Over the past eight weeks since the tragic Imperial Sugar Refinery combustible dust explosion I've been busy seeking any information that is available concerning the causes and prevention of combustible dust fires and explosions. One subject that has come up is minimum ignition energy (MIE), which is the energy in millijoules from electrostatic discharges or static electricity that can ignite combustible dusts generated from combustible particulate solids in the manufacturing process.
An excellent book published by the American Institute of Chemical Engineers is "Electrostatic Ignition of Fires and Explosions" by Thomas H. Pratt . This book is an easy read and no prior background in engineering is necessary, which enables everyone in obtaining an understanding of static electrical hazards in the workplace.
The chapters start out with basic concepts then moves on to accumulation, separation, and discharge of electrical charges. Once that concept is mastered, minimum ignition energies can be grasped into how they apply in the workplace. As the book progresses, the author takes the reader into various areas in the manufacturing process dealing with liquids, mists, and finally powders.
With the idea of how static electricity originates the reader is presented with design and operating criteria in addition to electrostatic measurements, and quantification of electrostatic scenarios. Finally at the conclusion and last chapter case histories are provided where the reader is actually able to see how combustible dust explosions and fires occurred when minimum ignition energy ignited dusts.
For many including myself I had no idea what the terms propagating brush or brush discharges meant in regards to minimum ignition energy. Prior to reading the book I thought brush discharges had to do with brushes in an electircal motors but that is not so.
If you have combustible dust in the workplace in any form it's imperative that you understand what minimum ignition energy is. Especially since in the material safety data sheets (MSDS) of the explosive and fire hazard section, this property is not listed like flash points are listed for flammable liquids.