Fireproofing, FIRESTOPPING and Fireblocking (Part 2 of 4)

Posted on 11/14/2017 10:44:04 AM By Sharron Halpert

We have all been on a construction project and heard someone talk about fireproofing something when they mean firestop, or firestop when they mean fireblock.  This is the second of a four part series where we look at the difference between Fireproofing, Fire Blocking and Firestop.  We will examine what they do, why they are needed and what materials can be used so that you may better understand the differences.  After this blog series, you won’t confuse the three again.  If you find someone using the wrong phrase, now you can just share this blog link with them.

In our last segment we talked about fireproofing, what it does, why its needed, how its tested and what materials can be used for fireproofing.   Today we will make the same examination of firestop materials. We will start with rated joints and our next blog post will be on through penetration firestop. Let’s get started.


For the sake of this discussion, let’s say that a building is one big block, made up of a series of smaller blocks.  If a fire starts in one of the smaller blocks, the building code requires that the building be built in a way that the fire stays confined in that smaller block for a designated period of time.  The weak points in that box are the joints where one rated assembly connects to another rated assembly.  This could be where the gypsum or block walls connect to the concrete deck above.  It could be where a floor slab meets another floor slab and will require specific movement capacity. Historically it was primarily sealants, but as the industry has evolved and now there are spray applied materials. In fact there is even a tape that can survive the rigors of these fire tests when installed properly with other materials such as mineral wool.


When firestop is installed in a rated joint assembly, it maintains the code required continuity from one rated assembly to the next.  This prevents the passage of fire, smoke and toxic gases from one part of the building to another; reducing the damage from fire, and maintaining the expected level of safety for the building occupants and first responders who may enter a building to fight a fire or rescue people.   Many rated joints are designed to accept the movement anticipated in different locations in a building, but they must be installed properly for them to be expected to function in this way.


Firestop is tested to the same standard regardless of the manufacturer and regardless of which test lab is used to.  The temperature inside the furnace needs to hit certain marks at key timelines during the test.  This is called the Time Temperature Curve.

The test for rated joints and rated through penetrations is slightly different. First, let’s discuss the common ground.  Firestop used in rated joints is tested to either ASTM E1966 or UL 2079.  The time temperature curve used in this test is the same as the one used in ASTM E119, which is the test for the rated walls and rated floors.  This makes sense because we want the rated wall to match the same requirements as the joints.   If it didn’t, we could not assume the code required continuity of rating.

This is not to say that the temperature during an actual fire will be reached at these specific times.  This is simply a way to test all materials to the same standard, in hopes of being able to guess how they might function in a real fire scenario.  The trouble is, a real fire scenario has too many variables to quantify in a laboratory test. When there is a fire, the temperature rises and the pressure in the room of origin increases, things fall over and crash into the walls.  Because of this, the last requirement of the firestop laboratory testing requires that the assembly must be subject to a hose stream test.  Both the duration of the test and pressure from the hose will increase as the hourly rating increases.  The hose stream test subjects the assembly to erosion and pressure impact.  The purpose is to ensure that the firestop installation is durable enough to endure an actual fire.  The expectations are that if the installation passes this test, it will also be durable enough to survive:

- the impact of expansion and contraction caused by thermal changes during a fire

- the increase in pressure in the room of origin

- the movement of interior finishes or trades materials failing and impacting a rated assembly

All of these events are likely to happen during a fire and they all have the potential to dislodge firestop installations.

There are two main differences between how firestop rated joints are tested and how through penetration firestops are tested.   Rated joints are classified as either static, meaning that they won’t be subjected to movement; or they are dynamic, which means they are expected to be subjected to movement over the lifecycle of the building.  Because of this, the firestop rated joints are subjected to movement prior to being placed on the burn furnace.  The class of movements are:

- Class I  - Thermal- 1 cycle/min 500 cycles

- Class II  - Wind- 30 cycles/min 500 cycles

- Class III – Seismic- 300 cycles/min 500 cycles

The other difference is that the rated joints need to ensure that heat does not penetrate to the non-fire side of the assembly for the duration of the test; or at least heat sufficient to ignite something as simple as cotton.  It makes sense if you think about it.  Flash point is the temperature at which something can ignite, so we want to be sure that a fire is not able to spread to the non-fire side of the wall just because the curtain or the bookshelf gets hot enough.  All it takes is for something to dry out and that lack of moisture lowers the flash point and makes it more combustible.   This T rating requirement will help reduce the risk of fire spreading prematurely through a rated assembly.


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Firestop rated joints typically have two parts. First is a backing material. Second a seal on the joint. Backing materials in smaller joints can be combustible materials such as backer rod or maybe even fiberglass; but only when it is listed in the test detail.  In some cases it may not even be required, but again this is only the case with smaller joints.  When the joints get larger, the only material allowed will be mineral wool.  If you look back at the time temperature curve again, know that fiberglass will degrade around 1200F and mineral wool will require temperatures in excess of 2000F, so these materials are NOT interchangeable.  Also note that mineral wool density and compression requirements are critical to these joint systems functioning as expected.  Old school installation of the sealant on these joints would be a sealant; but sprays are often a faster solution. In the last few years, there are two materials that are starting to challenge these methods.  The first is an intumescent strip that may be factory installed to a drywall track, or a wider strip that is laid in place prior to the installation of traditional track systems. These allow for greater movement in many cases.  Even more recently, a tape has come on the market that can be taped to the joint.  This will likely still require the use of mineral wool. Maybe someone will come up with a backer rod that is infused with intumescent material that will provide a one step solution for smaller joints.  If that sounds like a challenge to the manufacturers, it just might be.  If you are interested in firestop challenges, stay tuned to this blog for more challenges.  If you come up with something, please share your product with me.

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Tune in next time for a discussion about through penetration firestop and maybe another challenge.