Minimum Ignition Temperature of a Dust Cloud (MIT)

1. Related standards:

  • EN 50281-2-1,

  • ASTM E1491.

2. Difference between standards:

  • Requirements for the moisture of dust:

      • EN 50281-2-1: Requirements for moisture of dust must not exceed 15%.

      • ASTM E1491: Requirements for moisture of dust must not exceed 10%.

  • Requirements for the particle size:

      • EN 50281-2-1: Requirements for particle size must not exceed 75 μm.

      • ASTM E1491: 95% -of the dust must be below 75 μm.

  • Initial parameters of the measurement:

      • EN 50281-2-1: The dust weighs 0.1 g with the compressed air pressure of 0.1 bar test at a temperature of 500°C.

      • ASTM E1491: at a temperature of 600°C.

  • Final results measurement accuracy:

      • EN 50281-2-1: Above 300°C an accuracy of 20°C must be determined, below 300° C an accuracy of 10°C must be determined.

      • ASTM E1491: An accuracy of 10°C must be determined.

  • The number of negative tests:

      • EN 50281-2-1: 10 negative tests.

      • ASTM E1491: 5 negative tests.

3. Measuring equipment:

A Godbert-Greenwald furnace which an electrically heated, measuring range is between 20°C and 1000°C (Figure 9.).

Godbert-Greenwald furnace

4. The amount of sample required:

  • Total of approx. 200-250 g.

5. Aim of the test:

  • Determining the minimum ignition temperature of a dust cloud in contact with a hot surface.

6. The procedure of the measurement:

  • There is a tube vertically placed tube in the Godberg-Greenwald furnace with the bottom open to the environment. The horizontal tube is connected to the dust sample dispensed by a glass observation chamber.

  • The dust to be tested is transferred from the sample through to the inside of the furnace using compressed air.

  • Flammation occurs when a flame appears on the bottom of the device which is also visible through the monitoring chamber. The temperature is measured by two thermocouples connected to the furnace wall.

  • Relationship between concentration and amount of dust:

Relationship between concentration and amount of the sample

7. Results, evaluation:

  • EN 50281-2-1:

      • If the test is negative (when no flame is experienced), it must be carried out at a temperature 50°C higher.

      • If the test is positive (when a flame is experienced), the test must be repeated with different amounts of dust and compressed air pressure to determine in which case the flammation was most severe.

      • Then the test must be repeated in increments of 20°C until no more flammation is experienced.

      • At this temperature, the amount of dust and the compressed air pressure must be changed again and if no flame is experienced this test temperature will be the final result. If this is experienced, the test must be repeated at a temperature reduced by 20°C.

      • At temperatures where no flammation was experienced, 10 negative tests must be produced.

  • ASTM E1491:

      • If the test is negative, the temperature must be increased in steps of 50-100°C.

      • At the highest temperature where no flammation has yet been experienced, change the amount of powder and repeat the measurement.

      • If flammation is observed, the test must be repeated after lowering the temperature.

Example of a MIT result

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