What caused the tunnel disaster in Sikkim’s Namchi? How did 25 people die? Why is methane trapped in mountain rocks? Why are the Himalayas fragile?
NHPC’s under-construction Head Race Tunnel at Namchi, Sikkim, saw a suspected methane-release ignition during tunnelling on 20 July, killing 25 workers.
- A head race tunnel carries water from a reservoir to a hydropower unit; during tunnelling and drilling, workers operate inside the excavation space.
- Methane can be trapped in porous rock or as gas pockets; sudden changes during tunnelling can release trapped methane.
- Routine tunnel safety checks look at stability and underground conditions using multiple tests, while routine methods may not reliably detect methane because methane is colourless and odourless.
- The explainer links higher underground gas and risk in Himalayan areas to tectonic instability, frequent seismic activity, and heavy tunnelling and blasting for infrastructure.
What happened in Namchi, Sikkim (20 July): suspected methane release in an NHPC tunnel
A suspected methane release led to an explosion at an under-construction NHPC hydropower project’s Head Race Tunnel in Sikkim’s Namchi district. The explosion killed 25 workers and caused partial damage to the tunnel.
NHPC and the Sikkim government have ordered thorough investigations. Preliminary reports point towards suspected methane formation within the tunnel area.
UPSC can frame the incident as a case study on how geological processes (methane generation and trapping in porous/young formations and tectonic migration) combine with construction activities (drilling sparks and tunnel ventilation/air mixing) to create an ignition pathway. The policy discussion can focus on what “safety investigation” must cover when routine tunnel surveys cannot detect colourless, odourless methane.
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