temperatures and mass loss were observed during the tests. The first one, shown in figure 9a, was a cooling towards ambient temperatures, after the heating source was turned off. This temperature development is typical for a non-smouldering behavior. Still, there was a mass loss of 9-25 %. The second behavior is shown in figure 9b, with a temperature decrease followed by an increase. The corresponding total mass loss was %. This is typical for the self-sustained smouldering experiments. This applies for both types of pellets. a b Figure 9. Temperatures during a non-smouldering experiment (a) and a smouldering experiment (b), measured along the vertical centerline of the sample. The time when the heating source was turned off is marked with a vertical line. The residue that remains after a completed experiment contains useful information on the process. Interestingly it was found that even for non-smouldering cases some of the pellets in the upper region of the sample were affected. To obtain a better understanding of how the pellets in various parts of the sample was affected, the residue from the non-smouldering cases was manually sorted and categorized as virgin fuel, partially brown, brown and black/charred. For the smouldering cases the residue was black/charred pellets and ash.

9 The different categories are shown in Figure 10. Some of the virgin fuel had dried but did not change color. Figure 10. Residue categories after experiments. The sample was removed 2 cm at a time from the top, and sorted layer by layer, as shown in Figure 11a. As can be seen from the diagram, all layers of the sample contained discolored pellets, which had been affected by the external heating source. At the top of the pipe, the pellets were mainly virgin or partially brown. Further down the amount of virgin fuel decreased and the amount of brown and black/charred pellets increased. Closest to the heat source at the bottom, there were mainly black/charred pellets as illustrated in Figure 11b. This was the case for all non-smouldering experiments, regardless of total sample height and pellets type. a b Figure 11. a) Example of the residue sorted layer by layer, after a non-smouldering experiment. 12 cm sample height, heated to 300 C. b) Illustration of a typical residue layering after a non-smouldering experiment.

10 The results for ten non-smouldering cases are displayed in Figure 12. This is the accumulated residue material from the layer by layer sorting in Figure 11. The broken lines represent the mass loss during the external heating period, denoted as mass loss during heating, and the mass loss after the external heating was turned off, denoted as mass loss during cooling. There are 4 sample heights, 6, 8, 10 and 12 cm. The bottom layer, 2 cm above the aluminum plate, was heated to different temperatures as displayed in the diagram. The table below the diagram displays the residue in grams for each category. Figure 12. Overview residue after non-smouldering experiments and mass loss during heating and cooling. As shown in the diagram in Figure 12, all residue material categories except for ash are represented in all the non-smouldering cases. The amount of each category varies with the total sample height, but not necessarily with the heating temperature within each sample height. The lowest sample size, 6 cm, has the highest percentage of discolored pellets. These samples also had high relative mass losses during heating and cooling. The largest sample size, 12 cm, has a trend of decreasing amount of virgin fuel with increasing heating temperature. It is reasonable that more of the sample is affected by the external heating, when the duration of the external heating is longer. Such a trend is also present but less clear for sample size 10 cm. For the 8 cm sample height, the input parameters of the tests were the same, but there were small variations in the amount of residue material. This may be due to stochastic variations in the pyrolysis and oxidation processes occurring in the sample during the test, or due to the manual sorting of the residue material. The results indicate that there clearly have been pyrolysis processes occurring in the samples, since the residue contains black/ charred pellets. The mass loss of % also supports this, as this is higher than the 7-8 % water content. In addition, there may have been heat-generating oxidation processes simultaneously. Despite these processes, the ten samples in Figure 12 cooled down after the external heating was turned off. This indicates that for these non-smouldering cases the pyrolysis at the bottom was not strong enough to obtain a self-sustained smouldering process. The question then arises of how far away from smouldering these non-smouldering cases were. The extent of black/charred pellets may give an indication of the size of the reaction zone. The height of the black/charred layer was found by the dividing the mass of the black/charred pellets by the total mass multiplied with the height of the sample. For the non-smouldering cases this was in the range of cm independent of sample height. The corresponding size for the smouldering cases in this study cannot be determined, as this would require the reactions to be quenched after the preheating, which in turn would make it impossible to predict whether that sample would smolder or not. Concluding summary This study gives an indication of the physical appearance of a wood pellets sample in the moments before a self-sustained smouldering fire is established. The whole sample is affected by the external heating, which is quantified by the discoloration of the pellets. It can be speculated that a reaction zone larger than 1.9 cm is needed to obtain a self-sustained smouldering fire in the wood pellets for this setup, independent of sample height.

11 OVERALL SUMMARY OF THE ACTIVITIES The results from the experiment with transition from smouldering to flaming fires, with cotton as base material, are indicating that sample size affects transition to flaming. Low repeatability in transition to flaming fire was observed for sample size 15 x 15 x 15 cm. However, samples with size 40 x 60 x 15 cm showed a 100 % repeatability in transition from smouldering to flaming fire. The successful results in repeatability leads to that this experimental setup and method shall be used as preferred in further work when transition from smouldering to flaming fires are desired. More experimental work with different sample sizes will be conducted to enrich the knowledge within the research field. Multiple experiments in hot storage tests was conducted with mixed materials composed in majority of lignite coal mixed with inert materials as sand and magnesium oxide of different particle size distributions. The output from the multiple experiments was that an increased mass fraction of inert material lead to increase in the self-ignition temperature. It was also observed that for mixtures with up to 50 % inert material, sample temperatures up to 400 C higher were then observed during combustion. The conclusion from the experiments is that the particle size of the inert materials is an influencing factor as they form pores in the mixed materials when the lignite coal is combusted. The formation of pores and increased porosity and permeability of the material results in more optimized combustion conditions. The increase of the self-ignition temperature is seen as a result of the heatsinking properties of the inert material. A sensitivity study on the conditions leading to an onset of self-sustained smouldering combustion of wood pellets has been conducted using a small-scale top-ventilated experimental setup. By varying the heating condition of the sample it was found when a self-sustained smouldering fire was initiated. It was found that the mass loss for both smouldering and non-smouldering cases was larger than the measured water content, and a study of the residue after test displayed that the whole sample was affected by the heating. A critical mass of black/charred pellets needed to obtain a self-sustained smouldering is suggested.

12 FUTURE WORK The research within the different EMRIS work packages shall continue during Experiments will include analysis of the gaseous reaction products during thermal decomposition of biomass. Studies on varying the input parameters in the experimental setups, as well as detection and suppression of smouldering shall be performed. Medium scale pellet experiments will be done to investigate reactions during smouldering. Waste and substitute fuel (fuel made of waste) will be studied. Results will be compared to results from wood pellets experiments and evaluated for further analysis. Research will also be done on emergency response to smouldering fires. REFERENCES 1 Hornung, A. Transformation of biomass: Theory to Practise. (Wiley, 2014). 2 Krause, U. Fires in Silos: Hazards, Prevention, and Fire Fighting. (Wiley-VCH, 2009). 3 Persson, H. Silo Fires : Fire extinguishing and preventive and preparatory measures. (Swedish Civil Contingencies Agency (MSB), 2013). 4 Rein, G. in SFPE Handbook of Fire Protection Engineering, 5 ed. (ed Morgan J. Hurley) p. 591 (SFPE, 2016). 5 Babrauskas, V. Ignition handbook : principles and applications to fire safety engineering, fire investigation, risk management and forensic science. (Issaquah, WA : Fire Science Publishers, c2003., 2003). 6 Janzé, G. F. P. Biomass storage pile basics, < (2011). 7 Purser, D. A. & McAllister, J. L. in SFPE Handbook in Fire Protection Engineering, 5 ed. (ed Morgan J. Hurley) p (SFPE, 2016). 8 Purser, D. A. in SFPE Handbook of Fire Protection Engineering, 5 ed. (ed Morgan J. Hurley) p (SFPE, 2016). 9 Ohlemiller, J. Forced smolder propagation and the transition to flaming in cellulosic insulation. Combustion and Flame 81, (1990). 10 Tse, S. D., Fernandez-Pello, A. C. & Miyasaka, K. in Symposium (International) on Combustion (1996). 11 B. C. Hagen, V. F., G. Kleppe and B. J. Arntzen. Transition from smoldering to flaming fire in short cotton samples with asymmetrical boundary conditions. Fire Safety Journal 71, (2014). 12 Wakelyn, P. J. & Hughs, S. E. Evaluation of the flammability of cotton bales. Fire and Materials 26, (2002). 13 Schossig, J. Beurteilung und Verhinderung von Selbstentzündung und Brandgasemissionbei der Lagerung von Massenschüttgütern und Deponiestoffen., (Berlin, 2010). 14 Burt, D. Brunauer, Emmitt and Teller - The Personalities Behind the BET Method. Energeia 5 (1994). 15 in DIN EN (Beuth Verlag, Berlin, 2007). 16 Wanke, C. in ISHPMIE; 10 Proceedings of the tenth International Symposium of Hazards, Prevention, and Mitigation of Industrial Explosions (Bergen, Norway, 2014).