Fires and dust explosions are one of the biggest threats in many industries where dust layers and/or clouds forms during technology processes, which are capable of ignition.

The Layer Ignition Temperature Testing (LIT) test is basically heating a compound directly to flame on Bunsen burner and we observe the nature of the flame. This is a test used to determine the type of bonding in organic compound. For unsaturated compound, you will observe sooty flame.

STANDARD FOR LIT

EN ISO/IEC 50281-2-1:1999 method A of determining minimum ignition temperature &

BS EN ISO IEC 80079-20-2 2016 explosive atmosphere.

PURPOSE

The layer ignition test (LIT) test determines the lowest temperature at which a layer of    dust of specific thickness, usually 5mmand 12.7mm, ignites on a heated surface.

5MM LAYER IGNITION TEMPERATURE TEST

The layer ignition Temperature test (LIT) test determines the lowest temperature at which a layer of dust of specific thickness, usually 5mm, ignites on a heated surface. It is an important test for industrial premises where heat generating equipment is present - such as electric motors or light fittings - as it evaluates the maximum permissible surface temperature to prevent fires and smouldering material.

A layer of combustible dust of known thickness is created by placing two semicircular formers on the hotplate apparatus, filling them with the test sample and removing any excess above the formers. A thermocouple positioned on top of the layer monitors the dust temperature during the test and the temperature is continuously recorded using data logging equipment.

Tests are repeated with fresh layers of dust until a minimum ignition temperature has been found. This is the lowest temperature, rounded down to the nearest integral multiple of 10°C, at which ignition occurs in a layer of given thickness. The highest value at which ignition does not occur is also recorded. The latter temperature must be no more than 10°C lower than the minimum ignition temperature recorded and is confirmed by at least three tests.

Ignition is considered to have occurred if glowing or flaming is initiated in the material, or a temperature of 450°C or more, or a temperature rise of 250°C or more above the temperature of the hot surface, is measured in the test. Under the test standard, testing is discontinued if ignition of a dust layer does not occur below a heated surface temperature of 400°C. This fact will be reported as the result of the test.

Any thickness of dust layer may be investigated, but 5mm is generally regarded as representing the thickest layer of dust likely in a factory having fully enclosed plant and process operations allied to a good standard of housekeeping. Where there is the possibility that dust layers in excess of 5 mm may be formed, the maximum permissible surface temperature must be reduced.

By testing the layer ignition temperature, fires caused by hot surfaces may be avoided. The temperature of motor casings, light fittings etc can be limited to less than the layer ignition temperature (LIT) with a suitable safety margin - usually 75°C

Dust Layer (5 mm) Igniting on a Hot surface

12.7MM LAYER IGNITION TEMPERATURE TEST

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 Centre for guidance.

Dust Layer(12.7mm) Igniting on a Hot surface

LIT TEST RESULTS

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 A LAYER IGNITION TEMPERATURE TEST?

LAYER IGNITION TEMPERATURE  (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?

1. Prime Process Safety Centre is a leader in process safety testing with very experienced laboratory personnel. At Prime Process Safety Centre 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.
2. We are knowledgeable and experienced in performing layer ignition temperature test, ensuring accurate and reliable results.
3. We have state-of-the-art LIT testing equipment, providing precise and sensitive measurements.
4. We follow strict testing protocols and quality control measures to ensure consistent and reliable test results.
5. Our team can interpret and analyse the data obtained from the tests, providing valuable insights and recommendations for your specific application or research.

BENEFITS

1. The LAYER IGNITION TEMPERATURE  (LIT) test is one of the three core tests for accessing a materials ignition sensitivity, particularly where ‘Avoidance of Ignition Sources’ is the ‘Basis of Safety’ for the operation.
2. The data is required for defining the maximum operating temperature for electrical and non-electrical equipment used in areas where the test material is present.