Pressurisation (Ex 'n') Flashcards
What is Ex ‘p’?
Pressurised equipment is the technique of guarding against the ingress of the external atmosphere into an enclosure by maintaining a protective gas therein at a pressure above that of the external atmosphere.
Discuss the pressurising medium.
The pressurising medium should be from an area free from flammable gas. A protective gas such as nitrogen may be specified.
Caution: Beware of asphyxiation.
Why should warning notices or timed interlocks be fitted?
To ensure hot surfaces have cooled and capacitors have discharged prior to the door being opened.
When should a spark flame arrestor be used in the outlet air duct?
When it is not feasible to duct issuing air from purged equipment into a safe area.
What glands should be used for Ex ‘p’ equipment?
Certified glands are not required.
Glands are to be suitable for the cable, ingress protection required and the means of entry into the enclosure.
Where steel wired armoured/braided cables are used, glands with elastomeric inserts are to be used to provide seals onto the inner and outer sheaths.
What should you do if ductwork becomes detached from its hangers or leaks?
These would need to be corrected.
Failure to maintain the required minimum pressure may be due to several causes. Tests, adjustments or possibly replacement are required to ensure that:
- the internal pressure is maintainable at the required level (0.5mb minimum).
- overpressure relays and alarm set points are in accordance with the design data
- gas detectors, where used, function correctly. Tests on gas detectors probably require removal, laboratory testing and replacement. Reference to the manufacturers’ documentation would provide appropriate details.
What markings should be on Ex ‘p’ equipment?
Pressurised equipment conforming to the requirements of the ATEX directives is marked to indicate conformity with the Directive. It is also marked with the requirements of the standard (e.g. IEC 6007902).
For more information, refer to relevant standards, EEMUA 186 - A practitioners Handbook or the appropriate superior technical authority.
What are the controls if the protective gas fails?
- Devices should be fitted to monitor the overpressure or flow of protective gas.
- If these fall below minimum values the controls should raise an alarm, disconnect the power. Dependant on zone use.
In Zone 1—-
If the enclosure contains apparatus certified to zone 2 an alarm should be raised and immediate corrective action taken to restore integrity of the system. If the enclosure contains uncertified ignition capable apparatus then alarm and de-energise ignition capable components. As long as in doing so you do not create a more dangerous condition (may be time delay).
in Zone 2—–
if the enclosure contains uncertified ignition capable apparatus then alarm should be raised and immediate action taken to restore integrity to system.
How many times should the volume of the apparatus me removed for purging?
5 times. Zone 2 purging may be omitted if the interior of the enclosure and associated supply ducting is provided below the LEL.
Can non certified apparatus be used inside the enclosure?
Yes.
What glands?
Non certified but suitable for cable.
