Wall Fire Research Articles

Experimental study of the temperature profile induced by the tunnel wall fire plume at various source-ceiling heights

The smoke temperature profile beneath the ceiling of tunnel is one of the most important parameters to evaluate the tunnel fire risk and guide the early fire detection. This paper investigates experimentally the temperature profile induced by the tunnel wall fire plume at various source-ceiling heights. A series of experiments were carried out in a reduced-scale tunnel and a burner combustion inside. The burner elevation above the tunnel floor was changed at the center of the tunnel, and it attaches the side-wall of the tunnel to simulate the wall fire plume evolution with fire growth inside the tunnel. The temperatures beneath the ceiling were measured by the thermocouple array at the corner between the ceiling and side-wall of the tunnel. The maximum temperature beneath the ceiling could be correlated by the heat release rate and the source-ceiling height. A new characteristic parameter model considering the virtual point source at the side of the tunnel was proposed firstly considering the tunnel fire scenario to describe the tunnel plume temperature profile. The obtained experimental data and proposed temperature profile model in this work provide a basic understanding of the heat/thermal impact on the tunnel wall fire plume.

Evaluation of exterior wall cavity fires using an intermediate scale test method

AbstractCavities form an integral part of many external wall systems (EWSs). Numerous external wall fires worldwide have been primarily due to combustible exterior cladding. However, the Grenfell Tower and Knowsley Heights fire incidents (in the UK) are examples where wall cavity materials have impacted fire spread. Wall cavity materials are typically regulated by small‐scale fire test methods which do not necessarily represent the actual fire conditions that can exist within wall cavities. This experimental study proposes an intermediate‐scale test (IST) protocol to examine cavity wall fire behaviour. This protocol is a modified version of the FM Global Cavity Fire Test method (within the FM 4411‐2020 series). The study examines a broad range of cavity materials including sarking, polyester insulation, phenolic foam, PIR, and EPS. A low‐intensity (6–8 kW) and high‐intensity (~80 kW) ignition sources were used to represent two types of cavity fire scenarios. These two fire sizes were shown to differentiate reaction to fire behaviour between these materials and explore the “tipping point” in resulting fire behaviour (which may lie between these two intensities). This proposed cavity fire test protocol provides a suitable “elevated fire risk assessment tool” for combustible cavity materials.

Fire prevention structure design of exterior walls of existing residential buildings

In this paper, taking the thermal insulation of the exterior wall after the renovation of multi-storey old residential quarters as the object Pyrosis is used to simulate the fire, and the prevention and control effects of different fire isolation belts and the combination of fire isolation belts and fire isolation layers on the longitudinal spread of the exterior wall fire are simulated. The results show that the arrangement of one fire isolation layer and each fire isolation layer in five groups of working conditions can effectively delay the longitudinal spread of external wall fire caused by window fire. The research results can provide reference for outdoor fire prevention and control measures of multi-storey buildings, and gain valuable rescue time for firefighting.

Characteristic parameter evolutions and fire smoke patterns of the wall fire plume: Experimental and theoretical analysis

In the fire investigation field, fire smoke patterns are studied as one of the most important indicators for fire accident investigation and scene reconstruction. This paper studies the evolutions of wall fire plume characteristic parameter and the smoke patterns considering five oil pan sizes and three fuel types, with a wall fire plume experimental platform inside a large-scale laboratory. The mass loss rate (or heat release rate), flame height and near-wall centerline temperature are measured and analyzed quantitatively, and smoke patterns are extracted based on the image analysis. Results show that: (1) The heat release rate in the stable stage and the average heat release rate over the whole burning process are in linear relationship for various fuels. The relation of the near-wall temperature profile and dimensionless height is obtained, and the wall fire is divided into four regions. (2) Various fuels produce different smoke pattern characteristics due to the different composition and property. The wall fire plume smoke patterns considering the near-wall temperature profile can be divided into several conditions. In each condition, with the increase of oil pan size, the opening of fitting curve increases and the vertex height decreases. (3) The boundary of the smoke pattern increases with oil pan size. The non-dimensional wall fire plume smoke pattern model with the corresponding temperature profile is obtained. These can increase the data reserve of the wall fire plume smoke patterns produced by different fuels and enrich the experiment and numerical calculation basis of building fire.

Experimental and numerical study of the interaction between tempered glass fallout and enclosure fire dynamics

Tempered glass, as an important type of safety glazing, is extensively used in high-rise buildings. However, little is known about the fallout behavior of tempered glass in the compartment with different fire locations. Therefore, in this work, the exposed framed glass panes with the dimension of 815 × 815 × 6 mm3 were heated by a pool fire in the compartment. The fuel pans were placed at six different locations in the compartment. It was found that the fallout time of tempered glass increased with a decrease in the distance between the fuel pan and glass panes; when the fire was moved to the wall side, the fallout time of tempered glass was longer. Besides, the temperature gradient of the glass surface at the exposed area was insignificant when the fire source was at the center line of the doorway opening, while there was an evident temperature gradient of the glass surface on the height direction due to the apparent smoke layer in the upper of the compartment for near wall fire locations. In addition, CFD numerical simulations were conducted using FDS software to observe the temperature and velocity fields inside the compartment with different fire locations. It was found that when the fire was moved to the wall side, the circulation flow was formed at both the high-temperature region near the fire source and the low-temperature region on the left of the compartment.

An exploratory investigation into moisture content and wind impact on the fire behaviour of modular living walls

Vertical greenery systems (VGS) consist of vegetation biomass and organic materials as well as plastics or metal elements in supporting systems. In this work, we investigate fire properties of live and dead plants as part of complete VGS systems (living walls, LW). Small-scale tests using a cone calorimeter and medium-scale tests using the SBI method were used to determine reaction to fire properties. Full-scale experiments were carried out to approximate the flame spread with and without wind along a living wall. Highly moist plants lead to slower spread of the fire, but have not prevented spreading the fire on the plastic potting, which in all cases was eventually involved in the fire and burned down to a collapse. On dry vegetation and without wind, the vertical flame spread velocity was up to 90 cm/s, and horizontal up to 2.7 cm/s. Wind conditions have changed the living wall fire performance, accelerating the fire spread on the vegetation and the fire of plastic potting as well. For moist samples in PN-B 02867 test the test duration (until full destruction of the facade) was 2100 s without and 1150 s with wind. For dry samples, this was 1350 s and 590 s, respectively.

Fire behavior in compartment containing timber constructions focusing on pressure increase owing to pyrolysis gas

A series of full-scale compartment fire experiments was carried out to understand the fire behavior in compartment containing wooden constructions. The opening size and the surface area of combustible materials were adjusted to investigate the differences between ventilation-controlled and fuel-controlled fires. The results show that there was a time lag between when heat release rate (HRR) began to decrease and the time when the temperature in the compartment began to decrease in the case of with a wooden wall and ventilation-controlled fire; the HRR at the time when the temperature began to decrease was about the peak HRR of the case without a wooden wall. Although the HRR in case with a wooden wall was much higher than those without it, the temperature in the compartment with a wooden wall was slightly lower under ventilation-controlled conditions. These suggest that the amount of inflow air was limited by the increase in pressure in compartment due to pyrolysis gas.Furthermore, a model of compartment fires that takes this increase in pressure into account was developed, and it is able to more accurately reproduce the temperature characteristics than models that do not.

Leading edge stabilisation of vertical boundary layer diffusion flames

The leading edge stability of vertical boundary layer diffusion flames established over a 3D-printed porous gas burner is revealed through Planar Laser-Induced Fluorescence imaging of the OH radical (OH-PLIF). Flame stability is studied by premixing methane and ethylene with increasing volume fractions of bromotrifluoromethane (CF3Br/Halon-1301) to increase the characteristic chemical timescale. Blow-off occurs at 15.7% and 37.3% CF3Br addition for methane and ethylene respectively, which are remarkably large limits compared to other flame configurations. As CF3Br is added, the flame stand-off distance increases and the reaction zone broadens, thereby increasing the flame length. This accelerates the buoyancy-induced flow ahead of the leading edge, promoting O2 entrainment into the flame anchor. Consequently, the radical scavenging effects on the flame anchor reactivity are dampened, resulting in the flame re-anchoring slightly downstream along the plate. Towards extinction, the flame shortens dramatically due to efficient catalytic cycling and radiative quenching at the flame tip resulting from the brominated species and excessive soot formation. This reduces the O2 mass flux into the kinetically dampened flame anchor resulting in blow-off extinction. Therefore, blow-off is controlled by both the leading edge reactivity and trailing edge length. Methane is shown to be considerably more sensitive compared to ethylene to CF3Br owing to its larger flame speed. These results demonstrate that fire-induced buoyancy greatly increases blow-off limits when using chemically active or inert agents in vertical wall fire configurations.

Prediction of maximum ceiling temperature of rectangular fire against wall in longitudinally ventilation tunnels: Experimental analysis and machine learning modeling

In this work, experimental analysis and machine learning modeling of maximum ceiling temperature for wall fire in longitudinally ventilation tunnels were conducted. The results indicate that the maximum ceiling temperature is restrained by the longitudinal ventilation, and the maximum ceiling temperature induced by a free fire is significantly lower than that of a wall fire. The aspect ratio of the burner has an impact on the maximum ceiling temperature. The larger the aspect ratio of the burner, the higher the maximum temperature. Based on the “mirror” assumption, the difference in maximum ceiling temperature caused by the changes in entrainment characteristics between wall fires and free fires can be explained. The influence of longitudinal wind inertia forces on the aspect ratio of the burner was analyzed. It was found that when the aspect ratio was large, it is affected by the smaller longitudinal wind inertia force to generate a higher flame height, and this will lead to higher maximum ceiling temperatures. The classical model cannot explain the difference in maximum ceiling temperature between wall fires and free fires, as well as the effect of aspect ratio on the maximum ceiling temperature. Further explanation and verification were conducted by combining the temperature field and the flow field. In addition, genetic algorithms were applied to compensate for the shortcomings of back propagation neural networks in randomly generating initial weights and initial biases. A new model-free calculation (GA-BPNN) model was proposed to predict the maximum ceiling temperature in a ventilation tunnel. Experimental results were compared with the predicted results, and error analysis was conducted on the data from the training and testing sets, with a relative error within ±20%. The GA-BPNN algorithm proved to be a promising method that can provide direct guidance for the experimental analysis and the determination of relevant parameters in the fire situation analysis.

Influence of sidewall restriction on flame characteristics of double fires in a channel

In this paper, the influences of sidewall restriction on flame characteristics of double fires in a channel were studied. Two typical fire scenarios (center fire and wall fire), different heat release rates and burner separation distances were considered. The results show that ΔT = 300 K can be used as the boundary temperature of the flame. Further, the merging phenomenon is more likely to occur for wall fires, and the critical flame merging separation distances (Sc) of center and wall fires are around 0.13∼0.16 and 0.21, respectively. The flame tilt angle decreases with the increasing fire separation distance, and it is not sensitive to HRR for both center and wall fires. The flame tilt angle of wall fire is slightly larger than that of center fire under a given fire separation distance. Finally, two prediction models are proposed to estimate the normalized effective flame lengths of impinging and non-impinging flames for the center and wall fires in a channel. This study will provide a basis for exploring the interaction mechanisms of double fires under restricted boundary conditions.

Pipeline leak jet fire thermal characteristic induced by hydrogen-blended natural gas: Physical modeling of temperature profile based on virtual origin theory

Hydrogen-blended natural gas has widely used in energy fuel systems in industrial and domestic applications. During storage, transportation and usage of the fuel, temperature characteristics make a key contribution to energy leak gas fire accidents. In this manuscript experimentally, the buoyant turbulent diffusion axial temperature profile of a hydrogenated methane jet fire is experimentally investigated under free fire and wall fire. Different hydrogen addition ratios, nozzle diameters, and fire heat release rates were considered in the experimental conditions. Temperature profiles and virtual origins were recorded and analyzed. It is found that the wall fire temperature is somewhat higher than that in the free fire at a fixed height. And the vertical temperature of the jet fire increases with the increase of the hydrogen addition ratio, while the flame height decreases. With the addition of hydrogen, the virtual origin is increased, and virtual origin of wall fire is clearly larger than that of the free fire. Due to the restriction of air entrainment from the sidewall and the hydrogen addition, the physical mechanism of restricted air entrainment was analyzed. In addition, a non-dimensional model of the virtual origin was proposed and analyzed for different conditions. Finally, the normalized vertical temperature profile in the continuous flame region, intermittent flame region and buoyant plume region based on the virtual origin and mirror-approach are still well characterized for air entrainment under all conditions. The results of this paper may demonstrate the potential for the risk assessment of hydrogen-blended natural gas fire.

Combustion characteristics and fire hazard of polystyrene exterior wall thermal insulation materials

AbstractTo study the combustion characteristics and fire hazard of polystyrene building exterior wall thermal insulation materials, the combustion, fire, and pyrolysis characteristics of thermosetting polystyrene (TPS) insulation, graphite polystyrene (GEPS), and expanded polystyrene (EPS) are compared and analyzed using a cone calorimeter and a thermo‐gravimetric analyzer. From the structure and flame retardant components of thermal insulation board, their flame retardant mechanisms are described. Results show that in a nitrogen atmosphere, the pyrolysis range is 30–600°C. Only one weight loss stage in EPS and GEPS and two weight loss stages in TPS are observed. Comparison of the combustion characteristics of the three demonstrates that TPS has short ignition time, low fire performance index. This result indicates that TPS has the characteristics of good flammability and easy to explode. The smoke generation rate, total smoke production, time heat release index and total heat release of TPS are lower than those of EPS and GEPS. This result indicates that the fire thermal hazard and fire smoke risk of TPS are relatively small. Comparison of various indexes presents that the flammability and fire risk of TPS are evidently better than those of EPS and GEPS.

Flame height and axial plume temperature profile of bounded fires in aircraft cargo compartment with low-pressure

A series of n-heptane buoyancy bounded fire tests (center fires, wall fires, corner fires) are conducted in a full-scale simulated aircraft cargo compartment at 70 kPa, 80 kPa, 90 kPa, 100 kPa to measure the flame heights and axial plume temperatures. Based on the Heskestad's model, the flame heights at different horizontal positions are normalized by introducing the respective mirror coefficients β of wall fires and corner fires, a prediction formula for flame heights with pressure correction coefficients Kp is established. The influence of air entrainment on flame height is further revealed by analyzing the experimental data through Quintiere and Grove's model. In addition, by comparing with the McCaffrey's model after the introduction of the mirror coefficient β, it is found that the axial temperature values of wall fires and corner fires are lower than the predicted values because the model ignores the heat radiation feeding back into the plume from the heated sidewalls, and the longitudinal dimension of the corner fire plumes is stretched resulting in an extended intermittent region. The prediction equations for the axial temperature distribution of bounded fires in low-pressure are proposed by introducing pressure correction coefficients.

Thermal Characteristics of ISO 13785-2 Alternative Ignition Sources

In this study, the types of ignition sources suggested by the international standard ISO 13785-2 by external wall fire evaluation methods were examined. The suitability of these sources was reviewed through a large-scale test to determine the agreement between main and alternative fire sources. ISO 13785-2 implements external ignition of the flame by a propane burner, which is a standard ignition source, and uses liquid fuel or a wood crib as an alternative ignition source of the propane burner. The thermal characteristics of wood crib among alternative ignition sources were analyzed, and the maximum heat release rate of wood crib is approximately 5.11 MW which is calculated with formula. In the case of a full-scale experiment two repeated experiments were performed to ensure data reliability, and Test 1 was approximately 2.9 MW and Test 2 was approximately 3 MW. The standard temperature of the calibration range is defined as the average temperature of the top three thermocouples (T1~T3) above 800 ℃, and the measurement results showed that Test 1 was 472.4 ℃ and Test 2 was 514.9 ℃. Comparison of the value calculated using the formula derived in previous studies with that of the experimental results, it was concluded that there was a difference between the main and alternative ignition sources in the range of intersections suggested in the international standard.

Experimental study of oil pool shape and environment pressure on the wall fire behavior in an airplane cargo compartment

A series of pool fires were carried out to study the effect of pool shape and environment pressure on the wall fire behavior. Four sizes of annular pool and three sizes of rectangle pool were used as the oil container. The results showed that the burning rate of both the annular and rectangle pool fire increased with increasing length ratio of the poolside, which was defined as the ratio of the inside and outside diameter for the annular pool (η) and aspect ratio (n) for rectangle pool. At the stable burning stage, the pool burning rate increased with the environmental pressure. While the flame height was not a monotonous trend with the pressure for rectangle pool fire, and the flame height in two kinds of pools exhibited opposite tendencies as the length ratio was increased. In addition, by introducing the shape parameter of the pool into the classical model, correlations to calculate the mass burning rate and the height of the pool fire flame under the limited sidewall conditions at different pressure environments were established.

Study on the Fire Behavior of Sandwich Wall Panels with GFRP Skins and a Wood-Web Core

To investigate the temperature field and residual bearing capacity of the sandwich wall panels with GFRP skins and a wood-web core under a fire, three sandwich walls were tested. One of them was used for static load test and the other two for the one-side fire tests. Besides, temperature probe points were set on the sandwich walls to obtain the temperature distribution. Meanwhile, the model of the sandwich wall was established in the finite element software by the method of core material stiffness equivalent. The temperature distribution and performance reduction of materials were also considered. The residual bearing capacity of specimens after fire exposure were simulated considering the effects of web spacing, wall panel thickness and fire exposure time. Because the sandwich wall panels were stressed by eccentric compression after a fire, the residual compressive strength of the wall panel after the fire can be calculated through the eccentric loading analysis. Compared with the numerical results, it can be concluded that the effectiveness of calculation method of residual bearing capacity after fire exposure was proved.

Experimental and numerical study of upward flame spread and heat transfer over expanded polystyrene at different altitudes

Experimental and numerical study on upward, vertical flame spread was carried out on expanded polystyrene (EPS) at two different altitudes of 50 m and 3658 m to understand the effect that altitude has on flame spread of melted material. The experiments show that, with the altitude increase, the flame spread rate would decrease. At low altitude, the flame spread rate accelerated at later time, while at high altitude, the stagnant stage of pyrolysis front was formed. The numerical simulation could well give the trend of pyrolysis front evolution and the different flame spread behaviors with altitudes. It was found that, at low altitude, Raxincreased slowly in the turbulent period with relatively large entrainment air flow rate, mainly due to the increased and then decreased mass loss rate in the wall fire zone. While, at high altitude, the simulated increasing entrainment air flow rate, combined with the larger preheating length δf and the smaller flame heat flux qf", resulted in the stagnancy of pyrolysis front easily. It was hypothesized that extinction occurred eventually at high altitude due to competition between flame spread rate νf and preheating length δf.

Experimental study on wall fire behavior produced by n-heptane pools with different aspect ratios and orientations in arched tunnel

A series of experiments were carried out in an arched tunnel (50 m long, 2 m wide, 2.3 m high). Under the influence of aspect ratios (1, 2 and 3) of oil pool and pool orientation relative to sidewall, the flame length and temperature distribution under the arched ceiling was studied. Oil pools with 3 aspect ratios were placed in the center as a control group. Results show that the pool orientation relative to sidewall is a decisive factor affecting the fire behavior. The heat release rate decreases with the aspect ratio increases. According to the physical meaning of flame extending along arched ceiling, the heat release rate is modified and prediction formula of transverse flame length under arched ceiling is obtained. The transverse temperature decay rate of different sections is different because of buoyant force. By modifying the transverse travelling distance, the prediction formula of the transverse temperature distribution is obtained, and the prediction error is within ±15%.

Experimental investigations on the influence of ‘chimney-effect’ on fire response of rainscreen façades in high-rise buildings

In recent years, external wall fires (or façade fires) are occurring due to mixed contribution of exterior cladding and continuous insulation in the chimney like construction of rainscreen façades. In the present work, a new experimental setup is developed and demonstrated for the initial screening of façade assembly at a lab-scale. It incorporates the real physics for investigating the fire hazards of flammable polymeric materials and the chimney effect together. Different combinations of exterior cladding (Al-45, Al-45 Class 0, Al-45 Class B) and continuous insulation (Expanded polystyrene, Polyisocyanurate and Mineral wool) with and without chimney are selected for studying their fire behaviour. The pressure differential combining with re-radiation inside the cavity led 3–6 times higher mass burning rate, flame height and temperature in tests with chimney effect to that of without for the same combination of products. With chimney, secondary fire sources are generated due to the dripping of products which further enhanced the burning and spread rate. A critical width of the chimney (13–50 mm) is established at which maximum vertical fire spread was noticed. Furthermore, the visual observations indicated that the products having thin outer Al sheets are prone to 30% early structural failure. Comparison of results with large-scale tests validated the usefulness of the current setup as an intermediate test between small and large scale for studying fire behaviour of façade materials.

Fire resistance of external light gauge steel framed walls clad with autoclaved aerated concrete panels

This paper presents an investigation into the fire resistance of external light gauge steel framed (LSF) walls clad with autoclaved aerated concrete (AAC) panels exposed to fire on the external side. Past research has been limited to the fire resistance of internal LSF walls clad with gypsum plasterboard on both sides. A series of experimental studies including thermal material property tests, a full-scale (3 m × 3 m) ambient capacity test of LSF wall and full-scale standard fire tests of non-load bearing and load bearing LSF walls were conducted to investigate the fire resistance of external LSF walls clad with AAC panels. Finally, a small-scale (1.2 m × 1.2 m) fire test of a wall made of AAC panels was also conducted to investigate the performance of joints between AAC panels. AAC panels with very low thermal conductivity performed exceptionally well by keeping the temperatures low for 160 min achieving a fire resistance level (FRL) of 204 min in load bearing conditions and 240 min in non-load bearing conditions. Hence, LSF walls clad with AAC panels can be used when higher FRLs are required. Experimental studies such as these on the whole system enable a good understanding of the overall fire performance of external wall systems in terms of structural adequacy and integrity instead of focusing only on the cladding.