In hazardous environments involving flammable gases, conductive dust, corrosive gases, and combinations of these, you can place safe area electrical and electronic devices in continually pressurised enclosures called purged panels.
These electrical panels maintain a positive pressure to stop outside gases from entering the enclosure. This practice ensures that any harmful or hostile gases or vapours in the air don’t get into the interior devices.
The words “purge,” “pressurisation,” “Ex p,” or “EEx p” are all used to describe this idea. The idea operates under the tenet that the flammable substance should be kept from the ignition source and that the purged enclosure’s surface temperature should not be incendiary.
Pressurising and purging electrical equipment enclosures is a procedure used to stop the entry of an explosive atmosphere. The idea of purging is a well-liked explosive protection notion. It is widely acknowledged and reasonably simple to understand (using European Standards, NFPA, or IEC Standards).
Explosion prevention is achieved by preventing the potentially explosive environment from coming into contact with any thermal or electrical source of ignition. The possibly ignitable equipment is installed inside an enclosure, which is pressurised to a positive air pressure (a positive atmospheric pressure of only 0.5 bar is sufficient).
The interior equipment cannot be exposed to a potentially explosive gas as long as this positive pressure is maintained because no gas (or even dust) may enter the enclosure. A flammable gas mixture may have entered the section before reaching positive pressure.
The enclosure is ‘purged’ to flush out the existing contents and make sure that all parts of the chamber contain only the purging gas (purging of internal dust has not yet been studied) to make sure the chamber is pressurised with a non-explosive gas (i.e., Air or Nitrogen).
It typically requires 5–10 volume changes to guarantee the enclosure is ‘purged.’ (The first edition purge standard in Europe specified a minimum of five air changes; in North America, the minimum is 10.)
Power cannot be applied to Zone 1 equipment until the ‘purging’ process, which involves a specific flow of purging gas for a specific amount of time, is complete. The maximum leakage rate for the enclosure is also defined to ensure consistency in the purging effect. Power cannot be applied after the purging is finished until the required positive pressure (at least 0.5 mbar) has been reached.
If the purging cycle doesn’t finish (due to a decrease in flow or insufficient duration) or if the enclosure pressure falls below the required positive pressure, power to the equipment must be cut off (for Zone 1), or an alert signal must be issued (for Zone 2).
In either of these circumstances, the complete purging cycle must be repeated for the entire purge time. A “Purge Control Unit” (PCU) typically regulates automatic purging and pressurisation. Both flow and pressure must be measured, and the PCU must always be fail-safe.
The enclosure that houses the equipment that needs to be purged must be strong enough to withstand blows and overpressures. A free movement of air should be made possible by the enclosure’s design. Any non-metallic substance must undergo durability and longevity testing (against effects of heat and light) as enclosure integrity is necessary to a level of IP40 (no holes more significant than 1mm).
External factors, such as the equipment’s surface temperature or static from plastic components, need to be considered. A spark arrestor must be installed to ensure that incandescent particles cannot be released from the apparatus. This technique is limitless regarding the safeguarded instrument’s physical size or power rating.
