A 40-year-old man died and three others were critically injured while cleaning a sewer in Northwest Delhi’s Ashok Vihar on Tuesday, the Delhi police said.According to the police, the incident took place near Harihar Apartments in Ashok Vihar Phase II.“On Tuesday, at 11.36 pm, a PCR call was received regarding sewer cleaning near Harihar Apartments, Ashok Vihar Phase II, where four persons had fallen inside the sewer,” DCP (Northwest) Bhisham Singh said.The four individuals, as per police, were identified as Arvind, Sonu, Narayan and Naresh, who were working on contract for a construction firm, the police said.All of them were rushed to Deen Dayal Upadhyaya (DDU) Hospital, where Arvind, 40, was declared dead.“Arvind was declared dead on arrival at DDU Hospital. The other three were admitted to the ICU,” DCP Singh said.A police officer said that Arvind was cleaning the sewer in the dark when he fell unconscious due to a high volume of toxic gases — including methane and sulphur dioxide — inside.Story continues below this adHis three co-workers, the police officer said, rushed in to rescue him, but such was the volume of gases inside that they fainted as well.Arvind, Sonu and Narayan, all hail from Kasganj district in Uttar Pradesh while Naresh is from Bihar, the police said.“The crime team inspected the spot. The manager of Brijgopal Construction Company has been called for an inquiry. Sewer cleaning work was going on in the area for the past several days. Safety measures undertaken during the work are being reviewed,” DCP Singh said.A case has now been registered under sections 106(1)(death by negligence), 289 (negligent use of machinery leading to danger to life) and 337 (forging records of public register) of BNS along with sections 7 and 9 of Prohibition of Employment as Manual Scavengers Act 2013 at the Ashok Vihar police station, police said.Story continues below this adOn July 10, two workers, Brijesh, 26, and Vikram, 30, died after entering a sewage treatment plant (STP) at Balaji Action Medical Institute in Paschim Vihar, Outer Delhi, to clean its carbon fibre filters, the police had said.Five people, including the hospital head, and supervisor of the cleaning contractor Friends Enviro, were arrested in the case after two months.