JimboZA:
Now just to get the physical circuit working...
On the subject of which, are the components you plan to use, eg the Arduino and the servo, safe for use (either intrinsically or by flash-proofing) in hazardous areas? Or will they be outside the hazardous area?
Sorry for the delay.
As per any hazardous area installation, as many of the components and circuitry as possible will be installed in an adjacent safe area. So the Arduino itself will be outside and a zener barrier will be utilised along with appropriate cable and glands. Inside will be an oxygen meter and ventilation fan - these won't be in this model though, unless i find the time and motivation (and knowledge) to include them!