The minimum energy required for a static spark to ignite a substance depends on the substance, but here are some examples:
Hydrogen: 0.017 millijoules (mJ)
Hydrocarbon vapors: 0.2–2 mJ
Fine flammable dust: 1–50 mJ
Coarse flammable dust: 40–1000 mJ
Carbon disulfide, hydrogen, trichlorosilane, or acetylene gasses: 0.04 mJ
A static spark that's visible in the dark has an energy of 0.04 mJ. A static spark from a fingertip at 3,000 volts produces about 0.50 mJ of energy. A static discharge from a human can be 60 mJ or more.
The minimum ignition energy (MIE) of dust depends on the dust's chemical composition, size, shape, and moisture content.
Minimum ignition energy (MIE) is the minimum amount of energy needed to ignite a flammable material in air or oxygen. It's a safety characteristic that helps prevent explosions and assess the likelihood of ignition during handling and processing.
Here are some things to know about MIE:
How it's measured
MIE is measured by determining the lowest spark energy that can ignite a powder when it's dispersed in the air as a dust cloud.
What it measures
MIE measures how sensitive a flammable material is to electrical spark ignition.
How it's used
MIE is used to define explosion prevention methods. For example, an MIE of less than 100 mJ indicates a potential for ignition from static discharges.
How it varies
MIE varies depending on the material and its concentration:
Methane: The MIE for methane depends on the type of gas and concentration. For example, at 25° C and 1.0 atm, it takes 0.3 mJ to initiate an explosion chain reaction.
Acetone: The MIE for acetone is 1.15 mJ.
Acrolein: The MIE for acrolein is 0.13 mJ.
Propane: The MIE for propane is 0.26 mJ.
n-Butane: The MIE for n-butane is 0.26 mJ.
Acetylene: The MIE for acetylene is 0.017 mJ.
Starch: The MIE for starch is 41 mJ.
Wheat flour: The MIE for wheat flour is 30 mJ.
Protein: The MIE for protein is 87 mJ.
Polypropylene: The MIE for polypropylene is 116 mJ.
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