To limit the probability that combustible grilles, diffusers and other devices for supply, return, and exhaust-air openings will have higher flame-spread and smoke-development properties than those required for the interior finish of the surface on which they are installed, which could lead to the development of an inappropriate amount of smoke and the spread of fire across the exposed surfaces of the combustible grilles, diffusers and other devices, which could lead to the spread of fire and smoke to other parts of the building, which could lead to harm to persons.