To perform the test, the entire planned assembly is constructed on a standardised test rig two storeys tall, with a window opening in the middle, and is continuously ignited with
gas burners from two different angles for 30 minutes.
[192] The assembly must satisfy numerous performance criteria to pass, including a requirement that flames cannot spread more than 10 ft (3.0 m) vertically from the top of the window opening or 5 ft (1.5 m) horizontally.
[190][192]
A single NFPA 285 test can cost over US$30,000, and it certifies only a particular assembly (i.e., a particular combination of parts from specific manufacturers as they are currently fabricated), meaning that any change to any part used for any reason requires a new test.
[189][193] As of mid-2017 ACM cladding with a polyethylene core had not been able to pass the NFPA 285 test, and thus had been effectively banned on US high-rise buildings for decades.
[190][194] The UK does not mandate the use of such realistic simulations
[190][194] and allows its own similar full-scale tests to be bypassed as long as "the wall assembly components, when tested individually, pass small-scale combustibility tests."
[195]
