Influence of fire source locations on the actuation of wet-type sprinklers in an office fire

An experiment is conducted on a full-scale model office and an actual sprinkler system to explore the influence of fire source locations on sprinkler actuation. The office space is a brick structure that measures 5.7 m in interior length, 4.7 m in width and 2.4 m in ceiling height, and equipped with a sprinkler system. The investigated fire source (100 kW LPG burner) locations include the room center, wall centers, room corner, and other locations at different distances from sprinklers. The results show that actuation of the sprinklers is affected by the fire source locations and the heat conduction properties of the glass temperature-sensing bulb. Average actuation time of all the tests is 102 s, around 40 s faster than if the fire source is located in the room center. For fire sources in corners, sprinklers are quickly activated at the experimental time 75 s, showing concentrated hot gas flow.     

Experimental data and numerical modelling of 1.3 and 2.3 MW fires in a 20 m cubic atrium

Atria and large spaces are common architectonical features in modern buildings such as high rises, auditoria, warehouses, airports and mass transport stations among others. There is currently an international trend towards the performance-based design for fire safety of these building elements. This design process relies heavily on fire modelling but the knowledge in fire dynamics and the movement of smoke in atria and large spaces still presents some gaps. This paper aims at contributing to close these gaps and reports the three Murcia Atrium Fire Tests conducted in a 20 m cubic enclosure using pools of 1.3 and 2.3 MW. Detailed transient measurements of gas and wall temperatures, as well as pressure drop through the exhaust fans and airflow at the inlets were recorded. The study also includes the effect of the mechanical exhaust ventilation. Results have been compared with those predicted by the computational fluid dynamics (CFD) model Fire Dynamics Simulator FDSv4. In general terms, the comparisons between experiments and simulations show good agreement, especially in the far field of the plume, but the accuracy is poor at the lower plume region and near the flame.     

The use of impulse ventilation for smoke control in underground car parks

Impulse ventilation systems (IVS) are used to provide ventilation for covered car parks and to control the smoke in the event of fire. In this paper the interaction between the fire ceiling jet and the flow driven by jet fans is studied using CFD simulations. A sensitivity analysis considering important parameters as position and intensity of fire source, transversal distance between jet fans, restriction of exhaust flow rate and dimension of car park exhaust opening is carried out and rules for the design of 50 N thrust jet fans are deduced. An analytical model for the flow field near the ceiling is developed and compared with CFD simulations. This model is intended to support a first approach of the design of IVS.     

Numerical simulation of the spread of smoke in an atrium under fire scenario

The Fire Dynamics Simulator code is used to investigate the smoke movement in an atrium under fire scenario. At first, by comparing with experimental data of the atrium fire under low and high heat release rates, reasonable model constants of C_s and Pr_t and appropriate grid system are determined for simulating smoke movement in the atrium, the simulation results are in good agreement with those experimental data. Then, the performance of different smoke exhaust methods in the atrium is studied. Smoke filling processes are investigated under different natural and enhanced smoke exhaust methods. Simulated results show that natural smoke exhaust method is preferred when the smoke exhaust vents are located at the ceiling of the atrium. On the other hand, when the smoke exhaust vents are located on the walls of the atrium, the higher positions of the smoke exhaust vents are preferred. In addition, the influence of the fire source locations on the smoke spreading process is presented in this paper, three kinds of fire source locations are studied, they are central fire, side wall fire and corner fire. Results indicate that the descending process of the smoke layer is the slowest when the fire source is at the corner of the atrium.     

Influence of fire ignition locations on the actuation of smoke detectors and wet-type sprinklers in a furnished office

Experiments were conducted in a full-scale model office equipped with movable and fixed fire loads to explore the influence of ignition source (movable fire load(s)) conditions on smoke detector and sprinkler actuation. The interior plan dimension is 5.7 m × 4.7 m and the net ceiling height is 3.3 m. Both northeast and southeast wings have a 2.1 m × 0.9 m single door to be opened. Seven fire scenarios (seven different ignited fire load configurations) under natural ventilation were investigated experimentally. The results show that the amount of fire load at the initial stage in a room fire does not markedly affect smoke generation and does not significantly impact the actuation time of the smoke detectors. When the fire source is located near a corner, the plume corner effect greatly increases; smoke detectors and sprinklers can activate quickly and effectively actuate the fire suppression. When the fire source is located in the room's center, given the uncertainty regarding smoke detector and sprinkler actuation, it may not be possible to control the fire spread.     

A smoke model and its application for smoke management in an underground mass transit station

This paper discusses the development of a smoke model for CFD. The model evaluates smoke visibility based on line of sight. Using a compartment fire, the deficiency in determining visibility by the conventional surface-based approach is first demonstrated. Smoke management in an underground rail station is investigated using the smoke model. For a medium growth rate fire, the results show that the platform is blocked by smoke within 2–3 min. On the mezzanine, the designed smoke exhaust controls the smoke only for a limited time of less than 4 min. The variations of smoke obscuration are quantified at three locations, which are used to start the tunnel ventilation at 4 min. This can be related to a video-based smoke detection. The smoke model would be useful in tenability, egress and other life safety assessments. Future development of the model includes local lighting effects and experimental validation.     

某物流中心中庭风幕取代防火卷帘的数值模拟

利用FDS模拟某物流中心中庭火灾场景中风幕的挡烟效果。中庭高32m,顶部有6个机械排烟口,总排烟量为240000m3/h。火源功率为4MW,快速t2火位于中庭下方。机械排烟系统和风幕系统均在火灾开始后60s时启动。风幕风速分别为0、0.5、1、2、3和4m/s。模拟结果:当风速低于1m/s时,挡烟效果不明显;风速高于3m/s会妨碍排烟系统的排烟效果。2m/s风速既能发挥风幕的挡烟效果,又不使烟气在下层积聚。结论:设置合理风速的风幕在一定程度上可取代防火卷帘。     

Cooling characteristics of hot oil pool by water mist during fire suppression

Generally water is not favored for use in suppressing hot liquid fuel fires due to concerns of vapor explosion and boil-over, which could present potential danger to nearby personnel or firefighters. This paper reports on a series of full-scale fire experiments in which water mist was used in extinguishing large hot cooking oil fires. It was shown that water mist not only extinguished large fires effectively but also cooled hot oil from its ignition point (up to 360 °C) to below its flash point (200 °C) in a short period of time and prevented the fire from re-igniting. No vapor explosion was observed in the experiments when water droplets touched the hot oil whose temperature was higher than the superheat-limited temperature of water. A boiling layer of mixed bubbles, water droplets and oil was formed in the hot oil after all flames were extinguished, as water droplets boiled, bubbled and expanded in the hot oil. No boil-over or spillage of the oil over the container was observed in the experiments when water mist was discharged into the oil at high temperature (>300 °C) but boil-over did occur in experiments when the water mist was discharged into oil at a relatively moderate temperature (∼200 °C). In this paper, the mechanisms of cooling of hot oil by water mist are investigated, and the formation and development of the boiling layer during cooling are analyzed both experimentally and theoretically.     

Influence of different make-up air configurations on the fire-induced conditions in an atrium

In this paper, the influence of the make-up air velocity as well as the position and area of the vents in an atrium is assessed both experimentally and numerically. In the experiments, the effect of different make-up air supply positions and inlet area on the fire-induced inner conditions and smoke-layer descent was studied by means of three full-scale fire tests conducted in a 20 m cubic atrium. Detailed transient measurements of gas and wall temperatures, as well as pressure drop through the exhaust fans and airflow at the inlets were recorded. These data could be used as benchmark for future numerical validation studies. Later computational fluid dynamics (CFD) simulations of these tests were performed with the code Fire Dynamics Simulator (FDSv4). In the experiments, the lack of symmetry in make-up air vents and the large inlet area turn the flame and plume more sensitive to outer effects. However, no significant difference has been observed between the make-up air topologies assessed. Even make-up velocities higher than 1 m/s, with symmetric venting topology, have not induced important flame or plume perturbations. In the numerical simulations, the predictions agree well with the experiments for the cases with larger make-up air openings. Poor agreement has been found for the case with the smallest inlet openings.     

Development of a Gaussian glass breakage model within a fire field model

A glass breakage model has been implemented within the existing FDS fire field model. The field model allows the prediction of radiative and convective heating to solid-phase objects. This is utilised by filtering, within the code, the objects to be modelled as glass, and then linking a one-dimensional heat transfer across those objects to a Gaussian spread of breaking temperatures across panes within the compartment being modelled. The gas- and solid-phase heat transfer methods are described along with the implemented glass breakage model. A case study is then presented involving the modelling of a large-scale compartment fire in a building with a high degree of glazing. A key factor in the severity of the atmospheric conditions, and the variations in temperature prediction, comes as a result of the different breaking patterns of glass around the compartment. The Gaussian glass breakage model emphasises this, and equivalently high local temperatures are not predicted when the typically adopted method of solid-object removal is used, or when the assumption of an ‘open’ compartment condition, where all the glazing is removed, is modelled. Changing ventilation patterns from a Gaussian breakage model are thus shown to produce markedly different gas temperature predictions than other methods. The new glass brakeage model presented in this paper can be implemented into any existing CFD fire field model and is not exclusive to FDS.     

Optimization of emergency ventilation mode for a train on fire stopping beside platform of a metro station

This paper presents a computational fluid dynamics (CFD) simulation investigation of most effective cooperative operation mode of the tunnel rail track area exhaust system and the platform ventilation system for the emergency scenario of a train on fire stopping beside the platform of a subway station. CFD simulations are carried out by fire dynamics simulator (FDS) to analyse and compare the computed field distributions of smoke temperature and visibility, as to find out the most optimal cooperation mode of these ventilation systems. Results show that only starting the over track exhaust (OTE) system can control the smoke more effectively than starting both the OTE system and the under platform exhaust (UPE) system at the same time. In addition, setting the platform ventilation system as exhaust pattern can provide better control performance than setting it as air supply pattern, in counteracting the smoke flowed into the platform from the fire train. Therefore, it is found out and suggested that in such an emergency condition, the most effective strategic cooperative ventilation mode is only starting the OTE system of the tunnel rail track area with the aid of activation the smoke exhaust pattern of the platform ventilation system.     

Fire resistance of biomass ash panels used for internal partitions in buildings

The main purpose of this study has been to develop fire-resistant panels with a high biomass ash ratio (from the combustion of olive pomace) at an industrial scale to be used in different fire-resistant internal partitions in buildings and industrial constructions. To this end, fire resistance, thermal and mechanical parameters were measured. The panels (100×60 cm by 4 cm thick) were prepared following an easy manufacturing technique. The results of this study show that biomass ash panels can be fabricated at large scale easily to give products with thermal and mechanical properties reproducing those previously found in smaller test pieces. The product here studied in the form of low-density panels (800 kg/m³) has a great potential for an industrial use, showing similar properties to those found in commercial gypsum plasterboard, a material of generalised use for this type of application. Thus, among other panel characteristics, a thermal conductivity of 0.256 W/m K (25 °C) and a fire resistance of 78 min were measured in standard conditions by an accredited Spanish fire resistance laboratory for panels showing a compressive strength of 1.24 MPa, and a flexural strength of 1.78 MPa.     

CFD modelling of air flow and thermal performance of an atrium integrated with photovoltaics

The thermal performance of an atrium integrated with photovoltaic (PV) modules has been evaluated. Computational fluid dynamics (CFD) was applied to the prediction of air flow and temperature distribution in the atrium. CFD was then used to investigate the effect of ventilation strategies on the performance of PV arrays. CFD modelling indicated that for effective cooling of roof PV arrays, cool outdoor air should be introduced through an opening positioned close to the roof or an air channel underneath the roof.     

Thermal and structural behaviour of a full-scale composite building subject to a severe compartment fire

This paper presents a numerical investigation of the thermal and structural results from a compartment fire test, conducted in January 2003 on the full-scale multi-storey composite building constructed at Cardington, United Kingdom, in 1994 for an original series of six tests during 1995–1996. The fire compartment's overall dimensions were 11 m×7 m with one edge at the building's perimeter, using largely unprotected steel downstand beams, and including within the compartment four steel columns protected with cementitious spray. The compartment was subjected to a natural fire of fire load 40 kg/m² of timber, in common with the original test series, but the composite slab forming its ceiling was subjected to a uniform applied load of 3.19 kN/m², which is higher than the original.     

Effects of roof tile permeability on the thermal performance of ventilated roofs: Analysis of annual performance

This paper shows the results of the second part of an experimental study aimed at analysing the effects of roof tile permeability on the thermal performances of ventilation ducts. Ventilation ducts under the layer of tiles are typically used in south European countries to limit the energy load during the summer period. The results of the first part of the study, carried out by analysing 14 different types of roof, proved that the air permeability of the layer of tiles determines a certain amount of heat to be released, in addition to the release connected with the stack effect, in ventilation ducts which have the same characteristics but are perfectly airtight. However, the study did not completely resolve some issues since it was carried out on a model roof (6 m × 1.5 m) with devices to raise the layer of tiles and to create the ventilation duct but without those building elements which are present in real roofs and are used to stop insects and small animals from entering the ventilation duct. These elements narrow the inlet and outlet and consequently cause important reductions in pressure. Moreover, the measurements were based on data collected for limited periods of time during the summer season.     

Forecasting fire growth using an inverse zone modelling approach

A new methodology to effectively forecast fire dynamics based on assimilation of sensor observations is presented and demonstrated. An inverse modelling approach with a two-zone model is used to forecast the growth of a compartment fire. Sensor observations are assimilated into the model in order to estimate invariant parameters and thus speed up simulations and recover information lost by modelling approximations. A series of cases of a compartment fire radially spreading at different growth rates (slow, medium and fast) are used to test the methodology. Spread rate, entrainment coefficient and smoke transport time are the invariant parameters estimated via a gradient-based optimization method with tangent linear differentiation. The parameters were estimated accurately within minutes after ignition and the heat release rate reproduced satisfactorily in all cases. Moreover, the temperature and the height of the hot layer are forecasted with a positive lead time between 50 and 80 s, depending on the fire growth rate. The results show that the simple mass and energy conservation equations and plume correlation of the zone model are suitable to forecast the main features of a growing fire. Positive lead times are reported here for the first time in fire dynamics. The results also suggest the existence of an optimal width for the assimilation window. The proposed methodology is subject to ongoing research and the results are an important step towards the forecast of fire dynamics to lead the emergency response.     

Experimental analysis of cross-laminated timber panels in fire

Design models of timber structures in fire usually take into account the loss in cross-section due to charring of wood. For cross-laminated timber panels in fire only little information on charring is available. The paper describes and discusses the results of an extensive testing programme on the fire behaviour of cross-laminated timber panels under ISO-fire exposure. The fire tests were performed on the small horizontal furnace (1.0×0.8 m) at the Empa in Duebendorf. Particular attention is given to the comparison of the fire behaviour of cross-laminated timber panels with homogeneous timber panels. The results of the fire tests showed that the fire behaviour of cross-laminated timber panels is strongly influenced by the behaviour of the adhesive used for bonding the cross-laminated timber panels. Depending on the properties of the adhesives at elevated temperatures falling off of the charred layers was clearly observed during the fire tests, leading to increased charring rates in comparison to homogeneous timber panels. This is the same effect as observed for initially protected timber members after the fire protection has fallen off. For the specimens where no falling off of the charred layers was observed the fire behaviour was similar to that of homogeneous timber panels.     

Fire simulation in road tunnels

The catastrophic tunnel fires since the year 1999 and a series of accidents in some tunnels in the summer of 2001 triggered extensive discussions and proposals relating to tunnel safety. When a fire occurs in a tunnel, and in absence of sufficient air supply, large quantities of smoke are generated, filling the vehicles and any space available around them. Unless a strong flow is created and maintained, hot gases and smoke migrate in all directions. With a weak airflow, smoke forms a layer along the tunnel ceiling and can flow against the direction of forced ventilation, interfering with personal evacuation. This paper shows the results of a computer fire simulation in a tunnel and the results of this simulation: air velocity, air temperature and wall temperature in the case of fire. The simulation started before the emergency ventilation system is activated and continued with the fans activated to control the smoke.