ISO 21530:2004 specifies test methods for determining the resistance to chemical disinfectants of all materials used for external surfaces of dental equipment intended for such disinfection.Three test methods are specified: an immersion test, a spray test and a contact test. The choice of test method to be used is left to the discretion of the party conducting the testing.ISO 21530:2004 does not address the bactericidal, virucidal and fungicidal effectivity of the disinfectants.ISO 21530:2004 does not provide for testing the possible detrimental effects of applied stress on the resistance of test materials to the test reagents.