It has been found that natural gas transported by pipe lines also contains mercury vapor which is discharged from natural gas deposits. The mercury vapor precipitates as mercury in the pipes and installation parts. Mercury vapor as a contamination in natural gas occurs in extremely small amount, but after years of use of the natural gas pipelines, mercury and possibly mercury compounds are found in such quantities that when the conduits are scrapped, the pipes must not be melted down, for environmental reasons, because the mercury, rising in vapor form into the atmosphere during the melting down, would poison the air for a long time.
Therefore, wherever mercury vapors are not filtered out from the start as the crude gases enter the installations, it is necessary to clean conduits and installation parts. This necessity exists not only where old natural gas lines are to be disposed of, but also where still usable lines are to remain in use. For whatever work is being done on these lines, whether to weld in outlet pipes or to carry out other repairs, there is always a health hazard for the persons on the site and danger of pollution.