Jaipur, May 28 -- Four workers died by inhaling toxic fumes after they entered a 10-foot deep septic tank underneath a jewellery factory in Jaipur to try and retrieve gold and silver particles from the sludge, police said on Tuesday. The incident took place on Monday night in Sitapura Industrial area of Jaipur when eight workers were employed to recover gold and silver particles lost during the washing of jewellery from the toxic sludge. The workers were initially reluctant to undertake the work because of the toxic fumes, but agreed to do it after they were offered extra money, police said. "The workers initially refused to do the work because of the hot weather that may cause buildup toxic gas in the tank," Sanganer police station house officer (SHO) Anil Jaimani said. "Vikas Mehta, the CEO of the company that owns the factory, and director Arun Kothari convinced the workers to go into the tank by offering them extra money." Jaimani said all eight workers entered the tank to recover the sludge. While cleaning the tank, however, the workers lost consciousness. Police reached the site upon receiving information about the incident from the control room, and the workers were brought out of the tank. The workers were rushed to a local hospital, where doctors declared four of them dead. The deceased were identified as Rohit Pal, Sanjeev Pal, Himangshu Singh, and Arpit Yadav -- all between the ages of 25 to 30. "Two workers -- Ajeet Chauhan and Raj Pal -- remain in critical condition and are undergoing treatment," the SHO said. "The remaining two -- Amit Pal and Suraj Pal -- were discharged." Police said that the workers were operating without any safety gear. "We are probing why the workers were forced to clean an underground septic tank without any safety measures during a heatwave. We are also investigating the legality of the storage of gold particles in the tank," the SHO said. "Mukesh Pal, brother of deceased Rohit Pal, runs the contract agency through which the eight workers were employed," Jaimani said. Following the incident, Mukesh filed an inquest on Tuesday morning. "No FIR (first information report) was lodged. It will be done after a thorough investigation," the SHO added. Meanwhile, the National Human Rights Commission (NHRC) has taken suo motu cognisance of the matter and directed the district administration to submit a detailed investigation report by June 16....