Chamberlain Samuel, Modarres Mohammad
Center for Technology Risk Studies, University of Maryland, 2100 Marie Mount Hall, College Park, MD 20742, USA.
Risk Anal. 2005 Apr;25(2):377-87. doi: 10.1111/j.1539-6924.2005.00596.x.
This study assesses the fire safety risks associated with compressed natural gas (CNG) vehicle systems, comprising primarily a typical school bus and supporting fuel infrastructure. The study determines the sensitivity of the results to variations in component failure rates and consequences of fire events. The components and subsystems that contribute most to fire safety risk are determined. Finally, the results are compared to fire risks of the present generation of diesel-fueled school buses. Direct computation of the safety risks associated with diesel-powered vehicles is possible because these are mature technologies for which historical performance data are available. Because of limited experience, fatal accident data for CNG bus fleets are minimal. Therefore, this study uses the probabilistic risk assessment (PRA) approach to model and predict fire safety risk of CNG buses. Generic failure data, engineering judgments, and assumptions are used in this study. This study predicts the mean fire fatality risk for typical CNG buses as approximately 0.23 fatalities per 100-million miles for all people involved, including bus passengers. The study estimates mean values of 0.16 fatalities per 100-million miles for bus passengers only. Based on historical data, diesel school bus mean fire fatality risk is 0.091 and 0.0007 per 100-million miles for all people and bus passengers, respectively. One can therefore conclude that CNG buses are more prone to fire fatality risk by 2.5 times that of diesel buses, with the bus passengers being more at risk by over two orders of magnitude. The study estimates a mean fire risk frequency of 2.2 x 10(-5) fatalities/bus per year. The 5% and 95% uncertainty bounds are 9.1 x 10(-6) and 4.0 x 10(-5), respectively. The risk result was found to be affected most by failure rates of pressure relief valves, CNG cylinders, and fuel piping.
本研究评估了与压缩天然气（CNG）车辆系统相关的消防安全风险，该系统主要包括一辆典型的校车及配套的燃料基础设施。研究确定了结果对部件故障率变化和火灾事件后果的敏感性。确定了对消防安全风险贡献最大的部件和子系统。最后，将结果与当代柴油校车的火灾风险进行比较。由于柴油动力车辆是成熟技术且有历史性能数据，因此可以直接计算其相关安全风险。由于经验有限，CNG公交车队的致命事故数据极少。因此，本研究采用概率风险评估（PRA）方法来建模和预测CNG公交车的消防安全风险。本研究使用了通用故障数据、工程判断和假设。本研究预测，典型CNG公交车的平均火灾死亡风险约为每1亿英里0.23人死亡，涉及的所有人包括公交车乘客。该研究估计仅公交车乘客的平均死亡风险为每1亿英里0.16人死亡。根据历史数据，柴油校车的平均火灾死亡风险分别为每1亿英里0.091人和0.0007人死亡，涉及的所有人和公交车乘客。因此可以得出结论，CNG公交车发生火灾死亡风险的可能性是柴油公交车的2.5倍，公交车乘客面临的风险高出两个数量级以上。该研究估计平均火灾风险频率为每年每辆公交车2.2×10^(-5)人死亡。5%和95%的不确定性界限分别为9.1×10^(-6)和4.0×10^(-5)。研究发现风险结果受泄压阀、CNG气瓶和燃料管道故障率的影响最大。
