Hazard classification test for combustible dust

• Group A (hazardous) – the dust cloud propagates flame from the ignition source and is classed as a combustible and potentially explosible material.
• Group B (non hazardous) – the dust cloud does not propagate flame from the ignition source and is classed as a non-combustible material.
• Group A dusts (combustible) may form Zone 20, Zone 21 and Zone 22 hazardous areas, depending upon the frequency and duration of the explosive atmosphere.

Explosion indices test (Kst value and P max)

Dust explosion classes ST1, ST2 & ST3

• ST class 0 – Kst value = 0
• ST class 1 – Kst value less than 200 bar m/sec
• ST class 2 – Kst value between 200 and 300 bar m/sec
• ST class 3 – Kst value greater than 300 bar m/sec

and explosion containment). Results of testing from our database for common dusts are shown in the table below.

Testing for minimum ignition energy (MIE)

Dusts sensitive to ignition by electrical spark

The minimum ignition energy (MIE) test measures the ease of ignition of a dust cloud by electrical and electrostatic discharges. The test is carried out according to EN ISO/IEC 80079-20-2:2016 (Explosive atmospheres Part 20-2: Materialcharacteristics – Combustible dusts test methods).

The MIE apparatus consists of a borosilicate tube placed over a dispersion cup and fitted with two electrodes. The electrodes are connected to a circuit that produces an electrical spark of known energy. A weighed sample of combustible dust is placed in the dispersion cup, which is blown up through the tube with compressed air past the ignition source. If flame propagation is observed, the energy of the spark is reduced until no flame propagation is seen for 10 consecutive tests. At that spark energy, a range of dust sample weights is tried to thoroughly investigate potential dust explosion concentrations.

The test result is stated as an energy range, indicating that ignition took place at the higher value and no ignition took place at the lower value. The MIE is a measure of how sensitive an explosive dust cloud is to electrical spark ignition. Testing for minimum ignition energy gives guidance on whether ignition by electrostatic discharge from plant personnel or process conditions is likely to occur in practice.

Minimum ignition temperature (MIT)

Minimum ignition temperature of a dust cloud

We offer a large scope of dust testing options, such as: 

• Layer Ignition Temperature (LIT)
• Limiting Oxygen Concentration
• Lower Explosible Limit
• Isothermal Basket Test
• Powder Volume Resistivity

To find out about all the testing options available and to speak with our dust testing specialist, click here or contact us below and we will be happy to handle your enquiry.