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#163426 05/07/07 11:21 PM
Joined: Jan 2004
Posts: 1,507
Ever since I can remember there has always been a controversy about what product are suitable for "firestop" in various types of construction. I've always found that checking with the building department prior to installing the job worked best. Some would allow fiberglass insulation, some wanted duct seal and some wanted a Listed firestop product- even when the type of construction was combustible construction. What I find interesting is that the NEC at 334.80 (2005 Edition) recognize thermal insulation or sealing foam as products suitable for firestop or draftstop in wood construction. Am I reading this correctly?

George Little
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Joined: May 2005
Posts: 984
Likes: 1
Not quite.
334.80 only says that IF you are using one of those methods at the penetration, you need to derate the cables. They're neither recognizing nor endorsing that particular method. It's still strictly the Building Department's call.

Joined: Mar 2005
Posts: 1,213
I think of lot of the problem is that if you take a small tuft of fiberglass insulation and hold a lighter to it, it "burns" and "melts" away like a piece of wet cotton candy, complete with glowing red embers as the fibers "burn". I think we've all seen this- leads to a complete distrust of fiberglass as a fireblocking material. I've heard many a fireman lecture about how fiberglass is no firestop, based completely on this simple try-it-at-home demostration!

But if you take a larger sheet of fiberglass and repeat the experiment, you get no such "burning" or "melting"- just a small black scorch mark, as the fiberglass does its insulating job and traps the gas of the flame, slowing the flame's spread.

I haven't been motivated yet to build an actual wall cavity to simulate this for real for myself (would make for great youtube, ah?) but I've been thinking about it- not like I have a shortage of construction scraps to use to build a model!

Last edited by SteveFehr; 05/08/07 12:07 PM.
Joined: Jan 2004
Posts: 1,507
Ghost- I can't agree with your point of not recognizing thermal insulation as a firestop or draftstop. I do know that these products are used for combustible construction and the Code panel obviously knows also or they would not address thus senerio in the code with the result being a derating of the ampacity.
Article 300 Section 300.21 clearly says I can use anything I want to as long as the "possible spread of product of combustion will not be substantially increased"
Of course if it's a fire rated assembly then we are required to us products that would maintain the integrity of the assembly.

Last edited by George Little; 05/08/07 06:05 PM.

George Little
Joined: May 2005
Posts: 984
Likes: 1
Hi, George;

I never claimed that they couldn't be used as a firestop/draftstop, only that 334.80 doesn't state whether they're okay or not and shouldn't be taken as blanket approval...only that if they are used as such you need to derate the conductors.

I agree that 300.21 says "Electrical installations in hollow spaces, vertical shafts, and ventilation or air-handling ducts shall be made so that the possible spread of fire or products of combustion will not be substantially increased. Openings around electrical penetrations through fire-resistant-rated walls, partitions, floors, or ceilings shall be firestopped using approved methods to maintain the fire resistance rating"; but as I read it it's still up to the AHJ to rule up or down on what I'm using to close up my penetrations.

As to the suitability for the use I, as always, defer to the Building Code.

Joined: Aug 2003
Posts: 64
I don't mean to be nit-pickey but just as using electrical terms incorrectly can cause confusion, so can the incorrect use of other building code terms. Here are some difinitions from the IBC (and they are used the same in other building codes):
DRAFTSTOP. A material, device or construction installed to
restrict the movement of air within open spaces of concealed
areas of building components such as crawl spaces, floor/ceiling
assemblies, roof/ceiling assemblies and attics.

FIREBLOCKING. Building materials installed to resist the
free passage of flame to other areas of the building through
concealed spaces.

PENETRATION FIRESTOP. A through-penetration
firestop or a membrane-penetration firestop.

device or construction installed to resist for a prescribed time
period the passage of flame and heat through openings in a protective
membrane in order to accommodate cables, cable trays,
conduit, tubing, pipes or similar items.

assemblage of specific materials or products that are designed,
tested and fire-resistance rated to resist for a prescribed period
of time the spread of fire through penetrations. The F and T rating
criteria for penetration firestop systems shall be in accordance
with ASTM E 814. See definitions of “F rating” and “T

I think what George is asking about is Fireblocking rather than fire stoping. In the right application and if installed properly, I think fiberglass works as a fireblocking material. The IBC in fact mentions fiberglass as an acceptable fireblocking material. Fiberglass does not burn, but it does melt. I have looked up the melting temperature of glass befor. I can't remember offhand what it is, but it is about the same as sheet metal or gypsum.

Fire Stopping on the other hand is a completley differant animal. Fire stopping is used when a penetration is made through a fire rated wall or other assembly (penetrating a top or bottom plate of a wall is not an example of this). A fire stopping assembly needs to be tested for the required fire rating. I know of no tested fire stop system that consists of fiberglass used to fill up a hole through a rated assembly. It can be used within a tested assembly that uses gypsum board or other materials as the primary material to resist the fire, but I doubt there is a tested assembly that uses fiber glass as the primary material to resist the fire.

NEC 300.21 correctly uses the term fire stopping in conjuction with penetrations through rated assemblies. 334.80 seems to use the term incorrectly because it seems to use that term for any penetration through wood framing. Remember, it is the building code, not the NEC, is the primary authority on where fireblocking or firestopping is required.

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