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 a 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 had formed when sulphuric acid entered into contact with the steel of the tank.

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 steel-acid reaction, the formation of hydrogen and its ignition.
The root cause was the lack of inspection and maintenance of the tanks, in its own a consequence of inadequate safety management.

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.

The first fire brigade truck arrived on scene within 5 minutes of the explosion and sprayed a large amount of water into the tank farm area. The tank was equipped with spill collection boxes inside the dike that ran to a common header. The header ran to a valve box south of the tank farm, where it entered an internal sump system that directed flow to an acid neutralization system. However, the large amounts of acid and firewater overwhelmed the system, and acid flowed up through the sewer gratings onto the streets outside the diked area.

Immediately following the incident, there was concern that the remaining acid tanks could catastrophically fail due to damage from the fire and the spill of acid. Because of acid contamination and the amount of acid remaining in the undamaged tanks, workers were
unable to enter the diked area for one month, when the tanks were emptied–32 days after the incident.

Because of the presence of large quantities of H2SO4 and an ongoing search and rescue
operation, the area was an active emergency response site for many weeks.