Why is Ethernet not intrinsically safe?
Profibus is really low speed compared to ethernet and hanging components on the line to convert its energy levels to be compatible with intrinsically safe installations is quite trivial. I'm talking about a thing called a zener barrier - this consists of a fuse, 2 or 3 zeners (hazardous zone dependant) and a resistor.

The fuse protects the zeners, the zeners limit the voltage and the output resistor limits the current.

I can imagine that using such a zener barrier with high speed data systems like ethernet will be a real problem getting them to work. Having said that, such things do exist here: -



I haven't checked what speed it will run at - I'll leave that up to the OP.