Guwahati: Authorities have begun investigating a fatal accident in Shillong’s Lapalang area after five people suffocated inside a 33-foot-deep underground water reservoir.
Officials believe toxic carbon monoxide accumulated inside the tank during a cleaning operation involving a diesel-powered pump.
Water Resources Department Sub-Divisional Officer Larrypor Roy Nongbri said the victims were exposed to carbon monoxide released while water was being pumped out of the underground tank. He said the gas rapidly replaces oxygen in enclosed spaces, making it extremely dangerous.
Explaining the hazards, Nongbri said a person trapped in such conditions can lose consciousness within seconds, leaving little or no chance of escaping.
He added that the reservoir’s depth and poor ventilation created an enclosed environment where poisonous gases could quickly build up.
According to officials, four workers had entered the underground reservoir inside a residential compound on Friday evening to clean it. During the operation, three of them collapsed after inhaling the toxic gas, while the fourth managed to climb out and alert nearby residents.
Two men then went inside the chamber in an effort to rescue the trapped workers. They were also overcome by the oxygen-deficient atmosphere, taking the death toll to five.
Those who died were identified as Pynskhemlang Mawthoh (22), Rapborlang Nongspung (35) and Elka Shadap (25), all from the Smit area, along with brothers Sunil Thakuri (34) and Umesh Thakuri (30) of Nongrah Dongktieh, Block-5, Shillong, who lost their lives during the rescue attempt.
After the recovery operation, the bodies were taken to NEIGRIHMS. Doctors carried out virtual autopsies using MRI and CT scan imaging after the families declined conventional post-mortem examinations.
The bodies were subsequently released to the families on Saturday.
Family members from Thangsning and Umiew, accompanied by village representatives and Mawkynrew MLA Banteidor Lyngdoh, received the bodies before taking them home for the funeral rites.
Meanwhile, officials from the Water Resources Department and personnel from Rynjah Police Station inspected the site as part of the investigation into the incident.
East Khasi Hills Superintendent of Police Vivek Syiem said Rynjah Police Station has registered Case No. 106(1)/2026 under Section 125(a) of the Disaster Management Act, 2005.
A separate FIR has also been filed by the Sector Magistrate against the property owner and the contractor, alleging negligence in connection with the incident.
Lapalang Rangbah Shnong Pyndap Sohtun said the Dorbar Shnong received information about the accident at around 7.30 pm on Friday, following which he and the Assistant Rangbah Shnong immediately reached the location.
He said the workers had almost completed the cleaning work and were pumping out the remaining water when the incident occurred. According to him, operating the diesel pump inside the enclosed reservoir may have led to the build-up of carbon monoxide or a sharp reduction in oxygen levels.
Sohtun said no one else attempted to enter the reservoir after the two rescuers also collapsed. He added that the local MLA, Deputy Commissioner Abhilash Baranwal, magistrates, medical personnel and other authorities were informed without delay, after which rescue and recovery teams were mobilised.
He also said the Dorbar Shnong discourages residents from constructing private underground reservoirs or wells because the locality already receives sufficient water supply.
However, many households continue to build them as groundwater is readily available in the Lapalang catchment area.
Calling for preventive measures, Sohtun urged the state government to introduce clear regulations for the construction, maintenance and cleaning of underground reservoirs and wells.
He said mandatory safety procedures for work in confined spaces are essential to avoid similar accidents.
He said improving the public water supply remains a long-term solution to prevent residents from relying on privately excavated underground reservoirs.
To achieve this, work is being carried out under the Jal Jeevan Mission with support from the Public Health Engineering Department.