What makes Firestop different from other sealants?

Posted on 6/26/2017 8:12:27 AM By Sharron Halpert

There is one important element in firestop materials that makes them different from so many other sealants is the way they behave in a fire.  Of course the “secret sauce” that goes into the product that makes them more expensive than other sealants also.  The key element in many, but not all, firestop products is their capacity to expand when the product is exposed to the heat seen in a fire scenario.  The industry lingo is intumescent.  When looking at the sealants used in firestop they are either used in joint applications so they need to allow for movement, or they are used in through penetrations in which case many applications will require an intumescent product.  Today we will discuss why this more expensive material can not be substituted for the non-intumescent material.

First of all, this intumescent material is needed when dealing with combustible through penetration such as insulation around pipes or ducts.  As the fire causes the insulation to melt or soften, the expanding intumescent firestop will close the gap that is created.  It’s even more obvious that intumescent material would be needed around plastic pipes.  Plastic pipes will melt at temperatures around 300F-500F degrees, depending on their chemical composition.  For many pipes under 2” diameter an installer can use an intumescent sealant.  “Many” is a tricky word.  It alludes to the potential for exceptions, and in this case the exception is FRPP, plastic fire sprinkler pipes. Most manufacturers will not be able to firestop 2” diameter FRPP with just sealant. 

Some firestop materials are not even compatible with FRPP because over time the chemical incompatibility will etch holes in the plastic pipe.  It is recommended that installers check the Lubrizol website for a list of items that have been tested to be compatible, or the alternate list of things tested and found to be incompatible with Lubrizol, which is the element added to plastic sprinkler pipes.

So, if a plastic pipe can not be firestopped with sealant alone, it must be done in conjunction with wrap strips, collars or other materials that have more intumescent “umph”.  These other materials will expand faster and with more impact.  They are able to close down the larger pipes much faster and completely, where intumescent sealant alone is not able to.Please note however that sealant is still required in the installations.  The larger the plastic pipe, the more closely you should look at the tested and listed detail showing how to firestop it.  When you look at UL listed details you will find that the larger the plastic pipe, the more restrictive the annular space requirements will be.   Once the pipes are larger (possibly over 6”) there will be a requirement for 3mil aluminum foil tape to be installed on the pipe before the collar is placed on the pipe.  This is because the heat around the outside edge of the collar will cause the intumescent material to expand, char and insulate the inner layers of wrap strip, preventing them from expanding fast enough to close down the melting plastic pipe.  The foil tape helps to draw heat into the wrap strips located in the center of the firestop installation and allows enough heat to cause it to expand faster and effectively close down the large plastic pipes.  In a UL burn facility this will take place in about 5 minutes.  If you ever get the change to witness a burn, its is impressive.  If you are interested in seeing a sample of what happens when installations are done incorrectly have a look at the video HERE for an impressive example.

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Plastic pipes are not the only combustible material found penetrating rated walls on construction sites. Let’s look at pipes to start with.  They may be insulated with fiberglass, AB/PVC or other insulation materials. Let’s look at Fiberglass pipe insulation, it melts around 1200F, which will be quickly reached in a fire test scenario.  ASTM E119, which is the “Standard Test Method for Fire Tests of Building Construction and Materials” requires that the temperature inside a furnace 10 minutes into the test shall be 1300F.   Before this happens the fiberglass insulation will become soft and the intumescent material will begin to squish the insulation against the pipe.  That is if the installer used intumescent firestop, and if they installed it correctly so that there is material in the gap around the wall or floor through which the pipe is running.  There is a great deal more to consider when looking at pipe insulation and THIS LINK will show you some.

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Another not so obvious example of when intumescent material is required in a firestop installation would be around a non-dampered duct.  

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If the duct is insulated then it would obviously need an intumescent sealant but did you know that even a bare duct will require an intumescent sealant?  This is because of the thermal expansion that will cause the square duct to move in various different directions as the temperature increases during a fire scenario.  The only way to ensure that the firestop can successfully be subjected to the riggors of an ASTM E119 or UL 263 - Standard Test Method for Fire Test of Building Construction and Materials fire test include UL links is if the intumescent material is used.

Please note that all of these comments are GENERAL and installations vary by manufacturer due to the different materials used in the creation of the different products and different tested and listed assemblies from the various third party testing agencies.