25 Workers Are Dead in Sikkim. NHPC Knew the Gas Was There.

Twenty-five workers went into a mountain in Sikkim on Monday morning. By Thursday night, every one of them had been carried out dead.

The collapse at the under-construction Head Race Tunnel of NHPC's Teesta Stage-VI hydropower project, in Samardung village about 40 kilometers from Gangtok, ended a rescue operation that dragged on for nearly four days through toxic air and rubble. A suspected methane gas explosion and a landslide blocked the tunnel entrance, trapping the men inside ²³⁸. No survivors were found ⁹.

The death toll is the headline number, and the Sikkim government has constituted a high-level committee to investigate how it got there ⁴. But the figure that may matter more is older. According to reporting by The Hindu, NHPC's own 2024 technical paper documented recurring gas fires inside the Teesta-VI tunnels — the same network where 25 men died this week ¹¹.

What happened inside the mountain

The incident occurred on Monday, July 20, 2026, inside the headrace tunnel of the 500-megawatt Teesta Stage-VI project ⁷⁸. A suspected methane gas explosion was followed by a landslide that sealed the tunnel entrance ³⁷. Rescue teams worked in short rotations because the air inside was laced with methane, carbon monoxide and hydrogen sulfide — gases released when the blast fractured rock that had been holding them under pressure ²¹⁰.

Rescuers pulled bodies from the rubble and sent them to hospitals in Singtam, Gangtok and Namchi for medico-legal procedures ⁴. By Thursday evening, the last body had been recovered and the operation was formally closed ³⁸⁹.

Sources disagree on the precise length of the search. India Today described a 72-hour effort ⁵. The Hindustan Times called it nearly 96 hours ⁴. The BBC and The Independent both said four days ³⁹. The difference is small but worth naming: a four-day operation implies rescue teams believed survivors might still be found. A 72-hour window is closer to a recovery operation from the start.

The warning that was already on file

The most uncomfortable question raised by the disaster is not geological. It is documentary.

The Hindu reported that NHPC's own 2024 technical paper — an internal company document — recorded gas fires inside the Teesta-VI tunnels before this week's fatal blast ¹¹. The paper is now in the hands of investigators, along with the question of what was done about the risk it described.

NHPC, for its part, has framed the July 20 incident as sudden and unforeseeable. The company says the collapse likely occurred at an isolated patch near the face of tunnel 4B and gave no time for safe evacuation ¹¹. Engineering News-Record reports that investigators are examining whether the documented methane hazards contributed ⁷.

The tension between those two accounts — a company paper that flagged gas fires inside the same tunnels, and a public statement that the fatal event was sudden and isolated — is the live dispute at the heart of the inquiry.

If NHPC's own engineers wrote about gas fires in these tunnels two years ago, the question is not whether methane was present. It is whether anyone acted on the warning.

Who was inside

The victims came from at least four Indian states: Sikkim, where the project sits, and West Bengal, Uttarakhand and Assam ³. The geography of the dead maps the geography of India's hydropower labor — men recruited from across the Himalayan foothills to work a site they did not choose and could not leave.

The Sikkim government announced compensation for the families ⁵, though the details and any official statements from Prime Minister Narendra Modi or Chief Minister Prem Singh Tamang are not confirmed in the sources available to HeyDay News at the time of writing.

What is known, what isn't, what to watch

Known

All 25 trapped workers are confirmed dead; the last body was recovered on Thursday, July 23. 2 3 4 8 9
Methane trapped in rock is the suspected cause, and NHPC's own 2024 paper recorded gas fires in the Teesta-VI tunnels before the blast. 10 11

Unknown

The full cause, whether any workers were warned of gas hazards, and whether the 2024 paper's findings triggered any safety changes.
The composition of the Sikkim government's high-level committee and its terms of reference.
Whether any criminal or regulatory proceedings will follow the committee's findings.

The high-level committee's findings — and whether NHPC's 2024 paper becomes a central exhibit.
Whether other NHPC tunnel projects face renewed safety review after this disaster.
Compensation disbursement to the families of the 25 dead.

Why this story is not over

The bodies are out. The mountain is still there, and so is the paper.

Teesta Stage-VI is one of a string of hydropower projects pushing deeper into the Eastern Himalayas — geology that is young, fractured, and famously gas-bearing. The Teesta river basin has become the frontier of India's clean-energy push, and the workers who died this week were among the men building it.

For now, the official position and the documentary record are pulling in opposite directions. NHPC says the blast was sudden and isolated. Its own engineers wrote, two years ago, that the tunnels had been on fire. Between those two statements sit 25 families, a high-level committee, and a question that no company statement has yet answered: if you knew the gas was there, what did you change?