Calculating overpressure from BLEVE explosions

Although a certain number of authors have analyzed the prediction of boiling liquid expanding vapour explosion (BLEVE) and fireball effects, only very few of them have proposed methodologies for predicting the overpressure from such explosions. In this paper, the methods previously published are discussed and shown to introduce a significant overestimation due to the erroneous thermodynamic assumptions—ideal gas behaviour and isentropic vapour expansion—on which they are based (in fact, they give the maximum value of overpressure which can be caused by a BLEVE). A new approach is proposed, based on the—more realistic—assumption of an adiabatic and irreversible expansion process; the real properties of the substance involved in the explosion are used. The two methods are compared through the application to a given case.     

BLEVE: The case of water and a historical survey

After a short update of the current more accepted definition of BLEVE, the special features of water BLEVEs are analyzed. The stronger overpressure wave generated in the case of water as compared to that of other substances is justified in terms of volume change. Through a comparison with liquefied pressurized propane, three possibilities are analyzed: the simultaneous contribution of both the liquid and the preexisting vapor, the contribution of the liquid flash vaporization, and the contribution of the pre-existing vapor. Also a historical survey on a set of 202 BLEVE accidents –the largest sample of BLEVE accidents surveyed until now– is presented. LPG was the most common substances in this set of accidents. However, water and LNG (11% of water and 4% of LNG in the studied cases) have also been involved. Impact failure (44.8%) and human factor (30.3%) were the most common causes of BLEVEs. Transport, storage, process plants, and transfer were the activities in which more accidents occurred.     

LPG球罐BLEVE过程中超压与热耦合效应模拟研究

为评估LPG球罐发生BLEVE过程中超压与热耦合效应对化工企业抗爆控制室和避难所选址的影响,采用TNO多能法数学模型计算冲击波超压,采用多源数学模型计算火球热辐射。编写MATLAB计算程序,并应用ANSYS模拟二者破坏效应的耦合作用。LPG球罐发生BLEVE过程中,爆炸冲击波的传播速度、持续时间和火球的传播速度、持续时间不同,爆炸冲击波主要在燃料高速抛散的初期形成,之后基本与火球脱离。分别模拟计算冲击波超压和火球热辐射对抗爆控制室和避难所的影响,结果表明：抗爆控制室选址只需考虑爆炸冲击波的影响;避难所选址需要考虑冲击波超压和火球热辐射作用双重影响。在研究基础上提出,LPG球罐附近人员逃生的避难所应设置在球罐防火堤外紧邻防火堤处的地下,应具有抗震、防渗、防火、防中毒窒息等功能。人员应在BLEVE发生前进入避难所才能逃生。     

A methodology to predict shock overpressure decay in a tunnel produced by a premixed methane/air explosion

A methodology for estimating the blast wave overpressure decay in air produced by a gas explosion in a closed-ended tunnel is proposed based on numerical simulations. The influence of the tunnel wall roughness is taken into account in studying a methane/air mixture explosion and the subsequent propagation of the resulting shock wave in air. The pressure time-history is obtained at different axial locations in the tunnel outside the methane/air mixture. If the shock overpressure at two, or more locations, is known, the value at other locations can be determined according to a simple power law. The study demonstrates the accuracy of the proposed methodology to estimate the overpressure change with distance for shock waves in air produced by methane/air mixture explosions. The methodology is applied to experimental data in order to validate the approach.     

BLEVE: A new approach to the superheat limit temperature

Several methods proposed for calculating the value of the superheat limit temperature were analysed. The results obtained indicate that the procedures based on the thermodynamic stability approach introduce a significant uncertainty into the final values, depending on which equation of state is used. We propose a new approach based on the energy balance in the initial liquid mass just before the explosion. The temperature obtained using this method, T_sl−E, corresponds to the situation in which the energy transferred adiabatically between the cooling liquid and the vaporising liquid fractions is at its maximum. This leads to a minimum content of energy in the remaining liquid. Although these two approaches are equivalent—the procedures based on the thermodynamic stability approach use also the minimum energy state as a criterion—the new proposed method only uses the properties of the substance to obtain T_sl−E. Thus, T_sl−E represents the behaviour of each substance as a function of its molecular structure, while this influence is lost if a simple equation of state is used. Finally, some considerations are made on the limitations of the superheat limit temperature as a criterion for establishing whether an explosion is or is not a BLEVE.     

汽车爆炸的超压分布规律实验研究

测试了不同药量和不同车型的爆炸超压值,对汽车爆炸的超压分布规律进行了实验研究.结果表明,小汽车内发生炸药爆炸时,车门侧压力明显大于车尾部方向的压力,车外的冲击波超压值要大于空气中炸药爆炸的结果,前者约为后者的1.0～2.2倍.即车体对冲击波约束作用要小于车内底盘的反射作用.计算得到了实验中冲击波超压对人员的杀伤半径和最小安全距离,对汽车爆炸案件具有一定指导作用.冲击波的反射不可忽视,货车下地面炸药爆炸表现出明显的冲击波反射作用,测得超压值大于空气中爆炸的超压值.     

A closer look at the effects of subordinate–supervisor age differences

Relational demography research has emphasized a similarity–attraction paradigm in explaining employees' reactions to demographic differences from other organizational members. This study examined similarity–attraction (nondirectional age differences) and status incongruence (directional age differences) predictions of age difference effects. The nondirectional and directional differences between the age of a subordinate and the ages of his or her immediate and higher‐level supervisors were used to predict employee absenteeism, citizenship, and work change behaviors. Results revealed that there were more significant and marginally significant directional age difference effects than nondirectional age difference effects on work outcomes. The implications of these results for organizations are discussed. Copyright © 1999 John Wiley & Sons, Ltd.     

Influence of laneway support spacing on methane/air explosion shock wave

A laneway support system provides an available way to solve problems related to ground movements in underground coal mines, but also poses another potential hazard. Once a methane/air explosion occurs in a laneway, inappropriate design parameters of the support system, especially the support spacing, likely have a negative influence on explosion disaster effects. The commercial software package AutoReaGas, a computational fluid dynamics code suitable for gas explosions, was used to carry out the numerical investigation for the methane/air explosion and blast process in a straight laneway with different support spacing. The validity of the numerical method was verified by the methane/air explosion experiment in a steel tube. Laneway supports can promote the development of turbulence and explosion, and also inhibit the propagation of flame and shock wave. For the design parameters in actual laneway projects, the fluid dynamic drag due to the laneway support plays a predominant role in a methane/air explosion. There is an uneven distribution of the peak overpressure on the same cross section in the laneway, and the largest overpressure is near the laneway walls. Different support spacing can cause obvious differences for the distributions of the shock wave overpressure and impulse. Under comparable conditions, the greater destructive effects of explosion shock wave are seen for the laneway support system with larger spacing. The results presented in this work provide a theoretical basis for the optimized design of the support system in coal laneways and the related safety assessments.     

Attenuation of a point blast shock wave in the dusty air

The behavior of the blast impulse initiated by a point blast in the dusty air is investigated theoretically. It is shown that the jumps of parameters at the shock front in the dusty air follow other regularities in comparison with the case of an ideal gas, beginning from the distance of three dynamic radii, so at ten dynamic radii the difference in overpressure exceeds 60%. When the air heterogeneity is taken into account, substantial gradual changes of wave profile come over and the total blast wave impulse can't be determined by the front overpressure only. The known far asymptotic law takes no place in the point blast flow at the volume dust densities ρ₂₀ > 3·10^?3 kg/m³. In contrast to the ideal gas, the shock front discontinuity vanishes in the dusty air at a finite distance from its origin and the blast wave eventually turns into a dispersive wave without discontinuity. The wave structure changing is studied in the process of the shock wave transformation into the dispersive wave.     

Impact of a shock wave on a structure on explosion at altitude

The number of explosive attacks on civilian buildings has recently increased and the pattern of damage inflicted on structures when an explosion takes place at altitude remains quite difficult to predict. The primary aim of the work reported here was to enhance the understanding of how blast waves from an explosion at altitude interact with the ground and with a structure. Small-scale experiments were conducted using a propane–oxygen stoichiometric mixture as explosive. This approach is original because it models high-explosive detonation in terms of gaseous charge explosion using TNT equivalents. Several non-dimensional laws are expressed and validated by experiments. These relationships allow determination of the propagation of a blast wave and its interaction with a structure as a function of the position of the explosive charge when the explosion occurs at altitude. Then, from knowledge of the blast loading, using Hopkinson's scaling law and TNT equivalents, we can predict the interaction of blast waves with the ground and a structure on a real scale. Simulations were performed using the Autodyn code, and good correlation with the experimental results was obtained.     

A study of the blast wave shape from elongated VCEs

Elongated congestion patterns are common at chemical processing and petroleum refining facilities due to the arrangement of processing units. The accidental vapor cloud explosion (VCE) which occurred at the Buncefield, UK facility involved an elongated congested volume formed by the trees and undergrowth along the site boundary. Although elongated congested volumes are common, there have been few evaluations reported for the blast loads produced by elongated VCEs. Standard VCE blast load prediction techniques do not directly consider the impact of this congested volume geometry versus a more compact geometry.This paper discusses an evaluation performed to characterize the blast loads from elongated VCEs and to identify some significant differences in the resulting blast wave shape versus those predicted by well-known VCE blast load methodologies (e.g., BST and TNO MEM). The standard blast curves are based on an assumption that the portion of the flammable gas cloud participating in the VCE is hemispherical and located at grade level. The results of this evaluation showed that the blast wave shape for an elongated VCE in the near-field along the long-axis direction is similar to that for an acoustic wave generated in hemispherical VCEs with a low flame speed. Like an acoustic wave, an elongated VCE blast wave has a very quick transition from the positive phase peak pressure to the negative phase peak pressure, relative to the positive phase duration. The magnitude of the applied negative pressure on a building face depends strongly on the transition time between the positive and negative phase peak pressures, and this applied negative phase can be important to structural response under certain conditions. The main purpose of this evaluation was to extend previous work in order to investigate how an elongated VCE geometry impacts the resultant blast wave shape in the near-field. The influence of the normalized flame travel distance and the flame speed on the blast wave shape was examined. Deflagration and deflagration-to-detonation transition regimes were also identified for unconfined elongated VCEs as a function of the normalized flame travel distance and flame speed attained at a specified flame travel distance.     

Who's not driving among U.S. high school seniors: A closer look at race/ethnicity,socioeconomic factors,and driving status

Objectives: We examined associations among race/ethnicity, socioeconomic factors, and driving status in a nationally representative sample of >26,000 U.S. high school seniors.

Methods: Weighted data from the 2012 and 2013 Monitoring the Future surveys were combined and analyzed. We imputed missing values using fully conditional specification multiple imputation methods. Multivariate logistic regression modeling was conducted to explore associations among race/ethnicity, socioeconomic factors, and driving status, while accounting for selected student behaviors and location. Lastly, odds ratios were converted to prevalence ratios.

Results: 23% of high school seniors did not drive during an average week; 14% of white students were nondrivers compared to 40% of black students. Multivariate analysis revealed that minority students were 1.8 to 2.5 times more likely to be nondrivers than their white counterparts, and students who had no earned income were 2.8 times more likely to be nondrivers than those earning an average of ≥$36 a week. Driving status also varied considerably by student academic performance, number of parents in the household, parental education, census region, and urbanicity.

Conclusions: Our findings suggest that resources—both financial and time—influence when or whether a teen will learn to drive. Many young people from minority or lower socioeconomic families who learn to drive may be doing so after their 18th birthday and therefore would not take advantage of the safety benefits provided by graduated driver licensing. Innovative approaches may be needed to improve safety for these young novice drivers.     

爆炸空气冲击波在巷道转弯处的传播特性

为了探索爆炸空气冲击波在巷道内的传播规律,进行了数值计算和理论分析,讨论了爆炸冲击波通过45°弯曲巷道后的压力变化过程.研究结果表明: 爆炸空气冲击波通过45°弯曲巷道后的压力分布复杂,空气冲击波逐渐恢复为平面波需经过4倍等效巷道直径的距离传播.在该4倍等效距离内,冲击波反射叠加,在巷道外侧壁面Mach反射点取得超压最大值,恢复平面波以后超压随距离呈单调衰减.     

A numerical study of the evolution of the blast wave shape in rectangular tunnels

When the explosion of condensed materials occurs in square or circular cross-section tunnel, the subsequent blast wave reveals two patterns: three-dimensional close to the explosive charge and one-dimensional far from the explosion. Pressure decays for these two patterns have been thoroughly studied. However, when the explosion occurs in rectangular cross-section tunnel, which is the most regular geometry for underground networks, the blast wave exhibits a third, two-dimensional, patterns. In order to assess the range of these three patterns, several numerical simulation of blast waves were carried out varying the width and the height of the rectangular cross-section as well as the mass of the charge. Laws are presented to localize the transition zones between the 3D and the 2D patterns, and between the 2D and the 1D patterns, as functions of non-dimensional width and height. The numerical results of the overpressure are compared to existing 3D and 1D laws. An overpressure decay law is proposed to represent the 2D pattern. Knowing the two transition zones and the overpressure decays within these zones, an algorithm is presented to efficiently predict an overpressure map. This algorithm is validated by comparison with experimental data.     

深孔爆破孔底充填缓冲吸能材料减震试验研究

通过对影响爆破震波各种主要因素的分析,针对深孔爆破采用孔底装填吸能缓冲材料,来削减炸药爆炸在孔底的冲击压力和吸收部分能量,从而达到降低爆破震动对周边建(构)物影响的目的。并进行现场爆破试验,对爆破震动波进行测试,同时对减震爆破装药和非减震的常规爆破装药进行比较,获得的测试数据证明,采用孔底装填吸能缓冲材料其减震率达到3.23%～35.19%。     

非燃烧区瓦斯爆炸冲击波在单向分岔管道内传播规律的试验研究

在空间上瓦斯爆炸可以分为瓦斯燃烧区、非瓦斯燃烧区两个区域.在瓦斯燃烧区内冲击波和火焰是相互耦合的;当瓦斯燃烧完毕后燃烧波消失,只剩非瓦斯燃烧区冲击波,冲击波失去能量支持,最终恢复至正常大气参数.为了研究非燃烧区内瓦斯爆炸冲击波在分岔管道中的传播特性,搭建了截面为80 mm× 80 mm的方形管道,分别由1 m、1.5m、2.5 m、3m、4m等5种长度不等的管道组合而成.管道由3个部分组成,前端为直管道瓦斯填充区,中间管道为空气直管道和管道末端,末端设计了30°、45°、60°、90°四种单向分岔角度.通过瓦斯填充量和管道分岔角度两个变量,采用TST6300动态数据采集储存仪,对管道内瓦斯爆炸冲击波能量及冲击波在单向分岔情况下超压分流情况进行试验研究.结果表明,管道单向分岔条件下,非燃烧区瓦斯爆炸冲击波分流系数与冲击波初始超压及管道分岔角度有关,分流系数随冲击波初始超压及分岔角度的增加而增加.     

A new look at the psychological contract during organizational socialization: The role of newcomers' obligations at entry

Previous studies have demonstrated that the psychological contract is largely shaped during socialization. This study adopts a complementary perspective and analyzes how the psychological contract at the start of employment shapes the subsequent socialization process. Drawing upon social exchange theory, we propose that newcomers with a higher sense of their personal obligations at entry will perceive orientation training as more useful and develop better relationships with their supervisors and peers, which in turn will facilitate their work adjustment. Results of a longitudinal survey on a sample of 144 recruits from a European Army show that newcomers with a higher initial sense of their employee obligations toward their employer report higher perceived training utility, higher leader–member exchange (LMX) with their instructors, and higher team–member exchange (TMX) with their platoon peers. Moreover, perceived training utility and LMX predict the fulfillment of employers' obligations; and training utility predicts the level of newcomers' employee obligations. Finally, training utility, LMX, and TMX predict some of three indicators of newcomers' adjustment, namely, role clarity (training utility and LMX), group integration (TMX), and organizational values understanding (training utility). These results highlight how newcomers' obligations at the start of employment contribute to the social exchange dynamic underlying organizational socialization. Copyright © 2015 John Wiley & Sons, Ltd.     

Hardworking coworkers: A multilevel cross‐national look at group work hours and work–family conflict

This study investigates the relationship between coworker work hours and perceived work‐to‐family conflict (WFC) in a multinational sample of professional service employees. Building on recent research on the ways in which workgroups influence individual WFC, we demonstrate that the average hours worked by coworkers has a significant relationship to reported WFC independent of an employee's own work hours. Although this finding is universal across the multinational sample, national cultural differences were found to moderate the relationship, such that employees in more collectivist countries are more strongly influenced by average coworker hours than their counterparts in less collectivist countries. The multilevel analysis was conducted using a sample of 7,600 professional service employees in 497 different workgroups across 20 countries. The results provide support for the effect of culture on the relationship between group average hours and perceptions of WFC. We conclude with a discussion of how national culture affects WFC.