The ATEX directive concerning explosion safety is based on years
of research and well understood knowledge about the origins of
explosions. The most important causes are the occurrence of a spark,
or a surface temperature in excess of the auto-ignition temperature
of an explosive air-gas mixture. The accepted methods of protection
are all based on removing one or more of the necessary condition for
an explosion. The standard covering the general requirements to do
this is EN50014 (in CENELEC countries).
The best known methods of protection are:
Ex d based on EN50018
This method keeps an ignited air-gas mixture inside the
housing. Hot gasses are led to the outside though long narrow gaps
is such a way that they are cooled below the point that a new ignition
takes place outside the housing. This method places specific
demands on the construction of the housing, especially on the resistance
to internal explosions, dimensioning of the gaps, but also on the
use. For instance the equipments may not be opened while
energized. The advantage is the there are no particular
requirements in the electronics in the housing, only for wirings
that is led to the exterior. As a result the power supply
will often need to be Ex d or Ex e as well, while signal inputs
will be Ex i (see below).
Ex e based EN50019
This methods prevent sparking in passive equipment. In these
circumstances this would be caused by disconnecting or short
circuiting wiring. Therefore this methods attempts to prevent that
from happening by placing specific requirements on terminals and
connectors. As a result the method is mostly suitable for junction
boxes and the like.
Ex i based EN50020 (for use in Zone 0 EN50284 also
This method is called intrinsic safety. Here the stored energy
in the apparatus is limited to below the ignition energy of the
air-gas mixture. The surface temperature is kept below the auto-ignition
temperature of the air-gas mixture by limiting the supplied
Deviation of the methods in the standards are often necessary.
The manufacturer then needs to prove that the alternative measures
taken guaranty at least the same level of safety as when the
standards would have been followed. This often requires testing by manufacturer
and/or notified body/
Exalon Delft has ample experience in applying EN50014,
EN50018, EN50019, EN50020, EN50039 en EN500284.