A DOP-smoke penetration test is used for HEPA filters rated above 98 percent efficiency on an atmospheric-dust-spot test. The name comes from the gas dioctyl phthalate (DOP), which is used to perform the test. However, DOP use was widely discontinued several years ago due to the fact that it was a suspected carcinogen. Emory 3004 is now used extensively in the industry for testing HEPA filters, especially ceiling mounted or installed units.