World Grain - February 2008 - 65

GRAINOPERATIONS

Usually the best that can be practically achieved is a reduction in dust clouds by good plant design and housekeeping and
control of sources of ignition by technical measures, such as
bearing temperature and belt slip detectors, as well as procedural measures.
Despite controlling sources of ignition, there will be areas
in the plant where there is a residual risk of an explosion.
Therefore measures must be taken to protect against the worst
effects of an explosion should one occur. The protective measures employed include:
* Containment - The vessel or plant is built strong
enough to withstand the effects of an explosion. High pressures of approximately 118 psi with cereal dusts are typical.
Containment can be a useful and practical option for small
vessels and vessel connections but is rarely a practical or
cost-effective option for standard equipment in grain plants,
although heavily built equipment such as hammermills and
rollermills will likely be strong enough to withstand the effects of an explosion within the machine itself.
* Isolation - Explosions are isolated from other parts
of the plant by mechanical or chemical means to prevent explosion propagation. Equipment used for isolation are rotary
valves, screw conveyors with baffles and material plugs, fastacting shut-off valves, passive barrier valves and chemical
barriers.
* Suppression - Suppressant material, usually in powder
form, is rapidly injected into an explosion as soon as possible
after ignition is detected to quench the explosion at its source.
Optical and/or pressure sensors are used to detect the explosion and activate the release of suppressant. It is important
that the suppression system is well designed for the particular
application to avoid false activation.
* Venting - Extremely common in grain handling facilities, venting consists of weak panels designed to rupture in the
event of an explosion. These panels are fitted to vessels to relieve the explosion to a safe area. Where vents cannot relieve
to a safe area, flameless vents can be usefully employed. These
vents are fitted with membranes or diaphragms that are de-

A prime example of a secondary dust explosion risk due to poor housekeeping in a grain processing facility. Photo courtesy of Euratex Ltd.

carried out with the support of a competent person that is experienced and knowledgeable in the field of explosion protection and your particular industry.
In a nutshell, the objective is to identify solutions that will
achieve a basis of safety, providing maximum safety and simplicity at minimum cost.
You then must decide how and when the solutions will be
implemented. The timing will, of course, depend on local circumstances and resources available.
Draw up a plan that will include targets and milestones
to be achieved. Aim to stick to the plan until you achieve
your goals, remembering at each step you are improving
safety. Remember to regularly review your progress against
the plan.
PREVENTION AND PROTECTION MEASURES
Ideally, formations of dust clouds and sources of ignition
should be prevented completely. In practice, however, this is
often not possible or practical in the grain industry.

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Dieselstrasse 5-9, D-21465 Reinbek / Germany
Phone: +49 40 727 71 0, Fax: +49 40 727 71 100
info@amandus-kahl-group.de

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For more information, see Page 86.

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World Grain - February 2008

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