Rishi Pal, 40, along with Bishan, 30, Kiran Pal, 25, and Sumit, 30, fell unconscious after inhaling poisonous gases while cleaning the sewer at the Lok Nayak Jai Prakash Narayan Hospital.
"While Rishi Pal died, the other three are undergoing treatment," a DFS official told IANS.
The incident was reported around 12.30 p.m.
It is 10th such death in Delhi in just over a month.
On August 12, two brothers died of suffocation while cleaning a septic pit at a mall in Shahdara in east Delhi.
On July 15, four persons died after inhaling poisonous gases as they entered a water harvesting tank in Ghitorni in south Delhi.
(This story has not been edited by NDTV staff and is auto-generated from a syndicated feed.)