Safe practices / manuals to reduce deaths/accidents of sewerage workers

 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.

Till date, clear-cut safety practices are not practiced by sewer sector managers due to  non-availabilty of safety manuals of sewer operation. Full-fledged occpational health safety manuals need to be evolved in India to elliminate /minimise the sewer accident deaths.
Answers  for this question may yield good good environmental practices in india and minimise/elliminate occupational deaths.
I am asking this question t get earnest replies from virtual world to evolve and adhere such good practices to safeguard the sewer workers of India
N.Meenakshi Sundaram, Chennai 83