ExProtection_Dust-Basics.pdf

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the basics of
dust-explosion protection
Powders or dust like substances are processed or are byproducts of the production process in
many industries.
Whether the dust is useful (e.g. for the production of synthetics, pigments or pharmaceuticals)
or waste, a large majority of dustlike substances pose the danger of fire or possibly even
explosions. Eighty percent of all industrial dusts are combustible, and even a dust layer of 1 mm
in a closed room is sufficient to trigger an explosion when the dust is swirled up and ignited.
These facts, combined with the fact that those affected are not sufficiently aware of the danger
(in contrast to the danger of gas explosions) underlines the importance of preventing dust
explosions. This brochure is intended to help you analyse the danger of a dust explosion in your
facilities and to take the suitable technical and organisational steps to minimise this risk.
R. STAHL Explosion protection
contents
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Dust as a Risk Factor
Definitions and Parameters
Directives and Standards
Dust Explosion Protection Measures
Classification of Endangered Areas into Zones
Types of Dust Ignition Protection
Equipment Selection
Installation and Maintenance
Product Overview
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R. STAHL Explosion protection
dust-explosion protection
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dust as a risk factor
tinues, and under some conditions chain
reactions such as these sweep through entire
buildings or facilities, destroying them.
As is the case with gases, there are various
ignition sources for dusts, such as sparks from
electrical or mechanical processes, arcs,
open flames, an electrostatic discharge, electro-
magnetic waves and others.
Figure 2 shows the results of statistical studies in
North America, which examined the distribution
of the ignition sources of dust explosions. It shows
that mechanically produced sparks were re-
sponsible in almost one third of the cases. Add to
that the 13 % of explosions caused by open fire
and welding, and it becomes obvious that
many people are not aware of the danger of dust
explosions. Figure 3 shows that a wide variety
of industries are affected, including branches of the
food and wood processing industries, paper and
synthetics production, pharmaceuticals production
and others.
The data given above are confirmed by German
property insurers, who state that on average
there is one dust explosion per day in the Federal
Republic of Germany. Approximately one fourth
of these are caused by dust from food products or
animal feed.
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1. Dust as a Risk Factor
As with combustible liquids and the flammable
gas/air mixes that result from them, certain re-
quirements must be fulfilled for a suitable ignition
source to ignite a mix of dust and air and thus
trigger an explosion. No explosion can occur if one
of the following is not present: combustible dust,
air, ignition source.
Dust explosions have different characteristics than
gas explosions and can in some cases be
much more devastating. If a gas/air mix is ignited,
the force of the resulting explosion causes the
gas cloud to dissipate rapidly and thus dilutes the
gas/air mix to a concentration lower than that
necessary for further combustion. Thus, if no
further gas is added, the explosion is over after
several milliseconds.
Figure 1:
Explosion Risk Triangle
With combustible dusts it is different. If, for
example, a draft of air swirls up a layer of dust in
a small area, the dust, along with oxygen, forms
a combustible dust/air mix. If this mix is ignited by
an ignition source, an explosion is triggered.
The force of the resulting explosion swirls up more
dust, which is in turn ignited. This process con-
R. STAHL Explosion protection
5
Figure 2:
Ignition Sources of Dust Explosions
Static Electricity 9%
Smolder Spots 9 %
Friction 9%
Unknown 11,5%
Electrical
Equipment 3,5%
Other 2,5 %
Hot Surfaces 6,5 %
Fire 8 %
Self-Ignition 6%
Welding 5%
Mechanical
Sparks 30%
Figure 3:
Types of Dusts Involved in Dust Explosions
Wood 34 %
Grain 24 %
Other 6 %
Paper 2 %
Synthetics 14%
Coal/Peat 10 %
Metals 10%
R. STAHL Explosion protection

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