José C. Santos

Combustion completeness in a rainforest clearing experiment in Manaus, Brazil

Results are described for a forest clearing experiment conducted in the forest reserve of the Tropical Silviculture Experimental Station of the National Institute for Research in the Amazon (INPA), located 60 km from Manaus, the capital of the Brazilian state of Amazonas. An area of 1 ha of virgin forest was cut in July 1995 and left to dry until October of the same year. It was burnt using a procedure similar to that followed by native people in the region to prepare the land for cultivation. The fresh biomass content in the test location, 684.8 t ha−1, was determined using a formula with parameters from forest inventory. The dry biomass content was 401.5 t ha−1. Combustion completeness, 20.5 %, was estimated by selecting ten 2 × 2 m2 subareas, 20 trunks with diameter at breast height (DBH) between 10 and 30 cm, and 71 trunks with DBH higher than 30 cm. Their consumption rates by fire were measured. The 2 × 2 m2 areas were used to determine the combustion completeness of smaller plant components (characteristic diameters lower than 10 cm) and the trunks to determine the efficiency of the medium and large components (characteristic diameters between 10 and 30 cm and larger than 30 cm, respectively). Combustion completeness for small, medium and large components were 88.2%, 4.39%, and 0.43%, respectively. On the basis of the biomass content (684.4 t ha−1), the average biomass moisture and carbon contents (41.6% and 47.8%, respectively, the latter on dry basis), and the obtained combustion completeness (20.5%), the average carbon, CO2 and CO mass rates released to the atmosphere were estimated to be 37.7, 121, and 8.6 t ha−1, respectively.

Biomass fire consumption and carbon release rates of rainforest-clearing experiments conducted in northern Mato Grosso, Brazil

Biomass consumption and carbon release rates during the process of forest clearing by fire in five test plots are presented and discussed. The experiments were conducted at the Caiabi Farm, near the town of Alta Floresta, state of Mato Grosso, Brazil, in five square plots of 1 ha each, designated A, B, C, D, and E, with different locations and timing of fire. Plot A was located in the interface with a pasture, with three edges bordering on the forest, and was cut and burned in 1997. Plots B, C, D, and E were located inside the forest. Plot B was cut and burned in 1997. Plot C was inside a deforested 9-ha area, which was cut and burned in 1998. Plot D was inside a deforested 4-ha area, which was cut in 1998 and burned in 1999. Plot E was inside a deforested 4-ha area, which was cut and burned in 1999. Biomass consumption was 22.7%, 19.5%, 47.5%, 61.5%, and 41.8%, for A, B, C, D, and E, respectively. The effects of an extended curing period and of increasing the deforested area surrounding the plots could be clearly observed. The consumption, for areas cut and burned during the same year, tended toward a value of nearly 50% when presented as a function of the total area burned. The aboveground biomass of the test site and the amount of carbon before the fire were 496 Mg ha−1 and 138 Mg ha−1, respectively. Considering that the biomass that remains unburned keeps about the same average carbon content of fresh biomass, which is supported by the fact that the unburned material consists mainly of large logs, and considering the value of 50% for consumption, the amount of carbon released to the atmosphere as gases was 69 Mg ha−1. The amounts of CO2 and CO released to the atmosphere by the burning process were then estimated as 228 Mg ha−1 and 15.9 Mg ha−1, respectively. Observations on fire propagation and general features of the slash burnings in the test areas complete the paper.

A tropical rainforest clearing experiment by biomass burning in the Manaus region

A tropical rainforest clearing experiment by biomass burning performed in a one hectare area of INPAs forest reserve located 60 km from Manaus, the capital of the Brazilian state of Amazonas, is described. The experiment is part of a major effort to quantify the amounts of carbon dioxide generated by this kind of clearing process. Following the procedure used by native people in the region, the trees were cut and the biomass left to dry on the ground for three months before burning. The fire burned through the whole one hectare area. The results include a carbon mass balance of the test site, air temperatures and heat transfer rates inside the ground. The carbon balance allowed the estimation of the carbon gasification efficiency for this kind of fire.

Flammability limits: A review with emphasis on ethanol for aeronautical applications and description of the experimental procedure

The lower and upper flammability limits of a fuel are key tools for predicting fire, assessing the possibility of explosion, and designing protection systems. Knowledge about the risks involved with the explosion of both gaseous and vaporized liquid fuel mixtures with air is very important to guarantee safety in industrial, domestic, and aeronautical applications. Currently, most countries use various standard experimental tests, which lead to different experimental values for these limits. A comprehensive literature review of the flammability limits of combustible mixtures is developed here in order to organize the theoretical and practical knowledge of the subject. The main focus of this paper is the review of the flammability data of ethanol-air mixtures available in the literature. In addition, the description of methodology for experiments to find the upper and lower limits of flammability of ethanol for aeronautical applications is discussed. A heated spherical 20L vessel was used. The mixtures were ignited with electrode rods placed in the center of the vessel, and the spark gap was 6.4mm. LFL and the UFL were determined for ethanol (hydrated ethanol 96% °INPM) as functions of temperature for atmospheric pressure to compare results with data published in the scientific literature.

Understorey fire propagation and tree mortality on adjacent areas to an Amazonian deforestation fire

Fire characteristics in tropical ecosystems are poorly documented quantitatively in the literature. This paper describes an understorey fire propagating across the edges of a biomass burn of a cleared primary forest. The experiment was carried out in 2001 in the Amazon forest near Alta Floresta, state of Mato Grosso, Brazil, as part of biomass burning experiments conducted in the same area since 1997. The vegetation of a 200200-m 2 forested area was clear-cut in early June and burned in late August. The understorey fire that escaped from the main burn was monitored across the four sides of the land clearing area. Flame-front spread varied between 0.14 and 0.35mmin 1 . Maximum flame height was about 30cm and typical flame depth was 10 to 15cm. Tree mortality was investigated in 2003 in four areas adjacent to the biomass burning experiment. A total of 210 trees were counted in the four areas, 29.5% were dead as a consequence of the understorey fire that had occurred 2 years before. This fire-caused mortality is evidence of the synergistic effect between slash burning, tree mortality and future fire vulnerability on the forest-land clearing interfaces.

Flammability limits of hydrated and anhydrous ethanol at reduced pressures in aeronautical applications

There is interest in finding the flammability limits of ethanol at reduced pressures for the future use of this biofuel in aeronautical applications taking into account typical commercial aviation altitude (<40,000 ft). The lower and upper flammability limits (LFL and UFL, respectively) for hydrated ethanol and anhydrous ethanol (92.6% and 99.5% p/p, respectively) were determined for a pressure of 101.3 kPa at temperatures between 0 and 200°C. A heating chamber with a spherical 20-l vessel was used. First, LFL and the UFL were determined as functions of temperature and atmospheric pressure to compare results with data published in the scientific literature. Second, after checking the veracity of the data obtained for standard atmospheric pressure, the work proceeded with reduced pressures in the same temperature range. 295 experiments were carried out in total; the first 80 were to calibrate the heating chamber and compare the results with those given in the published scientific literature. 215 experiments were performed both at atmospheric and reduced pressures. The results had a correlation with the values obtained for the LFL, but values for the UFL had some differences. With respect to the water content in ethanol, it was shown that the water vapor contained in the fuel can act as an inert substance, narrowing flammability.

Probability of surface fire spread in Brazilian rainforest fuels from outdoor experimental measurements

This paper describes the development of a logistic model to predict the probability of surface fire spread in Brazilian rainforest fuels from outdoor experimental measurements. Surface fires spread over litter composed mostly of dead leaves and twigs. There were 72 individual outdoor experiments in eighteen sites. The fire propagated in 49% of the experiments. In each experiment, the litter height, litter temperature, unburned litter mass, wet and dry litter mass, soil temperature, wet and dry soil mass, ambient wind velocity, ambient air temperature, ambient air relative humidity and duration of fire spread were measured. Using these data, the rate of fire spread, litter bulk density, litter and soil moisture content, litter load and litter residue fraction were determined. For the sake of analysis, experimental results were classified into two groups: one for which the fire propagated and the other one for which the fire self-extinguished. Analyses of a logistic regression model showed that the relevant parameters for fire propagation are litter height and litter moisture content. Concerning the probability of successful fire propagation, the model showed a true positive rate of 71% and a true negative rate of 84%. The outdoor experiments also served to gather data to improve the understanding of surface fires and to provide input data for future computer simulations.