Namchi(Sikkim), July 22: The tunnel tragedy at Namchi in Sikkim that took place on Tuesday claimed at least 20 lives.

The incident took place in the Head Race Tunnel (HRT) project that was under-construction by the National Hydroelectric Power Corporation Limited(NHPC).

According to sources, the HRC collapsed all of a sudden with tremendous sound while at least 30 crew members of the executing agency, including a few geologists, skilled technicians and construction workers were at work within the structure.

Despite, all security measures were reportedly put in place for safety of the workforce, the walls of the tunnel caved in and were pounded into dust and rubbles with thundering explosion inside.

The incident buried the entire workforce under the debris while two workers who were near the arch-entrances could hardly exit with life.

On being informed, the savior teams rushed to the spot to pull the trapped workers from the scene. However, it was too difficult for the rescue team as the entire area was almost filled with dust & smokes with pungent smelling gases.

Though the precise reason behind the mishap is yet under examination, the NHPC authorities, while took stock of the incident, suspected firedamp behind the burst.

The NHPC said the burst might be an effect of methane trapped within the rock strata that caused the massive explosion, producing fumes and toxic gases. The public sector undertaking said emergency response protocols were activated immediately after the incident. Officials added that the presence of methane continues to hamper search and rescue operations.

In most of the mining operations and deep excavations in the hilly or mountainous areas, methane trapped in rock strata can cause massive, highly destructive explosions.

This hazard is most common in coal and shale formations, where the hazardous gas, historically called "firedamp" is trapped under immense pressure and released during mining or tunneling.

Though the Methane gas is highly flammable, it sometimes explodes when mixed with damp air at concentrations between 5% and 15%.In general, when mining machinery, electrical sparks, or friction ignite these pockets of rocks locking methane gas inside, a violent explosion occurs, sending intense shockwaves through the rock mass.

In coal mining, the initial methane blast can loft fine coal dust into the air, causing a secondary, much larger, and more devastating explosion.

Natural and Geological Explosions Beyond human excavation, natural methane trapped in deep geological formations or frozen permafrost can also build up until it violently breaches the surface, leaving behind massive craters in and around the operation area, says experts.

In view of the vulnerability, rescue teams work with full-fledged security measures with coordinated teams remaining outside, well connected with sophisticated electronic devices, so that no further mishap if any, can be dealt with care and precision.