San Francisco-based Petra  (Greek for rock) says it has developed a new way of tunnelling through rock which will make it cheaper to put utilities underground.

According to Wired, Petra says it’s developing tech to cut through rock without grinding into it. The company first tested cutting through rock with a plasma torch in an industrial park in Oakland, California in 2018. A larger plasma torch later cut through slabs of stone at temperatures above 10,000 degrees Fahrenheit.

Petra later abandoned plasma for a mix of gas and heat above 1,800 degrees Fahrenheit that breaks rock into small pieces. Sensors attached to small rods touch the rock, but the excavation is carried out by the heat and gas. Using this tech, which was created in part by one of Tesla’s cofounders, Petra wants to make tunnelling through bedrock cheap enough to encourage utilities to bury electricity and other lines underground.

 In a test, Petra says its method is moving through rock is around 40 feet an hour. Once the rock is broken into tiny pieces, a vacuum is used to suck rock fragments out of the hole.