While a subcontractor was performing hot work on the renovation of a walkway placed above tank at an oil refinery, tank , containing a mix of sulphuric acid (H2SO4) and so-called “spent” H2SO4 hydrocarbons, exploded around 1:30 pm. The affected tank rose and then collapsed towards the north, causing the walkway to fall and leaching 1,000 m³ of H2SO4. The force of the explosion damaged Tank 396, which in turn released 1,332 m³ of H2SO4. The acid, whose surface was on fire by the burning of inflammable materials, overflowed the retention facilities and wastewater network, before spreading into the site’s aisles. The operator estimated that 375 m³ spilled into the DELAWARE River, killing some 2,500 fish and 250 crabs. The American Environmental Protection Agency (EPA) estimated the total volume of H2SO4 lost at 4,164 m³.
The toll stood at 1 death and 8 injured by eye and lung burns as well as nausea from the vapours. Due to the acid contamination and quantities remaining in the intact tanks, emergency response teams were not able to enter the zone until August 17th, i.e. 32 days after the accident. The search for the dead worker’s body was called off on September 18th. The Federal agency assigned to report on chemical accidents (Chemical Safety Board, CSB) conducted an investigation.
The Board’s final report pointed to several areas of negligence. Tank had been converted from storing “clean” H2SO4 to the “spent” category in 2000 without any precautions taken. As opposed to “clean” H2SO4, the “spent” form of H2SO4 contains hydrocarbons, and inflammable vapours are capable of forming, thus requiring a CO2 inerting treatment. On Tank, this system consisted of a simple rubber pipe inserted into the tank and delivering only a small flow of CO2. The tank also displayed a number of holes caused by corrosion, through which inflammable vapours were able to escape; moreover, the most recent inspection dated back to 1996.
The refinery owner was aware of these shortcomings, yet nonetheless issued a hot work permit. Subcontractors were not informed of the presence of such vapours and only initiated gas detection as of the morning of the explosion, upon arrival at the site. They should have repeated controls at the beginning of the afternoon, especially given that the temperature had already risen. Also, they had not yet installed protection against flying sparks, in failing to comply with permit specifications.
Both the federal government and the state of Delaware filed lawsuits. The operator paid €370,000 in pollution cleanup measures, another €6 million on safety upgrades, €32.4 million for bodily injuries, €130,000 to reimburse public rescue services and €10.2 million in fines for ecological violation
