MIE Test

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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