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Fire rating of exposed steel

  • 1.  Fire rating of exposed steel

    Posted 08-20-2018 13:04
    Working on a concrete/steel project. Owner doesn't want to see fireproofing, but project needs a fire rating of the floor and supporting structure. (1 hour rating req'd).  The strux engineer believes that he can come up with a fire rating for exposed (un protected) steel. I think what he thinks he can do is to determine at what point the steel will lose strength, and if it's more than 1 hour, then we don't need to fire rate the steel.
    I'm very uncomfortable w/this, but honestly, that's the same thing that spray fireproofing is doing - eventually the steel will lose strength in the fire, we are just delaying it until after 1 hour.
    This might end up being a non-issue - he might not be able to make his calcs work.
    Have you ever done something like this, or even heard of it? It's a new one for me.
    The project is a large garage (Storage use group) with a tiny apartment (residential use group). 1 hour rating required. The garage is 2 level, apartment on the upper level. We get a 1 hour rating out of the concrete/steel deck floor, so it's just the beams I'm worried about. I've offered intumescent paint as an option, but the owner wants nothing on the beams.
    I'm also concerned because I'd imagine that anything that's stored in the garage (IE: gasoline in the tanks of cars) can potentially burn hotter and faster than typical fire loads. Although I haven't researched it yet, I know they make "high temp rise" spray applied fire proofing. Not sure this is the correct application or no.

    David Sisson AIA
    David Sisson
    Providence RI
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  • 2.  RE: Fire rating of exposed steel

    Posted 08-21-2018 15:04
    If I were a betting man, I would say you and your engineer are barking up the wrong tree.  The strength of the steel decreases with temperature, and it's fire resistance rating is further affected by size/shape and load.  From : "For small, fully loaded hot rolled sections, exposed on all four sides, the inherent fire resistance without added protection can be as little as 12 minutes."  There is a reason there are approved fire-resistant rated assemblies, and it should be noted that the IBC does not have provisions for calculating the fire resistance of bare steel.  I can't imagine a building codes official taking the responsibility of approving exposed steel when the code requires a 1-hour rating or higher.  This may be a case of what your client wants and what he gets are two different things.

    Without knowing more about your project, I wonder if an automatic sprinkler system in lieu of fire-rating would be allowed.  Your client may not like that (especially the cost), but if he likes the aesthetics of exposed steel, he might like exposed steel sprinkler pipes, too.

    Please keep us informed how this plays out.

    Daniel Scott Cooter, assoc. AIA
    Sparkman & Associates Architects, Inc.
    Knoxville TN

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  • 3.  RE: Fire rating of exposed steel

    Posted 08-21-2018 17:26
    Intumescent Paint


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  • 4.  RE: Fire rating of exposed steel

    Posted 08-21-2018 18:15
    David Sisson ---

    Wow, talk-about hot-doggin' it!  A few thoughts on "naked steel":
    1.    Truly naked:
    You'd probably need to grossly-oversize your members, to hope to play "1-hour-chicken" with unpainted steel.  And, as you said, what happens at "minute # 61"?
    2.    Caretaker's apartment:
    It's surprising that that's being done!  Is this job in this country?  Unless that unit has a direct fire-stair down to grade, that person's at severe risk.
    3.    Consultant:
    Have you considered a new "Strux" Engineer?  A serious person would "Just say 'No!' "...
    4.    Intumescent Paint:
    That's even weirder, w/ the Owner objecting to that.  The steel's gotta be painted anyway; is this paint available in the red "steel-rust" color?  And of course, the Owner will know it's there, when s/he gets the bill for the paint, at $150.00 per gallon.
    Also ---
    When they scrape-&-re-paint in 15 years, your intumescent paint is gone.
    5.    Insurance:
    Have you reviewed this with your liability insurance carrier?  Allow a few minutes for the laughing, before the yelling starts.  Is this project worth keeping?

    Please, give this a good, hard look; this job sounds like a nightmare, and very dangerous for all concerned.

    william j. devlin aia, inc.,
    Springfield, MA

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  • 5.  RE: Fire rating of exposed steel

    Posted 08-21-2018 18:57
    The engineer is hanging his hat on IBC 2012 722.1 which allows analysis per ASCE 29 chapter 5. Apparently, this is actually a thing. The issue will probably go away when his calculations fail. I'm honestly extremely uncomfortable w/this even if his calcs pass. My drawings currently show a spray applied system, and I won't change it unless I'm somehow convinced. And yeah, the local fire dept and building dept will get a letter from me if necessary.
    The apartment has egress to grade, so we don't have any exiting issues. Weird building, built into a hill. The bottom level is essentially a basement, two driveways serve the building, one to the upper level and one to the lower one.

    David Sisson AIA
    David Sisson
    Providence RI

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  • 6.  RE: Fire rating of exposed steel

    Posted 08-22-2018 11:53

    1. Truly naked:
    You'd probably need to grossly-oversize your members, to hope to play "1-hour-chicken" with unpainted steel. And, as you said, what happens at "minute # 61"?
    William Devlin,  08-21-2018 18:15
    Yep, this. Grossly-oversize. Sort of like the difference between using heavy timbers vs. 2x material.

    As for the owner not wanting the steel painted, I'm running into a lot of that sort of thing where people want some version of "rustic" finishes - exposed beams/joists/rafters, corrugated metal, etc. I just had an inquiry the other month where someone gutted a building to "expose the structure" (before talking to any professionals, mind you) and then was told by the building department that they needed the fire ratings for floors and walls and issued a stop work order.

    Thomas Bank AIA
    Principal Architect
    Simply Stated Architecture, P.C.
    Lemoyne PA

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  • 7.  RE: Fire rating of exposed steel

    Posted 08-21-2018 19:26
    Intumescent paint is perfectly appropriate for this application. You can get it in a variety of colors. Intumescent paint colours and getting a good finish on steel | Rawlins Paints Blog
    Rawlins Paints Blog remove preview
    Intumescent paint colours and getting a good finish on steel | Rawlins Paints Blog
    Intumescent paints are fantastic for fire safety, as they help to protect the surface below. Additionally, intumescent paints can be used to achieve fantastic decorative finishes on steelwork. There are different finishes available to use on steel, depending on your desired look. How to get a good finish using intumescent paint on steel Base If ...
    View this on Rawlins Paints Blog >
      If your client accepts that, fine. My next suggestion would be to look into spray fireproof coverings and enclosures that meet some UL approved assembly and the aesthetic that your client will accept. Oversizing the steel is interesting, but the cost may turn out to be prohibitive. If this is residential then go back to the codes, especially if you have an exit to grade from each level. Depending on your local/state codes there are usually lots of exceptions for special circumstances. (sprinklers, heights above/below grade, etc..)

    Mark Forth, AIA, NCARB
    Principal | Mark Forth Architect
    Orange County, CA

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  • 8.  RE: Fire rating of exposed steel

    Posted 08-22-2018 17:35
    ​I missed out if there was a photo accompanying the inquiry.
    is there any reason some type of truss or engineered wood product couldn't serve the structural purposes within the roof plane and let the exposed steel be a decorative element?

    Rene Lusser Assoc. AIA
    Better By Design
    Driggs ID

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  • 9.  RE: Fire rating of exposed steel

    Posted 08-29-2018 11:04
    Engineer has come around to the idea that the steel needs to be protected. So, problem has solved itself. They should have listened to the architect up front, LOL.

    David Sisson AIA
    David Sisson
    Providence RI

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  • 10.  RE: Fire rating of exposed steel

    Posted 08-22-2018 19:25
    If the Height and area, based on the use, requires a "protected" (A vs. B) construction type, then it would be hard to convince a judge, in court, after the failure, that you followed the code prescription. The separation of uses usually defer to an assembly, independent-agency-tested, again, not ignored by the legal system.  I remember a Steel Institute "solution" of placing water inside round columns to maintain a lower temp. under fire. Would love to see the steam works when everything lets an hour.



    Peter Hart AIA
    Peter C. Hart & Associates, Ltd.
    Stamford CT

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  • 11.  RE: Fire rating of exposed steel

    Posted 08-23-2018 18:05

    I've got the perfect solution for your exposed steel dilemma!  Have you thought about pre-stressed concrete slabs for the floor/roof structure?  Then your exposed steel is purely decorative and can be left "naked" all you want.  I've used these slabs on similar conditions in Chicago where every square inch counts but you still need your fire separations.  My client actually suggested it!   It was very simple to do and since it sounds like you'll be doing block or concrete foundation walls on the lower floor due to the hillside setting, you will already have your support system. The cost of the concrete slabs did add an additional cost of $10,000 to the project but the owner was very happy that he got a roof deck and living space over his garage.


    Suzie Van Cleave, AIA



    4421 N Oakland Ave #200                 O 414.204.8917 

    Milwaukee, WI 53211                        C 847.778.1625




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  • 12.  RE: Fire rating of exposed steel

    Posted 08-22-2018 10:02

    The client wants to see unpainted steel? Intumescent paints can be overpainted if he wants the finish to match, or if he wants the look of raw steel, you could use an intumescent varnish. With the combination of residential and high risk storage, are you sure you do not need more than a one hour separation? Or are you using sprinklers for the second hour?




    Christopher Blood, AIA, MArch.
    Sr.Designer - Architecture


    c/o Architecture49 Inc.
    150 Isabella Street, 10th Floor, Suite 1000, Ottawa, Ontario, K1S 1V7, Canada

    T+1 613.690.3996  C+1 514.839.2221



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  • 13.  RE: Fire rating of exposed steel

    Posted 08-23-2018 22:12
    It sounds like a barn-do. Living above a collection of classic cars?

    A properly configured misting sprinkler system should provide the actual protection and your steel would never get hot and the cars one bay away from the fire may not even require a repaint ....but may require 3rd party testing to get approval. The deluge system folks have really fought these systems that have been used on ships for half a century in a put out the fire or swim environment.

    Charles A Phillips, AIA, AIC-pa

    433 Phillips Rd
    Nacogdoches, Tx 75964

    640 Brookstown Ave
    Winston Salem, NC 27101

    From iPhone

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  • 14.  RE: Fire rating of exposed steel

    Posted 08-22-2018 17:42
    Please do be careful with terminology when getting into the world of intumescents. If you are looking to achieve a fire resistance rating for unprotected steel, you want an intumescent mastic or coating tested according to ASTM E119 or UL 263. If you want to achieve a Class A flame spread / smoke developed classification on materials, you want an intumescent paint tested according to ASTM E84. There's a world of difference!

    The intumescent coatings may be overpainted by certain finish paints identified by the coating manufacturer. Talk to Albi, Carboline, International Protective Coatings for advice.

    Philip Kabza AIA
    SpecGuy Specifications Consultants
    Mount Dora FL

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  • 15.  RE: Fire rating of exposed steel

    Posted 08-23-2018 01:55
    Intumescent paint seems perfect. Don't forget to protect the columns all the way down to the foundation (IBC 704.1).  Also, don't forget to insulate the apartment floor if the garage levels are unheated.  The Code takes a special interest in places where people sleep...

    Douglas F Julien, AIA
    Saint Louis MO

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  • 16.  RE: Fire rating of exposed steel

    Posted 09-18-2018 17:51
    I have renovated historic properties with steel columns where  we used the International Existing Building Code  to allow those columns to meet the fire protection requirements based on thickness.   That met the code and saved the historic quality of the structure.

    J. Perrin AIA
    J. Robert Perrin Architect
    Omaha NE

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