On the effect of pressure, oxygen concentration, air flow and gravity on simulated pool fires

The initial development of a fire is characterized by the establishment of a diffusion flame over the surface of a the condensed fuel and is particularly influenced by gravity, with most of the gaseous flow induced by natural convection. Low initial momentum of the fuel vapor, strong buoyant flows induced by the hot post-combustion gases and consequently low values of the Froude number (inertia-gravity forces ratio) are typical of this kind of scenario. An experimental study is conducted by using a porous burner to simulate the burning of a horizontal combustible surface. Ethane is used as fuel and different mixtures of oxygen and nitrogen as oxidizer. The magnitude of the fuel injection velocities is restricted to values that will keep the Froude number on the order of 10-5, when calculated at normal gravity and pressure, which are characteristic of condensed fuel burning. Two different burners are used, a circular burner (62 mm diameter) placed inside a cylindrical chamber (0.3 m diameter and 1.0 m height) and a rectangular burner (50 mm wide by 200 mm long) placed in a wind tunnel (350 mm long) of rectangular cross section (120 mm wide and 90 mm height). The first burner is used to study the effect of pressure and gravity in the absence of a forced flow parallel to the surface. The second burner is used to study the effect of a forced flow parallel to the burner surface as well as the effect of oxygen concentration in the oxidizer flow. In this case experiments are also conducted at different gravity levels (micro-gravity, 0.2 g(sub 0), g(sub 0) and 1.8 g(sub 0)) to quantify the relative importance of buoyancy

Organic liquid mobility induced by smoldering remediation

Laboratory column experiments plus analytical and numerical modeling together suggest that, under certain conditions, downward organic liquid mobilization can occur and impact smoldering behavior. This applies for organic liquids mixed with inert sand subjected to smoldering as thermal treatment. The observed effects include increased peak temperatures (here by up to 35%) and increased treatment times (here by up to 30%). Downward organic liquid migration occurs when (i) injected Darcy air flux is less than a threshold value (here less than 3 cm/s), (ii) treatment systems are tall (here 90 cm, not 30 cm), and (iii) the organic liquid is temperature-sensitive (viscosity less than 0.01 Pa s at 150 °C). The developed analytical equation provides the applied air flux that can negate the downwards organic liquid gradient required for migration. Smoldering behavior is demonstrated to adjust to liquid migration and thereby still destroy all the organic waste in the system. Smoldering is a relatively new, energy-efficient thermal treatment for organic liquid waste and these results are important for designing field applications of smoldering treatment

Experimental Characterization of the Effect of Charring on the Residual Load Carrying Capacity of a Structural Fibre Reinforced Composite

Research paper presented at the 10th Interflam conference in Edinburgh, 2004An experimental study conducted to investigate the residual load carrying capacity of a commonly used structural composite plastic, isophthalic polyester, reinforced with S-glass fibreglass when exposed to heat-fluxes representative of a fire is presented. The purpose of this study is to explore the relationship between fire insult and the remaining flexural strength of a thermally damaged commonly used composite plastic. The samples were subjected to 20 kW/m² through 40 kW/m² heat fluxes for varying amounts of time. Selected samples were allowed to ignite to ensure that both radiant and fire exposures were considered. Resulting sample temperatures and mass loss quantities were recorded as a function of time through the use of implanted thermocouples and a load cell. All samples were allowed to cool in a zero moisture environment prior to being structurally loaded to failure using a 3-point bending machine. The results obtained tend to demonstrate a clear linear relationship between the depth of un-charred material (on a Non-Ignition sample) and its residual load carrying capacity. Furthermore, a linear correlation between the total amount of energy imposed on a sample and its residual strength is evident. The type of correlation depends on whether the sample ignited or not

Integrated nonlinear structural simulation of composite buildings in fire

The collapse of several tall composite buildings over the last two decades has shown that the performance of tall, composite and complex buildings in fire is a necessary design consideration that ought to go beyond simple code compliance. To this end, several advancements in the field of numerical simulation of both the fire and the thermomechanical response of structures have been made. In isolation, the practical benefit of these advancements is limited, and their true potential is only unlocked when the results of those numerical simulations are integrated. This paper starts by showcasing recent developments in the thermal and thermomechanical analysis of structures using OpenSees. Integration of these developments into a unified simulation environment combining fire simulation, heat transfer, and mechanical analysis is then introduced. Finally, a demonstration example based on the large compartment Cardington test is used to showcase the necessity and efficiency of the developed simulation environment for thermomechanical simulation of composite structures in fire

Accessing the soot-related radiative heat feedback in a flame spreading in microgravity: optical designs and associated limitations

Novel, high-fidelity results related to soot from microgravity flames were obtained by an international topical team on fire safety in space. More specifically, embedded optical techniques for evaluation of the soot-related radiative feedback to the base material from a spreading non-premixed flame in microgravity were developed. The configuration used a non-buoyant axisymmetric flame propagating in an opposed laminar stream overa Low Density PolyEthylene coating of an electrical wire. Within this context, both the standard Broadband Two Color Pyrometry (B2CP) and its recent extension Broadband Modulated Absorption/Emission (BMAE) technique can be deployed to measure the spatial distribution of soot temperature and volume fraction within the flame. Both fields are then processed to establish the field of local radiative balance attributed to soot within the flame, and ultimately the soot contribution to the radiative flux to the wire. The present study first assesses the consistency of the methodology contrasting an experimental frame and a synthetic one, the latter being produced by a signal modeling that processes fields delivered by a numerical simulation of the configuration as inputs. Using the synthetic signals obtained, the fields of local radiative balance within the flame are then computed and significant discrepancies were disclosed locally between the fields originating from the synthetic BMAE and B2CP inputs. Nevertheless, the subsequent evaluation of the soot-related radiative heat feedback to the wire shows that a weak deviation among the techniques implemented is expected. This finding is corroborated by similar evaluations conducted with experimental BMAE and B2CP measurements obtained in parabolic flights. As BMAE is implemented in an ISS configuration within the SCEM rig, BMAE and B2CP will soon provide long-duration soot observations in microgravity. In order to contrast the upcoming results, this current study quantifies discrepancies originating from the post-processing regarding soot temperature and volume fraction, and shows that the radiative feedback evaluation from both methods should be consistent

Determination of the main parameters influencing forest fuel combustion dynamics

International audienc

Burning Rate of Liquid Fuel on Carpet (Porous Media)

Research paper published in the journal Fire Technology 2004The occurrence of a liquid fuel burning on carpet has been involved in many incendiary and accidental fires. While the research on a liquid fuel fire on carpet is still limited, much work on porous media has been performed using sand or glass beads soaked with liquid fuel. In this study, a heat and mass transfer theory was first developed to analyze the burning process of liquid on carpet, and then several small-scale tests were performed to validate the theory. This analysis is valid for pool fires intermediate in size (5-20 cm. in diameter). The experimental apparatus consisted of a circular pan (105mm) and a load cell. Varying amounts of fuels (heptane, kerosene and methanol) were spilled onto the carpet, which was allowed to burn in a quiescent environment. It was found that due to the different controlling mechanisms, the liquid burning rate could be less or more than that of a similarly spilled free-burning pool fire. For the worst-case scenario in fires, the maximum enhancement of the burning rate due to the porous media is predictable through the physical properties of the fuel. This analysis is valid for both combustion and evaporation. Several similar results in the scientific literature are analyzed to further describe the trend. This work explains the role of carpet in liquid pool fires and also helps to explain special risks related to the presence of carpet involved in arsons and will be useful in reconstruction of the early development of an incendiary or accidental fire

Performance Assessment of Pressurized Stairs in High Rise Buildings

Research paper published in the journal Fire Technology, special issue on Smoke Control in Buildings and Tunnels.Pressurized stair cases are an important part of the fire safety strategy of high rise buildings. Long egress times are compensated by creating safe environments within egress staircases allowing the displacement time within those stairs as time where occupants can be considered safe. The main mechanisms by which stairs are ‘‘made safe’’ are by guaranteeing structural protection of the enclosure and by elevating the pressure within the stair to ensure that smoke cannot enter. Despite the critical importance of this element of the fire safety strategy, the analysis and implementation of these systems remain simplified. Simple models have been developed using Bernoulli type formulations that account for static pressure and empirical constants to calculate flows through doors and other leakage areas. Implementation of these systems is even more simplified, consisting mainly of a direct feedback loop that controls a fan output on the basis of a pressure measurement inside the stair. The flow induced by the fan guarantees a minimum pressure. The pressure inside the stair needs to be limited to enable doors to be open, thus pressure dampers are introduced to release airflow in the event the pressure exceeds a specified maximum. Validation of these methodologies was done in the 70s and 80s with very limited field validation in real systems. This study presents an assessment of the performance of pressurized staircases in six high rise buildings. All systems have been designed using a similar methodology but implemented in different ways. In all cases the control mechanism for the fan is a direct feedback loop from a single pressure sensor. The results have been evaluated showing the limitations of the control system in the event of multiple doors being opened and the limitations of the pressure release dampers (as a response mechanism) if the pressure becomes unstable