"Class" fire ratings vs hour fire ratings

[Stephen Tashi]

TL;DR Summary

Do (USA) fire ratings for wall coverings (Class A,B,C) relate to fire ratings given in hours for materials like drywall?

Do (USA) fire ratings for wall coverings (Class A,B,C) relate to fire ratings given in hours for materials like drywall?

I'm particularly interested in how ornamental ceiling tiles that have a "class A" fire rating ( e.g. https://www.amazon.com/dp/B00319FP8Y/?tag=pfamazon01-20 ) affect the fire resistance of a drywall ceiling when they are applied over it.

My first idea is that the "class" type of fire rating indicates how much a fire would spread over a tiled ceiling but that the spread of the fire on the tile wouldn't have much effect on how long the fire would take to burn through the drywall. It would take very little time for a fire to burn through a wall covering. So, by this theory, people don't bother to fire rate wall coverings in hours.

 

[Lnewqban]

Do (USA) fire ratings for wall coverings (Class A,B,C) relate to fire ratings given in hours for materials like drywall?

Yes, we discuss and specify elements of fire rated walls, partitions and ceilings based on time of resistance to fire.
UL assembly penetrations and fire dampers and ceiling radiation dampers are also rated by time (example: 1-hour dynamic fire damper).

Please, see:
https://codes.iccsafe.org/content/F...smoke-protection-features#FBC2017_Ch07_Sec706

https://www.ruskin.com/model/dfd-lp

 

[AlexTheParticle]

It's a good question and one that I've also wondered about. From my understanding, the class A, B, C fire ratings for wall coverings do not directly relate to the fire ratings given in hours for materials like drywall. The class rating is more of a measure of how easily the material will ignite and spread fire, rather than how long it will take for the material to burn through.

In terms of ornamental ceiling tiles, having a class A fire rating means that the tiles are highly resistant to fire and will not contribute to the spread of flames. However, this does not necessarily mean that they will provide any additional fire resistance to the drywall ceiling they are applied over. In fact, in the event of a fire, the tiles may actually hinder the ability for firefighters to access the drywall and extinguish the fire.

In general, it's always best to follow the manufacturer's recommendations for fire ratings and installation methods when it comes to wall coverings and ceiling tiles. It's also important to ensure that any fire-rated materials are properly installed and maintained to ensure their effectiveness in the event of a fire.