Layer Ignition Temperature of Dust (LIT)

The Layer of Ignition Temperature or the Minimum Ignition Temperature of a dust layer is the lowest temperature at which the dust layer is capable of autoigniting on a hot surface. The test is used to assess the maximum operating temperature for electrical and non-electrical equipment used in areas where test material is present.


About 12.7mm layer of the material to be tested is placed on a preheated hot surface. A K-type thermocouple is stretched across the material on the hot surface. The temperature of the hot surface is kept constant while observing the reaction of the material for about 2 hours.

Ignition of the material is defined as an observation of a flame, incandescence or a rise in temperature of the material to at least 50ᣞC above the temperature of the hot surface. At the ignition of the material, the temperature of the hot surface is lowered with a fresh sample until there is no ignition. ASTM recommends the particles size of the material to be tested to be at least 95% less than 75 microns and less than 5% moisture. In certain unique cases where there is no chance of segregation of the material during normal operation, the material can be tested as received. In case of uncertainty on how to perform the testing please contact Prime Process Safety Center for guidance.


Dust Layer Igniting on a Hot surface

Applicable Standard

The LIT test is conducted in accordance with the American Standard Testing Method (ASTM) E2021. ‘’Standard Test Method for Hot-Surface Ignition Temperature of Dust Layers’’

Data interpretation

Materials with LIT values between 300ᣞC and 400ᣞC are common for most organic solids and some metal powders. Other organic solids such Lycopodium powder may be very sensitive to hot surface temperature and can have LIT values less than 250ᣞC. The results obtained from the Minimum Temperature of a dust layer test is used to assess the susceptibility of a dust layer to ignition by heated environments, such as hot surfaces.  It is also used in the selection of suitable electrical equipment for Class II locations.

When to perform (LIT)

LIT is performed when assessment of likelihood of ignition during powder handling is required and have specific application for the assessment and control of hot surface ignition of a dust layer. LIT is an important parameter used in assessing the fire risks associated with combustible dust layers and is essential in establishing safe handling practices and storage conditions to prevent potential dust-related fires

Why work with Prime Process Safety Center

  • Prime Process Safety Center is a leader in process safety testing with very experienced laboratory personnel. At Prime Process Safety Center our goal is to provide accurate, reliable and defensible data that meets industry and regulatory standards. We understand the need for the quality of your data, and we work assiduously to achieve just that.
  • We are knowledgeable and experienced in performing layer ignition temperature test, ensuring accurate and reliable results.
  • We have state-of-the-art LIT testing equipment, providing precise and sensitive measurements.
  • We follow strict testing protocols and quality control measures to ensure consistent and reliable test results.
  • Our team can interpret and analyze the data obtained from the tests, providing valuable insights and recommendations for your specific application or research.


What is the Layer Ignition Temperature (LIT) of a dust layer?

Answer: The LIT of a dust layer refers to the lowest temperature at which a layer of combustible dust can self-ignite and sustain combustion without an external ignition source.

Why is the LIT of a dust layer important in industry?

Answer: Knowing the LIT is crucial for assessing fire hazards associated with combustible dust layers. It aids in establishing safe storage, handling practices, and preventive measures in industries to mitigate fire risks.

How is the LIT of a dust layer determined?

Answer: Determining the LIT involves specialized testing where dust layers are subjected to increasing temperatures until ignition occurs, observing the lowest temperature at which self-ignition happens.

What factors influence the LIT of a dust layer?

Answer: Factors such as dust composition, particle size, moisture content, and specific characteristics of the dust significantly impact the MIT.

How does the LIT vary among different types of combustible dust?

Answer: Different types of dust have varying MITs based on their inherent properties. Finer particles, higher moisture content, or certain chemical compositions can affect MIT values.

What safety measures should be implemented based on the LIT of a dust layer?

Answer: LIT data aids in establishing safety guidelines, including safe temperature thresholds for storage, handling, and operational controls to prevent spontaneous ignition.

How do environmental conditions affect the LIT of a dust layer?

Answer: Factors like temperature, humidity, and airflow influence the LIT. Higher temperatures or dry conditions might decrease the LIT.

Does the LIT change over time for stored dust layers?

Answer: Aging, contamination, or changes in dust properties might impact the LIT over time, requiring periodic reassessment of safety measures.

In what industries or scenarios is knowledge of the LIT of a dust layer crucial?

Answer: Industries dealing with combustible dust, such as woodworking, food processing, or pharmaceuticals, find LIT data essential for fire prevention and workplace safety.