Death to persons after going into water well

One person entered for cleaning in one case, ,  and to retrieve a fallen hammer in another case, didn't come out. Others entered one after another,  7 in first case, 3 in second case. All died.

It is common to swim in normal water wells, but, poisonous gases will be present  in these types of wells also.

We should presume that any space having some enclosure shall be treated as dangerous and accordingly precautions required for confined space entry shall be taken including buddy system. 

https://www.msn.com/en-in/autos/photos/8-people-die-after-inhaling-toxic-gas-while-cleaning-well-in-madhya-pradesh/ar-AA1CfeKc?apiversion=v2&noservercache=1&domshim=1&renderwebcomponents=1&wcseo=1&batchservertelemetry=1&noservertelemetry=1