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Flammable Gas Installation
Requirements, Interlocks, etc.
Gas Coordination Panel 24/08/2004
• Zoning for explosives atmospheres
• Electrical components in a Zone 2
Current situation, requirements and problems.
• What are the alarm actions in case of a gas
alarms ? (Interlocks)
• Conclusions
Gas Coordination Panel 24/08/2004
Flammable Gas Zones
• Zone 0:
zone in which there is a flammable atmosphere during long
• Zone 1:
zone in which there can occasionally be an explosive
atmosphere during normal operation.
• Zone 2:
– zone in which an explosive gas atmosphere is not likely
to occur in normal operation, and if it occurs it will only
exist for a short time.
At CERN we have mostly Zone 2.
Gas Coordination Panel 24/08/2004
Safety Rules for Electrical Equipment in a
Zone 2
Much stricter due to new legislation.
Three Possibilities (Safety Note #13):
A. Use of certified components
B. Use of components built at CERN (or…) according to
similar safety requirements.
C. Use of normal apparatus not specifically protected, but
providing additional safety measures like gas detection,
interlocks, etc.
But, whenever possible we should be in case A.
Gas Coordination Panel 24/08/2004
Our Approach
• All gas racks containing flammable gas will be closed
cabinets. => Limit the Zone 2 areas to one rack.
– These racks will have gas detection and forced air ventilation.
• Wherever possible we will use only (ATEX)
certified components in a Zone 2. (If this is the case
there is no problem.).
• If certified components are not available
seek compensatory measures. This needs to be
approved by SC.
Gas Coordination Panel 24/08/2004
Components without ATEX certificate
• MFC’s in mixer racks containing at least one flammable
component (Case C).
– Make pressure on suppliers to provide certified components in
the future.
– Extra safety measures: gas detection, interlocks
– Inquiry for derogation from SC is ongoing.
• Distribution racks (TGC, HMPID):
– Connectors of flowcell (case C) –> discuss extra protection
– Control chassis (case B) – discuss EX-n or quasi EX-p solution.
– Valve positioners (case B) – quasi EX-d
• Control Racks:
– Low voltage power supplies (TBT versus TBTS) (solved)
This is currently causing some delays on Distribution units for TGC and HMPID
Gas Coordination Panel 24/08/2004
Additional Safety Measures
Gas Detection
Forced air ventilation
Gas loss measurements in the distribution racks.
Interlocks following on
a flammable gas detection signal
a gas loss measurement
a ventilation failure
Inertion failure
As we have non-certified components these additional
measures will be essential to operate the flammable
Gas Coordination Panel 24/08/2004
Interlocks (1)
Gas loss between input and output gas flow.
• Gas Loss Measurement in TGC or HMPID:
– Warning for losses > 5 l/h
– Alarm for losses > 10 l/h
• Required Alarm Action:
– The gas system will switch off the flow in the
distribution rack (sector) concerned. (handled by TA1)
– The detector parts concerned switch off all their
tensions (HV and LV). (handled by the experiment)
Gas Coordination Panel 24/08/2004
Interlocks (2)
Gas leak in the detector or in a rack
• Required Alarm Action:
– Level 3 alarm cuts power to entire gas system. There
will be no cut of individual racks or modules !
– All tensions (HV and LV) in the detectors surrounding
the leak area must switch off. (handled by the experiment)
– Cut flammable gas sources on the bottles (if leak in SG).
Gas Coordination Panel 24/08/2004
Interlock (3)
Ventilation failure in a flammable gas rack
• Possible Actions:
– Cut power (220V) to entire gas system concerned
(switching of flow and all electricity).
– Cut flammable gas sources on the bottles (if in SG).
Gas Coordination Panel 24/08/2004
Interlocks (4)
Other alarms related to the gas
• Following a failure or alarm in a system that is
part of a compensatory safety measure, e.g.
inertion system, enclosure flushing.
• Possible Alarm Action:
– Cut power (220V) to entire gas system concerned
(switching off flow and all electricity).
(In a few cases it might possible to react on a more modular level).
Gas Coordination Panel 24/08/2004
• There are some problems with the certification of a few
components for the Zone 2. Several discussions with SC
are ongoing.
• Compensatory safety measures ventilation, gas detection,
etc. will be compulsory for the running of the flammable
systems. These installations must be provided by the
• Alarm actions (for Level 3 or similar) will be handled
hardwired with global cuts on the full systems.
Gas Coordination Panel 24/08/2004