I did a search and couldn't find anything, so apologies if this has been asked before. I'm working for a large underground mine and we are looking to upgrade our communications infrastructure, and the consultant has put forward a VoIP solution over WiFi as well as fixed phones from fibre/Cat6. So far, so good. However they have also proposed the same for emergency locations such as refuge chambers. Traditionally we have used POTS systems for these (powered from the surface) so that we can communicate with the teams underground should things turn sour. My concern with the VoIP solution is obviously the switches need to be powered for it to operate, and there is only so much UPS autonomy we can have underground. So my question is - is it normal for VoIP to be used for emergency communications? Am I being over cautious here?