Explosion and fire in a desulphurisation unit of a refinery

An explosion and fire broke out at a heavy oil direct desulfurization unit at a refinery. The location of the explosion was approximately at 20 meters height.
The fire burned within a radius of approximately 30 meters on a portion of the refinery site, which covered approximately 15,000 m².

The fire was extinguished approximately 10 hours later. The refinery stopped the supply of heavy oil and the 1,000 kl of heavy oil and hydrogen remaining in the equipment was left to burn out. The fire department intervened attempting to extinguish the fire by injecting nitrogen into the piping.
According to the refinery, prior to the explosion, multiple gas detectors detected an abnormality in an area containing a high-temperature, high-pressure separation tank, which separates heavy oil from gas, and staff were on their way to inspect it.
(translation from Japanese by means of Google Translate)

separation tank

The supply of heavy oil was stopped, and the heavy oil - hydrogen inventory left in the desulphurisation unit was left to burn out. The fire department dispatched 27 fire engines, including chemical fire engines: they fought the fire by injecting nitrogen into the piping. A safety perimetner within a radius of 1-4 km was installed.