Triple PRCS fatality (1 entrant & 2 would-be-rescuers) incident in sanitary sewer (Oxygen Deficient atm)

See if this sounds all too familiar… three (3) workers remove a manhole cover to a sanitary sewer to check for water and blockage.  Unable to see anything, Employee #1 climbs down into the sewer to look for problems.  A co-worker working nearby sees Employees #2 and #3 enter the manhole and comes over to check on his co-workers.  He finds Employees #2 and #3 trying to revive Employee #1 down in the sewer.  This employee leaves to call 911.  Upon his return to the manhole, he could hear no more sounds from his co-workers.  The Fire Department arrived, tested the atmosphere, and found it to be 5% Oxygen.  They donned their rescue gear, made entry, and found all three (3) workers (1 entrant and 2 would-be-rescuers) deceased – presumably from the Oxygen Deficient atm.

Sources:

https://www.osha.gov/pls/imis/establishment.inspection_detail?id=1489694.015

https://www.in.gov/dol/files/Crosby%20Excavating%20Inc%20318125077.pdf