Masud died while undergoing treatment at the burn unit of DMCH on Sunday, said Prof Dr Shamanta Lal Sen, chief of the burn unit.
Earlier, on Thursday, Raihan, son of the owner of the storehouse, and on Friday, Nur Mohammad, helper of the lorry containing petrol, breathed their last at DMCH.
Two more critically injured, including Mizanur Rahman, owner of the godown, are also undergoing treatment at the hospital.
Prof Dr Sen said their condition is not good.
Five people were severely burnt after a fire broke out at an oil godown in Mijibari area of Bangabandhu Road in Chandpur town while unloading petrol from the lorry around 12.30am on Thursday.
Soon the fire engulfed the godown on the ground floor of a three-storey residential building and spread to the upper floors.
Five units of Chandpur Fire Station rushed to the spot and brought the situation under control after a hectic effort of four hours.