Testing the Draft ASTM Skimmer Test Protocol at Ohmsett

Testing the Draft ASTM Skimmer Test Protocol at Ohmsett

Over the past two years engineers at Ohmsett, The National Oil Spill Response Test Facility, have been working with the American Society for Testing and Materials (ASTM) F20 Committee on Hazardous Substances and Oil Spill Response to draft a test standard to more accurately determine skimmer nameplate capacity.

It is recognized that the current method is arbitrary and seldom reflects the actual performance of a skimmer, as a system, to collect oil. As a result, the U.S. Coast Guard derates nameplate capacity by as much as 80% in estimating the Effective Daily Recovery Capacity (EDRC).

“The goal of this standard is to develop a test that would establish a realistic nameplate capacity,” said Ohmsett Senior Test Engineer Dave DeVitis. “The test should be simple, inexpensive, and yield reproducible data that can be used to compare skimmer performance.”

During July and August 2007, researchers from SL Ross Environmental Research, Ltd. were at Ohmsett to assist in testing the draft standard. "The main objective in testing the protocol was to resolve issues relating to the slick thickness for a valid test," said Steve Potter of SL Ross and head of the ASTM committee. "We were also looking at measurement methods, and the minimum tank area required for the test."

During the tests, three generic skimmers types - disk, drum and weir - were used to measure the oil recovery rates under simulated conditions. The researchers focused on the testing methods, rather than the results of the individual skimmers.

The skimmers were tested in an 8 ft. x 8 ft. x 2.5 ft. (1000 gallon) portable open-top tank on the deck of the Ohmsett test basin. Oil collected by each skimmer was pumped to an overflow tank until steady state was achieved, then flow was diverted for 1 to 3 minutes, depending on skimmer recovery rates, to collection tanks located above the skimmer. Samples of the collected oil were analyzed to determine water content. These values were used with the collection volumes and collection times to calculate recovery rates and recovery efficiencies.

One recurring question about the test protocol is how much of a difference is there between testing in all oil and testing in an oil layer over water. Tests were conducted with the test tank filled with oil only, as well as various thicknesses of oil on top of a water layer. When testing with the oil water interface, the water depth was typically 20" and the oil layer varied from approximately 1" to 6".

Results from these tests were presented to the ASTM F20 Committee meeting in October 2007 in Tampa, Florida. The draft test protocol was revised based on the Ohmsett test results and in December 2007 was sent to the ASTM committee for final balloting.