Combustible Dust- Minimum Ignition Energy (MIE)

A common question that I receive is if I already know the product is combustible why do I need to bother having the material tested for combustibility parameters. The first reason is when you are dealing with process equipment it is important to know the material specific sensitivity to ignition by static electricity or electrical discharge. Some organic materials such as wood, coal or grain have well established ranges but individual products can vary substantially. Products in the chemical, pharmaceutical industries can have complex combinations and their specific characteristics should be documented so that an employer can be diligent in understanding the hazards and risks present.

The knowledge of your material’s MIE makes a difference in your controls that you select.  Most organics have a MIE above 30 mj. Chemicals, legacy metals, and pharmaceuticals are regularly below 30 mj. When a product MIE’s fall below 30 mj they are subject to ignition from sources such as static electricity, plant electrical switches, motors, and mobile equipment. For reference a household 10-amp circuit light switch arc will be 0.5 mj when activated, the MIE for gasoline is 0.5 mj, and in laboratory testing static charges between people can be up to 25 mj.

The selection of controls when dealing with low MIE materials can include dust explosion proof electrical cabling and equipment, intrinsically safe mobile equipment alternators and starters, employee grounding and fire-resistant clothing to mention a few. Lastly all attempts should be made to reduce the potential for dust cloud generation as ignition sources are frequently present in industrial environments.

This article is not intended to be a definitive explanation on combustibility parameters. It is just a primer to allow people to become more aware of the components of an effective Combustible Dust Management Program, and to understand which questions to ask when seeking assistance with setting up a program.