Burning rate polymer dust

The Air Over Layer/Powder Layer Test is a method used to assess the ignition properties and flammability of a layer of combustible dust when exposed to an air stream. This test helps in understanding the potential fire and explosion risks associated with combustible dust layers in industrial settings. In the Powder Layer test, hot air passes over a layer of powder in an oven. The test will be similar to hot air passing over a layer of dust in, for example, cross flows, trays and band dryers. The test also simulates the condition of deposits on the internal surfaces of all types of dryers.

Testing Principle and Methodology

A metal tray is filled with the test sample, about 15mm layer and heated by hot air passing around the tray. The temperature of the powder layer and the oven are monitored by using K-type thermocouples. The temperature of the air is controlled by controlling the temperature of the oven.

During the screening test, the oven temperature (air temperature) is increased at a rate of 0.5°C/min to a temperature of 400ᣞC. The isothermal test is based on the onset self-heating temperature obtained during the screening test. The test is repeated successively at different isothermal temperatures until the accuracy is between 2-10ᣞC. The isothermal test is run between 8-24 hours.

Applicable Standard

The powder layer test follows a procedure described by John Abbot in his book ‘’Preventing Fires and Explosions in Dryers’’.

Data Interpretation

The 20°C safety margin is generally recommended to minimize the risk of decomposition in the plant, but it should not be the sole basis of safety. The powder layer test, described in this test, determines the ignition temperature for material layers of 15 mm depth, which is representative of the powder layers commonly found in most plants. However, for deeper layers of material, the ignition temperature is lower and measurements should be taken with deeper layers. Further information on the effect of depth can be obtained from the Self-heating Evaluation and Analysis in Reactive Chemical Services.

When to perform Powder Layer

The test is designed to simulate conditions in dryers in which hot air circulates above a layer of the material being dried or settled deposits on internal surfaces. This information is vital for determining the operating conditions under which a layer of powder can exhibit exothermic reactions.

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 powder layer tests, ensuring accurate and reliable results.
  • We have state-of-the-art powder layer 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 Air Over Layer Test for combustible dust?

Answer: The Air Over Layer Test assesses the flammability and ignition properties of a layer of combustible dust when exposed to an airflow and a heated environment.

Why is the Air Over Layer Test conducted?

Answer: It is conducted to evaluate how combustible dust layers interact with hot airflow and in a heated environment, helping in assessing fire and explosion risks in industrial settings.

How is the Air Over Layer Test performed?

Answer: A layer of combustible dust is spread on a surface of a metal tray within a test apparatus, and controlled airflow is directed over this layer while observing the self-heating behaviors of the sample.

What types of materials are commonly tested using the Air Over Layer Test?

Answer: Various types of combustible dust, including powders, granules, or fine particles from different industries like woodworking, food processing, or chemical manufacturing, are tested using this method.

What parameters are monitored during the Air Over Layer Test?

Answer: Parameters such as ignition time, flame propagation, combustion behavior, and potential for explosion are observed and recorded during the test.

How does the test simulate real-world scenarios involving combustible dust layers and airflow?

Answer: The test replicates conditions where dust layers are exposed to airflow, such as through ventilation systems, by subjecting them to controlled air streams within the test setup.

How are the test results utilized in industrial settings?

Answer: The data obtained helps in evaluating fire risks associated with combustible dust layers, guiding risk assessment, preventive measures, and safety protocols in workplaces.