Update on tunneling at Petra The following article describes the technology Petra is now using for tunneling. It is high heat and gas but at a lower temperature than what a plasma torch would operate. Petra abandoned plasma torches because of the lava flow it creates. Wonder if Pyrogenesis has any doing in the new approach... As it is a low temperature 'Plasma' torch of sort... Interesting to note that one of the co-founder of Tesla has a role in the new tech development
https://www.wired.com/story/new-tech-cuts-rock-without-grinding-it/