Effectiveness of Various Concentrations of an Inert Gas Mixture for Preventing and Suppressing Mining Equipment Cab Fires: Development of a Dual Cab Fire Inerting System

The National Institute for Occupational Safety and Health (NIOSH/PRL) conducted a series of large-scale experiments to evaluate the effectiveness and safety of various concentrations of an inert gas mixture (CO₂, 8%; N₂, 50%; Ar, 42%) for preventing and suppressing cab fires. Comparison of concentrations effectiveness in yielding safe times has led to the choice of an optimum gas mixture concentration, discharged in the cab through a muffled nozzle system, for the development of a dual cab fire inerting system. Of note is that safety training programs, including the synchronization of performed tasks, need to accompany this technology to enhance operator’s efficiency and safety during fire emergencies within the safe times yielded by the cab fire inerting system. Cab fires are caused by the ignition of flammable vapors and mists (ball of fire) that penetrate the cab during prolonged hydraulic fluid and fuel fires, and electrical malfunctions involving other cab combustible materials. Often, these fires force the operator to exit the cab under hazardous conditions during a time needed to perform emergency tasks. Hence, it is important to provide the operator, not only with an engine fire suppression system (dry chemical powder), but also with a cab fire protection system, effective both in preventing the ignition of flammable vapors in the cab, and suppressing cab material fires. This paper details the results of the experiments, and presents the development of a dual cab fire inert system, using an optimum gas mixture concentration discharged in the cab through a muffled nozzle system. Of note is that the design of a gas mixture concentration volume according to cab volumes, and system fabrication/installation have been undertaken by cooperating industries. Disclaimer: This information is distributed solely for the purpose of pre-dissemination peer review under applicable information quality guidelines. It has not been formally disseminated by NIOSH. It does not represent and should not be construed to represent any agency determination or policy.     

Design Fire Characteristics for Probabilistic Assessments of Dwellings in England

In England, there are no fixed requirements on the parameters adopted when considering residential design fires, and analyses undertaken are often deterministic with limited consideration given to probabilistic assessments and the sensitivity of parameters. The Home Office dwelling fires dataset has been analysed, considering the fire damage area and the time from ignition to fire and rescue service arrival. From this, lognormal distributions for the maximum heat release rate (HRR) and fire growth rate of residential fires have been approximated. The mean maximum HRR ranges from 900 kW to 1900 kW, with a standard deviation ranging from 2000 kW to 3700 kW, depending on property type and room of fire origin. The mean growth rate, assuming a t2 relationship, ranges from 0.0022 kW/s2 to 0.0034 kW/s2, with a standard deviation ranging from 0.0071 kW/s2 to 0.0132 kW/s2. When considering incidents which result in immediate fire and rescue service call out following ignition, the mean growth rate increases to a range of 0.0058 kW/s2 to 0.0088 kW/s2. As a result of the analyses, design fire distributions are provided which can be adopted for probabilistic assessments. For deterministic analyses, it is proposed that an approximate 95th percentile fire may be adopted, aligning with a medium growth rate of 0.0117 kW/s2 and a maximum fuel-limited HRR in the region of 3800 kW to 4400 kW, depending on whether the dwelling is a house or an apartment. A 95th percentile design fire broadly aligns with values already specified in guidance, helping to substantiate the existing recommendations.     

The Effectiveness of Horizontal Barriers in Preventing Fire Spread on Vertical Insulation Panels Made of Polystyrene Foams

Expanded polystyrene (EPS) and extruded polystyrene (XPS) foams are both excellent exterior thermal insulation materials for buildings. However, their flammability also induces high fire hazard. Current regulation in China requires horizontal fire barriers with a minimum height of 30 cm when polystyrene foams are used as the external insulation. The present work evaluates the effectiveness of such barriers in inhibiting fire growth in insulation walls. The walls were made of B2 grade EPS and XPS foams without protective coatings but with mineral wool as horizontal barriers. Altogether six combinations of fire positions and barrier positions were tested for both EPS and XPS. The heat release rate (HRR) of the fire and the temperature distribution on the wall were recorded and analyzed. The results indicate that, without a barrier, fire starting at the middle of the wall generated higher peak HRR than that starting at the bottom, which was in turn higher than that starting at the top. When the insulation panel below the barrier was 1 m high, the upward fire spread from the bottom could be stopped by 40-cm, but not 30-cm, barriers. However, when the insulation panel below the barrier was 2 m high, even the 40-cm barriers failed. Lastly, the downward fire spread from above could not be stopped by 40-cm barrier due to dripping of burning plastics. The study highlights the limitations of horizontal fire barriers in preventing the vertical fire spread over exposed B2 grade polystyrene insulation and establishes protocols for further investigations.     

Emissions from Fires Part I: Fire Retarded and Non-Fire Retarded TV-Sets

The results of detailed measurements of the emissions from simulated fires with TV-sets are presented in this article. Results from both small- and full-scale fire experiments with flame retarded and non-flame retarded TV-sets are discussed. The measurements cover a broad range of chemical species including specific fire retardant agents and both chlorinated- and brominated dibenzodioxins and furans. The results from similar measurements, but in this case from simulated room fires, can be found in part II in this series of articles.The methodology applied for the measurement of this large range of fire gases is presented in this article. Further, the sampling and analysis methods common for both the TV fires and the simulated room fires are described in detail in conjunction with the experimental results from the TV fires. Additionally, recommendations are made concerning good practice when conducting fire gas determinations of similar complexity.     

Fire testing and design of stainless steel structures

Despite significant progress in recent years in the development of room temperature design guidance for stainless steel structures, fire resistant design has received relatively little attention. This paper reports on studies carried out to investigate the performance of unprotected stainless steel beams and columns in fire. Material tests were carried out on five grades of stainless steel to determine strength and stiffness retention factors at elevated temperatures; both strength and stiffness retention were shown to be superior to that of carbon steel beyond 600 ^°C. The temperature development characteristics of a range of stainless steel sections were investigated, and compared to those of carbon steel sections. Full scale fire tests were conducted on six stainless steel columns, and four stainless steel beams. Finite element modelling of the tests was carried out, and parametric studies were performed to supplement the test data. All tests were carried out as part of the European project ‘Development of the use of stainless steel in construction’. Design recommendations for stainless steel columns and stainless steel beams supporting a concrete slab, based on the ECCS model code for fire engineering, were validated against the test and finite element results. These recommendations have been incorporated into the Euro Inox/SCI Design Manual for Structural Stainless Steel, and implemented in Eurocode 3: Part 1.2, with minor adjustments for consistency with carbon steel.     

Effect of Location of Restraint on Fire Response of Steel Beams

Restrained steel beams, when exposed to fire, develop significant restraint forces and often behave as beam-columns. The response of such restrained steel beams under fire depends on many factors including: fire scenario, beam slenderness ratio, location of axial restraint at the supports, and high-temperature properties of steel. A set of numerical studies, using finite element computer program ANSYS, is carried out to study the fire response of steel beam-columns under realistic fire and restraint scenarios. Results from the parametric studies indicate that fire scenario, beam slenderness, location of axial restraint and high-temperature creep have significant influence on the behavior of restrained beams under fire conditions. Severe fires produce high axial forces at early stages of fire exposure; whereas in moderate fires, significant axial force develops only at later stages of fire exposure. Axial restraint enhances the fire resistance due to the development of tensile catenary action in restrained beams. Furthermore, restrained beams with low slenderness ratio exhibit better fire performance when the axial restraint at the support is located at the bottom flange.     

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。     

钢屋盖结构防火的性能化消防工程分析

因为建筑学上和构造上的原因,越来越多的建筑设计采用了钢结构。为了保证建筑结构构件的完整性,建筑规范提出了结构耐火性能的要求。但是,已规定的要求没有促进具有良好经济效益的设计,并且假定遵照规范是达到安全等级的唯一途径。本论文提出采用以性能设计为基础的消防工程理论方法来证明火灾中钢构件的性能。消防工程准则已发展至符合规范的要求,并能保证结构在火灾中的安全性能。本文采用一个游泳/跳水馆作为例子来讨论对钢屋顶结构进行耐火保护。本例的研究表明,游泳/跳水馆的钢屋顶结构可以不用耐火涂料,并且不会降低整个建筑的防火安全等级。     

Fire fighting in tunnels

In this article the author is to ascertain that it is difficult to fight a big fire such as the fires in the Euro tunnel, Mont Blanc tunnel and the Tauern tunnel. The measures implemented in tunnels are all measures to retain the tunnel structure. There are no measures (or at least not enough) taken for the purpose of extinguishing the fire as soon as possible. By dividing the tunnel into compartments and providing each compartment with sluice gates, the fire can be isolated and by lack of oxygen, the fire will not stir up or even extinguish itself. If the fire does not stir up, it will be easier for the Fire Brigade to get near and fight the fire.     

Fire Performance of Sandwich Panels in a Modified ISO 13784-1 Small Room Test: The Influence of Increased Fire Load for Different Insulation Materials

Four sandwich panel rooms were constructed as prescribed in the ISO 13784-1 test. However, the construction followed normal industry practice, and the panels were also subjected to the kinds of damage typically found in commercial premises, although such damage may not typically be concentrated in such a small room. The fire load was increased to simulate fires actually occurring in commercial premises by stepping up the propane burner output from the usual maximum of 300–600 kW, and by placing a substantial wooden crib in two of the rooms. The results showed significant differences in fire growth rate and burning behaviour between those panels filled with polyisocyanurate (PIR) and those filled with stone wool in both the experiments without and with the wooden crib. Most significantly, the PIR pyrolysis products caused earlier ignition (by radiation from above) of the wooden crib 11 min into the experiment (1 min after the burner was stepped up to 300 kW), whereas the crib ignited 22 min into the test (2 min after the burner had been stepped up to 600 kW, which is beyond the test standard both in time and heat input) for the stone wool panels. This interaction between building and contents is most often ignored in fire safety assessments. After a few minutes, the PIR pyrolysis products that escaped outside the room, from between the panels, ignited. The extra thermal exposure from the PIR-fuelled flames distorted the panels, which in turn exposed more PIR, resulting in large flames on both the inside and outside of the enclosure. From a fire safety perspective this is most important as it shows that with the large fire loads that are commonly found in commercial premises, steel-faced PIR filled panels are not capable of acting as fire barriers, and may support flame spread through compartment walls and ceilings. In addition, the PIR panelled rooms produced very large quantities of dense smoke and toxic effluents, whereas the stone wool panelled rooms produced small amounts of light smoke of lower toxicity. Furthermore, the experiments showed that modifications to the standard test can lead to extremely different outcomes for some of the products. As the modifications simulated real-life situations, it seems important to discuss whether the standard is robust enough for property safety scenarios encountered in industrial premises.     

Levoglucosan as a Tracer for Smouldering Fire

Detecting fires at an early stage is crucial for mitigating and extinguishing fires. The increased use of biofuels in Northern Europe has led to an increased number of fires in storage facilities. These fires are often caused by self-heating in the interior of the stored materials and slowly develop to smouldering fires. Consequently, these smouldering fires are usually detected several days or weeks after the initial smouldering fire had started. At this point, measures to extinguish the smouldering fire inside the material are difficult as the fire has grown for a long time and is located inside the material. This makes it difficult to gain a successful effect of any extinguishing agents. This paper presents a pilot study in lab scale suggesting levoglucosan as an early tracer for smouldering fires using 600 g cotton as the biomass source. The advantage of detecting levoglucosan as a fire signature is that it serves as a tracer compound for biomass burning and is produced at temperatures of 200–400°C reducing the risk of false alarms from emissions produced at lower temperatures. In this paper, levoglucosan was detected in aerosols emitted in an early stage from smouldering fires and was analyzed by ultrasonic assisted extraction followed by gas chromatographic separation and mass spectrometric detection. First detection of levoglucosan was made in the first sample, collected after 30 min when the smouldering fire was only a few cubic centimeters of the cotton package. In addition, levoglucosan was found in the solid residues of carbonized cotton after the initial smouldering process had moved through the material. The findings should be regarded as screening results to be used for the development of sensors and technology for smouldering fire detection.     

火灾下不锈钢梁—柱节点数值分析

评估了EC3中不锈钢梁-柱节点发生或不发生侧向扭转屈曲的设计准则的准确性和安全性。对焊接方式相同的H型钢梁-柱节点进行了大量数值参数研究,以此为基础进行评估。研究中考虑了残余应力、截面高厚比、弯矩图形状和不锈钢等级的影响。提出了火灾下不锈钢梁-柱节点的新设计方程,计算结果与数值分析结果进行对比,结果表明,新设计方程比EC3中设计方程更为安全。此外,对火灾时不锈钢梁在梁端弯矩与横向荷载共同作用下的侧向扭转屈曲进行了研究。     

EcoSmart Fire as Structure Ignition Model in Wildland Urban Interface: Predictions and Validations

EcoSmartFire is a Windows program that models heat damage and piloted ignition of structures from radiant exposure to discrete landscaped tree fires. It calculates the radiant heat transfer from cylindrical shaped fires to the walls and roof of the structure while accounting for radiation shadowing, attenuation, and ground reflections. Tests of litter burn, a 0.6 m diameter fire up to 250 kW heat release under a Heat Release Rate (HRR) hood, with Schmidt-Boelter heat flux sensors in the mockup wall receiving up to 5 kW/m² radiant flux, in conjunction with Fire Dynamic Simulator (FDS) modeling verified a 30% radiant fraction, but indicated the need for a new empirical model of flame extinction coefficient and radiation temperature as function of fire diameter and heat release rate for use in ecoSmartFire. The radiant fluxes predicted with both ecoSmartFire and FDS agreed with SB heat flux sensors to within a few percent errors during litter fire growth. Further experimental work done with propane flame heating (also with 30% radiant fraction) on vertical redwood boards instrumented with embedded thermocouples validated the predicted temperature response to within 20% error for both models. The final empirical correlation for flame extinction coefficient and temperature is valid for fire diameters between 0.2 and 7.9 m, with heat release rates up to 1000 kW. From the corrected radiant flux the program calculates surface temperatures for a given burn time (typically 30 s) and weather conditions (typically dry, windy, and warm for website application) for field applications of many trees and many structural surfaces. An example was provided for a simple house exposed to 4 burning trees selected on a Google enhanced mapping that showed ignition of a building redwood siding. These temperatures were compared to damage or ignition temperatures with output of the percentage of each cladding surface that is damaged or ignited, which a homeowner or a landscaper can use to optimize vegetation landscaping in conjunction with house exterior cladding selections. The need for such physics-based fire modeling of tree spacing was indicated in NFPA 1144 for home ignitability in wildland urban interface, whereas no other model is known to provide such capability.     

Evaluation of Surfactant Enhanced Water Mist Performance

Water-mist technology provides efficient fire suppression for compartments while minimizing water usage. Even with the many advantages of water mist systems, there is still room for improvement. Water mist systems have demonstrated effectiveness at suppressing flammable liquids (Class B) fires in compartments. However, an especially challenging fire suppression scenario for water mist systems is the small Class B fire. This scenario is often realized after a large fire has been reduced in size or ‘controlled’ by water mist. The small fire scenario is challenging because a small fire may not be able to generate enough vaporized water to displace sufficient oxygen for complete extinction. It should also be noted that even if the Class B fire is extinguished with a water mist system, re-ignition from the hot surrounding surfaces may occur at any time. In the present work, an additive is introduced into the water supply and its effect on the water mist suppression performance is studied. This Forafac^TM additive is a specific formulation, which includes fluorinated surfactants for creating a robust fire suppression foam. The enhanced suppressant exiting the mist nozzle is dispersed in the form of small droplets (not as a continuous foam) similar to a pure water mist spray. However, these droplets create a foam blanket on the surface of the fire, which acts to isolate the fuel from the air. With this formulation, the efficiency of the water mist system is improved even on small fires and most importantly the re-ignition of class B fires is prevented.

Thermal Analysis of Hollow Steel Columns Exposed to Localised Fires

In fires in large compartments like enclosed car parks, airport terminals and industrial halls, the uniform distribution of gas temperature of post-flashover stages are unlikely to occur; in these cases, the thermal actions of a localised fire must be taken into account. In order to design steel structures for a localised fire, very detailed data concerning the development of temperatures in steel is required. EN 1991-1-2 presents a simplified model for calculating the temperatures in ceiling slabs and in the beams that may support such slabs; however, no simplified calculation model for the heat transfer in vertical elements, such as columns, is yet available. There is a need for more experimental data on real scale structures exposed to localised fires. A research project on the evaluation of temperatures in steel columns exposed to localised fires was carried out at the University of Coimbra. Full-scale natural fire tests were used to test columns, instead of conducting the usual furnace tests. This paper presents and discusses the results of the experimental tests on unprotected hollow steel columns exposed to localised fires, each of them simulating a distinct fire scenario according to different fire loads, positions and ventilation conditions. During the fire tests, real measurements showed flame heights and burning times different to those preliminarily estimated: flame heights had been conservatively predicted; while, the duration of the burning had been significantly underestimated.     

电缆隧道L型防火隔板的隔热效果分析与侧板高度设计

为兼顾电缆隧道中L型防火隔板的隔热效果和施工安装的便捷性,需确定不同工况下L型防火隔板所需最低高度。为此,利用FDS模拟软件,设置不同侧板高度,针对不同火源功率条件下L型防火隔板对不同电压等级电缆的保护效果进行模拟,分析安装隔板区域的温度变化和烟气扩散。结果表明：火源功率为400,600 kW时,电缆充分燃烧阶段至衰减末期,烟气蔓延速度分别比火源功率为200 kW时约快50%和66%;当110 kV电缆层间距为0.5 m,火源功率为200,400,600 kW时,L型防火隔板侧边最优高度分别为0.20,0.25,0.25 m;当10 kV电缆层间距为0.25 m时,三种火源功率下L型防火隔板侧边最优高度分别为0.100,0.125,0.125 m,隔板上方被保护电缆护套层温度均低于热解温度。研究成果可为不同工况下防火隔板侧板高度设计提供参考。     

Protection of aluminum overcast constructions against fire

A test program was undertaken by the U. S. Mine Safety and Health Administration to evaluate various materials for protecting aluminum overcast constructions against fire. Selected coatings and one covering were tested under large-scale, simulated mine fire conditions to determine their effectiveness as a fire barrier for protection of aluminum.Coatings consisting of expanded vermiculite, limestone, and portland cement; mineral wool fibers in hydraulic setting, inorganic binders; cellulose mixed with liquid sodium silicate; and a fiberglass-reinforced surfacebonding mortar were particularly effective in protecting the aluminum structures against the heat of the simulated mine fire. Three inches of a ceramic-fiber blanket and a four-inch coating of phenolic spray foam also proved to be relatively effective barriers for fire protection under the conditions of the test.     

火灾下钢结构楼板的薄膜作用

通过对真实火灾中的足尺火灾试验和观察显示，合组合楼板和承载钢梁的建筑物的结构承载力比现行杭大设计方法的建议值高出许多。因此规范中规定所有承载钢梁都要添加被动防火保护是不必要的。现行设计方法和实际结构性能之间产生这种差异是由于设计方法中忽略了楼板的薄膜作用。本根据国外有关资料给出了几种简单计算方法，允许在钢结构杭大设计中考虑楼板的薄膜作用。从而可以更精确地评估火灾下建筑物的真实承载能力，在给定的耐火时间内能减少相当数量钢梁的防火保护。     

Fire development in a 1/3 train carriage mock-up

To study what parameters that control the initial fire spread and the development to local flashover in a metro carriage, a total of six fire tests were conducted in a mock-up of a metro carriage that is about 1/3 of a full wagon length. They were carried out under a large scale calorimeter in a laboratory environment. The focus was on the initial fire development in a corner scenario using different types of ignition source that may lead to a fully developed fire. The ignition sources used were either a wood crib placed on a corner seat or one litre of petrol poured on the corner seat and the neighbouring floor together with a backpack. The amount of luggage and wood cribs in the neighbourhood of the ignition source was continuously increased in order to identify the limits for flashover in the test-setup. The tests showed that the combustible boards on parts of the walls had a significant effect on the fire spread. In the cases where the initial fire did not exceed a range of 400–600 kW no flashover was observed. If the initial fire grew up to 700–900 kW a flashover was observed. The maximum heat release rate during a short flashover period for this test set-up was about 3.5 MW. The time to reach flashover was highly dependent on the ignition type: wood cribs or backpack and petrol. A full developed carriage fire was achieved as a result of intense radiation from the flames and ceiling smoke layer. This was mostly dependent on the amount of fire load nearby the ignition source and how strong the vertical flame spread on the high pressure laminate boards mounted to walls and ceiling above the ignition source was, leading to a ceiling flame. In such cases, the seats alone did not contain sufficient fuel for the fire to spread within the train, and additional fuel (luggage) is required near the seats. For fully developed carriage fires, the fire starting on the seat in the corner spread to the opposite seat on the same side of the aisle, then horizontally spread to seats on the other side of the aisle, and finally a longitudinal flame spread along the carriage was observed. When and where the fire stopped or whether it reached a fully developed stage was mostly dependent on the amount of fire load nearby the ignition source and how strong the vertical flame spread on the high pressure laminate boards mounted to walls and ceiling above the ignition source was.     

Fire detection, location and heat release rate through inverse problem solution. Part I: Theory

A proposed method of detecting, locating and sizing accidental fires, based on the solution of an inverse heat transfer problem, is described. The inverse heat transfer problem to be solved is that of the convective heating of a compartment ceiling by the hot plume of combustion gases rising from an accidental fire. The inverse problem solution algorithm employs transient temperature data gathered at the ceiling of the compartment to determine the location and heat release rate of the fire. An evaluation of the proposed fire detection system, demonstrating the limits on the accuracy of the inverse problem solution algorithm, is presented. The evaluation involves operating the inverse problem solution algorithm on transient temperature data from computer simulated compartment fires. The simulated fire data are generated assuming fires with quadratic growth rates, burning in a 20 m wide by 20 m deep by 3 m high enclosure with a smooth, adiabatic ceiling. The accuracy of the inverse problem solution algorithm in determining the location of a fire is shown to be insensitive to the errors in the fire model used in the forward problem solution, but sensitive to errors in the measured temperature data. The accuracy of the heat release rate of the fire is sensitive to both errors in the fire model and errors in the temperature data. The validity of the use of computer simulated data in the evaluation is verified with a second evaluation using fire data interpolated from published measurements taken in large-scale compartment fire burns.