Good housekeeping : avoid secondary explosions

Making sure the process area remains dust free to avoid secondary explosions

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Section summary
What it is about
What must be done

Bulk Solids Handling Safety
# Dust explosion physical properties # MIT - Minimum Ignition Temperature of dust

1. What it is about

It is not uncommon, when visiting a plant processing powders, to realize that a fine layer of dust is covering the equipment, the surrounding of the process, sometimes the floor.

One must realize that it is a safety risk.

Indeed, dust layers outside the process equipment can have the following effect :

- Cover motors and increase their temperature : it can lead to an ignition of the powder, but if the motor has been designed according to the ATEX zone it is positionned, the temperature should be lower than the MIT and SIT of the powder.

- Create a dust cloud if the powder is put in suspension

This last risk is very often overlooked. Dust deposits may not be seen as harmful, but they can trigger a secondary explosion that can be very dangerous and may even destroy a building. Indeed, if an explosion happens in the process, the explosion shock wave and draft can put in suspension all the dust in the surroundings. If the dust cloud reaches a non ATEX equipment, like a very hot light bulb, a secondary explosion will be triggered.

This type of accident has been very frequent in large grain or sugar facilities. One can refer to the Imperial Sugar Accident in 2008.

2. What must be done

Housekeeping, means cleaning the process area, is MANDATORY for any process industries using powders.

The maintenance must be such that no dust leak is allowed from the process to the surroundings. The operators must be trained to understand the risk and take actions to stop dust emission sources and clean any spill of powder in the process area.

Good housekeeping must be part of the actions from the dust explosion risk analysis and the procedures put in place to do so must be described and respected. Conclusions of the risks analysis must be implemented by the factory.

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