Project no. FP6-018505 Project Acronym FIRE PARADOX Project Title FIRE PARADOX: An Innovative Approach of Integrated Wildland Fire Management Regulating the Wildfire Problem by the Wise Use of Fire: Solving the Fire Paradox Instrument Integrated Project (IP) Thematic Priority Sustainable development, global change and ecosystems D3.1-5 Probability of ignition modelling in forest fuels – First results Due date of deliverable: Month 18 Actual submission date: Month 19 Start date of project: 1st March 2006 Duration: 48 months Organisation name of lead contractor for this deliverable: Mediterranean Agronomic Institute of Chania (P04) Revision (1000) Project co-funded by the European Commission within the Sixth Framework Programme (2002-2006) Dissemination Level PU Public PP Restricted to other programme participants (including the Commission Services) RE Restricted to a group specified by the consortium (including the Commission Services) CO Confidential, only for members of the consortium (including the Commission Services) X Table of contents 1. Introduction (State of the art) ................................................................................. 3 General objectives ...................................................................................................... 5 PART I – Ignition probability in dead fuels (Ex Situ), MAICh ........................................... 7 Laboratory ignition data collection ............................................................................... 7 Materials and methods ............................................................................................... 7 Experiment 1: ............................................................................................................ 9 Experiment 2: .......................................................................................................... 12 Experiment 3: .......................................................................................................... 14 Results and Discussion ............................................................................................. 15 Experiment 1: .......................................................................................................... 15 Experiment 2: .......................................................................................................... 17 Experiment 3: .......................................................................................................... 19 Additional tests: ....................................................................................................... 22 Future work ............................................................................................................. 23 PART II – Ignition probability in live fuels (In situ), AUTh ............................................ 24 Objectives ............................................................................................................... 24 Methods .................................................................................................................. 24 Results .................................................................................................................... 27 References .............................................................................................................. 31 ANNEX I ................................................................................................................. 37 D3.1-5-18-1000-1 Page 2 1. Introduction (State of the art) Ignition is required for the initiation of any fire, large or small. Ignition can be described as “the process by which a rapid, exothermic reaction is initiated, which then propagates and causes the material involved to undergo change” (Drysdale, 1985). In this process fuel is transformed from “a non reactive equilibrium state to a self-sustaining reactive state” (Atreya, 1998). There are two types of ignition, spontaneous and piloted. Spontaneous ignition occurs without the aid of a pilot source (Drysdale, 1985). In forest fires, however, piloted ignition is the usual procedure for initiation and spread of the fire. Pilot sources are generally small in comparison to the size of the fuel and have locally high temperatures in order to initiate combustion (Atreya, 1998). Piloted ignition occurs at a lower temperature than spontaneous ignition and it is the mechanism responsible for fire growth (Atreya, 1998). The first phase of ignition is called preignition (Susott, 1984). During preignition a heat source provides heat to the fuel. The temperature of the fuel starts rising. During this endothermic reaction the energy that is absorbed from the ignition source is used to increase the temperature of the fuel and the moisture it contains. In the process volatiles start being released in the gas phase. At the temperature of 100oC a significant amount of energy is consumed for evaporation of the moisture in the fuel. The amount of heat required to convert a unit mass of water into vapor without a change in temperature is 2257 kJ/kg and is called “the specific latent heat of vaporization”. The amount of heat necessary to ignite 1 kg of fuel, measured in kJ/kg, is called the “heat of preignition”. Obviously, it is dependent on the amount of moisture present in the fuel. The more moisture in the fuel, the more energy is needed to evaporate the water and then bring the dry fuel to ignition temperature. Furthermore, the presence of moisture dilutes any flammable volatiles evolved, limiting their ignitability (Atreya, 1998). Once the density of flammable volatiles is sufficient, ignition can occur providing there is enough oxygen present. Ignition is marked by the onset of flaming. Ignition temperature has been defined as the critical temperature that the fuel needs for burning to begin (Williams, 1982; Saito, 2001). A number of temperatures have been reported in the literature for the piloted ignition of cellulosic fuels. The most commonly reported ignition D3.1-5-18-1000-1 Page 3 temperature is 320°C (Anderson, 1969; Schroeder, 1969; Rothermel, 1972; Frandsen, 1973; Wilson, 1990), with other temperatures including 325°C (Stockstad, 1975), 327°C (600K) (Albini, 1993; Albini and Reinhardt, 1995), 350°C (Simms, 1963; Williams, 1982; Drysdale, 1985; Saito, 2001) and 384°C (Atreya, 1998) also used. Many authors report a range of ignition temperatures (eg: Anderson, 1970; Susott, 1984; Wilson, 1985; Liodakis et al., 2002), due to its dependence on fuel type (Susott, 1984). Moisture content and amount of fuel being heated also appear to affect ignition temperature (Xanthopoulos 1990). The ignition probability for a given fuel is the probability that an ignition source has an effective heat equal to or greater than the heat required for pre-ignition (Schroeder, 1969). Fuel moisture content (FMC) is recognised as the variable with the greatest influence on fuel ignitability (e.g. Gisbourne, 1928; Byram, 1959; Pompe and Vines, 1966; Anderson, 1969; Schroeder, 1969; Blackmarr, 1972; Luke and McArthur, 1978; Green, 1981; Xanthopoulos and Wakimoto 1993, Cheney and Sullivan, 1997; Atreya, 1998; Nelson, 2001, Plucinski, 2003, Larjavaara et al. 2004). It has been used as the primary variable in ignition and flammability studies by Pompe and Vines (1966), Anderson (1969), Montgomery and Cheo (1969), Schroeder (1969), Parrot and Donald (1970), Blackmarr (1972), Muraszew and Fedele (1976), Trabaud, (1976); Gill et al. (1978), Countryman (1980a), Wilson (1985; 1990), Latham and Schlieter (1989), Weber (1989), Fransden (1991; 1997), Lawson et al. (1997a), Anderson, (2000), and Fernandes et al. (2002). Most of the wildland fires around the world are human caused (Kruger and Bigalke, 1984; Whelan, 1995; Perry, 1998; Weber, 2000). Natural causes such as lightning or volcanoes are only prominent in specific regions. For example, lightning ignitions are most likely to occur in high-elevation areas (McRae, 1992; Latham and Williams, 2001; Anderson, 2002). Anthropogenic ignitions are of two types: deliberate and accidental. Deliberate ignition is used for prescribed fire or arson. Accidental ignitions are usually a result of negligence. Determining the probability of an ignition source is practically impossible due to the variety of sources and their causes. The probability of ignition sources varies spatially, depending on land use, and temporally due to weather conditions, season and day of the week (Catchpole, 2001). Some effort has been devoted recently to the prediction of specific causes such as cigarettes that can be used for prevention planning (Dainier, 2003, Xanthopoulos et al., 2006). D3.1-5-18-1000-1 Page 4 FMC is not the only fuel property that affects ease-of-ignition. Other fuel characteristics such as fuel particle thickness (expressed as surface-area-to-volume ratio), chemical composition, density, arrangement (such as packing ratio), continuity and quantity, also influence ignitability. Each of these characteristics can be evaluated separately experimentally, allowing comparisons between fuels (Liodakis et al., 2005), but using such information for practical purposes is not easy. As a result, many researchers have focused on experimenting with fuel types of interest and selected heat sources, developing empirical estimates of ignition probabilities (Countryman, 1980a; Markalas, 1985). Accidental ignition sources are numerous. They may find their way on the fuels either truly accidentally or due to human negligence. They include sparks, matches, cigarettes and car exhausts. Studies using discarded cigarettes as firebrands dropped on pine needles and dead grass have found that ignition seldom occurs, even when the FMC is very low (Countryman, 1980a; Markalas, 1985). Car exhaust systems have been found to ignite grass by direct contact for varied periods of time (Knight and Hutchings, 1987). Spark ignitions can come from mechanical sources, such as bulldozers and slashers scraping rocks and careless use of welding and grinding equipment (Luke and McArthur, 1978), and electrical sources, including spark ignitions from power lines (Rowntree and Stokes, 1994; Conroy, 1996). They can also come from other fires such as fireplaces or barbeque fires. Sparks need to come into contact with dry fine fuel for ignition to succeed as they only produce small amounts of heat for short times (Cheney and Sullivan, 1997). Finally, it should be pointed out that the properties of all ignition sources and the heat transfer to the fuel are affected by the presence of wind. This is especially true when the heat source itself, such as a cigarette, is combustible. The wind may favour this combustion but if it is too strong it may even lead to extinction of the heat source (Satoh et al., 2003). General objectives Following a similar approach to the researchers cited above, and aiming to cover gaps in the literature on ignition, especially in regard to Mediterranean conditions, the present study focuses on the following: To evaluate the threshold of fuel moisture content that allows a fire to start. A range of fuel types (pine needles, grass and Quercus coccifera leaves) are examined, as are different ignition sources (kitchen matches, cigarettes, D3.1-5-18-1000-1 Page 5 machinery sparks and electrical discharge), with the presence/absence of wind in order to determine the probability of ignition of selected natural dead fuels (MAICh). To measure the probability of ignition of annual live herbaceous fuels, at various moisture contents, in the field (AUTh). Fuel moisture content (FMC) is used as the main predictor variable throughout these experiments because it has a major effect on fuel ignitability, is easily altered and can be accurately measured. Only the first results of the study are presented within this deliverable: Probability of ignition of pine needles (Pinus halepensis) with kitchen matches and cigarettes as ignition sources conducted in the wind tunnel of MAICh. Probability of ignition of grass (Hyparrhenia hirta) with kitchen matches as an ignition source conducted in the wind tunnel of MAICh. Some preliminary test of pine needles with machinery sparks as well as grass with cigarettes conducted in the wind tunnel of MAICh. Fuel moisture extinction in live annual herbaceous plants (Avena barbata) in the field (AUTh). The final results will be presented within deliverable D 3.1-10 due in month 46 of the project. D3.1-5-18-1000-1 Page 6 PART I – Ignition probability in dead fuels (Ex Situ), MAICh Laboratory ignition data collection There were many advantages for experiments to be conducted in the laboratory. Laboratory experiments allow control over fuel and environmental variables and precise measurement of fuel and fire behaviour. Many of these would be impossible or impractical to measure in the field and are subject to a great degree of variation, which can be avoided in the laboratory. Gill et al. (1978) used the laboratory for an investigation into the role of moisture in flammability to avoid fuel and weather variation in the field. The three processes investigated in the laboratory experiments would not be able to be investigated separately in field ignition experiments without excessive site preparation. Laboratory experiments are also safer and less expensive than field experiments to conduct (Burrows, 1999a) and allow for more replicates to be accomplished and fewer gaps in datasets. The laboratory used for all experiments is located at the Mediterranean Agronomic Institute of Chania. The laboratory was a well ventilated concrete room. All fuels were stored and prepared in the laboratory. The experiments were conducted inside a wind tunnel Materials and methods Experimental ignitions were attempted in the Forest fire laboratory of MAICh using reconstructed fuel beds made with fuel of uniform moisture content. Fuel was collected by hand, with caution taken to avoid collecting fallen leaves or other photosynthetic organs from the desired species, twigs, rocks and soil. The pine needles of Pinus halepensis were collected from sites near the Mediterranean Agronomic Institute of Chania. The selected grass species was Hyparrhenia hirta a perennial native species, which is very common next to the roads (Pict. 1). The samples were collected from the area of Elafonisi on the western part of the prefecture of Chania. The fuels were transported to the laboratory in garbage bags, where they were subjected to different treatments, depending on the desired moisture content. D3.1-5-18-1000-1 Page 7 Picture 1. Hyparrhenia hirta growing next to the road in the area of Elafonisi D3.1-5-18-1000-1 Page 8 Experiment 1: Fuel type: Pine needles (Pinus halepensis), Ignition source: kitchen matches. Dead pine needles of Pinus halepensis were collected, cleaned and put in the oven at 70C for 48 hours to dry. Two different methodologies were used to prepare samples at different moisture contents as follows: 1. Samples preparation (tests 1 to 44): Samples of 50 g dry needles were put in plastic bags and sealed. The desired level of moisture content (percent) was achieved by adding the appropriate amount of moisture to the dry fuel: The dry sample was placed on a balance and then water was added using a squeeze-type sprayer bottle to evenly distribute the moisture over the sample until the desired total weight (based on the initial oven dry weight and the desired moisture content) was reached. The plastic bags were then quickly sealed and placed in a 50C drying oven for 24 hours to ensure equal distribution of the moisture within the sample (moisture equilibrium) (De Groot et al. 2005). (Pict. 2) Picture 2. Samples of pine needles sealed in plastic bags. D3.1-5-18-1000-1 Page 9 2. Samples preparation (tests 45 to115): Pine needles were put on a fuel bed. Water was added using a squeeze-type sprayer bottle and the fuel bed was exposed to the sun. Pine needles were mixed continuously to evenly distribute the moisture over the fuel bed (Pict. 3). Around 50 g of Pine needles were placed in plastic bags at different time intervals (1 to 5 minutes). Plastic bags were quickly sealed and placed for at least 2 hours in room at ambient conditions to ensure equal distribution of the moisture within the sample (Pict. 4). Picture 3. Pine needles mixed continuously to evenly distribute the moisture over the fuel bed. D3.1-5-18-1000-1 Picture 4. Plastic bags with pine needles placed in the lab. Page 10 Experiments All ignition tests (115 experiments) were completed by removing about 30 g of pine needles from the plastic bag and placing them in an aluminium disk. The aluminium disk had a diameter of 20 cm and the fuel depth was 3 to 3.5 cm. The bulk density of the samples was 27 Kg/m3 to 31 Kg/m3. The remaining 20 g of pine needles were placed in a small aluminium disk and oven dried at 70C for 48 hours to calculate the real moisture content of the sample. A wooden match was lit and randomly dropped on the pine needle sample from a height of approximately 10 cm. If the match started a fire, it was considered a positive test and classed as “burn”. If the initially dropped match did not result in a positive test, a second match was dropped. A third match was dropped if the second match did not result in a positive test. The ignition test was classed as “non burn” if all three matches failed to provide a positive test (De Groot et al. 2005). During the experiments air RH (%), air temperature and fuel temperature were recorded. All the experiments were done indoors in the wind tunnel with no presence of wind. The RH was in the range of 57% to 71%, the air temperature in the range of 25C to 26C and the fuel temperature, measured by a thermocouple in contact with the needles, in the range of 23C to 27.7C. D3.1-5-18-1000-1 Page 11 Experiment 2: Fuel type: Pine needles (Pinus halepensis), Ignition source: Cigarettes. Dead pine needles of Pinus halepensis were collected and cleaned. Four different methodologies were used to prepare samples at different moisture contents as follows: 1. for FMC between 1 % and 3 %: Needles were dried in the oven at 70C for 48 hours and then left in the open air inside the wind tunnel (RH around 62%) for different time intervals for moisture absorption. 2. for FMC between 3 % and 8 %: Pine needles were taken from an open big box stored indoors. Their moisture content was around 12%. Samples of 50 g were prepared in disks and placed in the oven at 70C for 5-20 minutes. The samples were removed from the oven at different time intervals (1 to 2 minutes) and were placed in plastic bags. Plastic bags were quickly sealed and placed for 1 hour in a room at ambient conditions to ensure equal distribution of the moisture within the sample. 3. for FMC between 8 % and 10 %: Samples were used directly from the needles kept indoors, inside an open big box, at a relative humidity higher than 60 %. 4. for FMC higher than 10 %: Water was added using a squeeze-type sprayer bottle and the needles were mixed to evenly distribute the moisture over the sample. D3.1-5-18-1000-1 Page 12 Experiments: All ignition tests (116 trials) were completed by removing about 30 g of pine needles from the plastic bag and placing them on an aluminium tray. The sample had a diameter of 16 cm and the fuel depth was 5 cm. The bulk density of the samples was 30 Kg/m3. The remaining 20 g were placed in the oven at 70C for 48 hours to calculate the real moisture content of the sample. A cigarette was lit and when it had a remaining length of 4 cm, its tip was placed at 1 cm depth inside the fuel (Satoh et al. 2003) with a 45 degree angle. If the cigarette started a fire, it was considered a positive test and recorded as “burn”. The ignition test was recorded as “non burn” if the cigarette failed to start a fire. All experiments were done indoors in the wind tunnel with no presence of wind. The RH was in the range of 57% to 67%, the air temperature in the range of 23C to 26C and the fuel temperature in the range of 24.5C to 26.5C. D3.1-5-18-1000-1 Page 13 Experiment 3: Fuel type: Perennial grass (Hyparrhenia hirta), Ignition source: kitchen matches. Fresh material of Hyparrhenia hirta were collected on June 8, 2007 and was air dried for 1 week in the laboratory. The material was cut into small pieces about 8-10 cm then it was oven dried at 70oC for 48 hours. The material was put on a large tray, and was sprayed with enough water to bring it moisture content to more than 35%. It was then exposed to the sun and was continuously mixed. Every 1 or 2 minutes, samples of about 50 g were taken and put in plastic bags. The samples were stored in the laboratory for at least 2 hours to achieve moisture equilibrium. Before the experiment, a sub-sample was taken for fuel moisture content measurement. The sub-samples were oven dried at 70oC for 48 hours. Experiments: All ignition tests (161) were completed by removing about 25 g of grass from the plastic bag and placing them in an aluminium disk. The aluminium disk had a diameter of 20 cm. The fuel depth was 4 to 4.5 cm and the bulk density of the samples was 14 to 17 Kg/m3. The remaining 20 g of the fuel were placed in a small aluminium disk and oven dried at 70C for 48 hours to measure the real moisture content of the sample. A wooden match was lit and randomly dropped on the fuel sample from a height of ~ 10 cm. If the match started a fire, it was considered as a positive test and classed as “burn”. If the initially dropped match did not result in a positive test, a second match was dropped. A third match was dropped if the second match did not result in a positive test. The ignition test was classed as “non burn” if all three matches failed to provide a positive test. (De Groot et al. 2005). All tests were done indoors in the wind tunnel with no presence of wind. The RH was in the range of 67% to 84%, the air temperature in the range of 20C to 22C and the fuel temperature in the range of 15C to 22C. D3.1-5-18-1000-1 Page 14 Results and Discussion Experiment 1: The first set of experiments was carried out with needles of Pinus halepensis as fuel and kitchen matches as ignition source. It resulted in a total of 115 experiments of which 52 resulted in “ignition” and 63 in “no ignition” (Fig.1). Pine needles - kitchen matches classification of the 115 experiments No ignition Ignition 35 No of experiments 30 3 25 20 26 15 10 21 26 25 5 8 6 0 5-12 12-18 18-24 24-30 >30 Fuel Moisture Content % Figure 1. Number of experiments at different classes of fuel moisture content. The results were analysed using logistic regression. The estimated parameters, their standard errors and significance levels are presented in table 1. Table 1. The estimated parameters and statistics associated with the logistic model. Variable β S.E. S.L. FMC (%) -69.174 14.133 0.000002 Constant 12.650 2.681 0.000002 The model based on the dataset with FMC (%) as the only independent variable is: D3.1-5-18-1000-1 Page 15 Ln(Pign/1-Pign) = 12.650 - 69.174*FMC where Pign = is the estimated probability of ignition and FMC is the fuel moisture content (%). For this model the following statistics were computed: -2 Log Likelhood, 45.304; Nagelkerke R2, 0.837. The model classifies correctly 89.6% of the values in the dataset. It can also be written as: Pign=1/(1+exp(-(12.650+(-69.174*FMC)))) A plot of the data and the equation is shown in Figure 2 Figure 2. Dataset points and logistic regression model (solid line) showing ignition probability of pine needles by kitchen matches as a function of needle moisture content (%). D3.1-5-18-1000-1 Page 16 Experiment 2: The second set of experiments was carried out with needles of Pinus halepensis as fuel and cigarette butts as ignition source and resulted in a total of 116 experiments of which 67 resulted in “ignition” and 49 in “No ignition” (Fig.3). Pine needles - cigarette butts classification of the 116 experiments No ignition Ignition No of experiments 35 30 8 25 20 30 15 25 10 5 0 13 8 2 2 0-1 1-2 2-3 3-4 4-5 9 5-6 12 5 6-7 2 7-8 >8 Fuel Moisture Content % Figure 3. Number of experiments at different classes of fuel moisture content. The results were analysed using logistic regression. The estimated parameters, their standard errors and significance levels are presented in table 2. Table 2. The estimated parameters and statistics associated with the logistic model. Variable β S.E. S.L. FMC (%) -249.185 53.537 0.00003 Constant 10.268 2.120 0.00001 The model based on the dataset with FMC% as the only independent variable is: Ln(Pign/1-Pign) = 10.268 - 249.185*FMC D3.1-5-18-1000-1 Page 17 where Pign = is the estimated probability of ignition and FMC is the fuel moisture content (%). For this model the following statistics were computed: -2 Log Likelihood, 67.770; Nagelkerke R2, 0.727. The model classifies correctly 83.6% of the values in the dataset. It can also be written as: Pign=1/(1+exp(-(10.268+(-249.185*FMC)))) A plot of the data and the equation is shown in Figure 4. Figure 4. Dataset points and logistic regression model (solid line) showing ignition probability of pine needles cigarette butts as a function of needle moisture content (%) D3.1-5-18-1000-1 Page 18 Experiment 3: The third set of experiments was carried out with the grass Hyparrhenia hirta as fuel and kitchen matches as ignition source and resulted in a total of 161 experiments of which 55 resulted in “ignition” and 106 in “No ignition” (Fig. 5). Grass - kitchen matches classification of the 161 experiments No ignition Ignition No of experiments 60 50 40 32 30 20 5 10 0 18 14 5-10 10-15 29 20 27 13 3 0-5 15-20 20-25 25-30 >30 Fuel Moisture Content % Figure 5. Number of experiments at different classes of fuel moisture content. The results were analysed using logistic regression. The estimated parameters, their standard errors and significance levels are presented in table 3. Table 3. The estimated parameters and statistics associated with the logistic model. Variable β S.E. S.L. FMC (%) -56.673 11.284 0.000001 Constant 8.942 1.842 0.000001 The model based on the dataset with FMC% as the only independent variable is: Ln(Pign/1-Pign) = 8.942 - 56.673*FMC D3.1-5-18-1000-1 Page 19 where Pign = is the estimated probability of ignition and FMC is the fuel moisture content (%). For this model the following statistics were computed: -2 Log Likelihood, 90.918; Nagelkerke R2, 0.709. The model classifies correctly 83.9% of the values in the dataset. It can also be written as: Pign=1/(1+exp(-(8.942+(-56.673*FMC)))) A plot of the data and the equation is shown in Figure 6. Figure 6. Dataset points and logistic regression model (solid line) showing ignition probability of grass by kitchen matches as a function of grass moisture content (%). D3.1-5-18-1000-1 Page 20 The results of the experiments until now do not present any surprises. More specifically: The role of fuel moisture content as one of the most important fuel characteristics affecting ignition is confirmed and quantified. Fuel type also has an influence on ignition probability. For 50% ignition probability with matches the corresponding FMC is 18.25% and 15.75% for pine needles and grass respectively. The type of the ignition source and its heat release rate is also a very important parameter for fire ignition. In pine needles, for 50% ignition probability the FMC should be 18.25% with matches, while with cigarettes it should be 4.11%. In grass, for 50% ignition probability the FMC should be 15.75% with matches while with cigarettes no ignition occurs even on completely dry fuels. Obviously, these findings will be augmented further by the experiments that will follow. A complete discussion, including some investigation on the general principles affecting ignition probabilities, will be provided after completion of all the experiments, within D3.110, which is due in month 46 of the project. D3.1-5-18-1000-1 Page 21 Additional tests: Two additional tests were carried out. The first test consisted of Hyparrhenia hirta grass as fuel and cigarette butts as ignition source with and without wind following the same methodology as that reported for experiment 2. About thirty, (30) trials with completely dry fuel (FMC=0%) resulted in no ignition (Pict. 5). Picture 5. Fuel bed of the grass Hyparrhenia hirta and cigarette butt as ignition source The second test was carried out with Pinus halepensis needles as fuel and machinery sparks as ignition source. An electrical grinding disk was applied on a plumbing tube and on iron stick for the production of machinery sparks (Pict. 6) Picture 6. Machinery sparks applied on completely dry pine needles The fuels were completely dry (FMC=0%) The sparks that were produced although they fell immediately on the fuel bed that was less than 10 cm away, did not cause any ignitions. The fuel temperature was measured with a thermocouple in contact with the D3.1-5-18-1000-1 Page 22 needles during the exposure of the fuel bed to the sparks. The fuel temperature increased slightly by only 2-3oC. Future work The ignition experiments will be continued until the end of the project as shown in the following table: Ignition source Machinery Electrical sparks discharge V T X V T X X Quercus coccifera leaves X X X X Grass (Avena barbata) X X X X Pine needles - X X X Grass (Hyparrhenia hirta) - T X X Quercus coccifera leaves - X X X Grass (Avena barbata) - X X X Matches Cigarettes Pine needles V Grass (Hyparrhenia hirta) Fuel type No Wind Wind V= Completed, X= Will be done, T= Tested no ignition The final results will be presented in deliverable D 3.1-10 due in the month 46 of the project. D3.1-5-18-1000-1 Page 23 PART II – Ignition probability in live fuels (In situ), AUTh A probabilistic model of moisture of extinction of live fuels in the field Objectives The objective of this study was to measure the probability of ignition under various moisture contents of annual herbaceous fuels in the field. Thus, threshold values of fuel moisture for fire extinction (non-ignition) can be determined. This study presents two novelties: It measures fuel moisture of extinction in live annual herbaceous plants throughout their life cycle. The experiments are conducted in the field (in situ), taking into account all the environmental conditions (air temperature, air relative humidity, and wind speed) that were present during the time of the ignition tests. Thus, a more realistic assessment of the fuel moisture of extinction of live herbaceous plants through their life cycle is achieved. Methods The annual herbaceous plant was Avena barbata. The plots were 100 m2 each; with plant cover > 90% and no litter understory. The firing method was drip torch in a straight line on the ground, with five trials per test (Pict. 1-4). The firing line was 3 m long and the criterion for ignition was vivid burning for 45 seconds. During this period, the fire was spreading at various distances (depending on the windspeed and the other environmental parameters) but this was not considered a criterion for ignition. In all cases, it was very obvious after the five trials in each test, whether it was successful ignition or not. The experiment consisted of a live herbaceous plant, whose moisture content was monitored through its life cycle. Of course, at the withering stage, it was more dry then fresh, but still there was no mixture of live and dead plants together, since we dealt with only one species (Avena barbata). Moisture content was determined by oven-drying at 105o C until constant weight. Plant samples were collected just before the tests. A sling psychrometer and a portable wind meter were used for the meteorological measurements. The wind speed was measured at 2 m height. The detailed results are given in the Annex I. D3.1-5-18-1000-1 Page 24 Due to the fact that the dependent variable (ignition or non ignition) has a dichotomous outcome, a stepwise logistic regression approach that allows the estimation of the probability of occurrence of event from a combination of fire weather and fire environmental factors was chosen (Hosmer and Lemeshow 2000). The SPSS 14.0 statistical package was used for the calculations (Norusis1997). The logistic regression model had the following form (Hosmer and Lemeshow 2000): e g ( x) P( yi 1) 1 e g ( x) Being the logit given by the equation: g ( x) 0 1 x1 2 x2 ... i xi where, P ( yi 1) is the probability of fire ignition, xi are the independent variables, and βι are the coefficients estimated through the maximum likelihood method, which will produce coefficients that maximize the probability density as a function of the original set of data. A decision criterion of 0.5 as the threshold of fire ignition was assumed. This cutoff value has been commonly used to discriminate the continuous model response in the interval between 0 (0%) and 1 (100%) (Wilson and Ferguson 1986, Ryan and Reinhardt 1988, Cruz et al. 2004) The model was analyzed through the rationality of the explanatory variables, the significance of the regression coefficients, the goodness of fit statistics and the discrimination capacity as measured by the area under a relative operating characteristic (ROC) curve (Wilson 1987). D3.1-5-18-1000-1 Page 25 Pictures 1-4. Ignition trials in the field D3.1-5-18-1000-1 Page 26 Results Table 1 presents basic descriptive statistics associated with the data set used in the development of the logistic fire ignition model. Table 1. Basic descriptive statistics associated with the data set used in the development of the logistic fire ignition model. Independent variables n Minimum Maximum Mean SD Air Temperature (0C) 108 11 33 26.088 5.099 Relative Humidity (%) 108 35 87 58.213 12.690 Wind Speed (km/hr) 108 0 24 8.537 4.506 Fuel Moisture Content (%) 108 8 200 34.648 46.099 Stepwise logistic regression indicated that only the moisture content was statistically significant (p<0.001), and consequently, it was the variable that was kept in the model. The estimated parameters, their standard errors, and significance levels are presented in table 2. Table 2. Estimated parameters and statistics associated with the probabilistic fire ignition logistic model Variable β S.E. S.L. Air Temperature (0C) -0.182 0.178 0.308 Relative Humidity (%) -0.116 0.080 0.146 Wind Speed (km/hr) 0.109 0.133 0.415 Fuel Moisture Content (%) -0.127 0.034 0.001 Constant 6.704 1.552 0.001 S.E. Standard Error, S.L. Significance Level Thus, only the fuel moisture content was kept as a significant independent variable in the model. Based on the complete data set (n=108) the model form is: D3.1-5-18-1000-1 Page 27 Probability of ignition = 1 / (1 + exp(-(6.704-0.127*Moisture Content)) A plot of the data and the equation is shown in Figure 1 Figure 1. Dataset points and logistic regression model (solid line) showing ignition probability of live grass as a function of grass moisture content (%). Goodness of fit statistics is presented in table 3. The Negelkerke R2 associated with the above equation is 0.902, while the -2 Log(Likelihood) was relative low (15.416). The McFadden R² which is the likelihood ratio index presented a value of 0.85. As the name suggests, this is an analog to the R² reported in linear regression models. The Hosmer and Lemeshow's goodness of fit test was not significant indicated that the model has an adequate fit. D3.1-5-18-1000-1 Page 28 Table 3. Goodness of fit statistics Descriptive statistic Values Observations 108 -2 Log(Likelihood) 15.416 R²(McFadden) 0.846 R²(Nagelkerke) 0.902 Hosmer and Lemeshow's goodness of fit test 0.812 (sig. 0.997) The Receiver Operator Characteristic (ROC) curve is often used as an index of how well a scoring system is able to classify events into one of the two alternatives (an area of 1 is perfect, 0.5 is non-informative) such as: fire ignition or non fire ignition. The logistic model yields an area under the ROC curve of 0.99. Overall, the logistic model correctly predicted fire ignition probability 97.2% of the time in the data set (table 4). Table 4. Classification table comparing observed and predicted fire ignition probability through the application of the logistic model to the data. Observed Non ignition Ignition Percent correct (%) Non ignition 17 2 89.47 Ignition 1 87 98.86 Overall 97.20 Probability analysis of fire occurrence as a function of moisture content with the logistic model is presented in table 5. D3.1-5-18-1000-1 Page 29 Table 5. Fire ignition probability with the fitted model based on lower and upper brackets (95%) of fuel moisture content values. Probability of ignition Lower bound 95% Upper bound 95% 0.01 0.05 71.326 moisture content 63.941 131.724 moisture content 113.062 0.10 59.895 103.222 0.20 54.830 91.472 0.30 51.005 83.174 0.40 47.562 76.256 0.50 44.139 69.996 0.60 40.443 64.009 0.70 36.091 58.002 0.80 30.350 51.619 0.90 21.158 43.995 0.95 12.664 38.605 0.99 -4.616 29.838 D3.1-5-18-1000-1 Page 30 References Anderson, H. E. (1969). Heat transfer and fire spread.'USDA Forest Service, Intermountain Forest and Range Experimental Station, Research paper, INT-69, Ogden, Utah, USA. Anderson, H. E. (1970). Forest fuels ignitability. 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D3.1-5-18-1000-1 Page 36 ANNEX I Moisture of extinction data from PART II Ignition probability in live fuels (In situ) D3.1-5-18-1000-1 Page 37 Date 25/5/2006 29/5/2006 30/5/2006 31/5/2006 2/6/2006 5/6/2006 6/6/2006 7/6/2006 8/6/2006 9/6/2006 12/6/2006 13/6/2006 14/6/2006 15/6/2006 16/6/2006 19/6/2006 20/6/2006 21/6/2006 22/6/2006 23/6/2006 26/6/2006 27/6/2006 28/6/2006 29/6/2006 30/6/2006 3/7/2006 4/7/2006 Time Air Temperature (0C) Relative Humidity (%) Precipitation (mm) Wind speed 1 2 3 4 5 Μoisture Content % IGNITION 10:50 11:30 11:40 13:30 11:50 11:45 12:10 12:05 11:40 11:45 13:10 12:05 12:15 11:50 12:00 11:30 12:10 11:50 11:40 11:25 11:40 12:05 11:10 11:40 11:20 13:30 11:20 27 28 27.5 30 29.5 27 28 26 22 23.5 26 25 24.5 27 30 29.5 33 31.5 31 28.5 31 32.5 32 31.5 33 25 25.5 66 57 53 59 55 47 45 49 62 52 42 54 57 44 36 58 45 51 51 67 63 55 58 63 50 84 84 0.8 4.8 6.9 1.4 1.1 12.4 - 4 6 8 8 4 10 4 7 13 11 7 6 9 17 11 0 0 4 0 6 5 6 10 4 7 5 10 X X X X X X X X X X X X X V V V V V V V V V V V V V V X X X X X X X X X X X X X V V V V V V V V V V V V V V X X X X X X X X X X X X X V V V V V V V V V V V V V V X X X X X X X X X X X X X V V V V V V V V V V V V V V X X X X X X X X X X X X X V V V V V V V V V V V V V V 186 200 191 189 178 164 132 103 158 138 106 89 63 71 44 16 12 34 16 16 17 12 14 17 13 20 24 NO NO NO NO NO NO NO NO NO NO NO NO NO YES YES YES YES YES YES YES YES YES YES YES YES YES YES D3.1-5-18-1000-1 Page 38 Date Time Air Temperature (0C) Relative Humidity (%) Precipitation (mm) Wind speed 1 2 3 4 5 Μoisture Content % IGNITION 5/7/2006 6/7/2006 7/7/2006 10/7/2006 11/7/2006 12/7/2006 13/7/2006 14/7/2006 17/7/2006 18/7/2006 19/7/2006 20/7/2006 21/7/2006 24/7/2006 25/7/2006 26/7/2006 27/7/2006 28/7/2006 31/7/2006 1/7/2006 2/7/2006 3/8/2006 4/8/2006 7/8/2006 8/8/2006 9/8/2006 10/8/2006 12:15 11:50 12:40 11:40 11:50 11:10 12:10 12:40 11:45 11:45 11:50 11:35 11:15 11:50 11:35 11:45 11:30 11:55 11:35 11:50 11:25 11:30 11:45 11:55 11:50 11:50 11:40 29 28.5 29.5 28 29.5 28.5 31 32 28 27 27 31 28.5 30 29.5 29.5 30 30 30.5 33 30.5 30 29.5 31 30 31 29 35 60 55 60 52 60 51 42 40 50 53 48 57 68 65 61 53 62 50 50 59 62 61 48 44 38 65 3.5 - 15 9 11 12 13 11 13 8 13 9 9 15 13 8 7 12 9 7 13 12 7 12 8 14 13 15 12 V V V V V V V V V V V V V V V V V V V V V V V V V V V V V V V V V V V V V V V V V V V V V V V V V V V V V V V V V V V V V V V V V V V V V V V V V V V V V V V V V V V V V V V V V V V V V V V V V V V V V V V V V V V V V V V V V V V V V V V V V V V V V V V V V V V V V V V 11 14 12 20 13 14 13 11 10 12 12 12 12 11 11 15 12 12 11 10 12 15 11 8 8 9 10 YES YES YES YES YES YES YES YES YES YES YES YES YES YES YES YES YES YES YES YES YES YES YES YES YES YES YES D3.1-5-18-1000-1 Page 39 Date Time Air Temperature (0C) Relative Humidity (%) Precipitation (mm) Wind speed 1 2 3 4 5 Μoisture Content % IGNITION 21/8/2006 22/8/2006 23/8/2006 24/8/2006 25/8/2006 28/8/2006 29/8/2006 30/8/2006 31/8/2006 1/9/2006 4/9/2006 5/9/2006 6/9/2006 7/9/2006 8/9/2006 11/9/2006 12/9/2006 13/9/2006 14/9/2006 15/9/2006 18/9/2006 19/9/2006 20/9/2006 21/9/2006 22/9/2006 25/9/2006 26/9/2006 11:40 11:30 11:20 11:25 12:00 11:30 10:55 11:50 11:30 11:25 11:55 11:30 12:20 11:30 11:15 12:35 12:00 11:20 12:05 11:30 11:45 11:50 11:45 11:50 11:35 11:30 11:35 32 32 31 30 29 29.5 26.5 31 23 25.5 27 28.5 31 28 27 28 26 23.5 26.5 25 24 26 26 25.5 24 23 23.5 61 39 39 53 52 49 52 48 38 72 63 54 39 57 56 51 55 48 46 54 60 76 62 51 64 67 63 3.7 0.6 - 6 11 13 9 5 20 6 9 24 15 4 5 19 10 6 8 7 5 7 5 4 7 11 6 11 8 4 V V V V V V V V V V V V V V V V V V V V V V V V V V V V V V V V V V V V V V V V V V V V V V V V V V V V V V V V V V V V V V V V V V V V V V V V V V V V V V V V V V V V V V V V V V V V V V V V V V V V V V V V V V V V V V V V V V V V V V V V V V V V V V V V V V V V V V V 11 10 9 13 11 12 10 12 9 9 12 13 10 10 12 19 11 12 10 12 14 13 26 13 19 16 15 YES YES YES YES YES YES YES YES YES YES YES YES YES YES YES YES YES YES YES YES YES YES YES YES YES YES YES D3.1-5-18-1000-1 Page 40 Date Time Air Temperature (0C) Relative Humidity (%) Precipitation (mm) Wind speed 1 2 3 4 5 Μoisture Content % IGNITION 27/9/2006 28/9/2006 29/9/2006 2/10/2006 3/10/2006 4/10/2006 5/10/2006 6/10/2006 9/10/2006 10/10/2006 11/10/2006 12/10/2006 13/10/2006 16/10/2006 17/10/2006 18/10/2006 19/10/2006 20/10/2006 23/10/2006 24/10/2006 25/10/2006 1/11/2006 1/11/2006 13/11/2006 13/11/2006 13/11/2006 15/11/2006 11:55 11:35 11:30 11:55 12:05 11:40 14:10 11:50 11:50 11:30 11:35 11:20 11:45 12:25 11:35 11:20 11:50 11:45 11:55 11:15 11:50 9:00 12:00 11:40 12:30 12:45 12:10 23.5 22 25 24.5 23.5 26.5 24.5 24 19 17.5 19 18 20 20.5 16.5 15.5 15.5 19 21.5 19 22 14 16 11 11 11 20 71 87 58 68 71 52 68 71 72 75 76 76 64 52 46 39 53 42 65 81 66 83 84 87 87 87 81 1.6 3 -1 2 - 7 8 16 9 7 10 8 6 12 4 0 0 0 14 5 11 0 7 9 0 4 4 6 12 11 14 11 X X V V V V V V X X X V V V V V V V V V V V V X V V V X X V V V V V V X X X V V V V V V V V V V V V X V V V X X V V V V V V X X X V V V V V V V V V V V V X V V V X X V V V V V V X X X V V V V V V V V V V V V X V V V X X V V V V V V X X X V V V V V V V V V V V V X V V V 51 59 32 16 20 18 16 19 44 82 55 28 28 16 18 17 18 16 18 28 18 39 17 78 35 48 21 NO NO YES YES YES YES YES YES NO NO NO YES YES YES YES YES YES YES YES YES YES YES YES NO YES YES YES D3.1-5-18-1000-1 Page 41