Raised Threshold at Fire Door?

[LGreene]

In buildings with combustible floors or combustible floor coverings, NFPA 80 requires a noncombustible sill for fire doors rated 45 minutes or more. The NFPA Glossary of Terms defines a sill as "The bottom part of an opening over which a fire door closes,” (not very specific), but there's a drawing in the Annex of NFPA 80 that shows a raised metallic threshold as one option for combustible floors. Although the threshold is drawn on top of a "fire wall (brick, masonry, concrete)".

View attachment 1999

My questions: Is a sill a threshold, or part of the floor construction? Are buildings allowed to have combustible floors these days? If we're working on an old building, is it likely to have a combustible floor? When (if ever) is an aluminum threshold required for a fire door? Here's the section from NFPA 80:4.8.2 Sills.4.8.2.1 In buildings with noncombustible floors, special sillconstruction shall not be required, provided the floor structureis extended through the door opening.4.8.2.2 In buildings with combustible floors or combustiblefloor coverings, special sill construction shall be required ifthe floor structure is extended through the door opening, ascombustible floor construction shall not be permitted to extendthrough the door opening.4.8.2.3 Door openings required to be protected by 1⁄2-hour or1⁄3-hour rated fire protection door assemblies shall be exemptedfrom the requirements of 4.8.2.2.4.8.2.4 Sills shall be constructed of noncombustible materials.4.8.2.5* For swinging doors with builders hardware andspecial-purpose horizontally sliding accordion or foldingdoors with frames having a jamb depth of 4 in. (102 mm) orless, the sill width shall be equal to the jamb depth.4.8.2.6* Where frames have a greater jamb depth, the sillsshall have a minimum width of 4 in. (102 mm) and shall beinstalled so that the sill extends from the face of the frame onthe door side into the frame.4.8.2.7 For swinging doors with fire door hardware, sills shallextend at least the depth of the door frame for flush-mounteddoors.4.8.2.8* For lap-mounted doors, sills shall extend beyond theopening for a length equal to the projection of the installeddoor or doors.4.8.2.9* For horizontally sliding fire doors and vertically slidingfire doors, sills shall be constructed of noncombustiblematerial and shall extend 6 in. (152 mm) past the edge of theopening on each side and 4 in. (102 mm) out from the face ofthe wall.View attachment 1999

/monthly_2013_10/Sill.jpg.464bb4e29c05641dca33d10bab183bb5.jpg

 

[Frank]

The section of the floor directly under the door needs to be noncombustible, this means that carpets, vinyl floor coverings, wood flooring etc need to interrupted at the door.

Aluminum thresholds are NOT permitted as aluminum does not pass the building code test for noncombustible.

 

[LGreene]

Aluminum thresholds are NOT permitted as aluminum does not pass the building code test for noncombustible.

Interesting...where can I find something stating that aluminum is not noncombustible?

 

[Frank]

It is dependent on the alloy and how the ASTM E136 test is run and especially sample containment. In the test with a thick sample the aluminum will melt and if it is contained in a pool in a nonstandard specimine holder then it does not lose weight and fail as it would in a standard mesh holder. Aluminum dust air mixtures can be explosive. Aluminum powder was used as the fuel component in the solid rocket booster fuel for the space shuttle. I have seen the aftermath of many fires where aluminum storefront material was consumed.

 

[IJHumberson]

Lori, combustible floor is not uncommon - especially in projects under 5 stories in height. We see a lot of multi-family construction utilizing horizontal exits as much of the required exiting. The construction at the fire door is tricky, especially when the fire walls are Type V construction using a U300 or U400 series fire wall assembly. Per NFPA 80, the combustible flooring (the subfloor and the surface) cannot extend through the opening, so a noncombustible sill is required. I treat the threshold as part of the sill assembly. However, I disagree with Frank - I would allow aluminum as a sill material. Per NFPA 220, one of the 3 ways to qualify as a noncombustible material is if "The material, in the form in which it is used, and under the conditions anticipated, will not ignite, burn, support combustion, or release flammable vapors when subjected to fire or heat." Although, as Frank pointed out, Aluminum dust can be explosive, in the form in which it is used in this case (it would have to be substantially heavy gauge to be used as a threshold) I would submit that it would meet the NFPA 220 definition of noncombustible. The combustibility of any material is very heavily dependent on the size and arrangement of the fuel - an extremely large log of wood is fairly difficult to ignite with a match, but wood dust in air can ignite with explosive force from just a spark. Even though aluminum dust is ignitable (and steel wool is ignitable), in a solid form, sandwiched between a fire door and a non-combustible fire wall assembly, one would not expect an aluminum threshold to ignite - it may melt and deform, but it is not going to propagate combustion through the opening - which is ultimately what we are trying to prevent.

 

[Yikes]

"Steel Wool is ignitible"...

Sometime try a YouTube search on "Steel Wool Fireworks".

http://youtu.be/gnRcDtMniVE

 

[Gregg Harris]

Lori, combustible floor is not uncommon - especially in projects under 5 stories in height. We see a lot of multi-family construction utilizing horizontal exits as much of the required exiting. The construction at the fire door is tricky, especially when the fire walls are Type V construction using a U300 or U400 series fire wall assembly. Per NFPA 80, the combustible flooring (the subfloor and the surface) cannot extend through the opening, so a noncombustible sill is required. I treat the threshold as part of the sill assembly. However, I disagree with Frank - I would allow aluminum as a sill material. Per NFPA 220, one of the 3 ways to qualify as a noncombustible material is if "The material, in the form in which it is used, and under the conditions anticipated, will not ignite, burn, support combustion, or release flammable vapors when subjected to fire or heat." Although, as Frank pointed out, Aluminum dust can be explosive, in the form in which it is used in this case (it would have to be substantially heavy gauge to be used as a threshold) I would submit that it would meet the NFPA 220 definition of noncombustible. The combustibility of any material is very heavily dependent on the size and arrangement of the fuel - an extremely large log of wood is fairly difficult to ignite with a match, but wood dust in air can ignite with explosive force from just a spark. Even though aluminum dust is ignitable (and steel wool is ignitable), in a solid form, sandwiched between a fire door and a non-combustible fire wall assembly, one would not expect an aluminum threshold to ignite - it may melt and deform, but it is not going to propagate combustion through the opening - which is ultimately what we are trying to prevent.

I would agree aluminum threshold not an issue

 

[tmurray]

Lori, combustible floor is not uncommon - especially in projects under 5 stories in height. We see a lot of multi-family construction utilizing horizontal exits as much of the required exiting. The construction at the fire door is tricky, especially when the fire walls are Type V construction using a U300 or U400 series fire wall assembly. Per NFPA 80, the combustible flooring (the subfloor and the surface) cannot extend through the opening, so a noncombustible sill is required. I treat the threshold as part of the sill assembly. However, I disagree with Frank - I would allow aluminum as a sill material. Per NFPA 220, one of the 3 ways to qualify as a noncombustible material is if "The material, in the form in which it is used, and under the conditions anticipated, will not ignite, burn, support combustion, or release flammable vapors when subjected to fire or heat." Although, as Frank pointed out, Aluminum dust can be explosive, in the form in which it is used in this case (it would have to be substantially heavy gauge to be used as a threshold) I would submit that it would meet the NFPA 220 definition of noncombustible. The combustibility of any material is very heavily dependent on the size and arrangement of the fuel - an extremely large log of wood is fairly difficult to ignite with a match, but wood dust in air can ignite with explosive force from just a spark. Even though aluminum dust is ignitable (and steel wool is ignitable), in a solid form, sandwiched between a fire door and a non-combustible fire wall assembly, one would not expect an aluminum threshold to ignite - it may melt and deform, but it is not going to propagate combustion through the opening - which is ultimately what we are trying to prevent.

One thing I find I need to be reminded on occasion is that you need to "keep it in the family" when it comes to codes. For instance I can't apply the definition of non-combustible from the building code to an NFPA standard. I have to figure out what NFPA determines what is non-combustible. Always good to keep in mind.