[Draft article - review and edit before publishing. Add anonymised project examples where marked.]
Every compliance failure we find on site was once a line on a drawing. That's the uncomfortable truth of hazardous area work: by the time an inspector flags a problem in the field, the cheap moment to fix it passed months earlier. These are the five design-stage mistakes we see most often in design reviews - and what each one turns into once concrete is poured.
1. Zoning drawn by habit, not by analysis
Zone boundaries copied from a previous project, or drawn generously "to be safe", cause trouble in both directions. Over-zoning forces expensive Ex-rated equipment where none is needed; under-zoning puts ordinary equipment inside an explosive atmosphere. Both start with a classification study that didn't reflect the actual release sources, ventilation and substances on this site.
2. Equipment category mismatched to the zone
A Zone 1 area demands equipment certified for it. We regularly find selections that look right at a glance - the datasheet says "Ex" - but the category, gas group or temperature class doesn't match the zone's requirements. On site this becomes a choice between replacement and formal justification, neither of which is quick.
3. Earthing and bonding as an afterthought
Static discharge is an ignition source like any other. Designs that treat earthing as a detail "for the installer to sort out" reliably produce isolated metalwork, missing bonds and undocumented connections - defects that are laborious to find and prove closed once the plant is live.
Rework on paper costs hours. Rework in a live hazardous area costs shutdowns.
4. Cable systems that can't be glanded correctly
Cable selection, gland types and entry arrangements have to work as a system with the enclosure's protection concept. Mixing armoured and unarmoured runs, or specifying glands the enclosure was never certified for, shows up on site as a wall of non-conformances - one per entry.
5. No thought for how it will be inspected
Equipment mounted where no one can reach it will not be inspected properly - whatever the maintenance plan says. Designing for inspectability (access, labelling, documentation structure) is what makes the ongoing inspection regime affordable for the life of the plant.
The takeaway
A design review is cheap insurance: a structured check of zoning, selection, cabling, earthing and layout against ATEX and IECEx requirements, at the stage where every fix is still a pen stroke. If your project is heading for detailed design, that's the moment to talk to us - not after the first inspection report lands.