Hi Paulus.v
I also have an emergency estop which cuts power to everything, except the pc and the BoB, but I have never used it. (this being the hardware stop). I did, however used the software estop (input terminals on BoB) a few times, when I messed up gcode programing, and it worked quite well.
Your representation of the work conditions in which the cnc will function are a bit dramatic for a work shop, as I.m quite sure it is not positioned under a waterfall, but as I cannot help notice the flag situated at the left side of your user name it.s quite similar with mine, I think such a Estop described by you, should be very helpful if assigned to our prime minister, leading party and most of the political machine that is running our country. :) Best whishes, and happy national day for 01.12.2018! :)