Guwahati, July 12 -- 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.

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