The Baffled Flask Test for Dispersant Effectiveness: A Round Robin Evaluation of Reproducibility and Repeatability ALBERT D. VENOSA *, DENNIS W. KINGà, 1 & GEORGE A. SORIAL§, 2  National Risk Management Research Laboratory, US Environmental Protection Agency, 26 W. Martin Luther King Dr., Cincinnati, OH 45268, USA àStatking Consulting Inc., Fairfield, OH 45014, USA §Department of Civil and Environmental Engineering, University of Cincinnati, Cincinnati, OH 45221-0071, USA Aftertwopreviousinvestigationsdemonstratedthatthebaffledflasktestwasaneffectiveandreproducible method for screening the effectiveness of dispersant products in the laboratory, the US Environmental ProtectionAgencydecidedthatbeforethenewprotocolcouldbeconsideredforreplacementoftheswirling flask test, it would have to be subjected to an interlaboratory round robin investigation. This paper de- scribes how the round robin evaluation was carried out and presents repeatability and reproducibility calculations that demonstrate the superiority of the new method over previous methods. Probabilities for passing various threshold levels of effectiveness values were computed, and the results will be used by the Agencytodevelopfinalpass–faildecisionrulesfordispersantmanufacturerswishingtohavetheirproducts listed on the national contingency plan product schedule. Published by Elsevier Science Ltd. Keywords: Baffled flask test, swirling flask test, dispersants, round robin test, interlaboratory test, dispersion effectiveness, crude oil Introduction In September, 1994, the US Environmental Pro- tection Agency (EPA) officially adopted the swirling flask test (SFT) as its official laboratory screening methodology for testing the effectiveness of disper- sants in seawater. The SFT is based on the protocol first developed and adopted by Environment Canada in the 1980s (Fingas et al., 1987, 1989a,b). It essen- tially consists of a procedure in which a pre-mixed solution of crude oil and dispersant is added to a specially designed glass side-arm flask containing 100 ml artificial seawater and the contents of the flask mixed on an orbital shaker for 10 min followed by a settling time of 10 min. The dispersed oil mixture is then extracted and measured in a spectrophotometer to determine the quantity of oil that had been dis- persed into the water column. Listing of a dispersant on the national contingency plan (NCP) product schedule has been contingent on the dispersant being at least 45% effective (50  5%) in dispersing Prudhoe Bay and South Louisiana crude oils in the laboratory test. An important aspect of the test is that a product may be less than 45% effective on one of these oils but Spill Science & Technology Bulletin, Vol. 7, Nos. 5–6, pp. 299–308, 2002 Published by Elsevier Science Ltd. Printed in Great Britain 1353-2561/02 $ - see front matter PII: S1353-2561(02)00072-5 299 *Corresponding author. Tel.: +1-513-569-7668; fax: +1-513-569- 7105. E-mail addresses: venosa.albert@epa.gov (A.D. Venosa), stat- king@statkingconsulting.com (D.W. King), george.sorial@uc.edu (G.A. Sorial). 1 Tel.: +1-513-858-6514; fax: +1-513-858-3022. 2 Tel.: +1-513-556-2987; fax: +1-513-556-2599.