question: Which  Performance has a Test Standard of bs en779, and a Particulate size approaching 100% retention of >2µm, and a Class of f6?
answer: SELECT performance FROM table_name_39 WHERE test_standard = "bs en779" AND particulate_size_approaching_100_percentage_retention = ">2µm" AND class = "f6"
context: CREATE TABLE table_name_39 (performance VARCHAR, class VARCHAR, test_standard VARCHAR, particulate_size_approaching_100_percentage_retention VARCHAR)