Meaning of "Exposed members"

[fpst]

What does "exposed" mean in the phrase "exposed members"? How would you convince the AHJ that's what it means?

In NFPA 13 2013, Table 8.6.2.2.1(a) has many interesting things going on...

A short snippet from the handbook giving us additional info:

If you look at the table where it says "Combustible unobstructed with no exposed members" under "Construction Type", I want to ask how this is possible to be constructed?

A couple of senior sprinkler nicet IV's have given me the interpretation that "exposed members" means "combustible members" such as wood. So having rigid metal frames or steel bar joists would not be counted as "exposed members", meaning this "Combustible unobstructed with no exposed members" type of construction is entirely practical and common.

However, if you interpret it literally, "exposed members" does not say "combustible members" and I would say it would literally apply to any member - including steel ones. But then the question is, is it even possible to construct a large-area roof without exposed members? If not, obviously there is more here than just the literal interpretation.

What does "exposed" mean in the phrase "exposed members"? How would you convince the AHJ that's what it means?

 

[MatthewJWillis]

Exposed means just what it says. That it is visible.
Combustible = burns. (Wood for the most part but could be any other type building material like a plastic board.

How is "Combustible unobstructed with no exposed members" possible to be constructed?
How about support of mezzanine with glue-lam beams 7'-7" on center. Place a ceiling 7" below the bottom of the glue lams.

R/
Matt

 

[fpst]

In the space above the "ceiling 7" below the bottom of the glue-lams" and the top of the glue-lams, aren't the glue-lams visible and therefore exposed?

If so, what's an example of a non-exposed (invisible) member?

 

[fpst]

FWIW Matt I read it the same way, sprinklerdesigner2 standing over my shoulder told me it had to do with the combustibility and it seems idiotic not to just call them "combustible members" or "noncombustible members" which isolates them from ceilings, but who knows.

 

[MatthewJWillis]

The definition of exposed as referenced from NFPA #13...



Full Definition of EXPOSED


1

: open to view


2

: not shielded or protected; also : not insulated <an exposed electric wire>

R/
Matt

 

[fpst]

what version of NFPA 13 is that from? I looked for it in the definitions of the 2013 edition and I couldn't find it

completely agree though that exposed shouldn't have anything to do with combustibility in-of-itself

still perplexing as to why it seems to be associated with combustibility from multiple people who have never met and some of whom are very experienced

https://www.mail-archive.com/sprinklerforum@lists.firesprinkler.org/msg41822.html

https://www.mail-archive.com/sprinklerforum@lists.firesprinkler.org/msg41814.html

usually such behavior is a sign of something that was different in the past, talked about in a tech note, or something at least, because I agree it's a weird leap to go from a term like "exposed" to mean "combustible"

 

[MatthewJWillis]

Your links are not complete.

Chapter 3
Section 3.1, is the definition.

R/
Matt

 

[fpst]

fixed links:
Link
Link

about the definition of exposed, in the context in which it is used, seems like fire treated wood could be considered shielded or protected (from fire), steel could be considered shielded or protected (from fire), but non treated wood could be considered exposed (not protected from fire)
yet a see-through plastic ceiling down below some structural members means the beams are open to view, but obviously isn't what is intended

in short I don't think a merriam-webster dictionary definition is enough to get an answer, especially when the definition includes talk about "shielding/protection" and "shielding/protection" can change something from being "combustible" to "limited-combustible" or even "noncombustible".

 

[stookeyfpe]

This is an interesting question given that I am starting to see some fairly large (and engineered) cross linked laminated wood members being used as framing elements. Designating a structural element as either combustible or noncombustible really rests with the Building Official who is enforcing the building code. As someone who reviews plans the issue of combustibility arises a great deal, especially if the combustible member is FRTW (Fire Retardant Treated Wood) or Limited Combustible as defined in the International Building Code or NFPA 220. My approach in my jurisdiction (which has adopted the 2012 IBC) is to use the IBC definition of noncombustible, which is a material that has successfully passed ASTM E-136, Standard Test Method for Behavior of Materials in a Vertical Tube Furnace at 750°C. A material that does not pass this test is considered combustible. When the material is FRTW or Limited Combustible, we still treat it as combustible construction for the purposes of concealed spaces and sprinkler spacing but follow the appropriate NFPA 13 rules for these materials or construction methods.

 

[MatthewJWillis]

Exposed means just what it says. Open to view/Open to heat exposure. It has nothing to with if it is combustible or not. That is a separate definition.
The definition is correct. There is no way talk about "shielding/protection" can change the combustibility of an item. It changes if the heat can reach it, but not how it burns.

Is you pipe concealed or exposed in an office bldg. with ceilings?

If we use your interpretation and consider the glue-lams above the ceiling in my example as exposed, wouldn't the maximum listed spacing for a residential sprinkler attached to CPVC be 15'-0"? This is because to be installed "exposed", CPVC piping has specific criteria. One of which is no more than 15'-0" on center for sprinklers.

Why do you think we have an entire chapter, 8.15.1 addressing concealed installations?

Even in the link that works above, the terms are very distinct and different. Exposed/Concealed, Combustible/Non-Combustible.

You are trying to get wine from mixing apples and oranges...

R/
Matt

 

[msquared48]

I consider the meaning of "exposed" as "unprotected" from whatever it could be exposed to as in water, fire, heat, cold, chemicals... whatever.

Mike McCann, PE, SE (WA)