Hi, welcom to the forum.
You have to know how to handle the mains voltage in a dusty environment.
The input can be a Current Transformat (CT), that is a core with coil around a single mains wire. It is isolated from the mains. It might even be possible to turn on the dust collection system if the total current of the workshop is above 5A, or something like that.
Here is some info: http://openenergymonitor.org/emon/buildingblocks/ct-sensors-interface
You could add an Ethernet Shield and show the current of the workshop in a graph on internet.
The output can be a relay or a solid state relay (search on ebay for SSR-25DA or SSR-40DA).
With a CT for input and a relay or SSR-25DA the Arduino is safe from the mains voltages. However the wires should be protected agains the dust. With such high currents for the tools, the wires to the Arduino could pick up some nasty spikes. Perhaps some protection is needed for the Arduino pins.