MIE Minimum Ignition Energy

MIE Test

Minimum Ignition Energy (MIE)

The Minimum Ignition Energy (MIE) is the lowest energy required to ignite the flammable material in air or oxygen. The lowest value of the Minimum Ignition Energy is found at a certain optimum mixture.

The Minimum Ignition Energy (MIE) lies between the lowest energy value (E2) at which ignition occurred and the energy (E1) at which in at least 10 successive experiments no ignition was observed. The energy range thus determined is called the Minimum Ignition Energy of a combustible dust in admixture with air. However, for purposes of simplification often only the lower limit value (E1) is specified as the minimum ignition energy (MIE): E1 < MIE < E2.

Depending on the specific application, there are several standard procedures for determining MIE of dust clouds, solvent vapours and gases.

The common element in all procedures is that the energy is generated by an electrostatic spark discharge released from a capacitive electrical circuit. The exact circuit components and the arrangement of electrodes between which sparks are generated are the principle differences between the methods.

The Minimum Ignition Energy is a measure of how sensitive an explosive dust or powder is to electrical spark ignition. In particular, it gives guidance on whether ignition by electrostatic discharge from plant personnel or process conditions is likely to occur in practice.


Minimum Ignition Energy Test

The Minimum Ignition Energy test measures the ease of ignition of a dust cloud by electrical and electrostatic discharges. The test follows guidance given in BS 5958 and BS EN 13821 and may be used for DSEAR risk assessments to determine likely electrical ignition sources and whether special precautions are required to guard against static electricity.

The MIE apparatus used for this test consists of a borosilicate tube placed over a dispersion cup and fitted with two electrodes. The electrodes are connected to a circuit which produces an electrical spark of known energy.

A weighed sample of dust or powder is placed in the dispersion cup, which is then blown up through the tube with compressed air past the ignition source. If flame propagation is observed, the energy of the spark is reduced until no flame propagation is seen for ten consecutive tests. A range of dust sample weights is tried to ensure a thorough investigation of potential dust explosion concentrations.

Test Results

The test determines the lowest electrical spark energy that will ignite a dust explosion. Results of a 10m Joules or less indicate electrostatic ignition by plant personnel is possible and special precautions are required for explosion prevention.

Examples of typical dangerous substances in the workplace:

  • Acrylic Polymer
  • Aluminium Dust
  • Amino Alcohol
  • Bronze Powder
  • Carbon Black
  • Carbon Fibre Dust
  • Cereal Flake Dust
  • Coal Dust
  • Coke Dust
  • Composite Dust
  • Curry Powder
  • Dimethyl-phenylpyrazolidone
  • Dried Sewage Sludge
  • Fibre Insulation
  • Flour
  • Glass Fibre Polyurethane
  • Grain Dusts
  • Gum Arabic
  • HDPE
  • Hydroxy-methyl-phenylpyraolidone
  • Leather Dust
  • Liquorice Powder
  • Melamine Dust
  • Paper Dust
  • Paraformaldehyde
  • Pharmaceutical Powders
  • Phenolic Resin
  • Pigment Powder
  • Polyelectric Powder
  • Plastic Dust
  • Potato starch
  • Refined sugar
  • Resin Dust
  • Sodium Flurbiprofen
  • Sulfuramide
  • Tea
  • Wood

MiE

  • MIE depends on type of gas and concentration
  • 8.0% volume methane is “sweet spot” for stoichiometric combustion of methane
  • Although flammability range for CH4 is 5 – 15%, concentration where it is easiest to ignite is 8% by volume
  • At 25° C, 1.0 atm, takes 0.3 mJ to initiate explosion chain reaction
  • Static electricity “zap” when insert key into ignition = 5.0 mJMIE for other combustible gases much lower

Minimum Ignition Energy


How to assess dust explosion risks using the MIE ?

The MIE is a key data to consider for every source of ignition as the energy that the source of ignition will be able to generate will or will not be susceptible to trigger an explosion depending if it is lower or higher than the MIE.

It is necessary to calculate the energy triggered by the source of ignition during a risk assessment, for example for the following sources of ignition :

  • Spark discharge
  • Brush discharge
  • Corona discharge
  • Propagating brush discharge
  • Cone discharges
  • Mechanical sparks

What are the values of MIE creating significant dust explosion risk ?

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.

In the following table MIE is quoted for flammable substances mixed with air. A reference is provided to indicate the source of the data. MIE values are provided for guidance only. Please check references for specific measurement conditions.

Substance MIE (mJ)
ABS 30
acetaldehyde
0.37
acetaldehyde 0.36
acetone 1.15
acetyl cellulose 15
acetylene 0.017
acrolein 0.13
acrylonitrile 0.16
adipic acid 60
alfalfa meal 320-5100
allyl chloride 0.78
aluminium 50
aluminium stearate 15
ammonia 680
antimony 1920
aspirin 25-30
aziridine 0.48
benzene 0.20
benzene 0.22
bisphenol-A 1.8
black powder 320
boron 60
1,3-butadiene 0.13
butane 0.25
butane 0.26
n-butyl chloride 0.33
cadmium 4000
carbon monoxide <0.3
carbon disulphide 0.009
carbon disulphide 0.015
casein 60
cellulose 35
cellulose acetate 20-50
charcoal 20
chromium 140
cinnamon 30
coal 40
coal, pittsburg 250
cocoa 100
cocoa 100-180
coffee 160
copal 30
cork powder                        45
cork powder 35-100
corn meal 40
corn flour 20
corn starch 30-60
cotton (filler) 25
cotton linters 1920
cyclohexane 0.22
cyclopentane 0.54
cyclopentane 0.24
1,3-cyclopentadiene 0.67
cyclopropane 0.17
cyclopropane 0.18
dextrine 40
dichlorosilane 0.015
diethyl ether 0.19
diethyl ether 0.2
2,3-dihydopyran 0.36
diisobutylene 0.96
diisopropyl ether 1.14
dimethoxymethane 0.42
dimethyl amine <0.3
2,2-dimethyl butane 0.25
dimethyl ether 0.29
2,2-dimethyl propane 1.57
dimethyl sulphide 0.5
dimethyl sulphide 0.48
dinitrobenzamide 45
dinitrobenzoic acid 45
dinitro-sym-diphenylurea 60
dinitrotoluamide 15
dioxane <0.3
di-(tert)-butylperoxide 0.5
di-(tert)-butylperoxide 0.41
epoxy resin 15
ethane 0.24
ethane 0.26
ethene 0.07
ether 0.19
ethyl acetate 1.42
ethyl amine 2.4
ethyl cellulose 10
ethyl chloride <0.3
ethylene 0.07
ethylene oxide 0.06
ethylene oxide 0.065
ethylene oxide 0.062
flour, cake 25-80
furan 0.22
gasoline 0.8
grain dust 30
grass seed 60-260
hemp 30
heptane 0.24
hexamethylenetetramine 10
hexane 0.24
hexane 0.29
hydrogen 0.011
hydrogen 0.017
hydrogen sulphide 0.068
hydrogen sulphide 0.077
isooctane 1.35
isopentane 0.21
isopentane 0.25
isopropyl alcohol 0.65
isopropyl amine 2.0
isopropyl chloride 1.55
isopropyl chloride 1.08
isopropyl ether 1.14
isopropyl mercaptan 0.53
lignin 20
lycopodium 50
magnesium 80
magnesium 40
manganese 305
melamine formaldehyde 50-320
methane 0.28
methane 0.3
methanol 0.14
methyl acetylene 0.11
methyl acetylene 0.115
methylal 0.5
methyl cyclohexane 0.27
methylene chloride 10000
methyl ethyl ketone 0.53
methylformate 0.5
methylmethacrylate 15
nitrostarch 40
nylon 20
nylon 20-30
paper dust 20-60
paraformaldehyde 20
pentaerythritol 10
pentane 0.22
2-pentene 0.18
petroleum ether (benzine) 0.25
phenol formaldehyde 10-6000
phosphorus (red) 0.2
phthalic anhydride 15
PMMA 15-20
polyacrylonitrile 20
polycarbonate 25
polyethylene 10
polyethylene 70
polyethylene teraphthalate 35
polypropylene 25-400
polystyrene 40-120
polyvinyl acetate 160
polyvinyl acetate alcohol 120
polyvinyl butyral 10
potato starch 20
potato starch 25
propane 0.25
propane 0.26
propene
0.28
propionaldehyde 0.4
propylchloride 1.08

 

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