Which of the following statements is true when a test system is pressurized with a halogen-air mixture prior to leak testing with a halogen diode (heated anode) leak detector?

halogenated gases should not always be tlushed out of systems after a leak test has been successfully conducted

halogenated gas should have a concentration of at least 1 000 ppm in order to achieve maximum sensitivity

vessels with a significant vertical height may require a means of rrllxing the test gases before and during the test

the element life of a halogen diode (heated anode) leak detector is relatively unlimited with proper maintenance and operation