Noida, July 27 -- Two men, a contractor who was cleaning a Sewage Treatment Plant (STP) and a guard who attempted to rescue him, allegedly died after inhaling toxic gases at a society in Sector 150 in Noida, police said on Sunday. Police said the incident took place around 3:30 am at the society and identified the victim as Shashikant Sharma, 40, a resident of Karauli, Rajasthan, and 22-year-old Akash Singh, who worked as a security guard and originally belonged to Firozabad. It was not clear why the contractor was carrying out the cleaning at this hour and police said they are investigating this. A case has been registered and four people from the society have been detained in connection with the matter, said police. According to police, the contractor was hired by the maintenance staff late on Saturday night to clean the STP installed inside the society for watering plants. Around 3.30 am, the contractor entered the 12-foot-deep tank with the help of a rope. He did not wear any safety gear, saying that it was routine work for him, said a police officer, part of the investigation, requesting anonymity. "After inhaling toxic gases, the contractor lost consciousness." Seeing his motionless body, people from the society at the spot called out for help, alerting the guards deployed at the society's gate. "Without wearing any safety gear, one of the guards jumped in to rescue the contractor," the officer added. He too fell unconscious after he entered the STP. The second guard then secured himself with a rope and entered the STP to help the two victims. However, he felt uneasy and shouted for help. He was pulled out by the people standing around. Neither the first guard nor the contractor had secured themselves with a rope and so could not be safely pulled out by people at the site without entering the STP. The police were informed and fire department officials arrived at the scene at 4am. Fire personnel, wearing masks and carrying oxygen cylinders, then entered the tank and pulled the two men out. They were rushed to a nearby hospital, where doctors declared them brought dead. Ravi Shanka Nim, DCP, Greater Noida said, "A case under section 106 (causing death by negligence) of the BNS and Prohibition of Employment as Manual Scavengers as their Rehabilitation Act was registered against the maintenance staff, management, and security supervisor of the society....