2. History of MIE
• Origin of the research of MIE began in 1910 by the US
Bureau of Mines.
• Bureau of Mines was founded by Congress to conduct
research and collect information concerning every
aspect of the mining trade.
• Primary focus was on methane
• Lewis and von Elbe are credited with the introduction
of a test method to determine MIE
3. Lewis and von Elbe
• “It is possible to pass small electric sparks
through an explosive gas without producing
ignition. When the spark energy is increased, a
threshold energy is eventually obtained at which
the spark becomes incendiary in the sense that a
combustion waved propagates from the spark
through the volume of gas”
• This was the defining criteria for MIE and the
understanding of ignition kernel formation
4. MIE Definition
• The minimum energy that can ignite a mixture of
a flammable material mixed with air or oxygen,
measured by a standard procedure
• The minimum energy of an ignition source, such
as a spark, required to ignite vapors or dusts
• The minimum energy required to establish the
flame kernel of the minimum critical size for
subsequent self-sustained flame propagation
5. Ignition Kernel
• An electric spark establishes a small volume of
hot gas immediately after spark discharge. The
temperature within the flame kernel increases
rapidly. As the kernel grows in size it is cooled by
the ambient/adjacent unburned gas/vapor and
the combustion wave dissipates
– Need adequate energy in the spark to generate a
kernel of sufficient size for sustained combustion
– Need enough ions to sustain combustion
– Analogy – flash point and fire point
– This energy is measured in millijoules (mJ)
7. Joule Definition
• It is the energy dissipated as heat when an
electric current of one ampere passes through a
resistance of one ohm for one second.
– Note that this energy source is electrical
• MIE “rule of thumb” for flammable vapors is
.025mJ
– A small coin dropped from a height of less than 1 mm
has more energy
– A spark that is detectable to the touch is about 20 mJ
8. Spark Gap/Quenching Distance
• Lewis and von Elbe understood that there were
important variables when determining the MIE
• Spark Gap - Typically slightly greater distance than the
quenching distance. If the spark gap is less than the
quenching distance then the electrodes act as a heat
sink for the flame kernel and cause inaccurate results.
• Quenching Distance - Minimum distance between
electrodes which allows optimal ignition with minimal
energy loss.
9. MIE Test Apparatus
•Fuel is vaporized, injected
into test chamber so
volume is in middle of
flammable range and
ignited using an electric arc
•Spark duration and energy
are measured
•Chamber pressure rise will
indicate a combustion
reaction
•Very similar but smaller
apparatus and theory to the
20L or 1 M3 test chamber
that determines if dusts are
combustible
10. Combustible Dust Test Chambers
•20 L test results can be misleading
- ST 1 dusts with Kst less than 50 can produce a
false positive indication in a 20L test chamber
- Test anomaly is called “overdriving”
- Igniters cause the pressure increase, not the dust
- Solution, use a 1M3 test chamber
12. Orders of Magnitude
• Explosives, hydrogen, unsaturated hydrocarbons,
and alkanes in oxygen have the lowest MIE, from
1-100 micro J
• Alkanes in air, distillate fuels, and hybrid mixtures
range from 0.1-20 milli J
• Combustible dusts range from .01-10 J
• Kerosene and diesel 20 mJ
13. Auto-ignition Temperature
• More common term for Marine Chemists
which is not based on electrical energy
• The minimum temperature required to ignite
a gas or vapor, in air, at atmospheric pressure,
without a spark or flame being present
14. K47000 Apparatus
Determines the lowest
temperature at which the
vapors of a liquid or solid
chemical sample will self-
ignite under prescribed
laboratory conditions. The
temperatures at which ‘cool
flame’ and ‘hot flame’
ignitions occur, as
evidenced by sudden
temperature increases in
the sample flask, are
measured and recorded,
and the delay time between
introduction of the sample
and ignition is timed.
15. Test Process
• Sample (100ul) introduced into a well insulated flask that is
uniformly heated.
• Gas/vapor temp is monitored as heating is performed
• Cool flame temp is recorded – slight blue flame, small but
fast temp rise
• Instant significant temp rise indicates combustion – hot
flame temperature.
• Recorded as the auto-ignition temperature
16. Cool Flame
• A flame having maximal temperature below
about 400 °C (752 °F). It is usually produced in
a chemical reaction of a certain fuel-air
mixture. Contrary to conventional flame, the
reaction is not vigorous and releases very little
heat, light and carbon dioxide.
• Incomplete combustion
17. Conclusions
• MIE and AIT are related in that they provide information
about the energy required to ignite a chemical.
• An ignition source must have adequate energy to
propagate combustion
• An electrical source of ignition is very small for most
chemicals we deal with and is measured in mJ. Don’t
underestimate the power of electrical energy
• Other, more conventional ignition sources (hot work, light
bulbs, heating coils) must be at or above the auto-ignition
temperature of the chemical to propagate combustion
18. Lithium Ion Batteries
• If enough microscopic metallic particles converge on
one spot, a sizable current begins to flow between the
electrodes of the cell, and the spot heats up and
weakens. As a small water leak in a faulty hydro dam
can develop into a torrent and take a structure down,
so too can heat buildup, damage the insulation layer in
a cell and cause an electrical short. The temperature
can quickly reach 500 C (932 F), at which point the
cell catches fire or it explodes. This thermal runaway
that occurs is known as “venting with flame.” “Rapid
disassembly” is the preferred term by the battery
industry.
21. Battery Operated Drones
• Should battery operated drones be considered
potential ignition sources when used inside cargo
tanks?
• Could the batteries or drones ignite residues
inside the cargo tanks?
• Should the cargo tanks be cleaned to the extent
that they are “Safe For Hot Work” or is a
cleanliness level of “Atmosphere Safe For
Workers” sufficient??
22. ASFW Level of Cleanliness
• Pros
– Permits the use of drones for inspecting cargo
tanks without fully cleaning the tanks
– Reduces cost
– Enhances the safety of the inspection team by
eliminating the fall potential
– Reduces the need for staging
• Cons
– Could be an ignition source
23. SFHW Level of Cleanliness
• Pros
– Eliminates the potential ignition of cargo residues
– Ensures total fire safety of the inspection team
• Cons
– No cost reduction in cleaning activity
– Staging required
– Fall potential for inspection team remains
24. MCA Action
• MCA is reviewing the use of drones to consider if
they present a new potential ignition hazard in
cargo tanks
• MCA recognizes the huge time/cost benefit to
using drones to perform internal structural
inspections in cargo tanks
• MCA is getting educated on the potential for
batteries to be considered ignition sources for
flammable atmospheres and residues
