Hydrogen explosion in a refinery

The explosion occurred when a spark from welding equipment ignited flammable vapours from a 415,000-gallon (ca. 1.5 million of litres) sulphuric acid storage tank at the refinery.
The investigation showed that the explosion was caused by the ignition of hydrogen leaking from the tank as result from years of neglect. Hydrogen is produced when sulphuric acid comes into contact with the steel tanks.

One worker was killed and eight other workers were injured. The surrounding sulphuric acid tank farm was heavily damaged in the blast, and an estimated 1.1 million gallons of the acid were released into the environment, including nearly 100,000 gallons (400000 l) that flowed into the river.

The INITIATING cause was the ignition of hydrogen leaked from H2SO4 tanks.
The root cause was failure to maintain and inspect the tanks, due to the lack of a safety and risk management plan.
Contributing cause was the loss of containment of the tanks due to corrosion and formation of gaseous hydrogen .

sulphuric acid storage

On the day of the accident, the maintenance contractor was repairing (grinding, welding, open flame) a corroded catwalk at the acid tank farm. The corrosion had been caused by SO2 vapours from the storage tanks combined with moisture in the air to form (H2SO3).

DESCRIPTION OF THE PROCESS
H2SO4 is used as the catalyst in the refinery’s alkylation process. In this process, smaller molecules (such as isobutane and butylene) are combined in the presence of H2SO4 to form compounds called alkylates, which are high-octane components of gasoline.
After being used in the alkylation process, the spent acid (typically 88 to 95% H2SO4 , 5% H2O and the rest (light) hydrocarbons) is sent through a regeneration process.

One worker was killed and eight other workers were injured.

An estimated 1.1 million gallons (1.5 millions l) of the acid were released into the environment, including nearly 100,000 gallons (400000 l) that flowed into the nearby river.