By Jeff Griffin, Fauske & Associates, LLC
For those in industry, the dangers of combustible/hazardous dust have been increasingly high-profile. Leadership at the Chemical Safety Board (CSB) has spoken recently about the importance of adopting a consensus standard so that there is a more uniform approach tocombustible dust safety.
Last week’s terrible accident in Taiwan illustrates that there is still a real lack of understanding about the dangers of dust explosions. The BBC reports that “a coloured powder ignited when it was dispersed into the crowd.”[i]500多人受伤，因为粉末被像香烟这样简单的东西点燃。虽然这次活动很严重 - 那是不是可燃/危险的灰尘爆炸。那是一场闪火。This blog defines how dust can manifest as an explosion hazard or in a flash fire, and then identifies two key steps necessary to prevent both.
了解限制和可燃的灰尘
Many people are familiar with the explosion pentagon, which illustrates the five factors needed to have a combustible dust explosion, namely, fuel, ignition, dispersion, confinement, and oxygen. However, oftentimes, the dangers of dust explosions are not considered because people presume that a lack of confinement means that they are safe. This is just not true. A lack of confinement of a dust means that the explosive pressure generated by a material dissipates to the environment. This is good for preventing an explosion event, but it is still possible for a flash fire to occur even if there is no containment.
什么是闪火?
Short Definition:The rapid burning of a material that is suspended in air.This could be a dust, a gas, a vapor, or a mixture of any one of these materials (we will discuss the danger of mixed or ‘hybrid’ systems later in this post). These types of incidents are quite common because they can happen with even very small amounts of material. This means that the injuries resulting from these events are often not as serious – and may not be reported in statistics. The Taiwan incident is a great example of how dangerous they can be. Another example occurred in the US in 2012.
示例：美国墨水
The Taiwan incident is not the first time a colored powder has ignited in a combustible cloud. One notable example is the US Ink incident in 2012.[ii]In this case, it injured seven workers. While there wasn’t an explosion, the event was sufficient enough to warrant an investigation by the Chemical Safety Board (CSB) and for OSHA to fine the company nearly $221k. This event illustrates two key steps before handling combustible/hazardous dusts, and offers an important lesson about hybrid systems.
Step 1: Know your Dust
在处理任何类型的有机灰尘时，重要的是要知道它是否可燃。如果没有有关设施中特定材料的测试数据，就很难知道您面临的风险。在某些情况下，有关某些材料的已发表文献。尽管此信息可能是一个有用的指南，但不足以了解风险或用于工程目的。NFPA 652的整个点，提议的可燃尘埃新标准，[iii]从测试阶段到实施安全协议，为管理灰尘提供统一的方法。测试灰尘以了解特征后，下一步是控制点火源以防止这些条件发生。
Step 2: Controlling Ignition Sources
如果灰尘是可燃的，那么控制潜在的点火源很重要。该活动说明了一个概念，我在现场访问客户网站时刚刚讲授的概念。这种特殊的设施具有出色的客房管理程序和防尘设备，以防止设施积累。但是，有几项操作将材料倾倒在袋子中，或者如果枪管意外掉落，则物料有可能被悬挂在空中。尽管此设施很干净 - 仍有点火资源 - 包括未适当粘合和接地的开放电源渠道和设备（有关键合和接地的更多信息，请参阅我们即将在2015年7月发布的帖子）。测试结果表明，要处理的几种材料的最小点火能（MIE）较低。即使有一些工程控件，它们也不足以防止可能点燃灰尘的火花。鉴于正确的条件，就像台湾灾难中的尘土一样，这些材料很容易被点燃。
最后一堂课：混合系统的危险
最后一个教训台湾事件的担忧danger of hybrid systems. Reports of the fire suggested that the dust was suspended in air along with a petroleum-based gas from a fog machine. If this is true, the combination could have impacted the ignition level needed to set off the suspended dust. Our experts have seen this behavior in both the lab and in the field. Sometimes, a process has operated safely for many years because it is only a vapor or powder system. Then, some accident or process change results in the two materials being suspended together. This results in a hybrid system, which requires much less energy to ignite than the dust material by itself.This is illustrated in Figure 2 (please note that these values are given as examples only).
Conclusion
The event in Taiwan is a sobering reminder of the dangers that exist when handling any type of organic dust. While nearly every industry has been impacted in some way by combustible/hazardous dust, accidents are still occuring. Moving forward, it is important to recognize the fire and explosion hazards associated with dusts. The best way to do this is to take the steps prescribed by the NFPA and other regulatory organizations. Only by testing and understanding the characteristics of a dust can you effectively take steps to control the risks.
Jeff Griffin是Fauske＆Associates，LLC的销售和业务发展总监。他的工作使他现场到北美的设施。他与一支专业的顾问团队合作，他们提供现场支持，以评估与可燃/危险尘埃相关的风险。这些专家坐在几个关键的NFPA委员会上。Fauske＆Associate，LLC还拥有北美粉尘和易燃性测试的主要实验室之一。联系Jeffgriffin@fauske.com，630-887-5278
[i]http://www.bbc.com/news/world-asia-33300970
[ii]http://www.csb.gov/csb-names-poor-design-and-teest-tost-tost-dust-collection-collection-system-among-causes-us-ink-ink-ink-new-jersey-jersey-jersey-fire-那个燃烧的七个工人在2012-OSHA中遇到的 - 到期新的新闻 - 可燃dust-neculations-///
[iii]http://www.nfpa.org/codes-and-standards/document-information-pages?mode=code&code=652
