On the ignition of a layer of combustible forest materials by light radiation

The ignition of a layer of combustible forest materials by luminous radiation was studied experimentally. The minimum radiant heat flux densities required to ignite combustible forest materials are determined for a neodymium-doped glass laser and a tungsten lamp. It is established that the heat flux, density increases with increase in the moisture content and density of the layer of combustible forest materials and decreases with increase in the diameter of the light spot, and the critical flux density is higher for the laser radiation than for the incandescent lamp. Translated fromFizika Goreniya i Vzryva, Vol. 35, No. 6, pp. 22–25, November–December 1999.     

Mathematical modeling of the stripping of combustible forest materials by explosion of a cord charge

The stripping of combustible forest materials (thin twigs and needles) by explosion of a cord charge are studied by mathematical modeling of blast-wave propagation in a forest canopy for the placement of the cord charge at different heights. The calculation results allow one to reduce the consumption of explosives in extinguishing crown forest fires. __________ Translated from Fizika Goreniya i Vzryva, Vol. 42, No. 3, pp. 92–99, May–June, 2006.     

On the thermal ignition of combustible materials

Formulas are derived for the time to achieve the ignition temperature as a function of the incident heat flux and the various thermophysical material parameters for thermally thick, thermally thin and thermally intermediate solid combustibles. Predictions are compared with recent experimental data for various natural wood species and wood products, and to previous data for wood and thermoplastics. The correlations are excellent when (1) the physical parameters used as the axes of the plots are chosen consistent with those of the theoretical formulas and (2) the experiments and the materials do not violate any of the restrictions imposed by the theory. From these plots it is easy to estimate the minimum heat flux for ignition, which is of great importance both in practice and for making theoretical predictions.     

Ignition of a condensed material with a disintegrated near-surface layer

Tomsk. Translated from Fizika Goreniya i Vzryva, Vol. 26, No. 2, pp. 18–23, March–April, 1990.     

Ignition of a porous layer with a flow of heat carrier

Thermal ignition of a porous layer of finite thickness with a moving heat carrier has been studied. The asymptotic character of the critical conditions at high velocities of the heat carrier has been established. A nonmonotonic dependence of the ignition delay on the heat carrier velocity has been observed. Possible ignition regimes and their characteristics are described.Tomsk State University, 634050 Tomsk. Translated from Fizika Goreniya i Vzryva, Vol. 30, No. 2, pp. 3–7, March–April, 1994.     

Study on flashover in a single chamber lined with combustible materials

With the theories of fire dynamics and relevant parameters of combustible lining materials, a predicted model of hot gas layer temperature during pre‐flashover stage of enclosure fires was established, and the effects of lining materials on the likelihood of flashover were theoretically analyzed. By using common commercial lining materials, such as wall papers, foam plastics, wood‐based panels, and fabric‐upholstered wall panel, the phenomenon of flashover was reproduced in a small‐scale firebox of 1/4 sizes of ISO 9705 test chamber. By comparing the theoretical results with experimental data, the equation predicting the hot gas layer of quasi‐steady enclosure fires was gained; an indicator I_FO to reflect overall the hazards of flashover and to classify flashover fires was proposed, and its application was initially studied. The study results can be helpful to explain further and overall the effects of lining materials on enclosure fires and can be used to guide the prevention of flashover by choosing appropriate interior decoration materials. Copyright © 2012 John Wiley & Sons, Ltd.     

Ignition of powder materials under friction

It is shown that ignition may occur under light frictional pressure. In the case of friction applied to a powder, there are two limits of ignition in terms of the frictional pressure. A frictional approach permits a high degree of compaction of powder at low frictional pressure (∼10 kg/cm²). The influence of the material of the frictional body on sample heating and ignition is investigated. Activation of chemically active powder under the action of friction is observed. A discussion of the results is presented. Institute of Structural Macrokinetics, Russian Academy of Sciences, Chernogolovka. Translated from Fizika Goreniya i Vzryva, Vol. 31, No. 6, pp. 14–19, November–December, 1995.     

Ignition of forest tracts by a high-altitude source of radiant energy

The problem of initiation of large-scale forest fires induced by technogenic catastrophes is solved in an axisymmetric formulation. Results of numerical calculations are given which imply that the ignition mechanism in this case is the same as for collisional catastrophes. A comparison of the limiting dimensions of ignition zones for nuclear charges of different energy yields shows good agreement between two-dimensional and quasi-one-dimensional approximations.Translated from Fizika Goreniya i Vzryva, Vol. 32, No. 5, pp. 107–115, September–October, 1996.     

The early fire behaviour of combustible wall lining materials

The development of the Australian Standard AS 1530 Part 3 ‘Test for Early Fire Hazard Properties of Materials’ from the study of the fire behavior of cellulosic wall linings in simulated room fires has been outlined. Similar studies for assessing a wider range of wall linings are now reported including various plastic facings applied to hardboard. Using similar parameters for ignitability, spread of flame, heat evolved and smoke developed, the behaviors of the linings in the standard test have been compared to the behavior in corner-wall burns. Two methods of ignition were used for the burns; (a) timber cribs; and (b) impressed radiant heat with a pilot flame. The results are discussed in terms of the validity of the standard test as a multi-parameter assessment of materials in a fire hazard situation. The test has been validated for the wider range of wall lining materials.     

Ignition of condensed systems interacting through a layer of high-melting product

The functional dependence of the ignition delay time on the main parameters of the problem is determined for condensed systems interacting through a layer of high-melting product by a power law. A formula for determining the ignition temperature from the equality between the external heat flux and integral heat evolution in a chemical reaction in a stationary combustion wave with temperature equal to the ignition temperature is proposed and substantiated. It is shown that at a surface temperature below the ignition temperature the heating can be considered inert and the duration of this stage makes up the bulk of the delay time.Institute of Structural Macrokinetics, Russian Academy of Sciences, Chernogolovka 142432. Tranalated from Fizika Goreniya i Vzryva, Vol. 31, No. 4, pp. 3–9, July–August, 1995.     

Ignition of forest tracts as a result of cosmic or technogenic catastrophes

Using a quasi-one-dimensional approximation, the problem of extensive forest fires caused by collisional or technogenic catastrophes is formulated and solved. Calculations show that the mechanism of ignition in both cases is the same, but the quantitative parameters of the processes (ignition time and limiting conditions, shape of ignition zone) differ significantly from each other. The cause is the difference in the mechanisms of energy release in the near-ground atmospheric layer during technogenic or collisional catastrophes.Translated from Fizika Goreniya i Vzryva, Vol. 32, No. 2, pp. 18–30, March–April, 1996.     

Ignition and flash-fire studies of cellulosic materials

Various celloulosic materials were evaluated for ignitability and flash-fire propensity, using screening test methods developed at the University of San Francisco. Time to ignition, using radiation from a high-temperature radiant source without a pilot flame, appeared to be primarily a function of heat flux and material density, rather than of type of wood or celloulosic board. At heat flux levels from 5.8 to 10.5 W cm^?2, time to ignition was shortest for cellulose fiberboard with a density of 0.2225 g ml^?1, followed by western red cedar at 0.314 g ml^?1, eastern white pine at 0.348 g ml^?1, southern yellow pine at 0.422 g ml^?1, Douglas fir at 0.565 g ml ^?1, and longest for hardboard at 0.878 g ml^?1. For the cotton and rayon woven-pile upholstery fabrics, time to ignition appeared to increase with increasing fabric weight. For Cellulose insulation treated with boron-containing additives, flash-fire magnitude decreased with increasing additive content. Flash-fire magnitude decreased more that could be accounted for by decreasing weight loss alone, indication reduction in the combustibility of the volatiles produced. Reduction in flash-fire propensity of cotton bating by treatment with boron-containing additives was also observed.     

Ignition and extinction of homogeneous energetic materials by a light pulse

Numerical calculations using a model of unsteady combustion of melting energetic materials were performed to simulate the results of qualitative experiments on the ignition and quenching of energetic materials by a light pulse. The parameters of the model composition were chosen to correspond to combustion with the burning-rate control reaction in the gas phase to ensure the stability of self-sustained combustion after the cessation of irradiation. Regions of stable ignition in the coordinates “radiant flux amplitude-irradiation time” were obtained for compositions with different transparency for igniting pulses of three shapes: rectangular, linearly decreasing to zero, and exponentially decreasing. Extinction conditions of the steadily burning composition by a rectangular light pulse were calculated.     

The influence of pressure on combustible and toxic properties of materials

Combustible and toxic properties greatly influence the application of materials in shipbuilding. These materials, especially plastics, create a serious toxic hazard during fire. Under fire conditions they decompose thermally, giving off considerable amounts of smoke and volatile toxic substances which cause a serious hazard to people overcome by fire inside a compartment.^1–3Lethal poisoning by the thermal degradation products of plastics has attracted the attention of many investigators to toxic hazards during a fire.^1,4 Underwater systems create, in particular, a serious fire hazard. Fire in a decompression chamber spreads in a different way to land fires and usually causes the death of the crew and complete destruction of equipment in the chamber. Theoretically, complete fire protection in a chamber could be achieved by the total elemination of combustible materials and their replacement by incombustible ones. However, from a practical point of view this is impossible. The general principles of materials selection used in underwater systems are defined by Det Norske Veritas.⁵ Unfortunately, these do not describe the methods of testing materials nor the criteria of materials selection. There is also a lack of information in the literature on toxic hazards under elevated pressures. This problem has been studied in detail with oxygen-enriched atmospheres in aerospace programmes,⁶ but because those studies are classified there is only fragmentary information in the literature.     

Two-stage ignition of energetic materials with a liquid surface layer

Two-stage ignition regimes of energetic materials with a liquid surface layer were revealed by mathematical modeling of transient combustion processes. First, under the action of a radiant flux, the regime of forced gasification of a condensed phase with a degree of its surface depletion of 0.1–0.3 was observed. Gas-phase combustion occurs in the blow-off regime. As the radiant flux decreases, the gas flame approaches the surface and becomes determining, and the degree of condensed-phase depletion decreases.Translated from Fizika Goreniya i Vzryva, Vol. 32, No. 3, pp. 140–142, May–June, 1996.