From the omega technical page about intrinsic safety:
Intrinsically safe equipment is defined as "equipment and wiring which is incapable of releasing sufficient electrical or thermal energy under normal or abnormal conditions to cause ignition of a specific hazardous atmospheric mixture in its most easily ignited concentration." (ISA-RP12.6). More info here, translation:

• Hire a competent field electrician to specify the proper zener barrier for a pair or two of RS485 digital Kellers and get one. Also get a length of approved cable.
• Buy an approved RS485 intrinsically safe repeater.
• Get a couple of approved, intrinsically safe Kellers.
• Get a FlyportPro module to "talk" to the Kellers and publish things on the internet, so you can look at production data, tank levels, etc., on your cell phone.

Info on intrinsically safe Kellers here.

Note: Since the RS485 repeater can drive cable up to 1200m, and since up to 128 devices can be on the same wired network, a single FlyportPRO module can replace several paper chart recorders... and who knows how many tank-level, long, wooden sticks?