The toll in the cooling tower blast at HPCL Refinery mounted to 23 with four more patients succumbing to burns on Sunday.

Two patients died at National Burns Centre in Mumbai and two others lost their life while undergoing treatment in the city. A HPCL spokesman said contract workers K. Tata Rao and M.V. Ramana died at Manipal and New Care Hospital here, the last two injured succumbed to burns after they were airlifted to Mumbai for specialised care.

As of now, 14 patients were undergoing treatment in the corporate hospitals in the city and six at National Burns Centre in Mumbai.

The blast on August 23, which was believed to have caused due to sparks originating from welding after heavy build-up of hydrocarbons in a pipeline, led to the collapse of the cooling tower. The cells of cooling tower were under commissioning as part of Rs.2,500-crore diesel hydro desulphurisation unit to roll out Euro-3 and 4-compliant fuels to tier-II cities by March, 2014.

A Special Investigation Team set up by the HPCL headquarters and another high-power committee announced by Ministry of Petroleum and Natural Gas under the chairmanship of Oil Industry Safety Directorate Executive Director Hirak Dutta have started investigation into the causes that led to the blast.