Maximum flame-spread ratings and smoke developed classifications of combustible grilles, diffusers and other devices for supply, return, and exhaust-air openings in rooms, in buildings described in Sentence 1.3.3.2.(1) of Division A.

This also applies to:

• the fire safety characteristics of heating, ventilating and air-conditioning systems, as stated in Article 6.2.1.2., and
• buildings to which Part 9 applies [see Sentence 1.3.3.3.(1) of Division A for application of Part 9], with respect to:
  • mechanical ventilation systems other than self-contained systems serving single dwelling units, as stated in Sentence 9.32.1.1.(2),
  • the ventilation of storage garages for more than 5 motor vehicles in residential occupancies, as stated in Sentence 9.32.1.1.(3),
  • mechanical ventilation systems used for the ventilation of rooms and spaces in dwelling units during the non-heating season, where natural ventilation is not provided in accordance with Article 9.32.2.2., as stated in Clause 9.32.2.1.(1)(b),
  • heating and air-conditioning systems other than those serving individual dwelling units, as stated in Sentence 9.33.1.1.(2), and
  • air duct distribution systems in which the rated heat input exceeds 120 kW, as stated in Sentence 9.33.6.1.(2).

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.