Pool Fires Research Articles

Study on smoke propagation in tunnel construction of a hydropower station: A full-scale fire experiment

In this study, full-scale fire experiments were conducted in a hydropower station to investigate smoke propagation during tunnel construction. The flame height, smoke temperature and stratification, smoke descent and spread velocity were analyzed via measurements and on-site observations. The initial combustion stage was largely affected by ignition source during tunnel construction for diesel pool fire, and the average flame height in the fully developed stage could reach 1.4–2.1 m in experimental fire scenarios. The gradient of the smoke temperature evolution near the fire was the opposite for the upstream and downstream regions. The longitudinal temperature distribution was concentrated in a small range at the heights of the smoke layer, and gradually decreased by air entrainment as the height decreased, while further increasing in the lower half of the tunnel height in the near-fire region under heat radiation from the fire source. Moreover, distinct and stable smoke stratification formed during the fully developed combustion stage, and the smoke layer interface was at approximately half the tunnel height. Smoke descent was aggravated in the decay stage of combustion, and the fire risk remained high after the fully developed period. The smoke front spread velocity was empirically determined for the full-scale tunnel fire scenarios. Conclusions from full-scale experiments can support smoke control design and on-site fire emergency response plans for hydropower stations.

Improved models of failure time for atmospheric tanks under the coupling effect of multiple pool fires

Fire accidents of chemical installations may cause domino effects in atmospheric tank farms, where a large amount of hazardous substances are stored or processed. Pool fire is a major form of fire accidents, and the thermal radiation from pool fire is the primary hazard of domino accidents. The coupling of multiple pool fires is a realistic and important accident phenomenon that enhances the propagation of domino accidents. However, previous research has mostly focused on the escalation of domino accidents induced by a single pool fire. To overcome the drawback, in this study, the failure of a storage tank under the coupling effect of multiple pool fires was studied in view of spatial and temporal synergistic process. The historical accident statistics indicated that the accident scenario of two-pool fires accounted for 30.6% in pool fires. The domino accident scenario involving three tanks is analyzed, and the typical layout of tanks is isosceles right triangle based on Chinese standard “GB50341-2014”. The thermal response and damage of a target tank heated by pool fires were numerically investigated. The volume of 500 m3, 3000 m3, 5000 m3 and 10000 m3 were selected. Flame temperature was obtained by FDS, and then was input onto the finite element model. The temperature field and stress field of target tanks were simulated by ABAQUS. The results showed that the temperature rise rate of the target tanks under multiple pool fires was higher than that under a single pool fire. The failure time of the tank under the coupling effect of multiple fires was lower than that under the superposition of multiple fires without the first stage. The stress and yield strength were compared to judge the failure of the target tank. The model of failure time for the tank under the coupling effect of pool fires was established. Through the verification, the deviation of this model is 4.02%, which is better than the deviation of 15.76% with Cozzani's model.

Fluorosilane-Modified Antireflash Sodium Bicarbonate Fire Extinguishing Agent with Advanced Hydrophobic and Oleophobic Properties

The poor antireflash performance of NaHCO3 dry powder fire extinguishing agent in class B fire is the key problem that restricts its application in large oil fires. In this work, the NaHCO3 was surface modified by sol–gel method to introduce functional fluorosilane structure (named FSi-NaHCO3) and enhance the hydrophobic and oleophobic properties. The water contact angle (WCA) and oil contact angle (OCA) of FSi-NaHCO35 are 147.0° and 144.2°, respectively, which means that FSi-NaHCO35 has advanced hydrophobic and oleophobic properties. The hydrophobic and oleophobic ratio of FSi-NaHCO35 are 92.35% and 91.59%, respectively. Furthermore, FSi-NaHCO35 dry powder fire extinguishing agent can extinguish aviation kerosene and n-heptane oil pool fires in 0.15 and 0.18 s, respectively, which is shorter than that of NaHCO3 dry powder fire extinguishing agent. After the secondary ignition, using FSi-NaHCO35 as dry powder fire extinguishing agent, the fire temperature of the aviation kerosene oil is significantly lower, and the full reburning time of the aviation kerosene oil fire is significantly longer than that of NaHCO3 dry powder fire extinguishing agent, which means FSi-NaHCO35 obviously has antireflash performance in an aviation kerosene oil pool fire.

Study on Dynamic Probability and Quantitative Risk Calculation Method of Domino Accident in Pool Fire in Chemical Storage Tank Area.

The domino event caused by fire is one of the common accidents in hydrocarbon storage tank farms, which further expands the severity and scope of the accident. Due to the different failure sequence of the storage tanks in a domino accident, the radiant heat generated by the failed storage tank to the target tank is different. Based on the influence of this synergistic effect, this study combined the Monte Carlo algorithm and FSEM, and proposed a fast real-time probability calculation method for a fire domino accident in a storage tank area, for the first time. This method uses the Monte Carlo algorithm to simulate all accident scenarios, and obtains the evolution of multiple escalation fire domino accidents under the synergistic effect according to FSEM, and then calculates the real-time failure probability and risk. Based on a comprehensive analysis of the accident propagation path, this method avoids the problem of a large amount of calculation, and is conducive to the rapid and effective analysis of the fire risk in a storage tank area and the formulation of corresponding risk reduction measures. The effectiveness and superiority of the proposed method were proved by a case study.

The Burning Characteristics of Transformer Oil Spill Fire on Horizontal and Inclined Substrate Under Continuous Leakage Condition

Abstract Spill fire is a typical fire type that endangers industrial safety. This work systematically investigates the burning characteristics of transformer oil spill fire under different fuel leakage rates and substrate tilt angles, and the fuel flow hydrodynamic parameters. According to the flame spread behavior and substrate temperature distribution, the spill fire spread process is divided into four stages and the substrate is divided into three zones. The relative difference between max burning length and stable burning length is positively correlated with the substrate tilt angle. The increase of fuel flow velocity contributes to the flame spread velocity, but the increase of fuel flow velocity and the decrease of fuel layer thickness weaken the accelerating effect of surface flow on flame spread, which leads to a decreasing trend of flame spread velocity increase. The spill fire mass burning rate is 0.161–0.358 times of pool fire, and the increase of heat loss due to fuel flow and the radiant heat loss through the fuel layer dissipated through the substrate are the main reasons for the lower mass burning rate than pool fire. The research results provide basic data and references for further research on the formation mechanism of heavy oil spill fire and the prevention and control of small-scale spill fire.

Phenomenological characteristics and flame radiation of dynamically evolving oil spill fires in a sealed ship engine room

Available references on ship engine room fires are mainly based on the pool fires, while in reality the leaked liquid fuel tends to form dynamically evolving spill fires, which are quite dangerous and scarcely investigated. In this paper, one-dimensional spill fire experiments with different leakage rates are tentatively conducted in a model-scale ship engine room to reveal their hazards. Due to the coupling effects of oxygen confinement and thermal radiation enhancement, the development of the spill fire for higher fuel leakage rate can be divided into continuous spreading, deceleration diffusion, quasi-steady burning, and decay stages, while the quasi-steady burning stage is nonexistent at lower leakage rates. The initial spread rate of the spill fire in the ship engine room is lower than that in open space, which may be attributed to the heat feedback enhancement in the ship engine room. The spread rate in the continuous spreading stage is about 2.3 times that in the deceleration diffusion stage. Using the modified solid flame model, a segmented theoretical model is developed to predict the radiative heat flux of the spill fire in the ship engine room, and the predicted results agree well with the measured results, with an error ranging from 9% to 19%.

Influence of longitudinal wind on mass burning rate of rectangular heptane pool fire with different aspect ratios

Fire is one of the primary disasters that threaten the safe operation of tunnel and underground space. Mass burning rate is a significant parameter in characterizing the behavior of pool fire which is related to thermal feedback, pool shape and ambient wind. Five convection-controlled heptane pool fires are examined inside a longitudinal wind tunnel with aspect ratio of 1, 2, 4, 8, and 16. The variation of burning rate with longitudinal wind is divided into increasing regime at v < 0.96 m/s, decreasing regime at 0.96 ≤ v < 1.98 m/s, and slightly-fluctuating regime at 1.98 ≤ v < 2.49 m/s. The effect of longitudinal wind on burning rate is attributed to heat feedback, flow disturbance and oxidizer supply around the flame. The increment of burning rate with wind speed is proved by the liquid evaporation theory. The heat transfer analysis proves that the enlargement rate of burning rate is linearly proportional to a coupling factor of longitudinal air flow speed and aspect ratio in a unified mathematical correlation Δṁ″/k′=(2n+1n)v which is fully consistent with measurements. The results provide guidance for tunnel fire protection design and prediction of fire development under the condition of vehicle tank leakage inside a tunnel.

Numerical study of the flame geometry of pool fires in longitudinally ventilated tunnels

In a windy environment, the flame tilt angle and base drag length are two parameters used to describe the flame geometry of liquid fuel fires. This work describes a numerical investigation using the FDS code to model three typical fire sizes in a longitudinally ventilated tunnel and a windy open space. The CFD modelling methodology was validated against experimental data from the literature. According to the findings, when the ventilation is weak, a backlayering flow occurs in the tunnel and causes a two-layer flow pattern upstream, which reduces the flow space and accelerates the ventilation. Consequently, the flame base drag length tends to remain constant, and the flame tilt angle becomes very difficult to predict. Unlike open fires, when the upstream is free of backlayering, the tunnel area and the heat release rate have been proven to be two additional factors that influence the flame geometry. The confined space causes more concentrated momentum of wind and speeds up the fuel consumption upstream of the dragging flame base. The former results in a more significant flame tilt, and the latter shortens the stay of fuel vapor on the floor. By introducing a dimensionless heat release rate and dimensionless tunnel cross-sectional area, a series of new prediction models covering all the governing parameters were derived, which have successfully estimated the longitudinal distance from the fire center to the maximum ceiling temperature in the tunnel.

A new approach to chemicals warehouse risk analysis using computational fluid dynamics simulation and fuzzy Bayesian network

This study aims to assess the risk of chemicals warehouse using a Bayesian networks (BNs) and computational fluid dynamics (CFD). A methodology combining Bow-Tie (BT), fuzzy set theory (FST), and Bayesian network was employed, in which the BT was drawn for chemical spill scenarios. FST was utilized for the estimation of the basic events (BEs) occurrence probability, and the probability of interaction among a set of variables was obtained using BNs. Pool fire scenario radiation heat flux was evaluated using CFD code, fire dynamic simulator (FDS), and the solid flame model (SFM). Fail in forklift brake system (BE1), was the most significant cause for a chemical spill. Based on the CFD model, the heat flux is 31 kW/m2 at a distance of 3.5 m from the fire, decreasing to 6.5 m gradually. The maximum safety distance of 4 m is predicted by the CFD for heat flux that exceeds 12.5 kW/m2; however, SFM predicts approximately 4.5 m. According to the results, the amount of posterior risk is higher than the prior value. The framework presented in the chemicals warehouse for consequence analysis and dynamic risk assessment (DRA) of pool fire could be used for preventing the accidents and domino effects in the chemicals warehouse.

Numerical Assessment of Thermostructural Instability of Cylindrical Tanks Subjected to Pool Fire

Numerical Assessment of Thermostructural Instability of Cylindrical Tanks Subjected to Pool Fire

Experimental study on mass burning rate and flame geometry of pool fires under two-way indirect ventilation in Ship's engine room

The influence of wind on the combustion of pool fires has been demonstrated experimentally. However, the complex pipeline ventilation in the engine room is often ignored by existing research. For the typical ventilation structure of the engine room in this paper, a type of two-way/indirect ventilation structure in a confined space with dimensions of 1.5 × 1.5 × 1 m3 is built. N-heptane is used as the fuel, and a circular pool with a diameter of 10 cm is used in the experiments. The variation of mass burning rate and flame geometry under ventilation speeds of 0–4 m/s are studied. The results show that two-way/indirect ventilation greatly changes the combustion characteristics of the pool fires. The mass burning rate fluctuates and increases with increasing ventilation speed. The tilt angle and length of the flame changes nonlinearly with different ventilation speeds, and the ‘swaying’ phenomenon of flame tilt is presented. In addition, the existing correlations of the flame geometry of pool fires under ventilation are further improved. The models predicting flame tilt angle and flame length of pool fires with different ventilation speeds under two-way ventilation structure are established.

Experimental investigation on RP‐3 aviation kerosene large‐scale pool fires at high altitude

AbstractRP‐3 aviation kerosene is a standard fuel that is used in civil aircraft and is a substitute for Jet‐A fuel. This paper investigates the combustion behaviour of RP‐3 aviation kerosene in an open space in the low‐pressure environment of a plateau. A series of large‐scale pools with diameters ranging from 0.4 m to 2.82 m combustion experiments are performed. Typical combustion characteristic parameters, including combustion rate, flame height and axial plume temperature distribution is measured. Results show that a low‐pressure environment significantly affects pool fires. With combustion rate, there is a linear variation law between oil pool size and combustion rate. The experimental data are fitted as a means of obtaining the large‐scale combustion rate relationship equation at low pressure. Experimental flame height data is compared using classical prediction models. Prediction model coefficients at low pressure are determined. The axial plume temperature distribution is greater than in the literature findings due to flames becoming longer in a low‐pressure environment. The three regimes in McCaffery's model are redefined and correlate well with the vertical temperature profile of the pool centreline. The results of the experimental investigation will help research fire hazards in low‐pressure environments while also contributing to the provision of basic data for the development of firefighting operation strategies.

Mass burning rate and merging behaviour of double liquid pool fires under cross winds

This paper experimentally investigates the effects of cross wind on flame interaction and burning characteristics of double liquid pool fires. Two burners were used including a square burner and a line burner. The separation distance between the double fires and the speed of cross wind were varied, providing a total of 66 test conditions. The experimental results showed that the mass burning rate increases initially with increasing separation distance until a critical value, after which the mass burning rate decreases with a further increase of the separation distance. This non-monotonic behaviour was attributed to the competition between an increase of air entrainment and a decrease of the flame heat feedback from the adjacent fire, as the separation distance increases. A correlation was developed for the mass burning rate based on the stagnant layer solution of liquid fuel evaporation and combustion, incorporating the separation distance between two fires and cross wind, and is found to predict well the experimental data for all experiments. Image analysis indicated that, with increasing separation distance, the flame merging of double pool fires can be divided into three regimes: the continuous merging regime, the intermittent merging regime, and the non-merging regime. A physical model was proposed for the flame interaction and merging behaviour of the double pool fires, based on which a piecewise function is developed for predicting the flame merging probability and the criteria for the merging/non-merging flames are also determined. The proposed formulations were found to correlate well with the current measurements of liquid pool fires and published literature data of single pool fires.

Fire and risk analysis during loading and unloading operation in liquefied petroleum gas (LPG) bottling plant

The article focuses on analyzing risks associated with the gas transfer operation in a liquified petroleum gas (LPG) bottling plant in India. The transfer operations involve transferring liquified gas from the transport tanker to the underground storage tank. Due to the rapid expansion of the cities, many LPG bottling plants in India got surrounded by residential areas and business centers. Moreover, to maintain the supply chain, the frequency of the transfer operations at the bottling plant also increased. In this scenario, an accidental release of LPG during the transfer operation may lead to various consequences such as a pool fire, a fireball, and even a catastrophic rupture of the tank with a successive explosion of its contents. In the study, the operations involved in bottling plants are classified into different hazard zones and analyzed. The probability of occurrence of events leading to an accident is modeled using modeling tools such as ALOHA and PHAST. The consequences of an accident following various events, such as jet fire, fireball, etc., are modeled, and the simulation results are compared. The thermal radiation has been estimated as 4–40 kW/m2, which could adversely affect the nearby population and could result in damaging plant machinery and equipment.

The investigation of the water mist suppression pool fire process's flame expansion characteristics

Flame expansion is a typical fire suppression phenomenon that happens during the water mist suppression of liquid fuel fires, particularly heavy oil fires, and poses a risk to process safety. A series of transformer oil fire expansion experiments were carried out to study the mechanism of flame expansion in the process of water mist suppression pool fires. A theoretical model of the interaction of water mist with flame and hot fuel was developed after a quantitative investigation of flame structure changes during expansion. According to the results of the study, the presence of a fuel-rich vapor layer on the oil pool's surface is a prerequisite for flame intensification, and the thickness of this layer is proportional to the height of the transformer oil flame, Lc=0.195Lf. Furthermore, the impact of water mist on the fuel-rich vapor layer is found to be the principal cause of flame expansion, and the transformer oil flame expansion rate is determined using a combination of theoretical and experimental methods, φv=13.9−41.8. Finally, one of the factors that aggravates flame expansion is the overpressure on the fuel surface caused by the water-oil mixture. Droplet size reduces as water mist pressure rises, and flame expansion shifts from the parallel effect of jet impact and water-oil mixing to the serial effect, lowering the flame expansion rate. As a result, reducing droplet size causes flame expansion to weaken.

Experimental investigation of flame height and air entrainment of n-heptane double open pool fires

ABSTRACT In this work, an experimental investigation is performed to study the flame height and air entrainment of 0.2 m n-heptane double pool fires (DPF) with various separation distances (S). The results show an inverse relationship between the flame height and air entrainment with S. The increase in the flame height of DPF with a decrease in the air entrainment is more than half of the standalone fire. A correlation is developed to predict the flame height of DPF considering the nondimensional air entrainment and heat release rate. Also, a correlation is developed between the nondimensional air entrainment and S.

Bench-scale fuel fire test for materials of rechargeable energy storage system housings

The fire behaviour of electric vehicles (EVs) differs from that of vehicles with combustion engines. Especially the rechargeable energy storage system (REESS) requires special fire protection measures. The fire behaviour of materials for REESS housings plays an important role in the fire resistance of such systems. Full-scale fire resistance tests like gasoline pool fire tests on complete REESS according to the UNECE-R100-8E standard are mandatory for EVs. However, these tests are not applicable for materials used for REESS housings in the material and process development state, due to the high material demand and production costs of the REESS. Standard tests like the limiting oxygen index test, UL94-V test or cone calorimeter test are insufficient to analyse the fire behaviour of thermoplastic and thermoset materials in a gasoline pool fire. This paper describes a bench-scale fuel fire test including several test criteria to evaluate materials for REESS housings on a laboratory scale. This bench-scale fire test is demonstrated on two case studies: fibre-reinforced thermoset plates and thermoplastic sandwich structures.

Effect of circulation on flame heights over liquid fuel pools

A striking feature of fire whirls is that they tend to have higher mean flame heights than free buoyant pool fires at the same heat release rates, which has been extensively studied in the past. Different from the mean flame height, the instantaneous flame height of a fire whirl reflects its dynamic nature in time domain, but has received less attention so far. This work experimentally investigated the effect of imposed circulation on flame heights over liquid fuel pools, including the mean and instantaneous flame heights, as a fundamental model of fire whirls. Both the rotating-screen and half-cylinder types of test facilities with different mechanisms for generating eddies were employed with circular ethanol pools of different diameters as fuel sources. Results showed that the scaling law proposed in previous studies can well estimate the mean flame heights of conical fire whirls, but does not work for the cases when a conical fire whirl-to-extinction transition or vortex breakdown occurs. Meanwhile, the characteristic flame pulsation frequency of a fire whirl is lower than that of a free buoyant pool fire with the same pool diameter, but increases with an increase in the imposed circulation due to enhanced air entrainment. A scaling law based on dimensional analysis is proposed to estimate the dimensionless flame pulsation frequency of a conical fire whirl by a combination of the fuel Froude number and the dimensionless circulation. Furthermore, with an increase in the imposed circulation, the instantaneous flame height transitions from a lower and less volatile position to a higher and more volatile position due to flame precession (an inherent instability of a conical fire whirl). Scaling laws for estimating the maximum instantaneous flame height difference in time domain and the flame precession frequency are deduced to summarize the data from small- and medium-scale tests.

Study of elevated- and ground pool fire flame horizontal lengths in cross airflows: Air entrainment change due to Coandă effect

The present study investigates experimentally the flame horizontal lengths of elevated pool fires and compares with those of ground pool fires in cross airflows. This, as a fundamental problem considering air entrainment and combustion structure change due to Coandă effect resulted from ground at leeward side, has not been quantified but is of practical significance. Experiments were performed employing both elevated- and ground square propane pool fires of various heat release rates in cross airflows from 0∼3.0 m/s with 224 test conditions in all. The overall flame horizontal length could be physically divided into two parts: 1) cross flow momentum-dominated length (base-drag part, Lm); 2) buoyancy-dominated length (plume-like part, Lb). Both the Lm and the overall flame horizontal length showed to be significantly larger for a ground pool fire than those of an elevated one, due to the ground constraint effect on air entrainment at leeward side (Coandă effect). Lb/(u2/g) or Lm/(u2/g) of elevated fires is proportional to that of ground fires. Large eddy simulations for two representative fire scenarios were further conducted utilizing an in-house version of FireFOAM. The purpose of the simulations was to uncover the underlying physics of combustion and flow structures observed in the experiment. Finally, a model was proposed based on analysis of air entrainment, momentum- and buoyancy effects, which described well the overall flame horizontal lengths of both elevated- and ground pool fires generally as a function of non-dimensional heat release rate, normalized volumetric air entrainment and Froude numbers using Lm and Lb as length scales. This work provides new observation and basic quantification on elevated- and ground pool fire flame horizontal lengths considering air entrainment change due to Coandă effect in wind.

Preparation and characterization of fire-extinguishing efficiency of novel gel-protein foam for liquid pool fires

The re-ignition of large-scale storage tank fires poses one of the greatest challenges in firefighting and it is thus of practical importance to develop efficient fire extinguishing agents to suppress and control liquid pool fires. In this study, a novel gel-protein foam was prepared. The microstructure, foamability, stability and water retention capacity of the gel-protein foam were analyzed systematically to identify three best formulations, which were then used to assess their fire extinguishing and burnback performance against a commercial film-forming fluoroprotein foam (FFFP). The experimental results indicated that the gel-protein foam with the best fire extinguishing efficiency is the one with a SA/CaCl2 ratio of 9:1 and a concentration of 0.1 wt%. The average size and water loss ratio are 126.46 μm and 30.6%, respectively, compared to 273.24 μm and 44.1% for FFFP. The fire extinguishing tests also confirmed that this gel-protein foam has the best cooling and burnback performance. Its 90% burnback time is 454s, a 54.42% increase that of FFFP, because it can float stably on the fuel surface to reduce the hazard of re-ignition. This work provides important data and guidance in further development of gel foams for extinguishing oil storage tank fires.