4.3.11.2.6 Materials within a ceiling cavity plenum exposed to the airflow shall (a) be noncombustible or (b)
exhibit a maximum flame spread index of 25 and a maximum smoke developed index of 50 when tested in
accordance with ASTM E 84, Standard Test Method for Surface Burning Characteristics of Building Materials,
or with ANSI/UL 723, Standard Test Method for Surface Burning Characteristics of Building Materials, or (c)
comply with 4.3.11.2.6.1 through 4.3.11.2.6.9, as applicable.