Four sanitation workers died of suffocation after inhaling toxic gases while cleaning the underground sewer of a Faridabad hospital on Wednesday afternoon, police said. Rohit, his brother Ravi, Vishal and Ravi Goldar, residents of Sanjay Camp in Delhi's Dakshinpuri, had come to the QRG Hospital in Faridabad Sector 16 for sewer cleaning through an agency named Santosh Allied Service, they said.