Gas explosion is a phenomenon that a combustible gas or vapor forms an explosive gas (vapor)/air mixture with a certain mixing ratio, and the mixture explodes in the presence of an ignition source.
A combustible gas or vapor forms an explosive gas (vapor)/air mixture with a certain mixing ratio, and the mixture explodes in the presence of a certain ignition source. Explosion can be prevented by eliminating one of three combustion elements, namely fuel, air (oxygen), and ignition source. Since the elimination is sometimes difficult in actual situations, it is necessary to evaluate an explosion condition of the target substance and handle it in atmosphere where the condition is never met. It is also important to understand explosion severity in order to minimize influence in the event of explosion. The following test meets this requirement. However, since explosion is affected by not only temperature and pressure but also test apparatus and method, thorough analysis of test results by specialists is needed. SCAS has the following two kinds of apparatus for more practical assessments.
Test Items
- Explosion range (upper and lower explosion limits)
- Limiting oxygen concentration
- Minimum ignition energy
Explosion range (upper and lower explosion limits), Limiting oxygen concentration, Minimum ignition energy
| 1L spherical explosion test apparatus | 2L spherical explosion test apparatus | |
|---|---|---|
| pressure | ruduces pressure to 1 Mpa gauge | reduces pressure to 1 Mpa gauge |
| temperature | room temperature to 200 degC | room temperature to 300 degC |
| ignition source | nichrome wire fuse | nichrome wire fuse |
Explosion range (upper and lower explosion limits)
The highest explosion concentration of a combustible gas (vapor)/air mixture is called upper explosion limit, and the lowest explosion concentration is called lower explosion limit. The concentration range between the two limits is called explosion range. Since the explosion limits depend on the temperature and pressure, the explosion range needs to be determined under the operating condition. SCAS can measure up to 300 degC for substances that do not decompose.
Limiting oxygen concentration
A combustible gas (vapor), oxygen, and inert gas (N2, CO2, H2O, etc.) mixture would not explode regardless of the combustible gas (vapor) concentration, if the concentration ratio of the inert gas to oxygen is increased to a certain value. This oxygen concentration is called limiting oxygen concentration. SCAS can measure using these inert gases.
Minimum ignition energy
When a combustible gas (vapor) forms explosive mixture, it would not explode if the energy of an ignition source is decreased sufficiently. The energy limit at which a combustible gas (vapor)/air mixture does not explode regardless of the combustible gas (vapor) concentration is called minimum ignition energy. SCAS can measure up to 100 degC if necessary.
Note: In 2016, JIS Z 8834 "Method for determining minimum ignition energy of dust/air mixtures" was issued.
*1 IEC 1241-2-3 "Electrical Apparatus for Use in the Presence of Combustible Dust, Part 2: Test Methods, Section 3: Method for Determining Minimum Ignition Energy of Dust/Air Mixtures", 1994
| equipment | 150mL cylindrical explosion test apparatus |
| pressure | atmospheric pressure |
| temperature | room temperature to 100 degC |
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