In the next part in the ATEX series, Tristan Pulford elaborates on the hierarchy of controls and hazardous area classification. If you missed the first part of this series please click here to catch up.

ATEX, as with all hazards has a hierarchy of control, used for risk reduction. Where possible an organisation should attempt these controls starting with the first, and finishing with the last:

Typically, these first two steps are easy to answer, because the substance is required as part of the process. This is rarely however documented, and it is important to be able to prove that no alternative or reduction is possible.

Hazardous Area Classification is also called Zoning when it comes to ATEX, and it is the process of defining a likelihood of an explosive atmosphere being present. There are various standards available that provide guidance on this, but the zones are split into 3 categories.

Typically, Zone 0/20 are easy to identify, but where possible equipment in those areas should be avoided. Typically, this is within pipework and within vessels, hoppers/ silos, areas where equipment is limited.

For the remaining zones, the word “likely” must be interpreted. In the oil and gas world the IGEM and Energy Institute standards provide guidance on when these zones occur, such as on a creep relief or condensate drain.

For dusts depending on the application there is guidance but in our experience there are some common areas that are frequently missed. That is items such as flexible connections, which are a common failure point as over time they can crack and provide small leakage points, and through breathers when the filter fails, etc.

One of the common items where zoning is missed is a manually loaded hopper with Local Exhaust Ventilation (LEV). In normal operation the LEV would remove any potentially explosive atmosphere, however if the hopper can be loaded when the LEV is not running (or is broken) then a Zone 22 would still be present. A similar principle is required with mechanical ventilation and any item which could foreseeably fail.

It is important to mention that for gases there is also a Zone 2 Negligible Extent (NE), which is a situation where, due to the ventilation and leakage rates, and potentially explosive atmosphere of no larger than 0.5m3 can be created. In this case ATEX equipment is not required in that area, however other controls for maintenance such as hot works are still required.

In the next installment in this series, we consider control ignition sources and lighting.

For any more information on ATEX or anything else you’ve read here please contact Tristan.pulford@finch-consulting.com

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