Lessons after Bhopal: CSB a catalyst for change

The Bhopal tragedy was a defining moment in the history of the chemical industry. On December 3, 1984, a runaway reaction within a methyl isocyanate storage tank at the Union Carbide India Limited pesticide plant released a toxic gas cloud that killed thousands and injured hundreds of thousands. After Bhopal, industrial chemical plants became a major public concern. Both the public and the chemical industry realized the necessity of improving chemical process safety.

Bhopal served as a wake-up call. To prevent the same event from occurring in the United States, many legislative and industrial changes were invoked—one of which was formation of the U.S. Chemical Safety and Hazard Investigation Board (CSB). The ultimate goal of CSB is to use the lessons learned and recommendations from its investigations to achieve positive change within the chemical industry—preventing incidents and saving lives.

Although it seems clear that the lessons learned at Bhopal have improved chemical plant safety, CSB investigations indicate that the systemic problems identified at Bhopal remain the underlying causes of many incidents. These include:

• Lack of awareness of reactive hazards.

• Lack of management of change.

• Inadequate plant design and maintenance.

• Ineffective employee training.

• Ineffective emergency preparedness and community notification.

• Lack of root cause incident investigations and communication of lessons learned.

The aim of this paper is to present common themes from recent cases investigated by CSB and to discuss how these issues might be best addressed in the future.

This paper has not been independently approved by the Board and is published for general informational purposes only. Any material in the paper that did not originate in a Board-approved report is solely the responsibility of the authors and does not represent an official finding, conclusion, or position of the Board.     

Bhopal and its effects on the Canadian regulatory framework

Instead of legislating after the Bhopal accident, Canada choose to innovate by adopting a consultative approach. In 1987, Environment Canada set up the Major Industrial Accidents Council of Canada (MIACC), a non profit organization financed by the federal and provincial governments and industry.

MIACC was a process rather than a structure. Governments, industries, responders, trade unions, NGOs, etc. have shared their expertise. It has worked as a partnership for the development of standards, guidance documents, etc. in prevention, preparedness, response and recovery.

MIACC ceased to exist in 1999. Although, MIACC disappearance is unfortunate, it is not dramatic. A culture of partnership, of working together towards common objectives, is now well in place and influences the development of regulations.

Natural disasters and the 911 terrorist attack on New York triggered the publication of regulations.

The legislative process started in 2001 with the Province of Quebec adopting a new Civil Protection Act for the protection of persons and property against disasters.

Year 2003 saw major developments in the regulation of emergencies—changes that are likely to have significant influences on how companies operate in Canada. Surprisingly, however, these changes have received little attention in the media, and many companies may not be aware of their implications.

This paper will review these developments, and will examine what has already taken place. Topics include:

• The federal regulation of environmental emergencies under the Canadian Environmental Protection Act;

• Extension of the Criminal Code of Canada to allow criminal charges and possibly heavy penalties for senior officials and corporations, including an explicit legal duty to protect workers from harm;

• Quebec Civil Protection Act designed to identify and manage risks;

• Ontario‘s stepwise regulation of municipal emergency preparedness with the intended goal of NFPA 1600 compliance by 2007, and the implications for the process industries;

• Potential regulation at the municipal level.

Effects of N2 and CO2 on the flammability of 2,3,3,3-tetrafluoropropene at elevated temperatures

The flammability characteristics of refrigerants are affected by environmental factors, making them prone to flammability and explosion accidents in cooling systems. In this paper, the flammability characteristics of R1234yf–air mixtures with N₂ and CO₂ were investigated comparatively at temperatures between 20 and 50 °C at 80% relative humidity. The lower and upper flammability limits of R1234yf were measured. The limiting oxygen concentration (LOC), critical flammable ratio (CFR), and critical flammable concentration (CFC) of the R1234yf–air mixtures with inert gases were investigated. The paper developed a linear formula between the flammability limit of R1234yf and the temperature. The changes in CFC with different temperatures were negligible for R1234yf. Furthermore, the mixed refrigerant had both non-flammability and the lowest vapor pressure when the CFR of the R1234yf/CO₂ mixture was 2.9. The experimental results were used to propose a new prediction model to estimate the flammability limits of R1234yf. Finally, molecular simulation explained the effect of inert gases on the flammability of R1234yf from a microscopic point of view. The research aimed to provide valid evidence and data for preventing flammable and explosive refrigerant incidents.     

Flammability envelopes for methanol,ethanol, acetonitrile and toluene

The flammability envelope was experimentally determined up to the point of vapor saturation for four flammable liquids: methanol, ethanol, acetonitrile, and toluene. The experimental apparatus consisted of a 20-L spherical chamber with a centrally located 10 J fuse wire igniter. The liquid was injected and vaporized into the chamber via a septum and a precision syringe. Nitrogen and oxygen were mixed from pure components using a precision pressure gauge. Pressure versus time data were measured for each ignition test. Flammability was defined as any ignition resulting in an increase in pressure of 7% over the initial pressure, as per ASTM E 918–83. All data were obtained at an initial temperature of 298 K and 1 atm. The experimental values of the LFL agreed well with published values. Limiting oxygen concentrations (LOC) were also determined—although these were somewhat lower than published values.The calculated adiabatic flame temperature (CAFT) method was used to model the data using a threshold temperature of 1200 K. A reasonable fit of the flammability envelope was obtained, although this could be improved with a higher threshold temperature.     

Disposal of hexachlorodisilane and its hydrolyzed deposits

Hexachlorodisilane (Si₂Cl₆, HCDS) is an important precursor used in semiconductor device manufacturing. It is a flammable as well as a water reactive liquid which hydrolyzes rapidly upon contact with water or moisture. The hydrolyzed deposits are also known to be shock-sensitive with explosion energy equivalent to trinitrotoluene (TNT). In this work, two phases of test program including disposal of HCDS and disposal of the shock sensitive HCDS hydrolyzed deposits were conducted. The first phase of the program was to find an agent that can completely dissolve/react the HCDS vapor without forming shock sensitive deposits. The second phase of the program attempted to find a suitable agent to suppress the Si–Si bonds, one of the essential roles of chemical functional groups in shock sensitivity of the HCDS hydrolyzed deposits to suppress the shock sensitivity. A variety of agents such as sulfuric acid solutions, aqueous sodium hydroxide (NaOH) solutions, aqueous potassium hydroxide (KOH) solutions, KOH/alcohol solutions were utilized as the suppressants in this work. Samples mixed with suppressants were not only tested for shock sensitivity by a Fall-hammer apparatus but also analyzed for chemical functional groups to identify the effect of each agent. Concentrated sulfuric acid was found to suppress the shock sensitivity of the liquid HCDS hydrolyzed deposits by acting as a medium that helps the hydrolyzed deposit to retain moisture. KOH/alcohol solutions can turn HCDS vapor into non-hazardous silica, so that, it provided a safe way to dispose HCDS. Finally, practical recommendations about handling and eliminating the risk of shock sensitivity are given for HCDS liquid spill, HCDS vapor vent and HCDS hydrolyzed deposits.     

Experimental studies of ignition and explosions in cyclohexane liquid under oxygen oxidation conditions

The safe operation of hydrocarbon liquid-phase oxidation by air or oxygen requires the knowledge on the flammability of hydrocarbon/oxygen mixtures in both the vapor space and vapor bubbles. The latter is of particular importance in situation where pure oxygen is used as the oxidant as most bubbles are expected to be flammable and explosive. New experimental findings are presented for ignition and explosion in cyclohexane liquid under oxygen oxidation conditions. A bubble column is constructed and fitted with multiple igniters. Experiments were performed at liquid temperatures between 373.15 and 423.15 K under various flow rates of pure oxygen. Two drastic different ignition and explosion behaviors were observed. The first is a typical bubble explosion from the direct ignition of the flammable bubbles in the liquid. The explosion occurs immediate following the ignition and do not produce significant energy that endanger the system. The other is a remote, delayed ignition and explosion in the vapor space that can produce significant overpressure and endanger the system. The explosion is attributed to the ignition of flammable vapor space by active free radicals from cyclohexyl hydroperoxide decomposition. A mechanism is proposed for the remote, delayed ignition to occur in the oxidation system. It is concluded that explosion in an oxidizing, bubbly liquid is not only a likely scenario but also a severe scenario, and cyclohexane oxidation should not be carried out directly with pure oxygen and without any inerting.     

Theoretical and experimental study of the inhibition and inert effect of HFC125, HFC227ea and HFC13I1 on the flammability of HFC32

HFC32 is a potential alternative refrigerant with excellent thermal performance, but the flammability is a main obstacle for its applications. The group contribution method is utilized to analyze the inhibition efficiency of nonflammable refrigerants in binary mixtures. Furthermore, a novel equation of predicting the minimum inerting concentration of nonflammable refrigerants has been proposed by analyzing the variation of the flame propagation velocity and the flammable refrigerant concentration. Experimental studies of the explosion limits of HFC125/HFC32, HFC227ea/HFC32 and HFC13I1/HFC32 were carried out and the ranges of explosion limits were obtained. At the same time, the relationship between the maximum charge of the flammable refrigerants and lower flammability limit (LFL) was analyzed. The result demonstrates that the proposed novel theoretical equation can effectively predict the minimum inerting concentration of nonflammable refrigerants to flammable refrigerants, and the theoretical results have significance on the security application of the binary mixtures.     

Prediction of flammability limits of fuel-air and fuel-air-inert mixtures from explosivity parameters in closed vessels

Flammability limits of fuel-air and fuel-air-inert gaseous mixtures, especially at non-atmospheric conditions, are essential properties required for establishing safety operating conditions for handling and processing flammable gases. For pure fuels, an important data pool exists, formed by the flammability limits of fuel-air and fuel-air-inert gaseous mixtures at ambient initial conditions measured by standard methods. Such methods can be used for experimental determination of flammability limits for multi-fuels mixed with air, with or without additives, under non-atmospheric conditions. Their use is however a time- and material-consuming process; in addition, the flammability limits obtained by various standard methods may be scattered as a result of different choices in the operating parameters, for each standard method. It appears that a preliminary estimation of the flammability limits for fuel-air and fuel-air-inert gaseous mixtures can minimize the effort of measuring them in specific initial conditions.The present paper describes a new method for estimating the flammability range of fuel-oxidizer gaseous mixtures based on measurements of explosivity properties e.g. the peak explosion pressure and maximum rate of pressure rise recorded during closed vessel laminar explosions of fuel-oxidizer mixtures far from limits. Data obtained for several hydrocarbon-air gaseous mixtures with or without inert gas addition are used to examine the accuracy of estimated flammability limits (LFL – the lower and UFL – the upper flammability limit) as well as of the Limiting Oxygen Concentration (LOC) and the Minimum Inert Concentration (MIC). The predictive ability of the proposed method is examined against the predictive ability of other recently described methods.     

低压下近熄灭极限区域纸火蔓延实验研究

对低压下的近熄灭极限区域水平纸火蔓延进行了实验研究。通过降低环境压力和氧气浓度,确定了水平纸火蔓延的着火极限,并得出了在极限氧气浓度条件下的火蔓延速度变化规律。在相同氧气浓度下(43%)进行了不同压力的水平纸火蔓延实验。结果表明,火蔓延速度在近熄灭极限区域内非线性增加,通过比较分析前人火蔓延速度实验结果,确定了火蔓延近熄灭极限区域和线性增长区域的分界压力值。此外,得出了压力分界处的火焰变化特征,并根据火焰图像与理论分析,得出了不同区域内的火蔓延传热机制。     

Dilution with air to minimise consequences of toxic/flammable gas releases

Dilution has long been considered a solution to many problems of toxic/flammable material releases. It implies diluting to a concentration that is below physiologically dangerous levels for a toxic substance (generally below TLV), or to a level below LFL for a flammable material release, ensuring that the process adopted for dilution does not itself enhance the risks.

In this paper, we discuss the dilution of a gaseous release by deliberate and cautious mixing with air to reduce its concentration to a harmless level. The idea bears its origin to the Bhopal Gas Tragedy where some families saved themselves by turning the ceiling fans on when MIC reached their bedrooms at the dead of very cold night on December 2–3, 1984. The air pushed in by the fans diluted the MIC to below the harm level.

Some of the advantages of using air dilution are: no cost of air, no air storage needed, no need to treat the air after use as in case of water curtains; required equipment, its maintenance and staff training in its use are very likely to cost less than in other ways of handling a release.

Air dilution may not be feasible in all cases, such as gaseous release within a congested equipment layout, release that forms a liquid pool, etc. The method needs to be evaluated for each case.     

The characterization of heat transfer fluid P-NF aerosol combustion: Ignitable region and flame development

Heat transfer fluids tend to form aerosols due to the operating conditions at high pressure when accidental leaking occurs in pipelines or storage vessels, which may cause serious fires and explosions. Due to the physical property complexity of aerosols, it is difficult to define a standard term of “flammability limits” as is possible for gases. The study discussed in this paper primarily focuses on the characterization of ignition conditions and flame development of heat transfer fluid aerosols. The flammable region of a widely-used commercial heat transfer fluid, Paratherm NF (P-NF), was analyzed by electro-spray generation with a laser diffraction particle analysis method. The aerosol ignition behavior depends on the droplet size and concentration of the aerosol. From the adjustment of differently applied electro-spray voltages (7–10 kV) and various liquid feeding rates, a flammable condition distribution was obtained by comparison of droplet size and concentration. An appropriate amount (0.3–1.2 ppm) of smaller droplets (80–110 μm) existing in a given space could result in successful flame formation, while larger droplets (up to 190 μm) have a relatively narrowed range of flammable conditions (0.7–0.9 ppm). It is possible to generate a more useful reference for industry and lab scale consideration when handling liquids. This paper provides initial flammability criteria for analyzing P-NF aerosol fire hazards in terms of droplet size and volumetric concentration, discusses the observation of aerosol combustion processes, and summarizes an ignition delay phenomenon. All of the fundamental study results are to be applied to practical cases with fire hazards analysis, pressurized liquid handling, and mitigation system design once there is a better understanding of aerosols formed by high-flash point materials.     

Study of the explosion parameters of vapor–liquid diethyl ether/air mixtures

The knowledge of the vapor–liquid two-phase diethyl ether (DEE)/air mixtures (mist) on the explosion parameters was an important basis of accident prevention. Two sets of vapor–liquid two-phase DEE/air mixtures of various concentrations were obtained with Sauter mean diameters of 12.89 and 22.90 μm. Experiments were conducted on vapor–liquid two-phase DEE/air mixtures of various concentrations at an ignition energy of 40.32 J and at an initial room temperature and pressure of 21 °C and 0.10 MPa, respectively. The effects of the concentration and particle size of DEE on the explosion pressure, the explosion temperature, and the lower and upper flammability limits were analyzed. Finally, a series of experiments was conducted on vapor–liquid two-phase DEE/air mixtures of various concentrations at various ignition energies. The minimum ignition energies were determined, and the results were discussed. The results were also compared against our previous work on the explosion characteristics of vapor–liquid two-phase n-hexane/air mixtures.     

二元混合液体闪点的计算

以混合溶液纯组分易燃液体闪点的饱和蒸气压为基础,应用乌拉尔定律、双液系的气-液相平衡理论,运用Le Chatelier方程和安托因方程导出二元混合液的闪点计算方法。并例举易燃液体与易燃液体组成的理想混合液、易燃液体与易燃液体组成的非理想混合液、易燃液体与不燃液体组成的非理想混合液的计算过程。乙醇溶液闪点的计算结果与现有的文献资料比较,误差在允许范围内。计算数据用Excel处理,快捷准确,用于确定二元混合液体的火灾危险性。     

圆柱形无约束气云爆炸高温效应研究

为了分析无约束可燃气云爆炸产生的高温伤害效应,建立了相应的数学模型,利用有限体积的离散方法,对无约束空间内甲烷浓度10％、高径比为1的圆柱形可燃气云爆炸的瞬态温度场进行了数值研究。研究结果表明,圆柱形可燃气云爆炸的温度场呈不对称性分布,靠近地面处足最危险区域,高温可能达到的最大怪直高度和最大水平距离分别约为圆柱体高的2倍和半径的3．2倍。对数值模拟结果的数据进行多项式拟合,得到了圆柱形可燃气云爆炸场最高温度随水平距离、初温及参与爆炸气云质量的函数关系式,给可燃气云爆炸灾害的预测及防护提供了科学依据。     

Flammability hazard analysis of imidazolium-based ionic liquid binary mixtures under high temperatures

Ionic liquid (IL) mixtures are promising because they can optimize the involved properties according to industrial needs. It has already been demonstrated that IL flammability is due mainly to IL decomposition generating flammable substances. Four different ILs, 1-Butylimidazolium tetrafluoroborate ([BIM][BF₄]), 1-butylimidazolium nitrate ([BIM][NO₃]), 1-butyl-3-methylimidazolium tetrafluoroborate([BMIM][BF₄]), and 1-butyl-3-methylimidazolium nitrate ([BMIM][NO₃]), were selected as the parent salts to form the different imidazolium-based IL binary mixtures. These mixtures were tested via isothermal thermogravimetric analyzer (TGA) at different temperatures (120, 150, 180, 210, and 240 °C), then tested by the flash point analyzer after isothermal heating pretreatment at the above temperatures. Results show that the mixtures' flash point values decrease with the heating temperature increase. Vaporization of the IL mixtures’ decomposition products results in a higher concentration of flammable gases and a flash point decrease, which lead to the flammability hazard increasing. Moreover, results show that the flash points of the studied binary imidazolium IL mixtures are more similar to those of the more unstable IL in their parent ILs. Also, the flammability hazard of IL binary mixtures may obviously increase under the high temperature environment for a long time.     

Study of the severity of hybrid mixture explosions and comparison to pure dust-air and vapour-air explosions

The explosion behaviour of heterogeneous/homogeneous fuel-air (hybrid) mixtures is here analysed and compared to the explosion features of heterogeneous fuel-air and homogeneous fuel-air mixtures separately.Experiments are performed to measure the pressure history, deflagration index and flammability limits of nicotinic acid/acetone-air mixtures in a standard 20 L Siwek bomb adapted to vapour-air mixtures. Literature data are also used for comparison.The explosion tests performed on gas-air mixtures in the same conditions as explosion tests of dust-air mixtures, show that the increase in explosion severity of dust/gas-air mixtures has to be addressed to the role of initial level of turbulence prior to ignition.At a fixed value of the equivalence ratio, by substituting the dust to the flammable gas in a dust/gas-air mixture the explosion severity decreases. Furthermore, the most severe conditions of dust-gas/air mixtures is found during explosion of gas-air mixture at stoichiometric concentration.     

R290制冷剂惰化燃爆特性实验研究

为了研究R290制冷剂惰化燃爆特性,采用带搅拌功能和氧浓度在线测定的20L球试验装置,对R290制冷剂进行了极限氧浓度测定。实验测定了丙烷在CO2和N2惰化气氛中的爆炸极限及极限空气浓度LAC,确定丙烷的极限氧浓度LOC;采用三元图爆炸区、丙烷-O2二维图爆炸区和ASTM标准分布图分析了混合气体爆炸区边界的燃爆特征,给出了极限氧浓度的确定方法和边界爆炸压力分布规律。实验结果表明:常温常压下R290的爆炸极限为2.1%～9.6%,CO2惰化气氛中的极限氧浓度为13.3%,对应的丙烷浓度为3.3%;N2惰化气氛中的极限氧浓度为10.8%,对应的丙烷浓度为2.7%。通过对比分析不同CO2和N2浓度下的爆炸区分布特征,表明CO2对丙烷的惰化效果要优于N2,以氮气和二氧化氮体积分数比为1∶2测试惰化气氛保护能力,惰化效果介于同浓度单种惰性气体之间。     

Comparing tools of varying complexity for calculating the gas dispersion

When handling flammable and/or toxic liquids or gases, the gas dispersion following a release of substance is a scenario to be considered in the risk assessment to determine the lower flammability distance (LFD) and toxicity thresholds. In this work a comparison of different gas dispersion tools of varying complexity ranging from a simple Gaussian model over a boundary layer model (BLM) and a Lagrangian model to CFD (in this case ANSYS CFX v14) is presented. The BLM covers the special case of liquid releases with formation of a pool. It does not only solve the gas dispersion but also calculates the evaporating mass flow out of the pool. The simulation values are compared to each other and to experimental data resulting mainly from our own open air experiments covering the near field and carried out on the Test Site Technical Safety of BAM (BAM-TTS) for different release types (pool evaporation, gas release) and topologies. Other validation data were taken from literature and cover large scale experiments in the range of several 100 m.