1/4 inch Set Back

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Re: 1/4 inch Set Back

the UBC did not break it down to either/or, but to smoke index and flame spread ratings.

on a side note, a torch, propane, mapp, or oxy will burn paper on concrete. my oxy might be able to burn paper on water, and the next opportunity, I will try.

paul
 
Re: 1/4 inch Set Back

Originally posted by macmikeman:
Ok, I'm in to. If gypsum wallboard is so noncombustable then why is it necessary for sometimes several layers of it on fire rated walls?. I alway's wanted to know that.
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Generally two layers (one on each side of the wall) of Type X fire rated 5/8" sheetrock will have a fire rating of 1 hour. Increasing the number of layers will increase the fire rating of the wall. A two hour wall may have four layers, two on each side.
 
Re: 1/4 inch Set Back

The following is from the Gypsum association "Fire Resistance Design Manual", 14th edition:

"Fire Resistive Properties of Gypsum: Gypsum is approximately 21 percent by weight chemically combined water which greatly contributes to its effectiveness as a fire resistive barrier. When gypsum board or gypsum plaster is exposed to fire, the water is slowly released as steam, effectively retarding heat transmission. it can, in a sense, be compared to what happens when a blowtorch is turned on a block of ice. Although the ice is being melted, one can hold a hand on the opposite side without being burned. even though the ice gets very thin it effectively blocks the transfer of intense heat and one's hand would not be burned until the ice is melted."

Gypsum Board is defined as "the generic name for a family of sheet products consisting of a noncombustible core primarily of gypsum with paper surfacing." It is further defined as Regular, Type X, Improved Type X, and Proprietary Type X.

Hope this helps.
 
Re: 1/4 inch Set Back

Originally posted by infinity:
Originally posted by macmikeman:
Ok, I'm in to. If gypsum wallboard is so noncombustable then why is it necessary for sometimes several layers of it on fire rated walls?. I alway's wanted to know that.
Click to expand...
Generally two layers (one on each side of the wall) of Type X fire rated 5/8" sheetrock will have a fire rating of 1 hour. Increasing the number of layers will increase the fire rating of the wall. A two hour wall may have four layers, two on each side.
Click to expand...
The "Fire Resistance Design Manual" will detail the way to achieve a certain fire resistance. As Bob mentioned, 1 layer per side = 1hr. rating. 2 layers = 2 hr., etc.
 
Re: 1/4 inch Set Back

Originally posted by jimwalker:
Everything will burn at some temperature including that receptacle itself. :D
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A firefighter told me that back east in steel mill country they have steel fires.
So yeah, everything is combustible given the right conditions.
 
Re: 1/4 inch Set Back

Fire resistance ratings have more to do with the temperature on the other side of the gypsum board than the burning of the board itself. A 1 hour wall will not necessarily catch fire any sooner than a 2 hour wall, but it will transmit more heat to the other side faster.

IMHO, all gypsum board is noncombustible. The small amount of paper is a non-issue.

Steve
 
Re: 1/4 inch Set Back

Fire resistance ratings have more to do with the temperature on the other side of the gypsum board than the burning of the board itself. A 1 hour wall will not necessarily catch fire any sooner than a 2 hour wall, but it will transmit more heat to the other side faster.

IMHO, all gypsum board is noncombustible. The small amount of paper is a non-issue.
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I believe this answers my question the best. I knew that adding layers increased the rating, but if it was non combustable I did not understand why it would increase the rating. Thanks Steve.
 
Re: 1/4 inch Set Back

Originally posted by steve66:
Fire resistance ratings have more to do with the temperature on the other side of the gypsum board than the burning of the board itself. A 1 hour wall will not necessarily catch fire any sooner than a 2 hour wall, but it will transmit more heat to the other side faster.

IMHO, all gypsum board is noncombustible. The small amount of paper is a non-issue.

Steve
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Almost. Neither wall will catch fire (unless you are talking the studs behind the fire rated covering), but yes the 2 hour wall will prevent the heat transfer for a longer period of time.
 
Re: 1/4 inch Set Back

Almost. Neither wall will catch fire (unless you are talking the studs behind the fire rated covering), but yes the 2 hour wall will prevent the heat transfer for a longer period of time. [/QB]
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I'll agree with that. I was thinking drywall could eventually burn, given Jimwalker's comment:

Everything will burn at some temperature including that receptacle itself.
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But now I'm wondering what temperature you need to burn water :eek:
 
Re: 1/4 inch Set Back

Almost. Neither wall will catch fire
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This might be true with sheetrock but consider some wooden doors are "fire rated".They are solid wood and will take longer to burn through..depending on the rating..but they are still wood, and will burn.Fire rated does not mean non combustible.
 
Re: 1/4 inch Set Back

Fire rated does not mean non combustible. I agree. But the topic was in reference to sheetrock. i.e. gypsum wallboard.
 
Re: 1/4 inch Set Back

I have seen some fire-rated pre-hung interior doors that had an interior made of a gypsum type material sandwiched between two layers of plywood.


Hank
 
Re: 1/4 inch Set Back

water burns at 212 degrees F.

there are tons of various fire rated assemblies, but once past one hour, the most crucial items seem to be blow through at penetrations, joints. In shafts, like stairwells, where the joints and treatment allow (improper install or application) a jet of air to penetrate through, the result is a long stream of heat akin to an oxy-acet cutting flame, rendering the stairwell unusable or deadly. Some treat all this as overblown, but when it's needed it makes a giant difference in survivability.

paul
 
Re: 1/4 inch Set Back

USG sent me a copy of the material handling data sheets for sheet rock. It is a mere 8 pages of info that one would never even think of.

There is a small section on fire safety.

the list part that deals with combustibility states it is "limited combustible"
 
Re: 1/4 inch Set Back

If a term is not in the NEC, the proper place to go for the definition is in the dictionary mentioned in the style manual.
I would look up combustible and then take the info you gather and see if it meets the definition.
I can't wait for you to prove that we have been doing it wrong all these years. ;) ;)
 
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