Dust Explosions

Top Tipps on How to Avoid Dust Explosions

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Ignition within enclosed area When a dust cloud ignites in an enclosed volume, it results in a very rapid rise in pressure within the container – e.g., a silo or closed room. The container may not be strong enough to withstand the pressure from the explosion, and it will fail in a sudden and uncontrolled manner. The plant or building will survive only if the design or other protective measures deliberately allow for the high pressure.

Where an item of the plant fails, or an explosion vent opens as a result of a dust explosion, a fireball and shockwave will emerge. The fireball is usually much larger than the vessel from which it comes, and is likely to spread burning particles up to a substantial distance. Dust clouds are formed by dust falling into an area or being raised by blasts of air. Dust is heavier than air, and therefore it will eventually settle, however an explosion within a piece of plant can stir up these dust deposits to create a secondary explosion, which is generally more destructive than the primary explosion.

Preventing Dust Explosions

In order to prevent dust explosions, companies should follow some practices. They should find out what dangerous materials are present in their workplace or plant, and define the resultant fire and explosion risks. They must take action to either remove those risks, or where this is not possible, control them. A target should be made to take action to reduce the effects of an incident involving dangerous materials. Preparation of plans and procedures to deal with accidents, incidents and emergencies involving dangerous materials is very essential. Identification and classification of areas of the plant where combustible dusts may occur, and avoiding ignition sources in those areas are very important.

Ideal plant design to Avoid Explosive Dusts

Ideally plant design should eliminate the risk of dust clouds forming, or make provision to eliminate the risk of ignition sources existing in the same area. If this cannot be achieved, then protection measures must be implemented – for example, explosion venting, explosion suppression or containment. Ignition can be caused by friction, static discharge, hot surfaces and mechanical sparks.

The probability of a hazardous area occurring in a particular area of the plant is defined by ‘zoning’ and certain types of equipment are certified as being suitable for each zone of use. Some electrical equipment is certified for gas hazards only. It is important therefore to select equipment that is certified for gas and dust hazards. For example: II2 GD for use in Zones 21 and 22.

Conclusion: How to Avoid Dust Explosions

Housekeeping within the plant must be kept at a very high standard. Regular visual checks should be made to ensure that areas remote from the process are dust free – to prevent the possibility of a secondary explosion. For example, floors, overhead pipes, the roof space above a suspended ceiling and ventilation ducts.

* Joint Managing Director of K Controls, UK.