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.