化学品安全委员会安全视频
2010年8月23日 位于阿拉巴马州西奥多的 August 23, 2010, the Millard Refrigerated Services facility
米拉德冷冻服务工厂 由于厂内冷冻系统中的 in Theodore, Alabama more than 32,000 pounds of anhydrous ammonia
一条管道发生灾难性失效 was released to the atmosphere after a pipe
向大气中释放了超过3.2万磅的无水氨 within the plant’s refrigeration system catastrophically failed.
化学品安全委员会调查发现 The Chemical Safety Board investigated and found that
管道破裂是由液击引起的 the ruptured pipe was caused by hydraulic shock
它是由于管道或设备内突然的 which is defined as a sudden localized pressure surge
局部压力波动 in piping or equipment
导致流动液体速度上的急剧变化而引发的 resulting from a rapid change in the velocity of a flowing liquid.
随着调查，化学品安全委员会发布了一份安全公告 Following its investigation, the CSB released a safety bulletin
叫做“预防工业制冷系统液击的 describing “Key Lessons for Preventing Hydraulic Shock
重要经验教训”，如果按照它来执行 in Industrial Refrigeration Systems” which, if followed,
就可以预防诸如米拉德所发生的这类危险事故 can prevent dangerous accidents like the one at Millard.
对系统的冲击
2010年 米拉德制冷服务 In 2010, Millard Refrigerated Services
在阿拉巴马州莫比尔附近运营一家冻禽出口工厂 operated the frozen poultry export facility near Mobile, Alabama.
该工厂有8个独立的冷冻机 The facility maintained a 143,000-pound capacity
14.3万磅容积的氨制冷系统 ammonia refrigeration system with eight separate freezers.
在这个系统内 Within the system,
低温液氨通过泵流经蒸发器盘管 low temperature liquid ammonia is pumped through evaporator coils.
当液氨蒸发时 As the liquid ammonia evaporates,
吸热，冷却冷冻机 heat is absorbed, cooling the freezers.
在这个过程中 During the process,
因为与周围空气的水分接触 the outside of the evaporator coils builds up frost
蒸发器盘管外部会结霜 due to contact with moisture in the surrounding air.
除非霜冻被除去 Unless this frost is removed,
否则它会影响 it will reduce the ability of the coils to
盘管有效冷却冷冻机的能力 effectively cool the freezers.
为了避免这点，会定期开启除霜循环 To avoid this, defrost cycles are initiated periodically.
除霜循环期间，低温液氨 During a defrost cycle, the low temperature liquid ammonia
被完全从蒸发器盘管清除 is removed from the evaporator coils completely,
取而代之的是高温气氨 and replaced by hot high temperature ammonia gas
它会填满盘管并且融化外表面的霜 which fills the coils and melts the frost on the outside surface.
一旦霜被融化 Once the frost is melted,
高温凝液以及残留的气体 the hot condensed liquid and remaining gas
就会在低温氨被泵送入 are removed from the evaporator coils
重新开始正常运行之前 before low temperature ammonia is pumped back in
从蒸发器盘管中被清除 to resume normal operations.
2010年8月22日 米拉德设施停电了 On August 22, 2010, the Millard facility experienced a loss of power
停电持续了7个多小时 that lasted more than seven hours.
这期间 冷冻系统被关闭 During that time, the refrigeration system was shut down.
第二天 系统恢复电力并开车继续运行 The next day, the system regained power and was up and running,
尽管操作员上报了一些问题 though operators reported certain problems.
但是 做了些故障排除之后 While doing some troubleshooting,
一个操作员清除了控制系统的警报 an operator cleared alarms in the control system
重置了之前处于除霜过程中 which reset the refrigeration cycle on a group of
的一组冷冻机蒸发器的制冷循环 freezer evaporators that were in the process of defrosting.
控制系统的重置使一个阀门被打开 The control system reset triggered a valve to open
低温液氨在高温气氨被清除之前 and low temperature liquid ammonia was fed back into
就被重新送回到蒸发器盘管中 the evaporator coils before removing the hot ammonia gas.
这导致了高压气态氨 This caused the hot high pressure ammonia gas
迅速冷凝成液体 to rapidly condense into a liquid.
气体冷凝的地方产生了真空 A vacuum was created where the gas has condensed.
这个真空空间通过管道被一股液氨迅速补充 The void sent a wave of liquid ammonia through the piping
引发了一个突然的压力冲击，即液击 causing a sudden pressure surge known as hydraulic shock.
压力冲击导致其中一个冷冻机内部的管汇 The pressure surge ruptured the evaporator piping manifold
在工厂屋顶12英寸管道 inside one of the freezers and its associated 12-inch
发生破裂 piping on the roof of the facility.
32100英镑的氨 32,100 pounds of ammonia
被释放到周围的环境当中 were released into the surrounding environment.
这一大团气云从工厂向正南方飘了1/4英里 The large cloud travelled a quarter mile from the facility
到达800名承包商员工正在为深水地平线号 south toward an area where 800 contractors were working outside
石油泄漏事故做善后工作的地方 on a cleanup site for the deepwater horizon oil spill.
153人接触了有毒的无水氨
32名厂区外工人需要住院治疗
他们中有4个被送进重症监护室
在调查期间 化学品安全委员会发现 During its investigation, the CSB learned that
试图排除设备故障问题的操作员 the operator who was attempting to troubleshoot equipment issues
在断电之后手动清除了警报 after the power outage manually cleared alarms
重置了蒸发器控制 that reset the evaporator controls.
由于这次重置 控制系统没能识别出 Due to the reset, the control system did not recognize that
蒸发器已经在进行除霜的过程 the evaporator was already in the process of defrosting
并且在还没清除蒸发器盘管内的高温 and allowed the refrigeration cycle to start
气氨的情况下就允许了冷冻循环的开启 without removing the hot ammonia gas from the evaporator coils.
化学品安全委员会指出 吸取到的一个经验教训是 The CSB notes that one lesson learned is
避免在除霜过程中手动中断蒸发器
并且确保控制系统备有安保装置
以便只有经过培训和被授权的人
才可以手动旁路程序化操作
设备运行意外中断之后
液击是可以通过
设计控制系统 在重新开始冷冻之前
自动清除蒸发器旋盘管内的物质来避免的
化学品安全委员会还发现 The CSB also found that
米拉德工厂蒸发器的设计是 the evaporators at the Millard facility were designed
一组阀门控制4个独立的蒸发器盘管 so that one set of valves controlled 4 separate evaporator coils.
结果 连接这个阀门组的所有盘管 As a result, the contents of all 4 coils connected to that valve group
都发生了液击事故 were involved in a hydraulic shock event
导致压力冲击变得更大更危险 leading to a larger more hazardous pressure surge.
化学品安全委员会指出 在设计氨冷冻系统的时候 The CSB notes that when designing ammonia refrigeration systems
每个蒸发器盘管都应该由一组独立的阀门控制 each evaporator coil should be controlled by a separate set of valves
化学品安全委员会发现 And the CSB found that immediately
在发现氨释放之后 after discovering the ammonia release,
操作员立即决定隔离泄漏源 a decision was made to isolate the source of the leak
然而冷冻系统仍然在运行 while the refrigeration system was still operating
而不是启动紧急停车 instead of initiating an emergency shutdown.
化学品安全委员会调查的最后一条经验教训是 A final lesson learned from the CSB’s investigation is that
在氨释放事故当中
应该启动紧急停车
如果泄漏不能被迅速隔离和控制的话
这样做 能够极大地减少 Doing so can greatly reduce the amount
事故中氨的释放量 of ammonia release during an accident.
化学品安全委员会认为 如果所有氨冷冻工厂 The CSB believes that if ammonia refrigeration facilities
都能够遵循对米拉德冷冻服务事故调查 follow the lessons learned from its investigation
所得到的经验教训 into the accident at Millard Refrigerated Services,
危险的液击事故就可以避免 dangerous hydraulic shock events can be avoided.
想了解更多关于化学品安全委员会 For more information about the CSB’s
关于米拉德冷冻服务的调查信息 Millard Refrigerated Services investigation,
请访问化学品安全委员会官网 please visit csb.gov.
化学品安全委员会安全视频 CSB SAFETY VIDEO