今天，美国化学安全委员会（CSB）发布了最新的safety video详细介绍了2010年8月23日在Millard冷藏服务公司发行的32,000磅无水氨的关键课程。事故导致了150多个暴露于异地工人，其中30名住院治疗，其中4个在一个重症监护室中。
The newly releasedseven-minute safety video,entitled“Shock to the System,”includes a detailed 3D animation of the events that led up the resulting ammonia release. The video is based on the CSB’s recent safety bulletin entitled“Key Lessons for Preventing Hydraulic Shock in Industrial Refrigeration Systems.”
Chairperson Rafael Moure-Eraso said, “The CSB’s new safety video is a valuable tool intended for use at the large number of facilities that utilize anhydrous ammonia. The key lessons learned from our investigation – examined in our report and in this video — can help facilities prevent a similar accident from occurring due to hydraulic shock.”
The CSB’s video is available at itsYouTubechannel and atwww.csb.gov
The CSB’s investigation found that the day prior to the accident the Millard facility experienced a loss of power that lasted more than seven hours. During that time the refrigeration system was shut down. The next day, on August 23, 2010, the system regained power and was up and running, though operators reported certain problems. While doing some troubleshooting an operator cleared alarms in the control system, which reset the refrigeration cycle on a group of freezer evaporators that were in the process of defrosting.
这导致同时存在于线圈和相关管道中的热，高压气体和极低的温度液体氨。这导致热高压氨气迅速凝结成液体。因为液态氨的含量小于氨气，因此在凝结气体的地方产生了真空。
The sudden pressure drop sent a wave of liquid ammonia through the piping — causing a sudden pressure surge known as “hydraulic shock.”
这种异常的瞬态条件导致压力急剧上升，可能导致管道，阀门和其他成分的灾难性失败。通常在发生液压冲击事件之前，制冷管道中有一个可听见的“锤击”。
CSB Investigator Tyler said, “The CSB’s animation details how the pressure surge ruptured the evaporator piping manifold inside one of the freezers causing a roof-mounted 12-inch suction pipe to catastrophically fail, resulting in the release of more than 32,000 pounds of anhydrous ammonia and its associated 12-inch piping on the roof of the facility.”
该新闻稿在一名米拉德雇员跌倒时摔倒在旅行的氨云中时跌倒时跌倒时造成了伤害。大云从该工厂向南行驶了四分之一英里，到达了800个承包商在户外工作的地区，在一个清理现场为深水地平线漏油事件进行了清理现场。共有152名异地工人和船员报告说，暴露于氨的症状疾病。有32名异地工人需要住院，其中4个在重症监护室中。
The video presents the key lessons learned from the CSB’s investigation including avoiding the manual interruption of evaporators in defrost and requiring control systems to be equipped with password protection to ensure only trained and authorized personnel have the authority to manually override systems. On the day of the incident, the control system did not recognize that the evaporator was already in the process of defrosting, and allowed an operator to manually restart the refrigeration cycle without removing the hot ammonia gas from the evaporator coil.
The CSB also found that the evaporators at the Millard facility were designed so that one set of valves controlled four separate evaporator coils. As a result, the contents of all four coils connected to that valve group were involved in the hydraulic shock event — leading to a larger, more hazardous pressure surge. As a result, the CSB notes that when designing ammonia refrigeration systems each evaporator coil should be controlled by a separate set of valves.
CSB发现，在发现氨释放后立即决定在制冷系统仍在运行时隔离泄漏的来源，而不是启动紧急关闭。关闭制冷系统可能导致较小的释放，因为与失败的屋顶管道相关的所有其他含氨的设备继续运行。CSB调查的最终关键课程是，如果释放泄漏，应迅速隔离和控制，应在释放氨时激活紧急关闭。这样做可以大大减少事故中释放的氨气量。
The CSB is an independent federal agency charged with investigating serious chemical accidents. The agency’s board members are appointed by the president and confirmed by the Senate. CSB investigations look into all aspects of chemical accidents, including physical causes such as equipment failure as well as inadequacies in regulations, industry standards, and safety management systems.
The Board does not issue citations or fines but does make safety recommendations to plants, industry organizations, labor groups, and regulatory agencies such as OSHA and EPA. Visit our website,www.csb.gov。有关更多信息，请联系public@csb.gov。
