A732-01-880 Issue D
Page 16
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Operation
4.5
Implication of ATEX directive
4.5.1
Introduction
This equipment is designed to meet the requirements of Group II Category 3 equipment in accordance with Directive
94/9/EC of the European Parliament and the Council of 23rd March 1994 on the approximation of the laws of the
Member States concerning equipment and protective systems intended for use in potentially explosive atmospheres.
(The ATEX Directive).
The ATEX Category 3 applies in respect of potential ignition sources internal to the equipment. An ATEX Category has
not been assigned in respect of potential ignition sources on the outside of the equipment as the equipment has not
been designed for use where there is an external potentially explosive atmosphere.
There is no potential source of ignition within the pump during normal operation but there may be potential sources
of ignition under conditions of foreseeable and rare malfunction as defined in the Directive. Accordingly, although
the pump is designed to pump flammable materials and mixtures, operating procedures should ensure that under all
normal and reasonably foreseeable conditions, these materials and mixtures are not within explosive limits. Category
3 is considered appropriate for the avoidance of ignition in the case of a rare malfunction which allows flammable
materials or mixtures to pass through the pump whilst within the explosive limits.
4.5.2
Flammable/pyrophoric materials
When flammable or pyrophoric materials are present within the equipment:
Do not allow air to enter the equipment.
Ensure the system is leak tight.
Dilute and flammable gases or vapours by using an inert purge, for example nitrogen, to the pump inlet and/
or gas ballast (if fitted) of the primary pump backing the XDS100B. Concentration levels of the gas or vapour
within the pumps and exhaust lines should be reduced to less than one quarter of the published lower
limits (LEL).
4.5.3
Gas purges
CAUTION
The following actions must be taken to ensure that the gas being pumped stays out of the flammable range.
The inert gas purge into the pump inlet or gas purge of the primary pump backing the XDS100B should be switched
on to remove air from the pump and exhaust before the process starts. The purge flow can be switched off at the
end of the process only after any remaining flammable gases or vapours have been purged from the pump and exhaust
line.
If liquids that produce flammable vapours could be present in the pump foreline then the inert gas purge to the
XDS100B should be left on all the time this liquid is present. Flammable liquids could be present in the foreline as a
result of condensation or may be carried over from the process.
When calculating the flow rate of inert gas required for dilution, consider the maximum flow rate for the flammable
gases/vapours that could occur. For example, if a mass flow controller is being used to supply flammable gases to
the process, assume a flow rate for flammable gases that could arise if the mass flow controller is fully open. The
inert gas purge flow rate should be continually measured and if the flow rate falls below that required, then the flow
of flammable gases or vapours to the pump must be stopped.
Edwards recommends obtaining and reading Vacuum Pump and Vacuum System Safety publication P400-40-100
available from Edwards or the supplier.
WARNING
If nitrogen purge is used to dilute dangerous gases to safe levels, ensure that the system shuts
down if the purge supply to the pump fails.
