Buried questions: on the Sikkim tunnel accident

India is grappling with another Himalayan tragedy. Workers in an under-construction tunnel at the Teesta Stage-VI hydroelectric project of NHPC Limited (formerly National Hydroelectric Power Corporation Private Ltd.), in Sikkim’s Namchi district, struck a pocket of suspected trapped methane. The resulting burst partially damaged the tunnel, killing at least 15 of an estimated 25 workers, with rescue operations still under way. The NHPC has announced a detailed investigation. Methane is a well-recognised hazard in underground excavation, and the geology of the Teesta basin makes it a likely one. The basin sits in a seismically active zone, with young and heavily fractured rock, and where compressed pockets of gas laid down long ago can lie hidden until an excavation breaks into them. The presence of the gas, in that sense, is not in itself surprising. What remains unclear is far more consequential: the precise circumstances in which the pocket was breached, whether its risk was assessed and modelled during project planning, and whether the gas-detection and ventilation safeguards that such conditions demand were in place and functioning.

Underground work in India’s difficult terrain has always been perilous. In February this year, an explosion at an illegal coal mine in Meghalaya killed about 30 workers, and in 2023, a stretch of a road tunnel under construction in Uttarakhand collapsed, trapping 41 workers for 17 days before they were pulled out. The circumstances vary, but together they underscore how lethal underground and tunnelling work remains across the country. A series of hydropower projects along the 400-kilometre stretch of the Teesta that links Sikkim, West Bengal, and Bangladesh have varied histories with environmental clearances but share a common feature — their location in the fragile Himalayan belt. That vulnerability was demonstrated tragically in October 2023, when a glacial lake outburst flood from the South Lhonak lake destroyed the Teesta-III dam and killed more than a 100 people downstream. Teesta-VI was absorbed by the public-sector NHPC Limited after its private developers, unable to afford escalating costs, went into insolvency. Relief and rescue must remain the immediate priority, and every effort to reach those still trapped is warranted. But once the emergency has passed, the government cannot treat the disaster as an isolated misfortune. It must order a thorough, independent review of whether the conditions attached to the project’s environmental clearance were, in practice, strictly met.