The Impact of Thermal Runaway on Sprinkler Protection Recommendations for Warehouse Storage of Cartoned Lithium-Ion Batteries

This study investigates the appropriateness of applying the standard large-scale fire test protocol developed for ordinary combustibles for energetic batteries. A large-scale fire test was recently conducted to determine sprinkler protection guidance for warehouse storage of lithium-ion batteries. The specific battery tested had a 20 Ah capacity, polymer pouch format, lithium iron phosphate chemistry and was at a typical state-of-charge (50%) for long-term storage. The batteries were packaged in single-wall corrugated containerboard cartons on hardwood pallets, as received from the supplier. Each carton contained 20 batteries separated by nested polystyrene plastic dividers. Acceptable ceiling-level sprinkler protection was achieved for 4.6 m (15 ft) tall rack storage under a 12.2 m (40 ft) ceiling using K-Factor of 320 L/min/bar^½ (22.4 gpm/psi^½), quick-response, sprinklers at a discharge pressure of 2.4 bar (35 psig). The effect that thermal runaway of the Li-ion batteries had on the design and outcome of the large-scale fire was evaluated. A focus was placed on the role of thermal runaway during three stages of the fire; ignition leading to sprinkler operation, active sprinkler protection, and conditions after the sprinkler system was turned off. An external ignition source was used in cases where induced thermal runaway, which refers to rapid self-heating of a battery under abuse conditions, did not lead to combustion of the battery contents. Through a combination of experiments and review of literature data, it was found that thermal runaway within a pallet load of cartoned batteries would result in a similar fire hazard as that associated with external ignition scenarios typically used in large-scale fire testing. Regardless of chemistry, evidence shows that fire propagation beyond the battery or carton of origin occurs external to the carton due to limited available air within the carton to support combustion. In addition, intermediate-scale testing showed that sprinkler water would be effective at suppressing a fire at a later stage of battery involvement than was achieved in the large-scale test. This work reinforces the sprinkler protection guidance resulting from the successful large-scale fire test.     

Technological breakthroughs in material flammability evaluations

A number of major innovations have recently been achieved using techniques that employ small-scale flammability measurements to predict full-scale end-use applications. The principles used couple ignition characteristics with combustion characteristics to assess fire performance. These techniques have been developed to classify the flammability of aerosol products; characterize liquid fuel spray fires, such as those involving hydraulic fluids; evaluate the fire propagation behavior of electrical cables; classify conveyor belts; and determine the fire propagation behavior of wall/ceiling materials.This paper was originally presented at National Fire Protection Association 97th Annual Meeting, May 23–27, 1993, Orlando, Florida.     

CFD Simulations of Fire Propagation in Horizontal Cable Trays Using a Pyrolysis Model with Stochastically Determined Geometry

In this paper, a pyrolysis model for a PVC cable is constructed using results from thermogravimetric analysis, microscale combustion calorimeter and cone calorimeter experiments. The pyrolysis model is used to simulate fire propagation in horizontal cable trays. The simulated arrangement corresponds to a cable tray fire experiment from OECD PRISME 2 project. As laying the cables loosely along the horizontal trays is a random process, a novel stochastic method is developed for making the simplified cable tray geometries for the computational fluid dynamics model. In addition, as the simplified cable tray geometry has significantly smaller surface area than a real tray full of cables, the surface area was parametrically adjusted. In contrast to most of the earlier published numerical approaches for simulating cable tray fires, the presented approach does not use empirical correlations for predicting fire propagation and does not require any results from full-scale experiments for calibrating the model. The simulation results are compared to experimental results in terms of heat release rate, mass loss, tray ignition times and lateral flame spread rates. The maximum heat release rate was overpredicted by 8% on average.

     

Flame Retardant Smoke Suppressant Protection for Poly Vinylchloride

Spread of fire along electrical cables may be alleviated by using flame-retardant smoke suppressant (FRSS) additives-based PVC compositions designed for use as insulation and sheathing. These compositions offer improved resistance to ignition, flame spread and smoke generation. FRSS protection may also be achieved by the application of intumescent coatings as fire-protective layers and barriers for electrical cables and cable installations.Metal-based organic (MBO) complexes were synthesized for use as flame retardant smoke suppressants in PVC formulations. Plasticized PVC compositions were prepared and evaluated for their fire performance. Excellent smoke suppression was observed when either of the two MBOs was used. The limiting oxygen index was also found to be fairly high, particularly when the PVC samples were plasticized with a phosphate plasticizer. Flame-retardant smoke-suppressant intumescent coatings were developed for PVC-sheathed electrical cables. The coatings were applied on cables, and their fire performance was evaluated by using national and international standard procedures. The coated cables did not show any surface spread of flame on exposure and their generation of smoke was found to be very low. The coatings were found to be quite effective in reducing the burning behaviour of power cables. Significant improvement in circuit failure time was noted for coated cable specimens.     

Ignition of Combustible Fuel Beds by Hot Particles: An Experimental and Theoretical Study

The process of spotting occurs in wildland fires when fire-lofted embers or hot particles land downwind, leading to ignition of new, discrete fires. This common mechanism of wildland fire propagation can result in rapid spread of the fire, potentially causing property damage and increased risk to life safety of both fire fighters and civilians. Despite the increasing frequency and losses in wildland fires, there has been relatively little research on ignition of fuel beds by embers and hot particles. In this work, an experimental and theoretical study of ignition of homogeneous cellulose fuel beds by hot metal particles is undertaken. This type of well-characterized laboratory fuel provides a more controllable fuel bed than natural fuels, and the use of hot metal particles simplifies interpretation of the experiments by reducing uncertainty due to unknown effects of the ember combustion reaction. Spherical steel particles with diameters in the range from 0.8 mm to 19.1 mm heated to temperatures between 500°C and 1300°C are used in the experiments. A relationship between the size of the particle and temperature required for flaming or smoldering ignition is found. These results are used to assess a simplified analysis based on hot-spot ignition theory to determine the particle size-temperature relationship required for ignition of a cellulose fuel bed.     

电缆防火封堵设计

结合现场的实际情况,介绍了在哪些场所敷设的电缆应采取防火封堵措施;国内常用的三种电缆防火封堵的材料;各种环境下(包括电气室盘柜底部、电缆桥架穿墙洞、电缆桥架穿防火门、电缆竖井内电缆桥架穿楼板孔洞、电缆保护管穿楼板、电缆穿越建筑物的外墙处)的电缆封堵设计。提出了设计和施工过程中切实可行的措施。     

基于CONE的超高温耐火电缆火灾危险性分析

利用锥形量热仪对超高温耐火电缆在不同辐射功率下的点燃时间（TTI）、热释放速率（HRR）、质量损失速率（MLR）和燃烧残余物进行了研究。研究表明,随着辐射功率增加,耐火电缆的TTI逐渐缩短,HRR和MLR逐渐增大,火灾危险性逐渐增加。超高温耐火电缆在35 kW/m2和50 kW/m2辐射功率下火灾性能指数相比于25 kW/m2分别增加了44.4%和176.5%,火灾增长指数分别增加了30.4%和83.0%。结合理论分析可以得出,耐火电缆的临界辐射功率为3.61 kW/m2、零辐射平均热释放速率为36.5 kW/m2,表现出较低的火灾危险性。     

Evaluation of duct opening protection in two-hour fire walls and partitions

There is a continuing debate among fire protection specialists on the value and role of fire dampers in preventing fire spread via HVAC duct systems. It has been recognized that fire dampers are not required under all circumstances. For example, NFPA 90A,Standard for the Installation of Air Conditioning and Ventilation Systems, does not require the installation of fire dampers in ducts penetrating one-hour fire-rated walls and partitions. Additionally, there are circumstances where the closure of dampers may affect critical environmental air systems. In these situations, the value of fire dampers must be determined in terms of an overall risk assessment. It has been suggested that the role of fire dampers be considered in terms of the total building fire protection system, but a quantitative approach for such an assessment has been previously unavailable. In particular, there has been no data related to the performance of a duct system when subjected to a standard two-hour fire exposure. Gewain et al. have described an equivalency approach and full-scale fire test data for the protection of duct openings in two-hour fire-resistant walls and partitions. The objective of this paper is to review and summarize the equivalency rationale and test data and describe engineering methods available to apply an equivalency approach more generally. The approach was developed for situations where horizontal steel ventilation ducts penetrate fire-rated walls and partitions. The approach does not address smoke dampers or ducts containing combustible materials.     

Statistical Characterization of Heat Release Rates from Electrical Enclosure Fires for Nuclear Power Plant Applications

Since the publication of NUREG/CR-6850/EPRI 1011989 in 2005, the US nuclear industry has sought to re-evaluate the default peak heat release rates (HRRs) for electrical enclosure fires typically used as fire modeling inputs to support fire probabilistic risk assessments (PRAs), considering them too conservative. HRRs are an integral part of the fire phenomenological modeling phase of a fire PRA, which consists of identifying fire scenarios which can damage equipment or hinder human actions necessary to prevent core damage. Fire ignition frequency, fire growth and propagation, fire detection and suppression, and mitigating equipment and actions to prevent core damage in the event fire damage still occurred are all parts of a fire PRA. The fire growth and propagation phase incorporates fire phenomenological modeling where HRRs have a key effect. A major effort by the Electric Power Research Institute and Science Applications International Corporation in 2012 was not endorsed by the US Nuclear Regulatory Commission (NRC) for use in risk-informed, regulatory applications. Subsequently the NRC, in conjunction with the National Institute of Standards and Technology, conducted a series of tests for representative nuclear power plant electrical enclosure fires designed to definitively establish more realistic peak HRRs for these often important contributors to fire risk. The results from these tests are statistically analyzed to develop two probabilistic distributions for peak HRR per unit mass of fuel that refine the values from NUREG/CR-6850, thereby providing a fairly simple means by which to estimate peak HRRs from electrical enclosure fires for fire modeling in support of fire PRA. Unlike NUREG/CR-6850, where five different distributions are provided, or NUREG-2178, which now provides 31, the peak HRRs for electrical enclosure fires can be characterized by only two distributions. These distributions depend only on the type of cable, namely qualified versus unqualified, for which the mean peak HRR per unit mass is 11.3 and 23.2 kW/kg, respectively, essentially a factor of two difference. Two-sided, 90th percentile confidence bounds are 0.0915 to 41.2 kW/kg for qualified cables, and 0.0272 to 95.9 kW/kg for unqualified cables. From the mean (~70th percentile) upward, the peak HRR/kg for unqualified cables is roughly twice that for qualified, increasing slightly with higher percentile, an expected phenomenological trend. Simulations using variable fuel loadings are performed to demonstrate how the results from this analysis may be used for nuclear power plant applications.     

低压电缆耐火试验国标和英标的差异分析

通过对比低压电缆耐火试验国家标准GB 19216.21-2003/IEC60331-21：1999《在火焰条件下电缆或光缆的线路完整性试验第21部分：试验步骤和要求额定电压0.6/1.0kV及以下电缆》和英国标准BS 6387：1994《Specification for Performance requirements for cables required to maintain circuit integrity under fire conditions》的差异,分析两个标准制订的出发点、试验内容和试验方法。对比分析存在的差异性,并详细介绍BS 6387：1994的试验内容,为设计人员了解两个标准的差别提供参考。     

城市综合管廊电力舱火灾行为试验研究

为了研究综合管廊电力舱火灾发展规律,本文分析了电力电缆火灾危险性和起火原因,建造了100 m×3 m×3 m综合管廊模拟火灾试验平台,基于真实电力电缆剖面结构,设计了模拟电缆火源模型并开展了燃烧对比试验和火灾燃烧相似性分析,开展了电力舱在非通风和1 m/s风速下的火灾模拟试验,分析了模拟电缆完成多层立体燃烧的全过程,研究了火焰和烟气蔓延规律以及氧含量变化规律,提出了电力舱火灾发展的4个阶段,试验认为火灾发生后,及时关闭通风系统和防火门等开口有利于抑制火灾发展,电缆层间设置防火隔板可以延缓多层电缆形成大规模燃烧的时间,舱内起火应立即切断所有电力回路,避免引发连环火灾爆炸。     

Cable tunnels—an integrated fire detection/suppression system for rapid extinguishment

The impact of a major fire occurring within the cable tunnel network installed under the city of Melbourne, Australia would be catastrophic to Telecom Australia and to Melbourne. The objective of this paper is to respond to the challenge to provide the most efficient method of rapid fire detection and suppression. The combination of the risk potential and the importance of the cables in the tunnels clearly identifies the need for a system capable of very early smoke/fire detection and suppression before any internal damage to cables occurs. Tests show that the maximum time that a petrol fire of 90 kW heat release rate can burn in the vicinity of the Telecom cables before the water suppression system is activated to successfully extinguish or prevent ignition of the cables is approximately 30 secs.     

110 kV高压电缆着火过程数值模拟研究

为了研究综合管廊局部空间内电缆接头内热源作用下的着火过程,通过运用数值模拟软件FDS三维传热和热解模型对110 kV高压电缆接头着火过程建模分析.研究了内外热源对电缆着火过程的不同影响,分析了不同运行状态下的温度分布情况,对比了不同缆芯材料的热传导作用对电缆着火过程的影响.结果表明,正常运行和短时过载状态下,电缆的火灾...     

PVC电缆及其护套原料燃烧性能的对比

利用锥形量热仪对PVC电缆护套原料和对应电缆试样进行了实验研究，对比分析两组实验的点燃时间（TTI）、热释放速率（HRR）等主要燃烧参数。探讨了两组实验结果之间的相关性。实验结果表明：在相同实验条件下，PVC护套原料与对应电缆试样的HRR在燃烧的初始阶段（约240s内）有很好的相关性。因此，以护套原料的实验数据预测电缆样品在燃烧初期的HRR具有可行性，这对电缆护套原料的选用、降低新产品的开发成本以及制定电缆护套原料阻燃标准都具有实际意义。     

Comparison of toxic product yields of burning cables in bench and large-scale experiments

Toxic product yields from five commercial cables obtained from a steady state tube furnace (SSTF) method (IEC 60695-7-50, Purser furnace) are compared with results from a large-scale test, which uses the physical fire model in the proposed prEN50399-2-2 test, with the addition of effluent gas analysis, using Fourier transform infrared (FTIR), and for further comparison, a static tube furnace method (NF X 70-100). This work represents one of the first attempts to establish a relationship between bench- and large-scale toxic product yields for burning cables. This is difficult because the cables have been formulated for low flammability, and therefore do not burn consistently. The tube furnace burns the cable completely, whereas the large-scale test effluent is the result of a combination of flame spread and toxic product yields, both of which are fire scenario dependant. There is significant differentiation between cable types based on composition, and arising because only a portion of the cables burn in the large-scale test, accompanied by possible decomposition of hydrate sheaths. The fire stage of the large-scale test appears to have been replicated in an appropriate manner, given the correspondence of the CO₂/CO ratios. The yields of CO₂, CO, HCl and smoke show reasonable agreement, given the differences in the extent of burning, and the accuracy of the mass-loss data available for the large-scale test. The yields and extent of burning have been combined to demonstrate the estimation of toxic hazard for a particular fire scenario based around the large-scale test, which shows only marginal sensitivity to the differences in toxic product yield between the SSTF and the large-scale test.     

Ignitor and Thickness Effects on Upward Flame Spread

The effects of a material's ignitor characteristics and burning duration on upward wall flame spread are investigated. The ignitor is represented as an energy line source. Its energy release rate and its duration after ignition are considered. The material is represented as a finite, thick noncharring material with properties representative of polymethylmethracrylate (PMMA). A Volterra integral equation is solved for upward flame speed by numerical methods, and a transient, noncharring burning rate model is included. Results show the influence on propagation of ignitor effects and material thickness. A propagation map is computed showing the domains of flames that spread and flames that stop. Criteria for propagation and how propagation affects fire growth are considered in a standard room-corner test.     

消防用电线电缆耐火性能试验方法研究

针对我国现有的电缆耐火试验方法不能满足相关规范对电缆的耐火性能的要求,借鉴国外试验方法,研究出新的耐火试验方法,即在同一根电缆试样上施加火焰燃烧、冲击振动和喷水试验。按该方法对市场上常见的6种不同结构耐火电缆进行验证试验,结果表明,电缆耐火性能的优劣主要取决于耐火层材料质量、电缆结构和电缆制造工艺水平。     

电缆燃烧典型火源模拟方法综述

针对电缆火灾问题,综述了国内外电缆火灾模拟试验及电缆燃烧测试中使用的火源模拟方法,并对比探讨了多种火源模拟方法的点火时间、火源温度、火源面积、火源功率、可扩展性、可移动性以及可持续使用性等方面的差异:燃气喷灯法和辐射加热法(锥形量热计)所需点火时间短;电加热法火源温度高,操作简便易移动;燃油点火法的点火面积大,可扩展性...     

Impact of Flashover Fire Conditions on Exposed Energized Electrical Cords/Cables

There has been prior research exploring the exposure of common electrical cords and cables to fire, but that has traditionally been at the lab scale and under near steady-state exposures. The goal of these experiments was to expose six types of cords and cables in a room-scale compartment with a fuel load sufficient to drive the compartment through flashover. The basic test design was to expose the cords and cables on the floor of a compartment to a growing fire to determine the conditions under which the cord/cable would trip the circuit protection device. All of the cords were energized and installed on a non-combustible surface. The six cables and cords were protected by three different circuit protection devices which were remote from the thermal exposure. This configuration resulted in 18 exposures per experiment. The room fires experiments consisted of three replicate fires with two sofas as the main fuel source, two replicate fires with one sofa as the main fuel source and one fire with two sofas and vinyl-covered MDF paneling on three walls in the room. Each fuel package was sufficient to support flashover conditions in the room. The average peak heat release rate of the sofa fueled compartment fires with gypsum board ceiling and walls prior to suppression was 6.8 MW. The addition of vinyl covered MDF wall paneling on three of the compartment walls increased the pre-suppression peak heat release rate to 12 MW. In each experiment during post flashover exposure, the insulation on the cords and cables ignited and burned through, exposing bare wire. During this period, the circuits faulted. Assessments of both the thermal exposure and physical damage to the cords did not reveal any correlation between the thermal exposure, cord/cable damage, and trip type.