Flame Spread Rating on HVAC Air Diffusers

Q: We are an existing healthcare occupancy, 100% sprinkled. In the kitchen, we have problems with existing metal HVAC diffusers rusting and would like to replace them with a non-metal option. Looking at Stratus brand, they say they are UL2043 fire and smoke rated, but not what the actual flame spread rate is. Seems like it should be okay, 2x4 lights have plastic lenses, not sure what the difference would be.

Any advice?

A: Flame spread rating only applies to interior finish on wall and ceiling coverings. Section 3.3.90.2 of the 2012 Life Safety Code says interior finish is the exposed surface of walls, ceilings, and floors within buildings. And the Annex section A.3.3.90.2 says furnishings should not be considered interior finish. An HVAC air diffuser is not an interior finish, but rather is a furnishing, or a piece of hardware used in the distribution of a ventilation system. Section 10.2.3.5 says the different classifications (i.e., Class A, Class B, and Class C) that limits the flame spread rating, is for interior finish only. Therefore, the HVAC air diffuser does not have to meet the requirements of flame spread rating.

Similarly, the plastic lens on the 2x4 fluorescent lights is also considered a furnishing and is not subject to flame spread rating limitations. Now, if someone got goofy and took all the plastic lens and attached them to the wall, well, now you’ve changed the use of them and they would have to meet the flame spread rating for their respective interior finish classification.