Enclosure Fires Research Articles

Real Fire Test on Concrete Columns and Post-tensioned Slabs

An enclosure fire test was conducted incorporating high strength reinforced concrete columns and normal strength post-tensioned floor slabs. The slabs formed part of the roof whilst the columns within the enclosure were unloaded except for compressive stresses induced by the prestressing bar located at the centre of each of the columns. The columns and slabs were made from commonly available but markedly different Australian aggregates. Some of the columns incorporated 6mm monofilament polypropylene (pp) fibres introduced into the concrete mix at a concentration of 1kg per m 3 of concrete. With the exception of columns with pp fibres, spalling commenced within 10 minutes of the start of the test with all columns experiencing extreme spalling. The test was terminated at 68 minutes due to failure of one of the posttensioned slabs. Minimal spalling was obtained for slabs constructed from basaltic aggregate. The implications of the findings are considered with respect to the design of reinforced concrete structures.

Enclosure and Facade Fires: Physics and Applications

Facade fires being a disastrous hazard for high rise building, as several historical and recent incidents have shown, have attracted the interests of numerous fire scientists, engineers and regulators. This work has as an objective to present issues in this area that are challenging and need further attention. It focuses on characterizing the flame height and heat fluxes from facade flames produced from under-ventilated enclosure fires on a facade that is not flammable. Such an investigation is an important consideration for practical applications as well as a prerequisite for examining fire spread on flammable facades and for designing a test for modern facade assemblies. The mass pyrolysis rates and burning of real fuels are discussed in under ventilated enclosures, rectangular or corridor like, for various openings presenting the current state and some critical issues. Facade flames are analyzed from experiments using gaseous burners to have control on the fuel supply rate by introducing physical length scales for the opening geometries to model flame heights and heat fluxes. An important parameter for the facade flames is the excess heat release rate of the fuel burning outside the enclosure. Finally, applications for facade flames with sidewalls and facade flames from two openings are presented.

Carbon monoxide production during underventilated fires in corridors

This work presents experimental results and non-dimensional correlations of factors and conditions affecting carbon monoxide (CO) production in corridor-like enclosure fires. Thirty eight experiments were performed in a three metre long corridor-like enclosure having a cross section 0.5 m x 0.5 m, door-like openings in the front panel and a propane gas burner located near the closed end being flushed with the floor. Measurements of carbon monoxide concentrations were performed at locations inside the enclosure and also in the exhaust duct of a hood collecting the combustion products for direct comparison. Visual observations through the opening revealed that flames were detaching from the burner for tests with global equivalence ratios (GERs) greater than one for the burning inside the enclosure (underventilated fires). After detachment, flames were travelling towards the opening then finally stayed anchored in the vicinity of the opening and emerged outside. After flames were visible outside, the concentration of CO inside the corridor increases to much higher levels owing to the recirculation of gases inside the enclosure behind the flames. A correlation between CO concentration inside the enclosure and GER was found with CO increasing initially but then decreasing for high global equivalence ratios. An additional correlation was found between the CO yield and the GER in the enclosure before the flames reached and then, anchored at the opening of the enclosure. Finally, it was found that the ratio of CO to smoke yield, yco/ys, is not constant but increases for global equivalence ratios of the enclosure greater than one in contrast to its value being constant for over ventilated conditions.

Thermal performance of window glass panes in an enclosure fire

Thermal performance of glass pane under fire was studied in this paper. Heat transfer to glass and associated fracture were reviewed first. Glass temperature profiles on the glass pane were then summarized into three stages based on heat transfer: The first stage is on rapid heating up, the second stage is on steady heating up and the third stage is on losing heat to a certain value. Partial differential equations were set up on predicting the glass temperature at each stage with appropriate boundary conditions.By proposing different glass temperature variations for those three stages, three sets of partial differential equations were set up and solved. These three equations were then applied to study the heat up of glass with experimental data reported in the literature. The derived solution agrees reasonably well with experiment.

Study on effect of wind on natural smoke exhaust of enclosure fire with a two-layer zone model

Effect of wind on natural smoke exhaust in enclosure fire with a two-layer zone model was studied in this paper. A “net wind pressure coefficient” was proposed to evaluate the significance of wind effect. Case calculations on quasi-steady vented stage of natural smoke exhaust were performed. It is shown that with a negative net wind pressure coefficient, performance of exhaust will be degraded by the wind, even invalidated. The critical wind speed invalidating natural smoke exhaust is found inversely proportional to the absolute value of the net wind pressure coefficient. Experimental data in a model room is presented and compared with the predicted values using the two-layer zone model. Good agreements were found between the predicted and experimental results except in the cases with a non-positive net wind pressure coefficient. Discrepancies are ascribed to the disturbance of the vent flow and stratification in the room by the wind. While activating natural smoke exhaust system in case of fire under the windy condition, positions of the smoke vent and air inlet should be located with consideration according to the wind direction to form a big positive net wind pressure coefficient as possible and to increase the exhaust efficiency.

Smoke concentrations inside and outside of a corridor-like enclosure

This work presents smoke measurements and correlations inside and outside of a corridor-like enclosure fires in order to determine the effects of burning on smoke concentrations inside and outside the enclosure. Thirty eight experiments were performed in a three metre long corridor-like enclosure having a cross section 0.5m×0.5m, door like openings in the front panel and a gaseous burner located near the closed end. Smoke concentrations were measured at two locations inside the enclosure and also in the exhaust duct of a hood collecting the fire gases from the enclosure. It was found that smoke concentration in the exhaust duct decreased whereas smoke concentration inside the enclosure increased after the flames started moving towards the opening and external burning occurred. This increased smoke concentration inside the enclosure was caused by reversion of the flow pattern inside the enclosure after the flames moved past a point towards the opening. Namely, the flow pattern changed direction behind the flame front in the sense that hot gases in the upper layer were travelling backwards towards the closed end of the corridor thus contributing to smoke increase inside the enclosure. This change of flow pattern was confirmed in all experiments by bidirectional probe velocity measurements in the upper and lower layer as well as by oxygen concentrations and temperature measurements inside the enclosure. These results are useful for CFD validation and specifically applicable for assessing smoke hazards in corridor fires in buildings where smoke concentrations can be much larger than anticipated owing to leakage to adjacent rooms behind a moving flame front.

Relative effects of inertia and buoyancy on smoke propagation in confined and forced ventilated enclosure fire scenarios

In this study, we focus on smoke propagation in confined and forced ventilated enclosure fire scenarios as it is a source of possible hazardous situations. The objective of the present contribution is to investigate the effect of the three physical mechanisms (buoyancy, gas expansion and forced ventilation) on diverse examples of smoke flow through transfer elements. Three types of pool fire scenario have been considered with several transfer elements typical of nuclear industry. The first scenario is a fire in one ventilated compartment and the propagation means are the release of smoke through the ventilation ducts. The second scenario is a fire in one ventilated room connected by a doorway to another ventilated room. The smoke flow investigated is the flow at the doorway. The last scenario is a fire in a ventilated compartment connected to an adjacent room with leakages. The smoke flow considered is a smoke leakage. Each scenario and the smoke propagation are analysed on the basis of large scale representative fire tests performed during the PRISME project and numerical simulations with a zone-modelling code, SYLVIA of IRSN. The results show ventilation is the driving mechanism for smoke propagation in the one-room configuration whereas buoyancy plays the major role for the doorway flow. Finally, depending on the kind of leakages, mechanical ventilation can act on the buoyancy-induced smoke propagation.

Facade Flame Heights from Enclosure Fires with Side Walls at the Opening

This paper presents an investigation of facade flame heights from an under-ventilated enclosure fire having an opening with side walls. A reduced-scale model, consisting of a cubic enclosure of 0.4 m with a vertical facade wall and two side walls was constructed for the experiments. The temperature profile inside the enclosure was measured by thermocouples whereas a CCD camera was employed to obtain the mean flame height of the ejected flames. It is found that the presence or the separation distance of the side walls have no impact on the critical heat release rate of the enclosure (1500 A √H in kW). The effects of the side walls on the mean flame height are pronounced for a relative larger flame than a small one having the same separation distance of the side walls. In addition as the side wall distance decreases, the effects become larger leading to flame heights much higher than those without sidewalls. A global dimensionless parameter K is proposed to account for the side wall effects, based characteristic length scales of the opening, and the distance between the side walls D. The experimental data for different opening dimensions and side wall distances are well correlated by this global parameter.

An Experimental Study on Buoyant Spilled Thermal Plume Temperature Profile from Over-ventilated Enclosure Fires in a Reduced Air Pressure

To investigate the effect of a reduced air pressure condition on buoyant spilled thermal plume temperature profile from over-ventilated enclosure fires, the same scale model experiments were performed correspondingly in both Hefei city (altitude: 50 m, ambient pressure: 1 atm) and Lhasa city (altitude: 3650 m, ambient pressure: 0.64 atm). Comparative experimental results for both the lateral (normal to façade) and vertical (along facade) spilled plume temperature profile show that the lateral decay of temperature in the reduced air pressure is much faster than that in the normal air pressure condition. Meanwhile, the normalized spilled thermal plume temperature near the façade wall is much higher in the reduced pressure atmosphere than that in the normal pressure condition at the same height, indicating possibly weaker air entrainment of the buoyant spill plume in reduced pressure. These results reveal that fire safety regulations to counteract the vertical fire spread to upper floors need to be specified more rigorous at high altitude.

Studies on Criteria of Wood Ignition in Case of Enclosure Fires

Studies on Criteria of Wood Ignition in Case of Enclosure Fires

Numerical Simulation of a Ceiling Jet Fire in a Large Compartment

The ceiling jet phenomenon of a 15 m long test hall fire with 1.5 MW was reconstructed by an in-house large eddy simulation (LES) model which incorporates fully coupled sub grid-scale (SGS) turbulence, combustion and radiation models. Fire spread of an enclosure fire is typically caused by the ceiling jet behavior when radically-outward gas motion produced by impingement of a rising fire plume on a horizontal ceiling allowing hot gas to travel along the ceiling transfer energy to the lower portion of the hall by gas radiation. The non- equilibrium combustion caused by microscopic mixing processes was modeled by a scalar dissipation conditioned combustion model coupled with SGS turbulence model. The performance of the two sub grid-scale (SGS) turbulence models, Smagorinsky SGS model and Wall Adapting Local Eddy Viscosity (WALE) model, were assessed by comparing predicted transient gas temperatures and velocities at various spatial locations.

A Simplified Mathematical Model for Predicting the Vertical Temperature Profiles in Enclosure Fires Without Vertical Opening

This paper presents a mathematical model to predict the instantaneous temperature profiles in sealed or ceiling vented compartment fires. It has been observed in the existing research that in compartments without vertical opening, smoke fills the volume very soon indicating that the so-called one-zone type distribution forms quickly, and the gas temperature inclines linearly with height above the fire source. These characteristics are different from the smoke filling properties in enclosure fires with vertical openings. An assumption of linear distribution for temperature was introduced and a modified one-zone model was subsequently proposed in order to predict the transient smoke temperature profiles after the smoke fills the enclosure. With the knowledge of the heat release rate, the prediction model was established based on unsteady energy conservation by changing the heat loss factor using the semi-empirical models for fire plume and ceiling jet. Experiments including sealed and ceiling vented conditions were conducted to validate the model and the comparisons between measurements and predictions suggested the model can give fairly satisfactory estimations for the transient temperature profiles for both tests.

Global behaviors of enclosure fire and façade flame heights in normal and reduced atmospheric pressures at two altitudes

Enclosure fire safety design and regulations are commonly specified for normal pressure conditions at sea level. There is need however to extend the design requirements for conditions in reduced pressure atmosphere such as city at high altitude, in which the corresponding fundamental behaviors should be clarified first. Experiments are designed and carried out in this work at two different altitudes (Hefei city: 50m, 1atm; Lhasa city: 3650m, 0.64atm) in a 0.4m cubic fire enclosure with various window dimensions and an attached 1m (wide)×2.2m (high) façade with and without an opposite facing wall. Gas temperature profiles inside the enclosure and façade flame heights are measured to find out their behavioral changes for these two pressures and to develop global correlations. It is found that, for a given fuel supply rate the gas temperature inside the enclosure is lower while the outside flame is higher in the reduced pressure atmosphere, owing to the lower fuel consumption inside the enclosure and air entrainment into the flame. The flame height (without a facing wall) normalized by a characteristic window length scale ℓ1 can be well correlated with the dimensionless excess heat release rate, but being a bit higher due to lower entrainment or larger fluctuations at lower pressure, but can be accounted for globally by a correction factor of 0.8. In addition, the characteristic length scale ℓ3 representing the horizontal projection of the flame is higher, and thus, the critical distance of the facing wall from the enclosure, at which interaction of the façade flame and the opposite facing wall starts, is larger at lower pressure. The relative higher façade flame height and the larger critical façade-to-facing-wall distance suggest that hazards of enclosure facade fires at low pressure (high altitude) are higher and it need more conservative regulations than those at standard pressure. By accounting for their behavioral changes, global models have been correlated for gas temperature inside the enclosure as well as façade flame height without and with an opposite facing wall applicable for these two atmospheric pressures. The present results and global correlations in both normal–and reduced pressure atmosphere provide fundaments of guideline for regulations extension to high altitude and are a significant supplement and improvement over previous results in literatures.

An Evaluation of Heat Generation in Enclosure Fires

An Evaluation of Heat Generation in Enclosure Fires

Numerical Simulation of Enclosure Fires with Horizontal Vents

The buoyancy-induced flow generated by a heat source, such as fire in a long square enclosure with single or multiple horizontal vents, has been of interest in the modeling of enclosure fires and heat removal systems for electronic equipment. This flow is studied using numerical methods. A two-dimensional laminar natural convection flow is investigated with the buoyancy term represented by the Boussinesq approximation. The governing equations are solved in the stream function and vorticity formulation using high accuracy finite difference schemes. The effect of single or multiple horizontal vents of different sizes on the induced flow is studied in detail for different Grashof numbers. The results show a significant change in flow behavior for varying vent width at a fixed Grashof number. A bidirectional flow across the vent occurs due to buoyancy, as previously reported in the literature. The results show that the flow becomes more stable with a decrease in the vent width. The critical Grashof number is identified as beyond which the flow becomes unstable, leading to chaotic flow in the partial enclosure. The main focus is on the time-dependent flow, though steady state flow is also obtained at a longer duration of time in most cases. The implications of these results in the modeling of a fire in an enclosed space with horizontal vents are also discussed.

Theoretical Analysis and Experimental Study on Whirling Flames in Enclosure Fires

Whirling flames are not commonly observed in enclosure fires, but some special hazards will be induced for their characteristics once they occur. Employing the theories of vorticity transport and fire dynamics, the formation mechanism of whirling flames in enclosure fires has been analyzed, and the factor expression governing the formation of whirling flames occurring in single rooms with ceiling and lower openings, which are familiar to us in industrial buildings, has been deduced. Using a small-scale firebox with a lower door and a ceiling opening, the experiments of whirling flames in enclosure fires were carried out. Based on the experimental results, the characteristics of whirling flames in enclosure fires were studied, and the basic parameters of fires with and without whirling flame were compared. Combining the results of the theoretical analysis and experimental study, the formation criterion of swirling flames in enclosure fires were derived. Furthermore the reasons that whirling flames cause increases in some parameters, such as hot gas layer temperatures and floor radiant heat flux, were analyzed.

Study on flashover in a single chamber lined with combustible materials

SUMMARYWith 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 IFO 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.

The physics of the outflow from the opening of an enclosure fire and re-examination of Yokoi's correlation

A new length scale is proposed for correlating, flame heights, plume temperatures and heat fluxes on external façades from flames in enclosures. Yokoi proposed a length scale ro (equal to the radius of a circle having half the area of the opening) and a dimensionless temperature Θ (from thermal plume analysis) that are widely used in correlating the temperature distribution in the hot gases issuing from the opening outside the enclosure. This paper revisits the physics of façade flames from enclosures by discussing the applicability of Yokoi's proposals and suggesting that two length scales are needed to describe the physics in over-ventilated and under-ventilated fires: one length scale is related to the thermal outflow at the opening and the other one represents the length after which the flow turns from horizontal to vertical owing to buoyancy. These new length scales correlate experimental data better than using Yokoi's length scale. Moreover the analysis and experiments show that the local plume density in the dimensionless Yokoi's temperature Θ has also to be replaced by the ambient density in conformity with an improved understanding of the physics of entrainment in buoyant plumes.

Thermal analysis of a pool fire test in a steel container

A pool fire test was conducted in an uninsulated steel container under low ambient temperature condition, at −20°C. The heat balance of the enclosure fire was analyzed. The size of the container was 12 m× 2.4 m and 2.4 m high, and it was made of 3-mm-thick steel. During the fire test, the fuel mass loss rate was recorded and the temperatures at different positions were measured with high-temperature thermocouples and plate thermometers. The fire scenario was simulated by using fire dynamics simulator software, and the simulated and measured results were compared. The coarse high-temperature thermocouple responded slower, and therefore, temperature measured by the high-temperature thermocouple was corrected to eliminate the effect of the thermal inertia. Furthermore, a simple two-zone model was proposed for estimating gas temperature in the enclosure of the highly conductive steel walls assuming a constant combustion rate. The convective and radiative heat transfer resistances at the inside and outside surfaces of the enclosure were analyzed.

Monitoring of Environment in a Flashover Container in the Course of Enclosure Fire Simulation

Monitoring of Environment in a Flashover Container in the Course of Enclosure Fire Simulation