Minimum Ignition Energy of dust
Physical meaning and use in risk assessment of powder MIE
Do you have a question, a remark ? Please contact the author at email@example.com
Solids Handling Safety
# Dust explosion physical properties # MIT - Minimum Ignition Temperature of dust
1. Definition of MIE
The Minimum Ignition Energy MIE is very important for dust explosion risks analysis, it will show how easy a dust cloud can be ignited. The MIE is equal to the minimal energy needed to be brought by a spark to a dust cloud of a given concentration in order to ignite it following a specific experimental procedure [Laurent].
2. Experimental determination of MIE
The MIE is measured experimentally. The experiment consists in putting in suspension dust of the material to be tested in a cloud that has a concentration in between the minimum explosion concentration and maximum explosion concentration (determining this concentration may need additional experiments). It may be necessary to standardize the particle size distribution prior to testing the powder [Glor] : having dust less than 63 microns is mentioned in European norm and in different research papers. It is important as the MIE decreases with the particle size and even if the product has a size larger than 63 microns, bulk solids handling operations like pneumatic transport may lead to the generation of fine dusts [Glor]. The humidity, an important contributing factor in dust explosion, should also be standardized for the test [EN13821].
Sparks are then created thanks to electrodes. Depending on the energy involves, the sparks are able or not to trigger an explosion.
The MIE is the smallest energy observed on the electrodes that triggers an explosion of the powder at the concentration tested. Smaller energies do not trigger explosion.
To be representative, such experiences must be carried out by reputable test institutes with a clear protocol (example : ASTM E2019 in US, IEC 1241-2-3 or EN 13821 in Europe). The test machine mentioned in the norm is also important as values may be slightly different from one apparatus to another (MIKE 3 and HARTMANN tube for example [Janes]). Many parameters can influence the result of the MIE measure, hence the need to get in touch with professional institutes.
Figure 1 : MIKE 3 Minimum Ignition Explosion test apparatus
It must also be noted that MIE can be tested with and without inductance in the test apparatus [Janes]. Testing with inductance is conservative and should give the lowest possible value of MIE. However, if the process conditions are well defined and risks only concern static electricity sparks, it may be interesting to discuss with the test institute in order to check if the MIE without inductance would be more relevant. If other sources of ignitions are to be considered or if the process conditions are not well known, tests with inductance will give more safety margins.
3. MIE typical values
MIE typically range from 1 mJ to 1000 mJ [Janes]. The lower the MIE, the higher is the risk of explosion as a very small energy input can trigger a dust cloud explosion.
MIE < 3 mJ should be processed with specific measures, the dust is extremely sensitive to ignition. Some equipment suppliers even refuse to handle projects with such low MIE as they are extremely sensitive even to small sparks.
MIE = 3 mJ and above requires special attention and measures to process the powder taking into account such risks as static electricity, mechanical sparks...etc...
Each processor must carry out a dust explosion risk analysis in order to assess the risk related to a specific material in a specific process and take necessary precaution and mitigation measures.
4. Use in risk assessment
|Wood flour||40 [Mills]|
|Do you want to
know more ?
www.powderprocess.net is covering all aspects of solids and powder processing and handling
The pages below will probably interest you !
Answers ALL your questions on pneumatic transport
of MIX / MEASURING DEGREE OF MIXING
All you need to know about measuring the degree of mixing (Coefficient of Variation) of a dry mix
OF POWDERS / DEMIXING
All on the physical phenomena causing segregation of particles and how to avoid them
All on main size reduction processes, key equipement, design consideration..etc..
All on powder key physical characteristics, among others : flowability, density...etc..
All equipment found in bulk solids handling industries, explained, with design tips...
|You can find much more through the menus at the top of the page !|