Electrostatic ignition risks

This is a topic on which much has been written, and there is an extensive body of guidance going back decades. There is also an extensive literature on test methods, to measure different aspects, but experience shows the results are very sensitive to factors such as cleanliness of surfaces, humidity, trace contamination and other factors that are hard to control in a real industrial environment. I wouldn’t claim to be an authority.

European guidelines have now turned into IEC documents, see Published Document International Electrotechnical Commission Technical Standard (PD IEC TS) 60079 32-1:2013 for 170 pages of guidance and part 32-2:2015 for another 40 pages describing the tests. I like also the AI Chem E book ‘avoiding static ignition hazards in chemical operations’ by Laurence Britton dating from 1999.

Often the guidance is sufficiently clear to define the precautions needed without measurements. If this is not the case, you need to go back to the fundamentals; where is charge being generated? where can it accumulate? and how is it dissipated? Then ask what can I do to control these factors?

Sometimes seemingly trivial changes can increase the risk; that might be a change in a polymer gasket to one that is much more insulating; creating a product much dryer (less conducting) than normal, or one which contains a second liquid phase, or a product that builds up a thin insulating coating on the inside surface of your process plant.

Where dusts are handled, it will often be the case that precautions against the consequences of an explosion are needed, and trying to eliminate the risks my control of ignition sources alone is not enough.

The following story counts among the ‘don’t try this at home category’

Prof Liu Shanghe told a Chinese Academy of Engineering conference that he had worked on understanding static electricity for 50 years including experimenting on himself. Along the way he had discovered the world’s first general differential expression of Ohms Law(?) We know that people can be charged up to 25 kV without ill effects. Was there an upper limit? His assistants wired the Professer up, and gradually raised the voltage. When he got to 70kV and a smell of burning the experiment was terminated. The Prof survived but reported many health issues caused by his years of research. Source http://wap.chinadaily.com.cn/2017-05/05/content_29221681.htm