When testing for the Minimum Ignition Energy (MIE) of a dust, there are two approaches – with or without inductance. Testing “with inductance” simulates the longer duration discharges from electronic circuitry that can occur from machines or control equipment. Testing without inductance better simulates discharges from “pure” static electric sources. The spark duration is shorter and thus the determined energy levels are less conservative. If you are certain of the type of equipment used in your facility or are confident that you are only dealing with electrostatic sparks, then you can determine if the MIE should be conducted with or without inductance.
The minimum ignition energy test is performed using ASTM E2019 as the guideline. This test is important because it tells you the smallest amount of energy that can be present in your process and still ignite your dust. This data is particularly important when you have applications like conveying, sieving, and pouring. Also, in housekeeping situations, the MIE can help you safely design collection equipment. Additionally, knowledge about the MIE level is important for establishing proper grounding and bonding protocols and designing ignition source avoidance methodologies.
If, after a review of your facility, you are only concerned about static-electric sparks, then the MIE test without inductance should be performed. If however, you are worried about sparks from electronic circuitry, other ignition sources or you wish to publish the MIE value on an Safety Data Sheet then the more conservative MIE method using inductance in the circuit is more appropriate (#3.2).
When testing your dust to find the minimum ignition energy (MIE), testing with inductance is a conservative approach that ensures you have the lowest value possible for your material. If there is any question about which form of the test should be used, you should consult a dust expert for guidance or use the conservative approach.
For more information on MIE or combustible dust testing, please contact Ashok Dastidar, PhD, MBA, Vice President, Dust & Flammability Testing and Consulting Services, Fauske & Associates, at dastidar@fauske.com or 630-887-5249