Field tests on human tolerance to (LNG) fire radiant heat exposure, and attenuation effects of clothing and other objects

A series of field tests exposing mannequins clothed with civilian clothing to a 3m x 3m square liquefied natural gas (LNG) pool fire was conducted. Both single layer clothing and double layer clothing were used. The radiant heat flux incident outside the clothing and incident on the skin covered by clothing were measured using wide-angle radiometers, for durations of 100-200 s (per test). The levels of heat flux incident on the clothing were close to 5 kW/m(2). The magnitude of the radiant heat attenuation factor (AF) across the thickness was determined. AF varies between 2 and higher for cotton and polyester clothing (thickness 0.286-1.347 mm); AF value of 6 was measured for 1.347 mm thickness. Single sheet newspaper held about 5 cm in front of mannequins and exposed to incident flux of 5 kW/m(2) resulted in AF of 5, and AF of 8 with double sheets. AF decreases linearly with increasing heat flux values and linearly increases with thickness. The author exposed himself, in normal civilian clothing (of full sleeve cotton/polyester shirt and jean pants), to radiant heat from a LNG fire. The exposure was for several tens of seconds to heat flux levels ranging from 3.5 kW/m(2) to 5(+) kW/m(2) (exposure times from 25s to 97 s at average heat flux values in the 4 kW/m(2) and 5 kW/m(2)range). Occasionally, he was exposed to (as high as) 7 kW/m(2) for durations of several seconds. He did not suffer any unbearable or even severe pain nor did he experience blisters or burns or any other injury on the unprotected skin of his body. The incident heat fluxes on the author were measured by a hand-held radiometer (with digital display) as well as by strapped on wide-angle radiometers connected to a computer. He could withstand the US regulatory criterion of 5 kW/m(2) (for 30 s) without suffering any damage or burns. Temperature measured on author's skin covered by clothing did not rise above the normal body temperature even after 200 s of exposure to 4 kW/m(2) average heat flux.     

Post-fire mechanical properties of marine polymer composites

Changes to the tensile and flexure properties of marine-grade glass-reinforced polyester, vinyl ester and resole phenolic composites after exposure to radiant heat are investigated. The properties were determined at room temperature after the composites had been exposed to heat fluxes of 25–100 kW/m² for 325 s or to a heat flux of 50 kW/m² for increasing times up to 1800 s. The stiffness and failure load of all three composites decreased rapidly with increasing heat flux or time due mainly to the thermal degradation of the resin matrix. The post-fire tension and flexure properties of the resole phenolic composite were similar to the properties of the other composites, despite its superior fire resistance. Models are presented for determining the post-fire mechanical properties of fire-damaged composites, and are used to estimate the reductions in failure load of composite ship materials caused by fire.     

Post-fire flexural performance of epoxy-nanocomposite matrix glass fibre composites containing conventional flame retardants

This paper investigates the effect of varied nanoparticles (silicate nanoclays and double-walled carbon nanotubes) and micro-sized flame retardants (FRs) on the post heat/fire flexural performance of glass fibre-reinforced (GFR) epoxy composites. The fire reaction properties of GFR epoxy composites containing different combinations of nano- and micro-sized FRs were studied at varied incident heat fluxes (35–75 kW/m²). The flexural stiffness and modulus values of radiant heat-damaged GFR composites decreased rapidly with increasing incident heat flux. On another hand, the post-fire flexural properties of these specimens exposed for 30–90 s post-ignition at 50 kW/m² retained only 20% of their room temperature flexural properties. Despite significant improvements in the fire reaction properties, their post-fire flexural performance was least affected. This suggests that, while these flame retardants are effective in promoting char formation, the formed char networks are not consolidated enough to effectively constrain the fibre reinforcements.     

Fire Retardancy of Natural Fibre Reinforced Sheet Moulding Compound

Due to environmental awareness and economical considerations, natural fibre reinforced polymer composites seem to present a viable alternative to synthetic fibre reinforced polymer composites such as glass fibres. This is a feasibility study to asses the potential application of natural fibre reinforced sheet moulding compound materials (NF-SMC) for the use in building applications, with particular emphases to their reaction to fire. The reinforcing fibres in this study were industrial hemp fibres. The cone calorimeter which asses the fire hazard of materials by Heat Release Rate (HRR) was used, radiant heat fluxes of 25 and 50 kW/m² were utilised to simulate an ignition source and fully developed room fire conditions respectively. The results acquired here demonstrate that the NF-SMC can compete with current building materials in terms of their fire behaviour. The peak heat release value for the fire retardant (FR) NF-SMC was 176 kW/m² conversely for a non-FR NF-SMC was 361 kW/m².     

聚磷酸铵-淀粉对木粉／聚苯乙烯复合材料的阻燃作用

利用锥形量热仪分析了聚磷酸铵(APP)-淀粉阻燃体系在木粉/聚苯乙烯复合材料(WF-PS)中的阻燃作用。结果表明,添加APP能有效降低WF-PS的热释放速率(HRR)和总热释放量(THR),增加成炭量,延长点燃时间(TTI),表现出显著的阻燃作用;APP对WF-PS的有效燃烧热影响不大,说明APP的阻燃作用为凝聚相机理,成炭是该机理的重要方面;添加淀粉作为APP的辅助成炭剂,能够提高阻燃效率并减少APP用量,APP-淀粉是WF-PS复合材料的有效膨胀型阻燃体系。APP-淀粉的添加对WF-PS的力学性质有一定不利影响,但是当APP用量在10%以下、淀粉用量2%以下时,WF-PS可保持良好的力学性能。     

热辐射对消防服热防护性能及耐久性的影响

为探讨低热辐射对消防服用织物热防护性能及物理机械性能的影响,选用两种常用消防服用外层织物,利用远红外石英灯管辐射仪,以不同的辐射强度(6.5kw/m2和9.7kw/m2)对织物分别进行5、10、20、30min的辐射,利用NI虚拟仪器记录辐射时织物表面温度,并测试其各项物理机械性能及TPP值变化。结果表明:当织物表面温度低于织物纤维玻璃化温度时,织物在半小时内能保持其68.9%～84.6%的撕破强力,且TPP值增大,即热防护性能变好;而当织物表面温度达到纤维玻璃化温度时,织物断裂强力及撕破强力随辐射时间增加显著下降,但其TPP值仍增大。     

标准火灾后钢管RPC柱抗近距离爆炸荷载的试验研究

利用野外抗爆试验场对4根大比例标准火灾后的钢管活性粉末混凝土（Reactive Powder Concrete FilledSteel Tubular,简称钢管RPC）柱进行了抗近距离爆炸试验研究,探讨了恒定轴向力条件下比例距离和受火时间对柱动力响应和破坏形态的影响。结果表明：标准火灾下钢管仍可以有效约束RPC芯柱,限制了RPC的高温爆裂,表现出良好的抗火性能。爆炸作用下火灾后钢管RPC柱的相对位移均超过2.0%,均达到了其屈服状态。当比例距离由0.58 m/kg^1/3减小到0.48 m/kg^1/3时,钢管RPC柱出现由弯曲变形过渡到弯剪变形的趋势。随着受火时间增加,钢管RPC柱跨中出现明显的塑性变形,最大位移和残余位移均显著增大,发生典型的弯曲破坏。与比例距离相比,钢管RPC柱的抗爆能力对受火时间更为敏感。采用LS-DYNA软件对试验结果进行了数值模拟,模拟结果与试验结果吻合较好。     

POSS/粘土/多壁碳纳米管杂化碳纳米纸基复合材料防火性研究

多壁碳纳米管(MWCNTs)、粘土和多面齐聚半硅氧烷(POSS)组成的杂化碳纳米纸是通过碳纳米管巴基纸制备工艺制备而成, 碳纳米纸可做为表面防火层与聚合物基复合材料共固化成型。利用场发射扫描电镜(FESEM)和BJH法分别对碳纳米纸和杂化碳纳米纸微观结构和平均孔径分布进行表征。利用锥形量热仪在热辐射功率50 kW/m²条件下分析外贴碳纳米纸复合材料及复合材料对比样的防火特性。燃烧实验结果表明: 碳纳米纸和杂化碳纳米纸作为防火层的复合材料的峰值热释放速率(PHRR)与复合材料对比样相比分别下降20.2%和35%, 同时CO释放量和烟释放量也明显降低。通过FESEM研究表明燃烧实验后外贴杂化碳纳米纸复合材料的燃烧残余物表面形成了一层致密的积炭物结构, 防火阻燃性能明显提高。     

Theoretical prediction of piloted ignition of polymeric fuels in microgravity at low velocity flows

A numerical model developed for the prediction of the piloted ignition delay of solid polymeric materials exposed to an external radiant heat flux is used to predict the ignition delay and critical heat flux for ignition of solid fuels in microgravity at low velocity flows. The model considers the coupled thermochemical processes that take place in the condensed phase, including oxidative and thermal pyrolysis, phase change, radiation absorption, and heat and mass transfer in a multi-phase and multi-composition medium. Ignition is considered to occur when a critical pyrolysate mass flow rate is reached at the sample surface. Microgravity experimental surface temperature and ignition delay data previously obtained in a KC-135 aircraft are used to infer, in conjunction with the theoretical analysis, the critical mass flow rate for ignition. This value is then used to predict the ignition delay as a function of the external radiant heat flux, and the critical heat flux for ignition. Calculations are made for Polymethylmethacrylate (PMMA) and a Polypropylene/Fiberglass composite at airflows of 0.09 and 0.15 m/s under microgravity conditions and at 1.0, 1.75 and 2.5 m/s under normal gravity. The experiments and theoretical predictions show that the ignition delay and critical heat flux for ignition decrease as the forced airflow velocity decreases. It is predicted that at the tested lower velocities, the critical heat flux for ignition is close to half the value measured in normal gravity. The results have important implications since they indicate that materials could ignite easier under the conditions expected in spacecraft, and consequently stricter design specifications may be needed for fire safety.     

Modelling the tension and compression strengths of polymer laminates in fire

Thermo-mechanical models are presented for predicting the time-to-failure of polymer laminates loaded in tension or compression and exposed to one-sided radiant heating by fire. Time-to-failure is defined as the time duration that a polymer laminate can support an externally applied load in a fire without failing. The models predict the temperature rise and through-thickness temperature profile in a hot decomposing laminate exposed to fire. Using this thermal data, mechanics-based models based on residual strength analysis are used to calculate the time-to-failure. A preliminary evaluation of the accuracy of the models is presented using failure times measured in fire-under-load tests on a woven glass/vinyl ester laminate. The model was evaluated at temperatures between ∼250 and 800 °C by testing the laminate at heat flux levels between 10 and 75 kW/m². It was found that the time-to-failure of the laminate decreased with increasing heat flux and increasing applied stress for both the compression and tension load conditions. The tests also revealed that the failure times were much shorter (by about one order of magnitude) when the laminate was loaded in compression. The models can predict the time-to-failure with good accuracy for both compression and tension loading for certain heat flux levels. However, because the models have only been evaluated for one type of laminate (woven glass/vinyl ester), further evaluation is necessary for other laminate systems. The paper also presents new experimental insights into the strengthening mechanisms of laminates at high temperature.     

Fibre mortar composites under fire conditions: effects of ageing and moisture content of specimens

Two small scale test series were performed using the cone calorimeter heating method to detect any differences in the way various fibres affect the thermal properties of a standard mortar. The cone shaped heater of the cone calorimeter produces a uniform heat flux on the sample surface over an area of 100×100 mm². The heat flux was adjusted to 50 kW m^?2, which corresponds to the early stage of a fully developed fire. The total exposure also corresponds roughly to the ISO 834 time-temperature curve during the first 30 minutes. Short ageing of the specimens gave very clear differences in thermal properties between fibre mortars. However, no such differences were observed with oven dried samples. This shows the importance of carrying out tests in conditions as close as possible to the end use conditions of the material or product.     

Exposure of a liquefied gas container to an external fire

In liquefied gas, bulk-storage facilities and plants, the separation distances between storage tanks and between a tank and a line of adjoining property that can be built are governed by local regulations and/or codes (e.g. National Fire Protection Association (NFPA) 58, 2004). Separation distance requirements have been in the NFPA 58 Code for over 60 years; however, no scientific foundations (either theoretical or experimental) are available for the specified distances. Even though the liquefied petroleum gas (LPG) industry has operated safely over the years, there is a question as to whether the code-specified distances provide sufficient safety to LPG-storage tanks, when they are exposed to large external fires. A radiation heat-transfer-based model is presented in this paper. The temporal variation of the vapor-wetted tank-wall temperature is calculated when exposed to thermal radiation from an external, non-impinging, large, 30.5 m (100 ft) diameter, highly radiative, hydrocarbon fuel (pool) fire located at a specified distance. Structural steel wall of a pressurized, liquefied gas container (such as the ASME LP-Gas tank) begins to lose its strength, when the wall temperature approaches a critical temperature, 810 K (1000 degrees F). LP-Gas tank walls reaching close to this temperature will be a cause for major concern because of increased potential for tank failure, which could result in catastrophic consequences. Results from the model for exposure of different size ASME (LP-Gas) containers to a hydrocarbon pool fire of 30.5 m (100 ft) in diameter, located with its base edge at the separation distances specified by NFPA 58 [NFPA 58, Liquefied Petroleum Gas Code, Table 6.3.1, 2004 ed., National Fire Protection Association, Quincy, MA, 2004] indicate that the vapor-wetted wall temperature of the containers never reach the critical temperature under common wind conditions (0, 5 and 10 m/s), with the flame tilting towards the tank. This indicates that the separation distances specified in the code are adequate for non-impingement type of fires. The model can be used to test the efficacy of other similar codes and regulations for other materials.     

Post fire behavior of carbon fibers Polyphenylene Sulfide- and epoxy-based laminates for aeronautical applications: A comparative study

Through the comparison of two carbon fiber-reinforced polymers (Epoxy and Polyphenylene Sulfide – PPS), this work was aimed at investigating the influence of different fire conditions on the high temperature tensile mechanical behavior. In order to better understand the influence of matrix nature on post-fire properties, the fiber – or matrix-dominated mechanical responses of laminates have been investigated by means of quasi-isotropic or angle-ply stacking sequences. Compared to carbon/PPS laminates, the mechanical properties of carbon/Epoxy laminates are higher in the virgin state (no prior fire exposure). The analysis of the post fire tensile properties shows that prior severe fire exposures are more detrimental to carbon/Epoxy than to carbon/PPS laminates. Although the PPS matrix behavior is highly ductile at a test temperature higher than glass transition temperature, it clearly appears that the decrease in the tensile properties laminates of PPS-based composites is much slower than the one observed in carbon/Epoxy laminates subjected to severe prior fire conditions. Provided the heat flux is high enough to lead to the outset of pyrolysis, PPS-based composites yield higher amounts of char, whose formation retains the structural integrity of fire-damaged composites.     

Fire structural resistance of basalt fibre composite

Basalt fibres are emerging as a replacement to E-glass fibres in polymer matrix composites for selected applications. In this study, the fire structural resistance of a basalt fibre composite is determined experimentally and analytically, and it is compared against an equivalent laminate reinforced with E-glass fibres. When exposed to the same radiant heat flux, the basalt fibre composite heated up more rapidly and reached higher temperatures than the glass fibre laminate due to its higher thermal emissivity. The tensile structural survivability of the basalt fibre composite was inferior to the glass fibre laminate when exposed to the same radiant heat flux. Tensile softening of both materials occurred by thermal softening and decomposition of the polymer matrix and weakening of the fibre reinforcement, which occur at similar rates. The inferior fire resistance of the basalt fibre composite is due mainly to higher emissivity, which causes it to become hotter in fire.     

锥形量热仪确定聚合物材料导热系数的方法

通过对聚甲基丙烯酸甲酯聚合物材料在锥形量热仪实验条件下加热过程的分析和研究,建立了材料加热过程的数学模型。利用该模型来计算材料的平均导热系数,需要测量的物理量仅仅是物体表面或内部的温度,通过一次测试就可以得到不同温度范围内材料的平均导热系数,方法简单,可靠。利用文中的计算方法,得到PMMA在不同温度范围内的平均导热系数,结果表明,随温度范围的增加,材料平均导热系数值有增大的趋势。计算出的导热系数值在低温度范围与文献值比较接近。研究表明在高的温度范围内不能将传统测量的导热系数值用作火灾条件下材料的参数值。     

Heat transfer coefficient during two-phase flow boiling of HFC-134a

This paper reports a study of the evaporation of HFC-134a inside smooth, horizontal tubes. Tests were performed with the pure refrigerant and with oil-refrigerant mixtures. The heat flux was varied from 2 to 10 kW m⁻². The inner diameter of the tubes was 12 mm. Two evaporators were used, 4 and 10 m long, and the oil content was varied from 0 to 2.5 mass percentage (synthetic oil, EXP-0275). Oil-free HFC-134a had a higher heat transfer coefficient than HCFC-22 at the same heat and mass fluxes. The effect of oil in the refrigerant is dependent on the heat flux. At 2 and 4 kW m⁻² the heat transfer coefficient had a maximum value for an oil content of around 0.5 mass percentage; no increase is registered for a heat flux of 6 kW m⁻². The heat transfer coefficients for the pure refrigerant were also compared with two existing correlations. The measured heat transfer coefficients averaged over the evaporator deviate less than 40% from the correlation according to Pierre. The heat transfer coefficients at the short evaporator lie within 20%. The correlation given by Jung overestimates the heat transfer coefficient by approximately 50%.     

Fire retardancy of clay/carbon nanofiber hybrid sheet in fiber reinforced polymer composites

In this paper, two kinds of clay/carbon nanofiber hybrid sheets containing 0.05 wt% and 0.20 wt% of Cloisite Na⁺ clay, were fabricated through a high-pressure filtration system. These sheets were integrated onto the surface of laminated composites like traditional continuous fiber mats through vacuum-assisted resin transfer molding process. The fire performance of the laminated composites was evaluated with cone calorimeter tests under an external radiant heat flux of 50 kW/m². Their residues were analyzed with scanning electron microscopy and thermal gravimetric analyses. It was found that the clay/nanofiber hybrid sheets survived on the combustion surface of composites and significantly reduced the heat release rate by 60.5%. The protective clay layer reduces the heat release rates and the nanofiber network reinforces the clay layer against the air bubbling and melt flow of the products degraded from the polymer resin. The clay/carbon nanofiber hybrid sheet combines the barrier and insulator effects of the clays with the re-emitting heat effect of carbon nanofibers on the combustion surface of composites.     

消防避火服外层织物辐射热防护效能研究

通过对高硅氧玻璃纤维织物(A1)、高硅氧玻璃纤维织物(B1)、连续玄武岩纤维织物(XW)三类消防避火服外层织物材料进行比热容、X射线衍射图谱与热射线反射率等织物辐射热防护性能相关指标的测定,比较了三类消防避火服外层织物材料的防护性能,并从微观纱线分子架构等角度对造成三类材料辐射热防护性能差异的原因逐一进行了解释与分析。根据分析与计算结果,认为纤维内部微观结构与织物辐射热防护能力有着较为紧密的联系,纤维结晶度对织物热射线反射能力的影响显著。     

Mechanical performance of heat/fire damaged novel flame retardant glass-reinforced epoxy composites

Novel glass-reinforced epoxy composites containing a phosphate-based intumescent and inherently flame retardant (cellulosic (Visil, Sateri) and phenol-formaldehyde (Kynol)) fibres have been fabricated. These components are added both as additives in pulverized form and as fibre interdispersed with intumescent as a fabric scrim for partial replacement of glass fibre. Fire testing has been performed using a cone calorimeter at an incident heat flux of 50 kW/m² and the results have shown that introduction of the intumescent/FR fibre to the matrix can significantly reduce the peak heat release values and smoke intensities evolved by composites. Mechanical testing in tensile and flexural modes of these samples has shown that inclusion of the intumescent/fibre system does not adversely influence their tensile and flexural properties. The effect of heat on mechanical properties has been observed by heating the samples in a furnace at 400 °C for 5 min and tested for their flexural and tensile strength retentions. The charred samples remaining after cone exposure were also tested for stiffness test. Some of the samples retained up to 21% of the initial stiffness after being exposed to high heat flux in the cone calorimeter whereas, the control sample was rendered unusable after cone calorimeter exposure.