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General · 26 Jul 2026
25 workers died in a tunnel when trapped methane exploded - here’s why that gas is so dangerous and how it got there.
By Ananya Sharma
On July 20, 2026, in Sikkim, a tunnel under construction exploded. The blast killed 25 workers. The cause: a sudden release of methane gas trapped in the rock.
Methane is odourless and invisible. It can build up inside rock formations over millions of years. When a drill breaks into that rock, the gas escapes. In a confined space - like a tunnel - a spark is enough to trigger a deadly explosion.
Methane (CH₄) forms when organic matter decays in the absence of oxygen. Think ancient plants and animals buried under layers of sediment. Over time, heat and pressure turn that organic matter into coal, oil, or natural gas. Methane is the main component of natural gas.
In tunnels that pass through sedimentary rock - especially rock containing coal or organic-rich shale - methane can be trapped in small pockets or adsorbed onto the rock itself. The pressure holds it there. But when a tunnel boring machine or a drill bit cuts into that rock, the pressure is released. The methane rushes out into the open air of the tunnel.
In a tunnel, there is limited ventilation. Methane is lighter than air, so it rises and accumulates near the roof. If the concentration reaches between 5% and 15% in air, the mixture becomes explosive. Any ignition source - a spark from a tool, a static discharge from a worker’s clothing, even the heat of cutting - can set it off.
The Sikkim tunnel explosion happened because workers hit rock that contained trapped methane. The sudden release created a toxic, flammable cloud. Then came the blast.
Engineers and mining crews take several steps to prevent these disasters.
Detection first. Continuous methane monitoring is standard. Sensors placed along the tunnel alert workers if gas levels rise. Many tunnels use portable gas detectors worn by every worker.
Ventilation. Powerful fans force fresh air into the tunnel and push out any gas that escapes. In high-risk areas, ventilation is designed to keep methane concentrations well below the explosive range.
Spark control. Tools and equipment in gas-prone areas are “explosion-proof” - they are designed not to create sparks. Workers also wear special clothing that prevents static buildup.
Slow boring. When drilling through rock known to contain methane, the pace is slowed. Workers drill small pilot holes first to relieve pressure gradually, rather than releasing all the gas at once.
None of these measures work if they are skipped. The Sikkim investigation will likely look at whether detection or ventilation systems were in place and working.
This accident is not unique. Methane explosions in tunnels and mines have killed thousands of workers worldwide. The gas is a natural part of Earth’s crust. The risk comes when we dig into that crust without understanding where the gas hides.
If you work with tunnels, mining, or underground construction, safety training should always include methane hazards. If you study geology or engineering, understanding gas behaviour in rock can save lives.
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Methane is a colourless, odourless gas. In a tunnel, it can form an explosive mixture with air. A single spark can cause a blast.
Methane forms when organic matter decomposes without oxygen deep underground. It stays trapped in porous rock or adsorbed onto coal and shale until drilling or excavation releases it.
They use fixed and portable gas sensors that continuously measure methane levels. If concentration rises, alarms sound and workers evacuate.
Strong ventilation, spark-proof tools, static-free clothing, slow drilling with relief holes, and real-time gas detection. All must work together.
Yes, if equipment fails or procedures are ignored. That’s why constant monitoring and training are critical.
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