6.3.1 Except for operational reasons access doors
or other openings should not be provided between:
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a non-hazardous space and a hazardous
area;
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a Zone 2 space and a Zone 1
space.
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Where such access doors or other openings
are provided, any enclosed space not referred to under 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 the access is fitted with a gas-tight door
opening into the Zone 2 space, and
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.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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.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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.1 the access is fitted with a self-closing gas-tight
door that opens into the non-hazardous location, and
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.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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.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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.1 the access is fitted with gas-tight self-closing
doors forming an air lock, and
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.2 the space has ventilation overpressure in relation
to the hazardous space, and
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.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 air lock may be replaced by a single self-closing gas-tight 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.