Archive · 12 Aug 2026
NHPC Knew of Methane Risk Before Deadly Sikkim Tunnel Blast
On July 20, there was a big explosion inside a tunnel in Sikkim, a state in India, where workers were digging a long passage for a hydropower project called Teesta VI.
The blast made rocks fall and blocked the entrance, trapping 25 workers behind it, and sadly none of them could be saved.
NHPC, the company building the tunnel, said the blast probably happened because a gas called methane suddenly burst out of the rocks.
Papers from the company show that NHPC already knew methane gas was in that tunnel since January, when a leak burned some workers.
Around that time, the company asked for machines that can detect methane gas and for experts to help manage it, but only about ten days before the accident.
Experts say the company should have stopped the work until the tunnel was made safe, instead of continuing to dig.
The area in the eastern Himalayas is known for having rocks that hold methane gas, so engineers knew this was a possible danger.
The power plant has been under construction for a very long time, since 2005, and has had many problems, including floods and earthquakes.
Many people are now asking why the work was allowed to continue when the danger was already known.
A blast on July 20 in the head-race tunnel of NHPC's 500-MW Teesta VI hydropower project in Sikkim's Namchi district trapped 25 workers, none of whom survived.
Company documents show NHPC knew of methane gas at the site since at least January, when a leak during excavation burned several workers.
Ten days before the accident NHPC floated a tender for methane management services, and in June it tendered for two methanometers-cum-toximeters; the estimated value of the two tenders was Rs 3 lakh.
Experts and a local social worker said tunnelling should have been paused until the tunnel was made safe, and questioned whether gas detection equipment and ventilation were in place and operational.
The project, begun in 2005 by Lanco and taken over by NHPC in 2019, has faced repeated geological problems, including a 2009 gas ignition, a 2011 earthquake, and a 2023 glacial lake outburst flood.
- Who
- NHPC, the public enterprise constructing the 500-MW Teesta VI hydropower project; 25 workers who died after being trapped in the tunnel; and experts and local officials who commented on the incident.
- What
- An explosion, apparently caused by a sudden burst of methane gas, triggered a rockfall that trapped and killed 25 workers in the project's head-race tunnel.
- When
- In the afternoon of July 20; rescue operations ended on the third day with no survivors.
- Where
- The head-race tunnel of the Teesta VI hydropower project in Namchi district, Sikkim, India.
- Why
- Methane gas trapped in the rocks is suspected to have suddenly burst and exploded; company documents suggest NHPC knew of methane at the site since January but had not yet fully installed monitoring and ventilation infrastructure.
Critics
NHPC & District Officials
Pausing work over methane risk
Critics
Experts and local critics say NHPC knew of methane at the site since January, yet continued tunnelling without adequate detection, ventilation and monitoring equipment; work should have been paused until the tunnel was made safe.
NHPC & District Officials
NHPC said it is carrying out a detailed investigation to ascertain the cause and had already floated tenders for methane management and monitoring equipment before the accident; it has not yet responded to questions about whether safety recommendations were implemented.
Monsoon excavation ban
Critics
Pravin Sharma argues that banning new earth excavation while allowing ongoing projects such as Teesta VI to continue is discriminatory, since disaster risk applies to ongoing excavation too.
NHPC & District Officials
The Namchi district office says its May notification applies only to new construction, while ongoing construction may continue as long as adequate protective and safety measures are ensured.
- Project
- Teesta VI hydropower project (500 MW)
- Location
- Namchi district, Sikkim, India
- Developer
- NHPC (public enterprise; took over from Lanco in 2019)
- Incident date
- July 20
- Fatalities
- 25 workers trapped; no survivors
- Suspected cause
- Sudden burst of suspected methane gas trapped in rocks (per NHPC press release)
- Earlier incident
- January methane leak during excavation caused burn injuries
- Expected completion
- 2028