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636 Dust Explosions in the Process Industries

process industries,by the three independent technical committees: CENRC 114,CENRC
305, and CENLECRC 31.Rogers (1996b) outlined the work performed by the European
Union working group CENRC 305/WG 2 on developing standardsfor nonelectrical appa-
ratus to be used in explosive atmospheres,including explosive dust clouds.
Makin (1999) described the essential features of the European Union Machinery
Directive, with particular emphasis on the links to the “Atex 1OOa”Directive in matters
related to accidental explosion risks. Wingerden (1999) described the basis and philos-
ophy underlying the development of the new explosion venting standard produced by
the European Union CEN/TC 305.
Various aspects of the Atex approach adopted by the European Union were discussed
by Radandt (2001), Grass (2001), Carruthers (2001), Dyrba (2001), Uth (2001), Ott
(2001), Rogers (2001),Wingerden (2001),Pineau (2001), Fuchs (2001), and Dill (2001).
These included superior legal issues such as the relationship between national and
European Union law, variousAtex directives, and a range of specific technical standards.
Feitenhansl(l996) outlined the new European Union system of standards and guide-
lines for testing, certifying, and control related to prevention and mitigation of dust
explosions in the process industries. Griesche (2001) and Fritsch (2001) discussed the
procedures required by the European Union for testing and certifying specific commer-
cial apparatus to be used in dust explosion protection in the process industries. Jockers
(2001) and Unruh (2001) focused on the problem that, in the new European Union
system, a given apparatus has to comply with several different standards.

9.4
STATUS AND OUTSTANDING PROBLEMS IN TESTING
DUST IGNITABILITY AND EXPLOSIBILITY

9.4.1
HISTORICAL BACKGROUND AND INTRODUCTION

The testing philosophy and test methods are discussed extensively in Chapter 7. When
some of the older test methods were designed, the ambition was, in fact, quite modest.
The originalintention was just to establish some relative measures of properties of prac-
tical relevance to preventing and controlling or mitigating dust explosions. Later, some
of these methods were adopted as official standards, and test data were sometimestreated
as basic physical constants for a given dust to an extent far beyond the originalpurpose
of the test. As more knowledge from systematic research became available, the lack of
justification for this use of these test data was pointed out and the arbitrary, relative
nature of the various test methods was brought to light again.
The current situation is complex. It is realized that only a few of the dust parameters
currently being used to characterizethe ignition sensitivity and explosibility of dusts can
be regarded even as approximate “physical or chemical constants” for a given dust. In
most cases, a great number of variables are involved and a differentiatedview is required.
In general, measurements or testing may be conducted on various levels of resolution,
ranging from pragmatic full-sale testing to highly detailed microscopic measurements.
However, all the way through, twin sets of measurable parameters and matching theory