IEC 60079-13:2010 pdf – Explosive atmospheres – Part 13: Equipment protection by pressurized room“p”.
6.2.4 Sequence of operations of the purging safety devices for type of protection px The sequence of operations of the safety devices shall be as follows:
a) Following the initiation of the sequence, the purging flow through and the pressure differential between the internals of the room and the external atmosphere shall be monitored in accordance with this part of IEC 60079.
b) The purge timer shall start once the minimum specified purging flow rate through the room is verified and the pressure differential is within the specified limits.
C) When the purge time has elapsed, the purging flow rate may be reduced to the level sufficient to maintain the required positive pressure In the room. At that point, the equipment is permitted to be energised
In the event of failure of any step in the sequence. the purging cycle shall be restarted except as specified below:
d) If the minimum specified pressure differential Is not maintained and a door switch indicates that the door is not closed, the timer shall be halted until the pressure differential is re-estabiished. II the loss of pressure differential persists for longer than 60 s the purging cycle shall be restarted regardless of the status of the door switch.
6.2.5 Enclosures within the room
During purging of the room, any enclosure which exceeds 5 % of the internal volume of the room and that contains electrical equipment not suitable for the equipment protection level external to the room, shall either be vented to the room so as to facilitate flow into and out of the enclosure or be individually purged.
NOTE Top and bottom vents providing not less than I cm’ of vent area for each I 000 cm’ with a minimum vent size of 6,3 mm diameter should be suffici•nt for adequate purging.
6.3 Dusts — Cleaning
Before energizing any electrical equipment which is not suitable for the equipment protection level external to the room, excessive quantities of combustible dust shall be removed from the room and Its contents
7 Temperature limits
Upon failure of the pressurization system, appropriate measures shall be taken to prevent the explosive atmosphere coming into contact with any hot surlace within the room that exceeds the value documented in 14.1.
NOTE This may be achieved by the design and construction of the room. leg, air Iods) or by bringing auxiliary ventilation systems into operation or by arranging that the hot surface within the room is in a gas tight or encapauLated housing
8 Minimum safety provisions, safety devices and electrical disconnects
8.1 Safety devices
All safety devices shall themselves be suitable for the equipment protection level external to the room or shall be mounted outside the hazardous area.
The pressurization system. its controls, electrical isolation means, the system fan and Its motor shall be suitable for the area external to the room unless located In a non.hazardous area.
NOTE I Au parts of the system in contact with the room. including inside me Inlet duct should be considered as being in the hazardous area
The safety devices shall be used within their normal operational limits.
Alarms shall be located where they will immediately be perceived by the responsiblepersonnel.
The safety devices required by this part of lEC 60079 form safety-related parts of a controlsystem.
The safety and integrity of the control system shall meet a level of reliability consistent with thefault tolerance required for the relevant types of protection,i.e.
– for type of protection px, or type of protection py, a single fault;- for type of protection pz,normal operation;
– for type of protection pv,single fault.
NOTE 2 For the integrity of satfety functions lEC 61511 series or similar standards may be used.
Electrical power disconnection to the room should preferably be in a non-hazardous area.