Silver Eagle Refining has delayed operations at the first crude unit of its Utah refinery, which was closed down following a fire in November 2009.
The US Chemical Safety Board said the blast occurred when a 10in pipe burst and released hydrogen gas because the defective pipe was too thin to meet minimum thickness standards, according to Reuters.
The firm is awaiting permits from the US Occupational Safety and Health Administration for re-opening the 10,250bpd refinery.
The permits will confirm that the plant's pressure values are in good enough shape to be put into service.
The refinery was voluntarily closed by the firm on 13 November 2009, after problems were found with the piping. It was initially due to restart on 16 February 2010.
