6.3.1 Except for operational reasons, access doors
or other openings should not be provided between a non-hazardous space
and a hazardous area or between a zone 2 space and a zone 1 space.
Where such access doors or other openings are provided, any enclosed
space not referred to under paragraph 6.2.3 or 6.2.4 and having a
direct access to any zone 1 location or zone 2 location becomes the
same zone as the location except that:
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.1 an enclosed space with direct access to any
zone 1 location can be considered as zone 2 if:
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.1.1 the access is fitted with a self-closing
gastight door opening into the zone 2 space,
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.1.2 ventilation is such that the air flow with
the door open is from the zone 2 space into the zone 1 location, and
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.1.3 loss of ventilation is alarmed at a manned
station;
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.2 an enclosed space with direct access to any
zone 2 location is not considered hazardous if:
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.2.1 the access is fitted with a self-closing
gastight door that opens into the non-hazardous location,
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.2.2 ventilation is such that the air flow with
the door open is from the non-hazardous space into the zone 2 location,
and
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.2.3 loss of ventilation is alarmed at a manned
station;
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.3 an enclosed space with direct access to any
zone 1 location is not considered hazardous if:
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.3.1 the access is fitted with two self-closing
gastight doors forming an airlock,
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.3.2 the space has ventilation overpressure in
relation to the hazardous space, and
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.3.3 loss of ventilation overpressure is alarmed
at a manned station.
Where ventilation arrangements of the intended safe space are
considered sufficient by the Administration to prevent any ingress
of gas from the zone 1 location, the two self-closing doors forming
an airlock may be replaced by a single self-closing gastight door
which opens into the non-hazardous location and has no hold-back device.
6.3.2 Piping systems should be designed to preclude
direct communication between hazardous areas of different classifications
and between hazardous and non-hazardous areas.
6.3.3 Hold-back devices should not be used on
self-closing gastight doors forming hazardous area boundaries.