Engineers at Rice University, in Houston, US, have developed a new computational model showing how the contents of failed aboveground storage tanks can spread through the atmosphere following disasters such as hurricanes.
The model is based on real data from the Houston Ship Channel, the largest petrochemical complex in the US, from Hurricane Ike, which hit in 2008, and Hurricane Harvey, which wreaked havoc in 2017. Winds like these can carry chemical and petroleum vapours a long way from the site of a tank. Atmospheric scientist Rob Griffin of Rice’s Brown School of Engineering says that the model can be used to predict potential consequences of future storms threatening storage tanks. If the storm also knocks out air quality monitoring systems, the model could also offer the only way to estimate the spread of pollutants afterwards.
Work on the model began following a 2015 study from Rice civil and environmental engineer Jamie Padgett and alumnus Sabarethinam Kameshwar, now an assistant professor of civil and environmental engineering at Louisiana State University, which found that a number of storage tanks would fail in a Category 4 hurricane, either through lifting them off their foundations, crushing them, or as a result of flying debris. They predicted that a 24’ (7.3 m) storm surge could release more than 90 million gallons (409.1 million L) of oil and chemical products.
The model subsequently developed by Griffin and the team looks at how vapours are carried on winds for 12 hours after a spill, at heights up to 5,000’. It showed that oil vapour plumes spread more widely than organic solvent plumes, which stay concentrated along the path of the wind. In addition, there is substantial formation of ozone and secondary organic aerosols in the solvent plumes, driven by factors like sunlight and other pollutants.
One simulation based on Hurricane Ike, with swirling winds showed that a diesel plume from a tank spill would spread slowly for the first six hours to cover 42 km2, before a rapid expansion covering 500 km2. A simulation based on Hurricane Harvey showed a narrower plume blown into the Gulf of Mexico.
“We had to make some assumptions about what would spill if there were a spill. But it’s valuable to think about what would happen to those chemicals once they’re in the atmosphere. The same results could be just as applicable to something like the Deepwater Horizon [rig explosion and subsequent oil spill]. Once that material reached the surface of the ocean, what happens to it when it evaporates? I would love to see some of the owners of these tanks use this to look at their structures. I can imagine folks like the Environmental Defense Fund or other advocates picking up on the study as well,’ says Griffin.
The model is not suitable for studying the effects of a single tank spill, as it is based on regional data, but Griffin believes that it could be adapted for that purpose and will make the chemistry and atmospheric code available.
The research has been published in Atmospheric Environment.