1. Burning Test - Evaluating the combustibility of material (what extent a fire started by an external source will propagate in a dust layer of a dried product).

Fire propagated in a dust layer of combustible powder is a major source of fire accidents in process industries. This source is in general neglected or unnoticed during safety checking.

The aim of the test is to determine if and to what extent a fire started by an external source will propagate in a dust layer. The combustibility of the dust sample is rated in accordance with the course of reaction and characterized as a class number from 1 to 6, respectively. On the basis of measuring examples the appropriateness of the method is demonstrated. In accordance with the guideline VDI 2263, the flammability and burning behaviour of dust layers are characterized as a combustion class number.

The dust to be tested is applied to a fire-resistant plate in the form of a continuous strip about 40 mm long and about 20 mm wide (volume about 5 ml). An electrically heated, glowing platinum wire at a temperature of about 1000°C is inserted along one end of the strip into the fabric to be tested for about 5 seconds.

2. Minimum Ignition Temperature for Airborne Dust (BAM) –

If an explosible dust cloud is generated on some uncontrolled way in the proximity of a hot surface of temperature above the actual minimum ignition temperature, the result can be a dust explosion. It is important, therefore, to know the actual minimum ignition temperature and to take adequate precautions to ensure that temperatures of hot surfaces in areas where explosible dust clouds can occur, do not rise above this valueHot surfaces capable of igniting dust clouds exist in a number of situations in industry, such as in furnaces and burners, and dryers of various kinds. In addition, hot surfaces can be generated accidentally by overheating of bearings and other mechanical parts.

This test is designed to determine the ignition temperature of airborne dust on a hot surface. The lowest temperature of the heated impact plate at which the dust blown into the oven ignites or decomposes producing flames or explosion in less or equal to 10 seconds is stated as the minimum ignition temperature. However, the minimum ignition temperature is not a true constant for a given dust cloud, but depends on the geometry of the hot surface and the dynamics of the cloud. In general this test is performed for <63 mm powders.

3. Decomposition Tests

1. Exothermic Reaction in an open Cup:  (Lütolf Oven)

This test is designed to determine the lowest temperature at which a substance shows an exothermic reaction under defined oxygen-lean conditions. It is done to products which are subjected to an elevated temperature over long periods of time, closed off from fresh air (e.g. in vacuum ovens, fluid-bed drier etc.). With this test, the maximum permissible temperature of the heating medium can be derived. The substance to be tested is heated up at a linear rate of 2.5°C/min (dynamic test) along with graphite powder as reference.

2. Decomposition Test (8 hrs Isoperibolic – DTA)

Elevated temperatures may subject a product to chemical transformations which will not require oxygen. The reaction may be endothermic or exothermic. An exothermic reaction is classified as an exothermic decomposition. It is, from a safety point of view, of great importance, contrary to endothermic decompositions. Such reactions may liberate gases of decomposition (smolder gases), which will result in a pressure rise in a closed vessel, which may subsequently tear or burst. The decomposition temperature measured is a relative value. It depends on the test method, and a conversion to actual conditions is problematic. In any case, the test method has to be stated together with the temperatures. If the temperature-programmed test results in an exothermic reaction, the sample is subjected to an isoperibolic test (at constant oven temperature). The isoperibolic test is repeated with fresh samples in decreasing 10°C steps until the substance does not show an exothermic reaction for 8 h (in certain cases even longer).

3. Decomposition Test in an Air stream (Grewer oven):

Determination of the lowest temperature at which a substance shows an exothermic reaction in a fresh air stream is done by this test. This test is designed to determine the relative auto ignition temperature of a product in a hot air-stream. It is applied to products which are subjected to elevated temperatures in an air-stream for a short period of time (e.g. spray drier, circulating air tray drier etc.). With this test, the permissible inlet temperature of the drier can be derived.    

4. Dust Explosivity Test in Modified Hartmann Apparatus:

 This test is designed as qualitative pre-test of the explosion behavior of a dust/air mixture. The product, which is milled down to a particle size of max 63 µm (main part), is whirled up in a vertical pyrex glass tube by an air blow.

5. Fall Hammer Test / Percussion Test:

For grinding processes and for paddle dryers with bars etc., the sensitivity of a product to shock has to be determined. A product is impact-sensitive and therefore explosive if it disintegrates with a bang upon its exposure to impact energy under given test conditions. For a single test, the result is regarded as positive if the test sample burns or decomposes with detonation, flame (sparks) or development of heavy smoke. Substances which detonate under the drop hammer are classified as explosives, and may not be milled in the plant.

6. Gas Evolution Test - Determination of amount of gas evolved on decomposition, along with the flammability of the gases of decomposition.
7. Heat Accumulation / Hot Storage Test - Determination of the lowest temperature at which, a substance shows an exothermic decomposition/reaction under insulated conditions in 400ml wire basket / Dewar flask(accumulation of heat).
8. Bulk Powder Resistivity :

Powders will nearly always acquire electrostatic charge during processing, the level of charge being largely determined by the violence of the process. The severity of the electrostatic problem can be evaluated by measuring of the resistivity of powder. Determines importance of static charge as a hazard

9. Minimum Ignition Energy (MIKE3):

A dust/air mixture would explode when ignition energy larger than a certain value that depends on the pressure, temperature, and dust concentration. The limiting energy of the ignition is called minimum ignition energy of the dust/air mixture. It is an important index to decide whether the dust can be handled in the air or should be handled in the inert atmosphere.

10. Deflagration Test:

This test determines whether a sample, when subjected to a standard initiation source, will deflagrate.

11. Charge Decay Test :

 It is the measure of electrostatic charge relaxation (or retention) on a powdered solid/liquid/solid substrate) and gives information about whether the powder is susceptible to accruing potentially hazardous levels of charge and if so for how long.