New Delhi, Aug. 13 -- NHPC Ltd had flagged methane as a risk at the Teesta VI hydropower project in Sikkim months before a methane explosion in an under-construction tunnel killed 25 workers on July 20, documents on the company's website show. The documents record a methane leak in January and show that safety measures and equipment to monitor the gas were subsequently recommended and sought.

The blast occurred in the head-race tunnel (HRT) of the 500-MW Teesta VI project in Namchi district. NHPC said it was caused by a "sudden burst of suspected methane gas" trapped inside the rocks, leading to an explosion, dense fumes and toxic gases. Twenty-five workers trapped after a rockfall blocked the tunnel died. A detailed investigation into t...