SAIMC


SAIMC: Johannesburg branch

September 2019 SAIMC

The July technology evening featured a presentation by Katlego Setwaba of Pepperl+Fuchs. The main focus of her talk was Ex p (purging and pressurisation). However, she started off by reminding us of the damage done by explosions, demonstrating the catastrophic effects if these are not prevented.

Ann de Beer (left) thanks Katlego Setwaba for the presentation.
Ann de Beer (left) thanks Katlego Setwaba for the presentation.

The three Gas Groups (IIA, IIB,and II C) and Dust Groups (III A, III B and III C) were tabled, A being the least sensitive to spark ignition, and C the most sensitive. She went on to cover zoning – Zone 0 being the most dangerous for gases, and Zone 2 has the least chance of the hazard being present. By contrast, dusts are correspondingly grouped into Zones 20, 21 and 22.

This was followed by the different explosion prevention techniques with a focus on flame proofing (Ex d, the containment of an explosion), intrinsic safety (Ex 1, limitation of temperatures and spark energy), followed by pressurisation and purging (Ex p, filling the equipment housing with clean air or inert gas).

Pressurisation is the maintenance of a positive pressure above atmosphere, after a preliminary purge. This can obviously not be done effectively in a dusty environment, so physical cleaning is required before pressurisation. In purging, the procedure is much the same, but instead of maintaining a static pressure, Katlego explained how there is a constant flow of clean air or inert gas through the enclosure. This of course requires a dedicated controller to carry out the pre-use purge, and to maintain the internal pressure.

It was an entertaining presentation, with plenty of questions, showing just how much expertise is required to prevent explosions. The branch thanks Pepperl+Fuchs for hosting the evening.


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