Precision Locating locates gas leaks (above and below ground).Below ground gas leaks are located by introducing helium into the system. Helium, being lighter than air, rises up through the soil, and is detected above ground using a helium detector. For above ground leaks inside a building, we use helium, or propane as a trace gas. Propane is detected with a combustible gas analyzer. Safety procedures include: determining the size of the leak to be located so as not to cause or introduce an explosion hazard, turning off all electrical devices, prohibiting smoking in the area, and clearing the building of all nonessential people.