Two sanitation workers and a policeman, who went inside a manhole to rescue them, died due asphyxiation while they were cleaning the sewage on the premises of police lines here, a police official said. One more sanitation worker was critically injured in the incident, he said. The incident occurred this evening when two workers Ravi Kumar and Krishan Kumar, who were cleaning the manhole, fell unconscious, he said. The third worker, Balvir, went inside the manhole to save them but he too did not come out. When constable Lachhman noticed that the three sanitation workers had failed to come out, he also jumped inside the manhole to rescue them but lost his life, the official said. Later, the incident was reported to senior officials and all the four people were rescued with help of fire brigade staff, he said. They were rushed to the civil hospital, where three of them were declared brought dead by doctors, he added.