Dust Explosion Testing

The dust explosion test laboratory at GexCon offers a wide range of standard tests for the determination of the ignition and explosion properties of dusts and powders. By knowing these properties for all materials handled in your plant or process allows the necessary safety precautions to be taken to prevent dust explosions and/or reduce their consequences. Performance of risk assessments regarding dust explosion hazards without the knowledge of such characteristics is virtually impossible.

Manufacturers of flammable dusts and powder products are obliged to know the ignition and explosion properties of their products and submit them to thier customers as part of the information given in their Material Safety Data Sheets (MSDS).

The test laboratory also provides specialist advice and assists when GexCon is performing accident investigations and explosion risk assessments since, only when the ignition and explosion properties of the material(s) being handled are known, can the exposion risk inside a powder handling plant be evaluated properly.

Examples of Some Standardised Tests for Dusts:

• Explosibility/flammability test.The explosibility test is performed to determine whether a dust/powder mixed with air (dust cloud) can give rise to dust explosions or not. The test is usually performed in the 20-litre apparatus but can also be performed in the open Hartman Tube for A/B dust classification (UK).
• Explosion Pressure Development (Pmax & Kst). This test is performed in the so-called 20-litre sphere apparatus. The flammability characteristics, maximum explosion pressure and rate of pressure rise are measured, from which the dust explosion constant, K_St -value of the dust/powder mixed with air can be obtained. This value is used to design explosion safe equipment, calculate explosion vent areas. It is also necessary for the correct dimensioning and design of explosion suppression and explosion isolation systems.
• Lower Explosion Limit (LEL). The lower explosion limit describes the minimum dust concentration of a dust, when mixed with air, for which dust explosions are possible. The lower explosion limit is a parameter used when assessing dust explosion hazards inside dust handling equipment and is measured in the 20-litre apparatus.
• Minimum Ignition Energy of dust clouds (MIE). This test yields data used to assess the ignition sensitivity of a dust cloud to electrical sparks. The parameter is used to assess the hazards of electrical, electrostatic and mechanical sparks. The test is performed in the Open Hartmann Tube apparatus.
• Minimum Ignition Temperature of dust clouds (MITdc). The Minimum Ignition Temperature of dust clouds is used to assess the hazards associated with hot surfaces and mechanical sparks. The test is performed in the Godbert Grenwald Oven and determines the minimum surface temperature which causes ignition of a dispersed dust cloud.
• Minimum Ignition Temperature of dust layers (MITdl).This parameter describes the minimum temperature of a hot surface that is able to ignite a dust layer of a given thickness resting on its surface. In practice the following hot surfaces may exist: surfaces of hot equipment, heaters, dryers, steam pipes and electrical equipment.
• Limiting Oxygen Concentration (LOC). The limiting oxygen concentration describes the lowest oxygen content for which a dust cloud, mixed with oxygen depleted air, can be ignited and is thus used during the assessment and design of inerting applications. The LOC is measured in the 20-litre apparatus.
• Self Ignition Temperature of dusts (SIT/AIT). The Auto Ignition Temperature of a powder material is used to assess self-ignition hazards of powder/dust stored in bulk (e.g. in silos). The test is performed in the warm storage oven and several test volumes are used to allow the test data to be extrapolated to industrial size vessels. The test also yields an estimate of the induction time or the time it takes for self-ignition to occur. The AIT of a bulk material deceases as the storage volume increases but the induction time increases.
• Volume Resistivity of dust layers. This test allows measurement of the volume restivity of a dust by measuring the charge transfer capability of a dust sample placed between two insulating electrodes.

More details concerning the test methods and the standards used can be obtained from GexCon/here.

Calibration Round Robin Tests

According to international standards (e.g. ISO 9000, GLP), test equipment must be calibrated at intervals by comparison with a standard or calibrated tests apparatus in order to assure measurement accuracy. Unfortunately there are neither internationally recognized reference samples nor reference equipment available for the determination of explosion characteristics. Therefore, a calibration round robin test (CaRo) is carried out every second year. CaRo is a collaboration between several explosion test laboratories in Europe including GexCon by which their test equipment for determination of explosion characteristics are investigated, compared and calibrated.

Screening Tests for Ignition and Explosion Risk Analysis

Although a majority of the testing work performed in the dust explosion laboratory consists of full standard tests like those described above, GexCon also provides a number of dust screening tests or screening packages, in which several of the test procedures above are used but the number of tests and scope of the variation of test conditions is reduced from that required for a fully-fledged standardised test in order to allow several of the most important  ignition and explosion properties to be characterised approximately. The results obtained from such screening tests, although not accurate enough or valid as "standard values" required for MSDS, are often more than good enough to be used as a basis for explosion risk analysis etc as required by the ATEX 99/92/EC directive .

If you require any help or advice concerning ATEX risk analysis or dust explosion tests or screening, please contact any of the following: