I am N. Meenakshi Sundaram, an engineer of Chennai metro water board working in the water and sewer sector for the past 30 yrs. Often accidental deaths of sewer workers occurs during the O&M activity of cleaning of sewerage network systems due to noxious gases. The kind of activities could be entry to manholes in separated/combined sewer system for cleaning /removing the sewer obstructions ,or removal of contaminated sludge removal from septic tanks or silt removal from storm water drains or silt cleaning from open wells  etc. Several accidents of these types occur in Indian cities.