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Fire Safety Journal

Fire Safety Journal

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Discussions on critical velocity and critical Froude number for smoke control in tunnels with longitudinal ventilation
Ying Zhen Li; Haukur Ingason;
Abstracts:Determination of critical velocity is a key issue for smoke control in any tunnel with longitudinal ventilation. The critical Froude model using single Froude number of 4.5 has for decades been widely used in engineering applications. This value was originally used by Danziger and Kennedy and they argued that the critical Froude number obtained by Lee et al. was in a range of 4.5 and 6.7 and therefore a conservative value of 4.5 was obtained. This paper explores the validity of using single critical Froude number of 4.5 by investigating the original sources and comparing it to recent research results. It was found that the value of 4.5 obtained in the original source corresponds to a large tunnel fire and it correlates well with data from other literature within a narrow range of large fire sizes. Using this value produces a significantly lower critical velocity for a wide range of fire sizes and therefore it is not conservative. The Froude number of 6.7 obtained by Lee et al. corresponds to another Froude number with a different definition and it is therefore not comparable with the value of 4.5. It is found that the use of a single value of 4.5 for the critical Froude number is not reasonable in calculation of the critical velocity for smoke control in tunnels with longitudinal ventilation.
Experimental investigation of eccentrically compressed stainless steel columns with constraints in fire
Shenggang Fan; Meijing Liu; Wenjun Sun; Yang Guo; Yun Long Han;
Abstracts:To study the behaviour reaction and failure mechanism of stainless steel columns in fire, a series of fire tests were performed on the eccentrically compressed columns with constraints, based on S30408 stainless steel. 7 specimens were used to investigate the effects of the load ratio n, eccentricity e and axial constraint stiffness ratio β on the fire-resistance performance of eccentrically compressed stainless steel columns. The failure process and failure modes of stainless steel columns in fire were revealed. The test phenomena, heating curve, deformation curve and buckling temperature were obtained. The test results show that the load ratio n (n = 0.22–0.35), eccentricity e and axial constraint stiffness ratio β (β = 0.0458 and 0.0495) are the key factors that determine the fire-resistance performance of eccentrically compressed stainless steel columns with constraints. The larger the load ratio n, eccentricity e and axial constraint stiffness ratio β are, the lower the buckling temperature of the specimen. There are two main types of failure modes of eccentrically compressed stainless steel columns with constraints in fire: the first is the overall buckling mode and the second is the local-overall interaction buckling mode. The failure modes depend mainly on the section dimensions and the section type of the stainless steel column. The process of bearing capacity of eccentrically compressed stainless steel columns with constraints in fire goes through two stages: the prebuckling stage and the post-buckling stage. It takes times for the specimen to progress from the buckling state to the ultimate failure state. The bearing capacity of the post-buckling stage can effectively improve the fire-resistance performance of the stainless steel column with constraints.
Experimental assessment of fire-exposed RC beam-column connections with varying reinforcement development lengths subjected to column removal
Zhi Li; Yanzhi Liu; Jingsi Huo; Huang Rong; Jun Chen; Ahmed Y. Elghazouli;
Abstracts:This paper describes an experimental investigation into the behaviour of RC beam-column connections under a column removal scenario induced by fire. A purpose-built hybrid heating furnace is employed to carry out the fire tests on five RC connections with varying reinforcement development lengths, with and without cooling effects. The thermal response of the RC connection specimens, including the temperature field and the axial force-furnace temperature curves, is firstly described. Subsequently, push-down tests are carried out on the beam-column connections, and the horizontal support reactions are closely monitored using a specially-designed sensor system. Based on the experimental results, the joint vertical load-displacement and bending moment-rotation relationships are presented, together with an account of the failure modes observed. The mechanical behaviour is discussed in detail, including the tying and rotation capacity provided by the connection specimens, with emphasis on the effect of the reinforcement development length as well as the heating regime. The experimental capacity interaction curves are also compared with the theoretical prediction for ambient condition, and employed to carry out a detailed examination of the underlying failure mechanisms. Finally, the findings are used to provide practical recommendations for enhancing the structural robustness of structural configurations of the form considered in this study.
Effect of pressure on the heat transfer and flame characteristics of small-scale ethanol pool fires
Jian Chen; Yanli Zhao; Xiao Chen; Changhai Li; Shouxiang Lu;
Abstracts:Fire research with regard to high pressure is important for safety design and fire prevention under a high-pressure environment, such as nuclear containment shells during a pressurized period and deep-sea submersibles. To investigate the effect of high pressure on fire behavior, studies on ethanol pool fires using 1.5-cm- and 2.0-cm-diameter glass vessels were conducted under a wide pressure range of 1–5 atm. Results show that high pressure significantly impacts the heat transfer and flame characteristics of small-scale ethanol pool fires. As pressure increases, the fuel burning rate decreases slightly and then increases considerably, which is attributed to the effect of pressure on heat transfers. As pressure increases, the flame becomes unstable with the color changing from blue to yellow. Moreover, the flame height of the 1.5-cm-diameter pool fire increases over the entire pressure range whereas the flame height of the 2.0-cm-diameter pool fire increases until its peak value is reached at 2 atm and then decreases gradually. Then, a global correlation of flame height for small-scale ethanol pool fires is analyzed and verified using the experimental results. Flame puffing frequency increases with pressure for both pool sizes; hence, the Strouhal number correlates well with the Froude number.
Fire behaviour of electrical cables in cone calorimeter: Influence of cables structure and layout
Carcillo Magalie; Caro Anne-Sophie; Sonnier Rodolphe; Ferry Laurent; Gesta Emmanuelle; Lagrève Christian;
Abstracts:The fire performances of small telecom halogen-free cables were measured using cone calorimeter by changing several test conditions (heat flux, number and spacing of cables) and cable properties (sheath thickness and insulation mass). An analytical phenomenological fitting was proposed to predict accurately main fire performances (time-to-ignition, peaks of heat release rate and time to peak of heat release rate) from a set of 42 tests. The phenomenological model also assesses quantitatively the influence of different test conditions and cable properties. It appears that time-to-ignition is only dependent on heat flux. Moreover the influence of sheath is pointed out to delay the occurrence of the main peak of heat release rate corresponding to the decomposition of non-flame retarded insulation. The fitting allows better predicting the fire hazard in case of cables burning.
The effects of information and hazard on evacuee behavior in virtual reality
A. Tucker; K.L. Marsh; T. Gifford; X. Lu; P.B. Luh; R.S. Astur;
Abstracts:Many contextual factors can influence evacuees' choice of egress route during an emergency. Anxiety caused by the emergency situation may lead to suboptimal choices, resulting in slower evacuation and greater risk of injury or death. The present pilot study tests the influence of hazard level (presence of visible fire and smoke) and information about an obstacle (delivered verbally or through signage) on evacuees' anxiety levels and choice of egress route in a virtual reality (VR) simulation of a fire evacuation with multiple possible exits. Physiological measures were recorded and used to validate the efficacy of VR in inducing anxiety germane to the situation of interest. Consistent with our expectations, providing information about the obstacle was shown to decrease total evacuation time. Contrary to our predictions, it did not significantly impact evacuees' choice of exit. Information also had a marginally significant effect on participants' self-reported anxiety. Providing more targeted information may further reduce anxiety and evacuation time. More generally, VR appears well-suited to assessing individual and psychological factors in evacuations.
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