The protective gas is normally air, but for certain applications may be an inert gas such as nitrogen.
When air is the protective gas, it may be provided from a safe area by a motor driven fan or
compressor, or from storage cylinders. Sometimes air is drawn from a Zone 2 area, with gas
detectors fitted to alarm at a level well below the LEL. Air from Zone 0 or Zone 1 is not permitted
under any circumstances! The air must not be oxygen enriched.
The protective gas must be non-toxic and free from contaminants such as moisture, oil, dust, fibres,
chemicals. And other contaminants which could jeopardise the safe operation.
The temperature of the safe gas entering the inlet duct should not exceed 40°C unless allowed for in
the marking on the pressurised enclosure. A duplicate safe gas supply may be necessary if, on loss of
pressure, it would be dangerous to de-energise the equipment.
When an inert gas such as nitrogen is used as the protective gas and personnel can gain access to
enclosures, it is essential that doors/covers are fitted with warning labels since there is a danger of
asphyxiation. Doors should also be fitted with suitable locks.
