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Dependence of maximum concentration from chemical accidents on release duration

机译：化学事故中最大浓度与释放持续时间的关系

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Chemical accidents often involve releases of a total mass, Q of stored material in a tank over a time duration, td, of less than a few minutes. The value of td is usually uncertain because of lack of knowledge of key information, such as the size and location of the hole and the pressure and temperature of the chemical. In addition, it is rare that eyewitnesses or video cameras are present at the time of the accident. For inhalation hazards, serious health effects (such as damage to the respiratory system) are determined by short term averages (<1 min) of concentrations, C. It is intuitively obvious that, for a ground level source and with all conditions the same (e.g., the same mass Q released), the maximum C near the source will be larger for a shorter than a longer release duration, t(d). This paper investigates the variation with downwind distance, x, of the ratio of maximum C for two time durations of release. Some simplified formulas for dispersion from finite duration releases are presented based on dimensional analysis. A primary dimensionless number of importance is the ratio of the release duration, t(d), to the travel time t(t) = x/u, at distance, x, where u is wind speed. Examples of applications to pressurized liquefied chlorine releases from tanks are given, focusing on scenarios from the Jack Rabbit I (JR I) field experiment. The analytical calculations and the predictions of the SLAB dense gas dispersion model agree that the ratio of maximum C for two different td's is greatest (as much as a factor of ten) near the source. At large distances (beyond a few km for the JR I scenarios), where t(t) exceeds both t(d)'s, the ratio of maximum C approaches unity. (C) 2016 Elsevier Ltd. All rights reserved.
机译：化学事故通常涉及在不到几分钟的持续时间td内释放总质量Q。由于缺乏关键信息（例如孔的大小和位置以及化学药品的压力和温度）的知识，td的值通常是不确定的。此外，事故发生时很少有目击者或摄像机。对于吸入危害，严重的健康影响（例如对呼吸系统的损害）由浓度的短期平均值（<1分钟）C决定。很明显，对于地平面源，在所有情况下都相同（例如，释放的质量Q相同），源附近的最大C值将比较长的释放持续时间t（d）短。本文研究了释放两个时间段内最大C的比率随顺风距离x的变化。基于维度分析，给出了一些有限持续时间的离散度简化公式。重要度的主要无量纲数是释放持续时间t（d）与行进时间t（t）= x / u（在距离x处）的比率，其中u是风速。给出了罐中加压液化氯释放的应用示例，重点介绍了Jack Rabbit I（JR I）现场实验的情景。 SLAB稠密气体扩散模型的分析计算和预测均认为，在源附近，两个不同td的最大C的比最大（多达10倍）。在长距离（对于JR I场景而言，超过几公里）处，其中t（t）超过了两个t（d），最大C的比率接近于1。 （C）2016 Elsevier Ltd.保留所有权利。

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