|2. Zones and
criteria of classification
|3. Example of zoning
The european ATEX directives 94/9/CE and 1999/92/CE, revised in
2014, have introduced the notion of zoning in order to identify and
classify areas within a factory that present a risk of presence of
powder cloud in explosive conditions. It is a notion related to
the european regulation but in general, for every Dust Hazard
Analysis - DHA - the areas where an explosion can occur should be
The factory operator must carry out a dust explosion risk analysis, often
called ATEX study, in order to classify the areas according to
the probability of presence of a dust cloud (zoning). On the
other side, the equipment supplier must supply an equipment that is
compliant for the zone defined by the process operator.
|Zone 20||Location where an explosive atmosphere is
permanently present or during long periods or frequently
Order of magnitude : Dust in explosive concentration is present 1000 h or more / y (= normal process conditions)
|Zone 21||Location where an explosive atmosphere is likely to be
present occasionnaly in normal working conditions
Order of magnitude : Dust in explosive concentration is present 10 h 1000 h / y (= in certain process conditions)
|Zone 22||Location where an explosive atmosphere is not likely to be
present in normal working conditions or, if it is present, it
is only for short duration
Order of magnitude : Dust in explosive concentration is present from 1h to 10h / y (= very rare process conditions or abnormal conditions - leaks)
The zoning is fundamental to help the process operator to put in
place the measures necessary to reduce the risks of inflammation
of a dust cloud, or to put in place protections in case of
Note that layers and deposits of powder must be considered as well
as it could start burning in case of high temperature or be put in
suspension and form an explosive dust cloud.
[Laurent] is giving some common examples of equipment often falling in one category or another. WARNING : this is only a general indication, only the specific risk assessment of a process will be able to confirm if one equipment belongs to one zone or another depending on a particular context.
|Zone 20||Inside silos,
Inside transport systems of bulk solids...etc...
|Zone 21||Immediate surrounding of silos, hoppers, mixers, dryers,
cyclones, filters and system of transport...etc...
Found also around tipping station, when powder is poured into a container or vessel
|Zone 22||Occasional leaks at manholes, filters, in case of failure of flexible...etc..|
The zoning definition and the reasons justifying a particular zoning, or the absence of zoning, must be described in the ATEX risk analysis and the measures to put in place explained. Conclusions of the risks analysis must be implemented by the factory.