The document discusses plasma arc cutting (PAC), a process that uses a high temperature electric arc to melt and remove metal. PAC operates at temperatures between 10,000-14,000°C and was first used commercially to cut holes in aluminum railroad cars. It is now commonly used for manual and mechanized cutting of metals like steel and aluminum in various industries. Common gases used in PAC include oxygen, nitrogen, acetylene, propane, and argon-hydrogen mixtures.