A probe is on into the accident, though prima facie a gas leak in the sea cooling water system was attributed to the fire.
Appala Raju (21), who was undergoing treatment at Old Care hospital in Visakhapatnam, succumbed to his burn injuries on Friday, according to HPCL sources.
Seven workers, who were airlifted to a burns hospital in Mumbai are responding well and their condition is stable, they said.
A massive blaze had broken out on August 23 at the HPCL complex here when staffers from private companies were at work.
Of the 25 persons killed in the mishap, only one was an employee of HPCL while rest of the victims were private workers engaged by contract companies.
At present 15 patients - eight in local hospitals and seven in Mumbai - are undergoing treatment.
A committee set up by Ministry of Petroleum and Natural Gas and HPCL headquarters, will submit its report soon on circumstances that led to the blast in the cooling tower, sources said.
Oil Industry Safety Directorate's executive director Hirak Dutta, who is heading the panel constituted by the Ministry, has already inspected the blast site.
Earlier, the Andhra Pradesh Directorate of Factories had said investigation in the mishap was on following which they will issue a notice to the Vizag facility of HPCL seeking an explanation for the accident.
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