Sewer Condition Assessments Using a Gas Analyzer

From Maintaining Sewers in the current issue of the Economist:

"Crucially from a practical point of view, Dr Hernandez found that the gaseous signal showing something amiss actually has two components. Hydrogen sulphide levels in the most corroded pipes were above 100 parts per million—putting a number on what was previously just a reasonable assumption that more hydrogen sulphide is worse. They also had high carbon-dioxide levels: above 1% by volume compared with 0.03% in normal air. That means a simple gas analyser can sniff out trouble, saving sewage companies money and everyone else the grief of broken sewers."