Risk analysis based research and application of land use planning

涉及易燃易爆、有毒有害危险品的工业设施或重大工程,一旦发生火灾、爆炸、毒物泄漏等事故,往往波及很大范围,造成大量人员伤亡和财产损失。若事故发生在城市区域或人员聚集区,造成的后果更加严重。 因此,有必要在风险分析的基础上对（ⅰ）工业设施或重大工程的选址,（ⅱ）选址周边土地利用,如哪些区域可做居民区,哪些区域需要限制人口密度等进行合理规划,从而平衡土地效用和风险之间的关系,既使土地得到最大限度的应用,又不会导致城市公共安全的重大风险。 借鉴欧洲国家在土地利用规划方面的先进经验,本文对 （ⅰ）基于风险指数RI的选址评价方法 （ⅱ）基于后果发生概率的土地利用规划方法 （ⅲ）基于个人风险的土地利用规划方法 进行研究,确定每种方法的框架和程序,并应用于某拟建LNG储备库的选址及其周边土地利用的规划。 首先,确定选址处的风险指数RI,在不改变周围土地利用现状的情况下,选址风险偏大。因此,需对选址周围的土地利用做出相应调整。 其次,分别应用基于后果发生概率和基于个人风险的土地利用规划方法制定土地利用调整方案。基于后果发生概率的方法则以人员死亡概率为1%时及不可逆健康效应的概率为50％时对应的距离为阈值划分风险区域,并给出调整建议;而基于个人风险的方法以个人风险10-5、10-6、3×10-7对应的距离为阈值划分风险区域,根据各区域的功能规定制定土地利用调整方案。两种方法划分风险区域的依据不同,但结果一致,LNG储备库附近有两处居民区和一个工厂需要搬迁。 以上三种方法在合理确定工业设施、重大工程选址及周边建筑与设施的布局上是行之有效的方法。     

区域定量风险评价方法及其在城市重大危险源安全规划中的应用

介绍了区域定量风险评价的基本原理和评价指标，建立了基于网格差分的风险计算模型，给出了定量风险评价的程序，开发了个人风险的计算软件，提出了区域定量风险评价方法，并在某油气库区风险评价与安全规划中实际应用。通过分析计算，给出了该区域的个人风险等值线分布图和社会风险（F-N）曲线。结果表明，由于该地区液化石油气储量大，事故后果严重，且库区离居民区较近，周边企业较多，人口密集，使得个人风险和社会风险均超出了推荐标准的要求。该方法为进行城市重大危险源的安全规划提供了基础理论和技术方法，对进行城市土地使用及其他灾害领     

天然气储罐蒸气云爆炸事故个人风险分析

采用TNT当量法计算天然气储罐蒸气云爆炸形成的冲击波超压,运用人体脆弱性模型计算死亡概率,得到了天然气储罐的个人风险模型。根据《危险化学品生产、储存装置个人可接受风险和社会可接受风险基准(征求意见稿)》所规定的个人风险可接受水平,结合实例,确定了安全距离,可为安全规划及防护措施的制定提供科学依据。     

液化石油气泄漏的危险性分析及其事故后果评价方法

液化石油气（LPG）在其运输和存储过程中存在着各种与火灾和爆炸相关的危险性。由于LPG的泄漏可能导致包括闪火，不可控蒸气云爆炸，沸腾液体膨胀蒸汽爆炸等一系列灾害的发生，针对上述的各种灾害的具体发生条件及其危险性进行了分析；在事故后果评价中采用量化风险分析，提出了沸腾液体膨胀蒸汽爆炸和不可控蒸气云爆炸对周围人员可能造成伤害的评价方法。     

民用爆炸物品安全生产可接受风险研究

可接受风险标准是民用爆炸物品安全生产风险评价的评判准则。WJ9048—2010《民用爆炸物品行业安全评价导则》基于事故发生周期,划分了民爆行业和企业事故概率等级,并将企业事故概率作为风险评价的可接受风险标准,该准则仅适用于现场作业人员。基于公众视角,界定可接受风险标准是民用爆炸物品安全生产风险评价的关键组成部分。总结了国内外安全生产可接受风险标准研究现状,介绍了安全生产可接受风险确定准则和计算方法,结合国内民爆安全生产形势、危险场所区域分布和风险评价特点,在参考国内外事故死亡率和可接受风险标准的基础上,建议了民用爆炸物品安全生产风险评价的个人和社会可接受风险标准。     

LNG容器蒸气膨胀爆炸特性研究

对液化天然气容器机械破损后的液体过热汽化建立了非平衡相变模型.根据非平衡相变理论,讨论了蒸气膨胀爆炸的过减压极限,并按照气泡半径是否超过临界半径,把气泡的增长分成了束缚和逃逸两个时区,分时区讨论了系统各物理量的变化.通过对液化天然气典型储运工况的计算,得出了不同条件下的过减压极限、压力下降及反弹演化过程,状态参量核化速率的变化过程及最大超压.分析了蒸气膨胀爆炸的基本特性:快速显著核化和沸腾延迟,以及初始条件、损口面积和容器尺度等对物理过程的影响.     

公路事故风险动态预警检测设备布局的优化方法

针对现有公路事故风险动态预警检测设备布局方案无法满足当前道路承载力条件和降低交通事故发生频率的问题,本文进行公路事故风险动态预警检测设备布局优化方案研究。通过公路事故风险动态预警路段划分、构建初始检测点集、基于AHP的设备布局节点重要度评估,实现公路事故风险动态预警检测设备初始点位集构建与重要度计算方法。通过建立检测设备多目标优化布局模型、基于模拟退火算法的布局优化求解,提出一种新的优化方法。将该方法应用于实际可以有效提升道路承载能力,并减少甚至避免交通事故发生。     

盐岩能源地下储备库群风险综合评价与管理体系

利用盐岩洞穴进行能源地下储备是我国能源储备的重点战略部署方向。我国盐岩地层埋深浅,呈层状分布,且夹层较多,地质条件相对复杂,增加储库灾变的可能性,因此建立一套盐岩能源地下储备库群风险综合评价和管理体系尤显重要。根据盐岩地下储库群灾变事故的统计结果,获取了盐岩地下储库的主要风险因子,对库群风险进行了辨识。建立了盐岩地下库群风险评价方法和风险分级标准,通过数值模拟方法对失效概率进行了核算,评价了金坛盐岩库群风险等级,并通过模型试验对结果进行了验证,开发了基于计算机网络技术的盐岩地下库群风险信息管理与评估系统,建立了盐岩能源地下储备库群风险综合评价和管理体系。     

LNG储备库风险评价研究

LNG储备库进行风险评价首先要进行风险源的辨识,主要包括第一类风险源(例如LNG本身可能出现的冻伤、火灾、爆炸、膨胀等风险)和第二类风险源(例如LNG储备库的环境因素、机械因素等可能引起的风险)两种,寻找到风险因素后,根据模糊理论,利用模糊积分法将LNG储备库的风险水平加以量化,这是运用模糊数学理论进行风险评价的一种方法。另外,通过模糊积分的方法对LNG储备库中的各个危险因素进行评价,对于具有较大潜在危险性的单元重点突出,从而实现系统化评估LNG储备库风险的目的。     

天然气爆炸效应及应用探讨

为防止天然气"井喷"发生蒸气云爆炸造成的伤害,运用TNT当量法估算爆源总能量,按爆炸冲击波超压值对爆炸伤害进行分区,经计算给出各分区的半径,认为天然气钻井中的最小安全距离为230 m.     

A simplified model to predict the thermal response of PLG and its influence on BLEVE

A simplified model has been developed to describe the thermal response of pressure liquefied gas (PLG) tanks subjected to fire. The development of the stratification layer is considered in this model. Comparison of results with available experimental data shows that our proposed model can reasonably predict the thermal response. The effect of stratification on the liquid energy is also summarized. Results show that the pressure in the tank rises faster as a result of thermal stratification, and for the same tank pressure the energy in the liquid is less when the liquid is stratified. Stratification can reduce the severity of hazards of boiling liquid expanding vapor explosion (BLEVE).     

Metallurgical failure analysis of a propane tank boiling liquid expanding vapor explosion (BLEVE)

A severe fire and explosion occurred at a propane storage yard in Truth or Consequences, N.M., when a truck ran into the pumping and plumbing system beneath a large propane tank. The storage tank emptied when the liquid-phase excess flow valve tore out of the tank. The ensuing fire engulfed several propane delivery trucks, causing one of them to explode. A series of elevated-temperature stress-rupture tears developed along the top of a 9800 L (2600 gal) truck-mounted tank as it was heated by the fire. Unstable fracture then occurred suddenly along the length of the tank and around both end caps, along the girth welds connecting the end caps to the center portion of the tank. The remaining contents of the tank were suddenly released, aerosolized, and combusted, creating a powerful boiling liquid expanding vapor explosion (BLEVE). Based on metallography of the tank pieces, the approximate tank temperature at the onset of the BLEVE was determined. Metallurgical analysis of the ruptured tank also permitted several hypotheses regarding BLEVE mechanisms to be evaluated. Suggestions are made for additional work that could provide improved predictive capabilities regarding BLEVEs and for methods to decrease the susceptibility of propane tanks to BLEVEs.     

Boiling liquid expanding vapor explosion: experimental research in the evolution of the two-phase flow and over-pressure

In a boiling liquid expanding vapor explosion (BLEVE), the superheating and boiling of the liquefied gas inside the vessel as it fails is important information necessary to understand the mechanism of this type of disaster. In this paper, a small-scale experiment was developed to investigate the possible processes that could lead to a BLEVE. Water was used as the test fluid. High-speed video was utilized to observe the two-phase flow swelling which occurred immediately following the partial loss of containment through a simulated crack. The velocity of the two-phase swelling was measured along with pressure and temperature. It was observed that initially a mist-like two-phase layer was rapidly formed on the liquid surface (~3-4 ms) after the vessel opened. The superheated liquid rapidly boiled and this accelerated upwards the two-phase layer, the whole liquid boiled after about 17 ms form opening. It was supposed that the swelling of the two-phase layer was the possible reason for the first over-pressure measured at the top and bottom of the vessel. From 38 ms to 168 ms, the boiling of the superheated liquid weakened. And from 170 ms, the original drop/mist-like two-phase flow turned into a churn-turbulent bubbly two-phase flow, rose quickly in the field of the camera and eventually impacted the vessel top wall. The force of its impact and "cavitation" and "choke" following with the two-phase ejection were maybe main reasons for the second obvious pressure increasing.     

Dust explosions-cases, causes, consequences, and control

Dust explosions pose the most serious and widespread of explosion hazards in the process industry alongside vapour cloud explosions (VCE) and boiling liquid expanding vapour explosions (BLEVE). Dust explosions almost always lead to serious financial losses in terms of damage to facilities and down time. They also often cause serious injuries to personnel, and fatalities. We present the gist of the dust explosion state-of-the-art. Illustrative case studies and past accident analyses reflect the high frequency, geographic spread, and damage potential of dust explosions across the world. The sources and triggers of dust explosions, and the measures with which different factors associated with dust explosions can be quantified are reviewed alongside dust explosion mechanism. The rest of the review is focused on the ways available to prevent dust explosion, and on cushioning the impact of a dust explosion by venting when the accident does take place.     

The boiling liquid expanding vapour explosion (BLEVE): mechanism, consequence assessment, management

Among the most devastating of accidents likely in chemical process industry is the boiling liquid expanding vapour explosion (BLEVE). It is accompanied by highly destructive blast waves and missiles. In most situations there is also a fireball or a toxic gas cloud. The damaging effect of BLEVEs is reflected in the fact that the 80-odd major BLEVEs that have occurred between 1940 and 2005 have claimed over a 1000 lives and have injured over 10,000 persons besides harming property worth billions of dollars. Release of toxic chemicals like chlorine and phosgene from BLEVEs have damaged large chunks of areas surrounding the BLEVE site. This paper presents an overview of the mechanism, the causes, the consequences, and the preventive strategies associated with BLEVEs.     

A risk-based approach to flammable gas detector spacing

Flammable gas detectors allow an operating company to address leaks before they become serious, by automatically alarming and by initiating isolation and safe venting. Without effective gas detection, there is very limited defense against a flammable gas leak developing into a fire or explosion that could cause loss of life or escalate to cascading failures of nearby vessels, piping, and equipment. While it is commonly recognized that some gas detectors are needed in a process plant containing flammable gas or volatile liquids, there is usually a question of how many are needed. The areas that need protection can be determined by dispersion modeling from potential leak sites. Within the areas that must be protected, the spacing of detectors (or alternatively, number of detectors) should be based on risk. Detector design can be characterized by spacing criteria, which is convenient for design - or alternatively by number of detectors, which is convenient for cost reporting. The factors that influence the risk are site-specific, including process conditions, chemical composition, number of potential leak sites, piping design standards, arrangement of plant equipment and structures, design of isolation and depressurization systems, and frequency of detector testing. Site-specific factors such as those just mentioned affect the size of flammable gas cloud that must be detected (within a specified probability) by the gas detection system. A probability of detection must be specified that gives a design with a tolerable risk of fires and explosions. To determine the optimum spacing of detectors, it is important to consider the probability that a detector will fail at some time and be inoperative until replaced or repaired. A cost-effective approach is based on the combined risk from a representative selection of leakage scenarios, rather than a worst-case evaluation. This means that probability and severity of leak consequences must be evaluated together. In marine and offshore facilities, it is conventional to use computational fluid dynamics (CFD) modeling to determine the size of a flammable cloud that would result from a specific leak scenario. Simpler modeling methods can be used, but the results are not very accurate in the region near the release, especially where flow obstructions are present. The results from CFD analyses on several leak scenarios can be plotted to determine the size of a flammable cloud that could result in an explosion that would generate overpressure exceeding the strength of the mechanical design of the plant. A cloud of this size has the potential to produce a blast pressure or flying debris capable of causing a fatality or subsequent damage to vessels or piping containing hazardous material. In cases where the leak results in a fire, rather than explosion, CFD or other modeling methods can estimate the size of a leak that would cause a fire resulting in subsequent damage to the facility, or would prevent the safe escape of personnel. The gas detector system must be capable of detecting a gas release or vapor cloud, and initiating action to prevent the leak from reaching a size that could cause injury or severe damage upon ignition.     

Explosion caused by flashing liquid in a process vessel

An explosion occurred at a polyvinyl chloride (PVC) resin manufacturing plant. The explosion originated at an atmospheric storage vessel when it received a slurry discharge from a suspension polymerization reactor. The pressure rise caused by the uncontrolled flashing of superheated liquid vinyl chloride resulted in the complete separation of the roof from the tank shell. A cloud of vinyl chloride vapor was released and ignited resulting in a vapor cloud explosion. The accident caused significant property damage but no serious injuries. An investigation was conducted to determine the causes of the accident. It was discovered that the facility had experienced numerous overpressure incidents in the atmospheric storage vessels used as slurry tanks. Many of these incidents resulted in modest structural damage to these slurry tanks. It was determined by Exponent that the rapid flashing of residual liquid monomer present in the product slurry stream caused the earlier overpressure incidents. The facility operator did not adequately investigate or document these prior overpressure events nor did it communicate their findings to the operating personnel. Thus, the hazard of flashing liquid vinyl chloride was not recognized. The overpressure protection for the slurry tanks was based on a combination of a venting system and a safety instrumentation system (SIS). The investigation determined that neither the venting system nor the SIS was adequate to protect the slurry tank from the worst credible overpressure scenario. Fundamentally, this is because the performance objectives of the venting system and SIS were not clearly defined and did not protect against the worst credible overpressure scenario. The lessons learned from this accident include: use prior incident data for recognizing process hazards; identify targets vulnerable to these hazards; explicitly define performance objectives for safeguards to protect against the worst credible overpressure scenario. The ultimate lesson learned here is that a liquid trapped under pressure above its normal boiling point represents an overpressure hazard. To avoid exceeding the design pressure of the receiving vessel, the superheated liquid must be discharged slowly so that the vapor production rate caused by flashing does not exceed the venting rate of the receiving vessel.     

Bubble spreading during the boiling crisis: modelling and experimenting in microgravity

Boiling is a very efficient way to transfer heat from a heater to the liquid carrier. We discuss the boiling crisis, a transition between two regimes of boiling: nucleate and film boiling. The boiling crisis results in a sharp decrease in the heat transfer rate, which can cause a major accident in industrial heat exchangers. In this communication, we present a physical model of the boiling crisis based on the vapor recoil effect. Under the action of the vapor recoil the gas bubbles begin to spread over the heater thus forming a germ for the vapor film. The vapor recoil force not only causes its spreading, it also creates a strong adhesion to the heater that prevents the bubble departure, thus favoring the further spreading. Near the liquid-gas critical point, the bubble growth is very slow and allows the kinetics of the bubble spreading to be observed. Since the surface tension is very small in this regime, only microgravity conditions can preserve a convex bubble shape. In the experiments both in the Mir space station and in the magnetic levitation facility, we directly observed an increase of the apparent contact angle and spreading of the dry spot under the bubble. Numerical simulations of the thermally controlled bubble growth show this vapor recoil effect too thus confirming our model of the boiling crisis.     

A possible mechanism of triggering a vapor explosion

Relations are derived which enable one to assess the size of fragments of a liquid-metal droplet after its fragmentation formed in the case of instantaneous contact between a hot metal surface and a coolant. The obtained experimental data demonstrate that the amplitude of pressure pulses generated during vapor film collapse (second boiling crisis) is several times lower than the values required for triggering a spontaneous vapor explosion. The assumption is validated according to which progress in studying the process of triggering a spontaneous vapor explosion is associated primarily with advances in understanding the mechanism of fragmentation of individual droplet.