A methane explosion in an under-construction tunnel of the Teesta Stage-VI Hydel Project in South Sikkim, India, has resulted in 13 fatalities with 12 workers still missing.Rescue teams faced extreme challenges including poisonous gases like methane and carbon monoxide, darkness, mud, and poor visibility.The incident occurred on Monday when 25 workers were trapped in Adit-3 of a 15-km-long tunnel.Officials believe the explosion was triggered by a methane gas leak from a rock pocket hit by machinery.Rescue operations have been delayed due to high gas levels exceeding safety limits, making it unsafe for rescuers without specialized equipment.Mud and water accumulation further complicated efforts, requiring earth movers and repaired pipelines to pump out debris.Despite these obstacles, teams continue searching for survivors while dealing with hazardous conditions inside the tunnel.