Manual scavenging refers to the unsafe and manual removal of raw (untreated) human waste or slug using buckets or other containers, from toilets or from the pits of latrines. However these sewers are very dangerous, as this debris decomposes to form Sewer gas, which is a mixture of inorganic gases created by the action of anaerobic (needing no oxygen) bacteria on sewage and sludge. Any human being entering the manhole of sewer pipeline, gets directly exposed to these harmful gases which ultimately claims his life. Suction type Handheld / Portable Gas detectors are preferably used for detecting excess accumulation of sewer gases like H2S, CH4, NH3, CO2 or depletion of O2 before any person enters into the underground sewer areas.