The Baffled Flask Test (BFT) was developed at the Andrew W. Breidenbach Environmental Research Center in the National Risk Management Research Laboratory, a division of the U.S. Environmental Protection Agency’s Office of Research and Development. This test will soon be adopted as the official method for evaluating oil spill dispersants. A dispersant must meet the minimum requirements of the decision rules set forth by the official method to be listed on the National Contingency Product Plan Schedule (NCPPS) for use during an oil spill event. Two priority studies were conducted with the BFT.
After the explosion of the Deepwater Horizon Oil drilling rig at the exploratory Maconda Well, U.S. EPA was asked to evaluate the eight dispersant products currently listed on the NCPPS, which had qualified under the current method, The Swirling Flask Test (SFT). There were three separate projects: 1) in vitro analyses to determine levels of cytotoxicity and endocrine disruption activity, 2) toxicity testing of dispersants alone, Louisiana Sweet Crude alone, and dispersant – oil mixtures using mysid shrimp and inland silverside fish, and 3) this lab, determination of dispersant effectiveness at two temperatures, 25 °C (the temperature on the surface of the Gulf) and 5 ° C (the temperature at the wellhead).
The results showed that only three products gave satisfactory results at both temperatures. Presumably due to the low viscosity and density of South Louisiana Crude, temperature did not cause a significant difference in performance. Final Dispersant Effectiveness (LCL95DE, lower 95% confidence level after correction for natural dispersion) ranged from 11% to 78%.
The other study was a request from the Department of the Interior’s Bureau of Ocean Energy Management, Regulation and Enforcement (BOEMRE), formerly known as Minerals Management Service (MMS). They funded a study to compare four different bench scale tests with results obtained from their large scale wave tank at Ohmsett, The National Oil Spill Response Test Facility in Leonardo, NJ. All facilities will test the same twenty oils using Corexit 9500 at 15 ° C to determine if any of the tests are predictive of field performance. For comparison purposes in our study, the two oils currently in use by the BFT and SFT protocols plus another reference oil were added.
The twenty oils ranged in density from 0.848 to 0.968 g/mL (35.03° to 14.39° API gravity) and kinematic viscosity from 9 to 32,326 cSt. Categorizing them by density, there are 2 light crudes, 6 medium crudes and 12 heavy crudes. Using Fingas’ definition (1990), by kinematic viscosity, there are 1 very light crude oil, 4 light crudes, 3 medium crudes, and 12 heavy crudes. Final Dispersant Effectiveness (LCL95DE) ranged from 3.4% to 77.1%. The 3 added reference oils, are by density – 2 lights and a medium and by kinematic viscosity – 1 very light and 2 light crudes. Their final Dispersant Effectiveness ranged from 64.8% to 93%. The results correlated to the viscosity of the oil with an R² of 0.84.