October 29, 2015

29/10/2015: Dust explosion: Is suppression the solution in grain hammer mills?

by Kevin Spiess, EMEA Sales Manager for Explosion Protection, BS&B Safety Systems, UK

First published in Milling and Grain, July 2015

There have been newsworthy examples of grain mill fires around Europe in recent years: 2010 Verdelot in France saw the destruction of Moulins Bourgeois mill; in 2014 a major fire broke out in Chancelot Mill in Edinburgh. Recently in 2015 a fire consumed Allied Mills at Tilbury Docks, London.

The originating causes of grain mill fires may be varied; a spark, a carelessly discarded match, electrical fault, or grinding and milling friction. However, the fuelling and propagation of a possibly fatal explosion is almost always caused by grain dust.

Why are hammer mills an explosion risk?
Among the locations commonly identified for primary dust explosions, hammer mills sit as a leading contender for explosion initiation. Hammer mills are sources of explosion ignition because they pulverize raw materials against a surface at high impact. When surfaces contact in this way, the impact and friction causes sparks and hot spots, which are ideal ignition sources for dust accumulations or dust clouds.

According to the UK Health and Safety Executive (HSE) guidance on Prevention of Dust Explosions in Food Industry (Milling and Grinding): “Hammer mills are often engineered to be strong enough to contain a dust explosion, but sparks or smouldering particles may spread from the mill to other more vulnerable equipment.”

However, what are the consequences when a hammer mill fails to contain such an explosion?

The very nature of the materials being processed and handled turn a hammer mill into a potential tinder box. Explosions are caused by the trinity of ignition, fuel and oxygen. When these three elements come together in an enclosed area, with rising pressure and rapid increases in temperature, a deflagration can occur. This primary explosion can cause a pressure wave carrying with it a flame that disturbs accumulated grain dust. Nearby personnel and property are now at great risk of harm.   

Read the full article in Milling and Grain HERE.  

The Global Miller
This blog is maintained by The Global Miller staff and is supported by the magazine GFMT
which is published by Perendale Publishers Limited.

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