Enclosure Fires Research Articles

Numerical Evaluation of Aluminum-faced Sandwich Panels in Large Enclosure Fires

Numerical Evaluation of Aluminum-faced Sandwich Panels in Large Enclosure Fires

Experimental investigation on effects of heat release rate and horizontal vent area on enclosure fire phenomena with upper horizontal and lower vertical vents

Experimental investigation on effects of heat release rate and horizontal vent area on enclosure fire phenomena with upper horizontal and lower vertical vents

Study on the window spill fire plume trajectory of over-ventilated intermediate-scale compartment fires

The fire plume behavior of over-ventilated compartment fire is believed to be related with the façade fire. When the fire plume is reattached to the façade wall, the combustible materials over building wall are potential to be ignited soon. To investigate the window spill fire plume trajectory of over-ventilated intermediate-scale compartment fires, a modeling of fire plume trajectory is set up by using the energy conservation equation and spread theory. The temperature history of over-ventilated compartment fire is conducted by using a 1.35 m (L) × 1.35 m (H) × 1.35 m (W) compartment with window opening aspect varied from 1.12 to 4.44 and HRR differed from 200 kW to 1000 kW. The temperature of fire plume is recorded by the thermocouple mesh and the IR camera. It shows that the modelling theory could be used to predict the shape of fire plume. It agrees well with experimental result. The heat release rate of compartment fire is found to impact little influence on the shape of fire plume regarding a fixed opening dimension. It could provide a reasonable method for fire plume trajectory prediction of the intermediate-scale enclosure fire under an over-ventilated condition.

Investigation of flashover occurrence criterion based on thermal equilibrium theory

Flashover is the rapid transition to a state of total surface involvement in a fire of combustible material within an enclosure fire, which is the most serious and fatal event in building fires. Although previous studies have provided quantitative and qualitative standards for flashover, the criteria of flashover were normally based on the independent measurement of experimental parameters and phenomena rather than the underlying physical reasons, resulting in a lack of mutual relationships between these criteria and the inability to reflect physical mechanisms. Moreover, the flashover criteria vary for different compartment fire fuels, which directly affects the calculation of compartment fire theory. This work was performed to provide a unified principle on the criteria of flashover based on the thermal equilibrium theory. The critical conditions for flashover are quantitatively developed by establishing a partial differential equation for the energy generation rate and energy loss rate with respect to the temperature inside the compartment. Moreover, based on the partial differential equation, inequalities were established for the relationship between the temperature of the hot gas and the heat flux of the floor at the onset of flashover, which was validated by the compartment experiment data. It was found that due to differences in emissivity and net heat transfer rate, at the onset of flashover, the hot gas temperature and the radiation heat flux at the floor were different for different fuels, and a high hot gas temperature does not necessarily indicate a high radiation heat flux at the floor.

Enclosure fire extinguishment with water mist and nitrogen as affected by fire size, obstruction and ventilation

Fire tests were conducted to evaluate the efficacy of incorporating nitrogen to enhance water mist's fire-extinguishing capability in an obstructed, naturally-ventilated 1.22 × 0.61 × 1.22 m high enclosure. Water mist and nitrogen were applied from the enclosure ceiling in the respective ranges of 0.35–3.89 lpm and 0.113–0.283 m3/min, with median droplet sizes ranging from 16 to 35 μm. The obstruction was facilitated with horizontal baffles with various vertical spacings to force the transport of water mist and nitrogen to follow an alternating path to a 76- or 152-mm heptane pan fire sitting on the enclosure floor. The enclosure ventilation was provided with a 0.23 × 0.15 m high base opening centered on the enclosure's front wall, together with a 0.33 × 0.05 m high opening centered on the enclosure's front wall or on the enclosure's back wall at the respective elevations of 0.36 m and 0.81 m above the enclosure floor, or with the presence of these two elevated openings. The tests showed that incorporating nitrogen in the water mist application did improve water mist’ fire-extinguishing capability in the enclosure. However, the improvement was highly affected by the fire size, obstruction and ventilation conditions.

Oscillatory burning regime in a gas-fueled compartment fire

The paper presents a series of 48 enclosure fire experiments carried out in a 1.40 m cubic compartment with a door-like opening of 0.80 m width and a variable height from 0.25 to 1.40 m. The fire source was a propane-fueled square burner of 0.17 m side length positioned in the center of the compartment and delivering a steady mass flux that has been varied in the tests from 0.5 to 5.0 g/s. In addition to the well-known well-ventilated and under-ventilated regimes, an oscillatory combustion regime has been uncovered for an opening height of 0.25 or 0.35 m. This regime is characterized by an alternation between the well-ventilated regime (combustion exclusively inside the compartment) and the under-ventilated regime (combustion inside and outside the enclosure). It is believed that the time for the onset of the oscillations is linked to the smoke filling time. Furthermore, depending on the specific conditions, the oscillations are either steady (until shut-off of the fuel supply) or transitory (leading to a sustained under-ventilated regime). The frequencies ranged from about 9 to 19 mHz. The oscillatory regime has previously been mainly reported for liquid fuels and thus associated to radiative heat feedback effects. The new data for a gaseous fuel calls upon a better understanding and a further analysis of the underlying physics.

A Cold Climate Wooden Home and Conflagration Danger Index: Justification and Practicability for Norwegian Conditions

The vast majority of fire-related deaths occur in residential buildings. Until recently, the fire risk for these buildings was only considered through static risk assessments or period-based assessments applying to certain periods of the year, e.g., Christmas holidays. However, for homes with indoor wooden panelling, especially in the ceiling, a dynamic fire danger indicator can be predicted for cold climate regions. Recognising the effect of fuel moisture content (FMC) of indoor wooden panelling on the enclosure fire development allows for the prediction of a wooden home fire danger indicator. In the present study, dry wood fire dynamics are analysed and experimental observations are reported to support in-home wooden panel FMC as a suitable wooden home fire danger indicator. Then, from previous work, the main equation for modelling in-home FMC is considered and a generic enclosure for FMC modelling is justified based on literature data and supported through a sensitivity study for Norwegian wooden homes. Further, ten years of weather data for three selected locations in Norway, i.e., a coastal town, an inland fjord town and a mountain town, were analysed using a three-dimensional risk matrix to assess the usability of the fire risk modelling results. Finally, a cold climate wooden home fire danger index was introduced to demonstrate how the risk concept can be communicated in an intuitive way using similar gradings as the existing national forest fire index. Based on the generic enclosure, the findings support FMC as a fire risk indicator for homes with interior wooden panelling (walls and ceiling). Large differences in the number of days with arid in-home conditions were identified for the selected towns. The number of days with combined strong wind and dry wooden homes appears to depend more on the number of days with strong wind than days of in-home drought. Thus, the coastal town was more susceptible to conflagrations than the drier inland towns. This aligns well with the most significant fire disasters in Norway since 1900. In addition, it was demonstrated that the number of high-risk periods is manageable and can be addressed by local fire departments through proactive measures. In turn, the fire risk modelling and associated index respond well to the recent changes in Norwegian regulations, requiring the fire departments to have systems for detecting increased risk levels. Testing the modelling for a severe winter fire in the USA indicates that the presented approach may be of value elsewhere as well.

A comparison of carbon monoxide yields and particle formation at various global equivalence ratios in vitiated and under-ventilated conditions

There have been previous studies comparing experimental methods for the purpose of capturing gaseous yields at a range of global equivalence ratios. However, no work has investigated the capability of the open controlled atmosphere cone calorimeter for collecting such data where its two modes of operation are directly compared. The aim of this study is to compare carbon monoxide yields collected using vitiated and under-ventilated modes of atmospheric control in order to identify the preferable method of replicating carbon monoxide yields reported from larger scale enclosure fire experiments. Cone irradiances of 30, 50 and 65 kW/m2 were applied to PMMA and plywood samples. Vitiated tests were conducted using a mixed air/diluent gas, with an inflow rate of either 100, 150 or 180 L/min, resulting in a reduced oxygen concentration of 17.5 vol. %. Under-ventilated tests were conducted using flow rates of 5, 10 and 20 L/min in an air atmosphere. Particle formations and emissions were also measured using a particle analyser and have been reported herein. Results indicate that the under-ventilated mode of equivalence ratio control offers a more promising method of capturing species yields with favourable comparisons to other bench scale methods.

Computational fluid dynamics simulations of water spray interaction with smoke in a confined and a mechanically-ventilated enclosure fire

The paper presents a numerical study on the interaction between two water sprays and smoke generated by a fire in a confined and mechanically-ventilated enclosure of 4.88 m × 8.67 m × 3.90 m (height). The fire source is a 1.2 m × 1.0 m × 0.6 m propane burner, generating a well-controlled heat source of 292 kW. The mechanical ventilation consists of an inlet and an extraction duct delivering each a flow rate of about 2500 m3/h. The two nozzles deliver a total flow rate of 109 l/min with a volume-median droplet diameter of about 470 μm. The CFD simulations carried out with the Fire Dynamics Simulator (FDS 6.7.9) show a very good agreement with the experimentally measured room pressure at quasi-steady state. The under-pressure peak of −993 Pa, occurring upon activation of the water spray system, is underpredicted by 25%. The overall thermal behavior is well-predicted. Nevertheless, the water spray mixing-induced loss of thermal stratification appears to be more pronounced in the CFD simulations, with over-predicted gas temperatures near the floor. The fraction of heat absorbed by the water at steady state is underestimated by 34%. The loss of chemical stratification upon water activation is well-predicted.

Enclosure Fire with Time-Dependent Changes in Ventilation Factor and Geometry—Field Model Parameters Analysis

The fire scenarios currently used for structural fire design are based on traditional methods that derive from the extrapolation of existing fire test data. The traditional “furnace” geometry test allows a good circulation of the fire gases and a relatively homogeneous temperature distribution throughout the enclosure. These conditions are different from what is observed in real-situation fires. As a result, the need for a field model for an enclosure fire has increased significantly, and appropriate deterministic models are necessary for fire safety engineering. The effects of different strategies involving the opening of doors and windows with changes in the enclosure’s geometry were observed to gain an insight into the impact of how ventilation and geometry influence changes during the development of a fire. This article presents and discusses the results of the field model compared with similar tests and experiments described in the technical and scientific literature. Generating data using a field model reduces experimental costs and facilitates sensitivity analyses of the parameters of problems.

An effect of ventilation on development of thermal and toxic environment in cubical enclosure fires

An effect of ventilation on development of thermal and toxic environment in cubical enclosure fires

Maximum ceiling temperature and longitudinal distribution in a corridor-like enclosure with opening

This paper reports a quantitative study on the effects of a side opening on the transition between the fuel-controlled and the ventilation-controlled condition and temperature distribution in a corridor-like enclosure fire. A side opening was introduced to simulate breakage of glass window in case of fire. Experiments were carried out in a 1/8 model tunnel with the dimensions of 3.14 m×0.42 m×0.368m(length×width×height), including 56 test conditions arising from variations of heat release rates (HRR) and opening sizes. The results showed that the transition was correlated with the fraction of the heat released to the heat convected through the opening and the ratio of the heat lost through enclosure boundary to the heat convected through the opening. The maximum temperature rise in the fuel-controlled condition was positively correlated with the fire heat release rate, but it was negatively correlated with the opening aspect ratio. There were two combustion stages in the ventilation-controlled condition, one with flame oscillation inside the corridor-like enclosure and the other with persistent flame ejection through the opening. The maximum temperature rise in the stage of flame oscillation inside the compartment was positively correlated with the air mass supply through the opening and negatively correlated with the heat loss through the corridor-like enclosure boundary. Non-dimensional correlations between the maximum temperature rise and the heat release rates (HRRs), opening sizes and the heat loss were proposed. Moreover, a piecewise equation was proposed to predict the longitudinal decay along the centerline of the corridor-like enclosure with an opening. All the proposed correlations were found to fit well with the experimental data, which established a basic relationship to quantify the (i) temperature variation, (ii) critical heat release rate and (iii) transition for various opening sizes and HRRs in a corridor-like enclosure fire. These new findings and the proposed non-dimensional model provide the basis for understanding fire growth and temperature distribution inside a corridor-like enclosure with opening.

PAST, PRESENT AND FUTURE FOR ENCLOSURE FIRE FIELD MODEL

Computational fluid dynamics (CFD) analysis became a popular solution as the complexity grew in applying the laws of physics directly to real fire scenarios in order to make analytical predictions. This fact became especially prevalent for fluid dynamics and heat transfer engineering problems for enclosure fire. The fire field model consists of the CFD code and the fire model. The CFD code is the core and provides the fire model with transport mechanisms for energy, momentum, mass. The fire model is a detailed specification of the fire description. The use of the fire field model in the enclosure strengthened our understanding of the actual fire scene, allowing us to fully characterize the time-dependent changes. The paper delivers a comprehensive review of the history, development, current state of field models and future predictions in enclosure fire field modeling.

Real-time detection and forecast of flashovers by the visual room fire features using deep convolutional neural networks

Flashover occurs in building fires whereby all the combustible materials in an enclosure begin to ignite rapidly. This detrimental phenomenon occurs because of the intense heat radiating from the hot smoke layer accumulated near the ceiling, which is one of the major causes of firefighter fatalities. Thus, forecasting flashover in real-time is of great importance to firefighters’ safety. Previous empirical and theoretical analysis of the flashover phenomenon provides criteria for predicting flashover on-set and fire size, yet they are based on the thermal sensor data in the room. It is not straightforward to transfer the flashover criteria and understanding from the previous studies in application to actual fire grounds since thermal sensor data are not readily available. As a novel non-invasive prediction technique of flashover onset, this investigation explores the potential of recognizing vision indicators of flashover, such as flame extrusion or rollover. Adopting artificial intelligence (AI) technologies for pattern recognition and feature extraction, we proposed to build an optimized convolutional neural network named “FlashoverNet”, a modern AI algorithm, to detect and forecast flashover occurrence in enclosure fire incidents. FlashoverNet was trained and validated by data from several full-size actual room fire experiments. FlashoverNet imitates the approach of flashover onset prediction by firefighters by monitoring fire growth and looking for early visible indicators in a room fire. Our investigations demonstrate that FlashoverNet can successfully detect and forecast flashover onset in real-time with more than 94% accuracy in full-scale actual room fire tests.

An Engineering Model for Water Spray Cooling: Application to a Mechanically-Ventilated Enclosure Fire

An Engineering Model for Water Spray Cooling: Application to a Mechanically-Ventilated Enclosure Fire

Two dimensional temperature distributions in a ceiling jet generated by a finite line-source fire: An experimental study

The temperature distributions of ceiling jets are fundamental characteristics in enclosure fire dynamics. It is also the basics in the designs of fire safety devices in buildings, like detection, sprinkler, smoke control and standard fire protection. However, the only exists equation is for the radial ceiling jet temperature profile induced by a point source. There are no studies on line source despite the fact that the non-axisymmetric sources are the more common fires in buildings. This paper, for the first time, investigates the temperature profiles in ceiling jet induced by a finite line-source fire plume impinging upon an unconfined ceiling. Experiments are carried out with a buoyant jet fire and a pool fire. The temperature profile under the ceiling was measured along with flow condition visualized by a laser sheet. It is found that the temperature profile is two-dimensional and decays slower in the y-direction (perpendicular to line source longer side) than that in the x-direction (parallel to line source longer side). The characteristic length scales for characterizing the temperature profiles in the two directions are then proposed on the basis of the dimensions of the plume impinging zone. An equation is derived to describe the two-dimensional temperature profile based on the characteristic length scales. The present study provides basic data and a new equation for temperature profiles of ceiling jet induced by finite line-sources for building fire science.

Temperature variation inside a corridor-like enclosure under limited ventilation

This paper investigates the temperature variation inside a corridor-like enclosure (for example, high-speed train compartment) with persistent flame ejection through an opening (for example, window). The fire heat release rate and opening sizes are varied with 28 different experimental conditions. An exponential function is built and found to be able to describe the longitudinal temperature distribution, in which the decay rate has a power function with the window aspect ratio. The maximum temperature shows a considerable difference for various heat release rates (HRR), due to the mass flow rate of the fuel supply through the opening is comparable to or greater than the air mass inflow rate. A general model characterizing the longitudinal temperature distribution of various opening sizes and HRR is proposed with heat release to heat loss ratio inside the compartment, HRR and window aspect ratio, which shows a good agreement with the experimental results. This study provides important and new contributions over previous knowledge and has potential practical applications concerning the corridor-like enclosure fire safety and occupant evacuation.

Numerical Simulations of a Postulated Methanol Pool Fire Scenario in a Ventilated Enclosure Using a Coupled FVM-FEM Approach

Numerical investigations have been carried out for a postulated enclosure fire scenario instigated due to methanol pool ignition in a chemical cleaning facility. The pool fire under consideration is radiation-dominated and poses a risk to the nearby objects if appropriate safety requirements are not met. The objective of the current study was to numerically evaluate the postulated fire scenario and provide safety recommendations to prevent/minimize the hazard. To do this, the fire scenario was first modeled using the finite volume method (FVM) based solver to predict the fire characteristics and the resulting changes inside the enclosure. The FDS predicted temperatures were then used as input boundary conditions to conduct a three-dimensional heat transfer analysis using the finite element method (FEM). The coupled FVM–FEM simulation approach enabled detailed three-dimensional conjugate heat transfer analysis. The proposed FVM–FEM coupled approach to analyze the fire dynamics and heat transfer will be helpful to safety engineers in carrying out a more robust and reliable fire risk assessment.

Replicating the activation time of electronically controlled watermist system nozzles in B-RISK

This paper presents two series of enclosure fire experiments in which the activation time of electronically controlled watermist system nozzles and concealed sprinklers have been obtained. The first series experiments were aligned to the procedure given in the BS 8458 standard whereas the second series were configured to give slower growing fires than in the standard test.The activation of the two systems have been simulated in the B-RISK zone fire model. Activation characteristics for the concealed sprinklers have been taken from elsewhere in the literature. Representative activation characteristics for the electronically controlled watermist system nozzles have been determined. The selection of these characteristics has required a balance between the results from the two experimental series. By using an effective response time index of 20 m½s½ and an effective conductivity factor of 0.25 m½s−½ the predicted activation times are on average 14% slower across all of the enclosure fires.

Large-Scale Enclosure Fire Experiments Adopting CLT Slabs with Different Types of Polyurethane Adhesives: Genesis and Preliminary Findings

This paper provides understanding of the fire performance of exposed cross-laminated-timber (CLT) in large enclosures. An office-type configuration has been represented by a 3.75 by 7.6 by 2.4 m high enclosure constructed of non-combustible blockwork walls, with a large opening on one long face. Three experiments are described in which propane-fuelled burners created a line fire that impinged on different ceiling types. The first experiment had a non-combustible ceiling lining in which the burners were set to provide flames that extended approximately halfway along the underside of the ceiling. Two further experiments used exposed 160 mm thick (40-20-40-20-40 mm) loaded CLT panels with a standard polyurethane adhesive between lamella in one experiment and a modified polyurethane adhesive in the other. Measurements included radiative heat flux to the ceiling and the floor, temperatures within the depth of the CLT and the mass loss of the panels. Results show the initial peak rate of heat release with the exposed CLT was up to three times greater when compared with the non-combustible lining. As char formed, this stabilised at approximately one and a half times that of the non-combustible lining. Premature char fall-off (due to bond-line failure) was observed close to the burners in the CLT using standard polyurethane adhesive. However, both exposed CLT ceiling experiments underwent auto-extinction of flaming combustion once the burners were switched off.