Layer Ignition Temperature (LIT)

1. Relevant standards:

• EN 50281-2-1,

• EN ISO/IEC 80079-20-2,

• ASTM E2021.

2. Differences between standards:

• Sample particle size rules:

  • • EN 50281-2-1: it is recommended that the test sample be less than 200 µm (in the case of coarser powder, particles should be below 500 µm).

    • ASTM E2021: it is recommended that the test sample be at least 95% minus 75 µm.

• Conditions for inflammation:

  • • EN 50281-2-1: Ignition is considered to have taken place when visible evidence of combustion is apparent, such as red glow or flame; or temperature is at least 450 ° C; or the hot plate temperature is higher at least with 250 K than the specified value.

    • ASTM E2021: Ignition is considered to have taken place when visible evidence of combustion is apparent, such as red glow or flame or temperature in the dust layer at position of thermocouple rises at least 50°C above the hot plate temperature.

3. Measuring equipment:

• CTL15 Chilworth (1. Figure):

  • • Maximum temperature: 400°C

    • Measurable sample thickness: 5, 12.5or 15 mm thickness in a 100 mm diameter „sample holder” ring

4. The amount of sample required:

• 500 g

5. Aim of the test

• To determine the minimum temperature of a hot surface capable of igniting a powder layer (5 mm in depth).

6. The procedure of the measurement

• Checking the homogeneity of the tested powder sample and its compliance with the standard requirements.

• During the test, the powder layer shall be placed in a metal ring with an internal diameter of 100 mm in a layer of 5±0,1 mm.

• To perform the test, it is necessary to adjust the temperature of the heated surface to the desired value and to reach a steady state. The metal ring should be placed in the center of the surface and the powder layer described above should be formed in 2 minutes.

7. Results, evaluation

• Inflammation of the dust layer occurs when:

  • • visible glow or flame is observed, or

    • the temperature of the powder reaches a value of at least 450 °C (EN 50281-2-1), or

    • the hot plate temperature is higher at least with 250 K than the specified value (EN 50281-2-1), or

    • the temperature in the dust layer at the position of thermocouple rises at least 50°C above the hot plate temperature (ASTM E2021).

• If no auto-ignition is detected after 30 minutes, the test should be terminated and repeated at a higher temperature. All tests must be performed with a fresh layer of powder.

• If inflammation or spontaneous combustion is observed, the test should be repeated at a lower temperature. The result of the test is the temperature at which ignition or spontaneous combustion is still present, but not at a temperature 10 K lower. This needs to be confirmed by at least three tests. If no inflammation is observed at 400 °C, the test must be repeated at 200 and 300 °C to confirm the non-inflamed result.

8. Limitations of the test

The standard test examines 5 mm layers (thicker layers may result in lower values).

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