A primary explosion takes place inside a process vessel – in this case a vertical glass tube – and propagates away from the ignition source.
The first video sequence, shot at 600 frames per second, shows just 1 gram of custard powder dispersed inside a 1.2 litre volume - a dust concentration of approximately 830 g/m3. Note how the explosion pressure drives the dust ahead of it and out of the tube. Debris from the explosion - mostly pieces of unburnt powder - continue to fall for some time afterwards. The second video sequence shows the same quantity of custard powder being ignited, but viewed from above. Note the thin plastic film held across the tube opening that acts as an explosion relief vent.