FIREPROOFING, Firestopping and Fireblocking (Part 1 of 4)

Posted on 9/25/2017 4:04:47 PM 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.  The next four blogs will 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 wont confuse the three again.  If you find someone using the wrong phrase, now you can just share this blog link with them.

Let’s start with fireproofing. 


Fireproofing is design to protect the structural members of a building.  You will find it applied to structural steel or structural concrete. 

Fireproofing is needed on primary steel and concrete. 

Why is it needed on steel?  Steel has great structural integrity until it reaches a certain temperature.  When it does, the steel will fail.  When this happens the structural integrity of the building fails and the building, or portions of it may collapse.  This was seen in the US on September 11, but also on other projects such as:

  • The collapse of the highway I-85 in Atlanta in March 2017
  • Windsor Tower or Edificio Windsor in Madrid Spain had a fire on the 21st floor (of 32) after 18 to 20 hours of fire the building was a total loss an there was extensive slab collapse above the 17th floor but fireproofing was incomplete above this level.
  • The Jackson Street Apartments in Ontario Canada on Feb 8, 2002 where there was partial collapse of a concrete floor ceiling assembly  
  • On February 27, 2001, the 4-story Faces Nightclub and Memories Lounge Bar building in Motherwell, Lanarkshire, UK experienced a total collapse after burning for approximately 2 hours 
  • One Meridian Plaza in Philadelphia PA where a fire in a steel framed building raged for 18 hr and caused significant damage to 9 floors
  • CESP Building 2 in Sao Paulo Brazil on May 21, 1987 where there was substantial partial collapse of the central core of the building
  • One New York Plaza in New York City on August 5, 1970 where bolts connecting steel beams were sheered during a fire causing the beams on floors 33 and 34 to fall

In some ways, wood has more structural integrity in a fire than does steel because the outer layer of wood burns and creates a char. This char insulates the inner layer of wood.  It is not until the outer layer of char falls away that the next layer is exposed, burned and then chars and insulates the inner layers again.  So, wood looses its structural integrity and the load it is capable of bearing very differently than does steel.  The wood becomes capable of supporting less and less weight as the layers are burned through.  Steel however, is strong until a certain temperature is reached and then it cannot be expected to support anything, not even its own weight in some cases.  

There were photos of the steel in the World Trade Center that were shown during the City of Phoenix Development Advisory Board in 1999. You could see a segment of steel beam.  The top and bottom of a segment of steel had fireproofing and the center did not.  The top and bottom were straight and the center segment was bent in an S shape.   The fireproofing that is installed on structural steel acts a bit like the char on the wood.  It insulates the steel and prevents it from reaching that critical temperature at which it will fail.

Why is fireproofing needed on concrete?  To answer this I will ask you to consider a few things.  

1) Concrete is considered ablative, meaning it has chemically bound water that is released during a fire.  This will help to reduce the speed with which the concrete can heat up.  What happens to water when it is heated?  It expands!  What happens to a pocket of water inside concrete when it expands?  It explodes and the concrete spalls.  This is one of the reasons concrete needs steel in it, to help hold it together even when it spalls.  When the concrete is thicker, spalling in smaller areas is not going to impact the structural integrity in the same way as thinner slabs that require fireproofing. 

2) One of the requirements of ASTM E119 states that a rated floor or wall must not allow the non-fire side of the temperature of the non-fire side of the assembly to raise above 325F  (above ambient) for the duration of the fire test.  Thinner concrete or concrete over metal deck will not be able to survive this test requirement unless it is protected with fireproofing material.  This requirement is called a T rating, and in a future blog I will propose a challenge to you to develop a new product for the industry.  Stay tuned friends!

Any material tested to the various required standards and listed with a third party-testing agency can be used.  Typically however there are three means of protecting structural elements.   The most common is a cementicous or gypsum based compound mixed with other things such as mineral wool, quarts, perlite or vermiculite.  It is typically applied to steel or concrete with a sprayer leaving a popcorn finish that some consider unsightly.  SFRM (Spray applied Fire Resistive Material) can also be troweled on to give a more uniform or shaped finish.   It is often hand packed when patching areas as well.  Adhesion, density and thickness are all critical elements to the material performing as expected. 

If you visit Las Vegas and go to the Paris hotel, the Eiffel tower inside the building was required by Clark County Building officials to be fireproofed.  SFRM would have been unsightly and even if it were troweled on, it would have lost the look of the dimensions of steel that designers were looking for.  In cases like this where aesthetics are important, an intumescent paint is often used. When this material is used mil thickness is important to performance in a fire scenario.

Another option to protect structural elements is to encase them in gypsum board, endothermic mats, insulative blankets or an array of other potential options.  Regardless of the choice made, the installations should be installed in accordance with a tested and listed assembly to ensure that the expected results will be achieved.

So now, you have a handle on what FIREPROOFING is.  Next time we will talk about Firestop.   This is a favorite topic of mine, so see you soon.