Firestopping cable and pipe penetrations through fire-rated walls and floors is a critical consideration for anyone responsible for the design, specification and construction of new buildings, or for the ongoing maintenance of occupied premises. To achieve this challenging task, specially approved or listed systems have to be used. This is what is called passive fire protection, or simply firestop. Most of these solutions are based upon a core technology known as intumescence. But how does it work, what’s the secret behind it and why is it so important in modern building practice? 

Intumescent materials expand in fire

Intumescence at a glance 

The word intumescence has its origins in the Latin “intumescere”. The term derives from the medical field and means swelling under inflammation. Chemically it is the swelling of certain substances due to the impact of heat. 

In general, fire needs three components to start: fuel, oxygen and a heat source. When ignited, a fire develops heat, flames, gas and smoke. A fire can be extinguished by inhibition of any one of fuel, oxygen or heat source. 

The basic principles of fire protection is detection, suppression, containment. Intumescence plays a primary role in the containment area. It’s meant to assist in cutting off the unaffected areas of the building from the heat source. Two different intumescent principles exists:

• First principle - there is an intumescent reaction that results in pressure. The material expands when exposed to heat and exerts pressure to close gaps and joints and forces melting plastic pipes closed.
• The second principle is insulating intumescence. Here the material expands when exposed to heat and creates a carbonated, insulated foam to protect, for example, metal penetrants or cables. 

How the technology works – an excursion into the world of chemistry 

Intumescent systems are “intelligent” material compositions. They react to a change in temperature of the surrounding environment, such as that caused by a fire. When a certain temperature is exceeded, the material produces a voluminous layer, which protects the underlying building parts. Expansion temperatures can vary from 150°C up to 350-400°C. The expansion tends to be largely contained and extends outwardly to as much as 700 percent or even more. 

 Intumescent material: Hilti firestop foam

The actual result is based on some important temperature-dependent chemical reactions. Most intumescent materials, therefore, are a mixture of different components like polymeric basic components and binder agents, gas-creating agents, sources of carbon, and some catalysts which steer the reactions of other ingredients. One key raw material in many passive firestopping systems is vermiculite, which acts as a blowing agent in firestop collars, sealants, blocks or other systems. In the pictures below the different stages “expanded” vs. “non-expanded” are shown.  

 One key basic raw material: vermiculite in microscopic view (non-expanded), Source: Hilti 

Expanded vermiculite in microscopic view, Source: Hilti 

Intumescence in action, firestop collar during a fire test 

Why is this technology used for firestopping? 

Referring to our firestopping triangle above and more specifically containment, the Model Building Codes support this by requiring building to be compartmentalized. Between these compartments are fire or smoke rated walls. These walls are meant to restrict the flow of fire or smoke from leaving these compartment areas of the building. However, other building systems need to run from these areas into non-rated areas. Plastic pipes, burnable insulated pipes or cables and cable trays go through these fire-rated walls and floors. They react differently in a fire according to the type of material they are made of. Most of them will soften, melt and just burn away, leaving a hole, gap or simply a leakage point. It may also, in many cases, destroy or damage the substrate during the melting or burning process.

Passive Firestop solutions use intumescent material inlays and components so by swelling or expanding directly within the wall or floor structure it helps to stop the destructive process caused by these melting, burning or moving penetrants. Therefore, Firestopping Systems are designed to help effectively keep the fire contained to a certain area. 

 

Pipes and cables burn and melt, the leakages and gaps are closed by intumescent Firestop products

To help, something needs to quickly constrict this process. This is the application domain of the passive firestop systems. Why passive? These systems are integrated into the structure of a building during the build process and do not react until there is fire or significant heat generation. Furthermore, they do not require any other items, such as alarms or external detection method to perform. Simply, with just an increase in heat and they begin the compartmentation process.  

How manufacturers use this technology – the challenges 

As many different pipe, cable and insulation materials exist, reactions in a fire can be quite different. When it comes to the development and testing of a certain pipe and cable applications, the process is heavily dependent on pipe or cable material, pipe or cable diameter and pipe wall thickness.  
 

For example, a PVC plastic pipe (e.g. heating system) with a diameter of 6 inches / 160mm. Pipe wall thicknesses can be as thick as 6mm or greater. Due to the thickness of the pipe, the burning/melting process is time consuming and is characterized by continuous melting over time. In this case, the intumescent reaction should not be too fast. You still must have enough material left to close the rather big hole (6 inches, plus annular space) with enough material left at the end of the melting/burning process. Also, due to the thickness of the pipe, a certain pressure is needed to squeeze away any pipe material. Too much fast-reacting intumescent material may lead to an uncontrolled expansion. 

So, the challenge for a manufacturer of firestopping solutions is to develop systems that are able to cover a vast range of pipe and cable materials. Manufacturers who are able to research, develop and test existing applications in a building can provide adequate solutions, which have been tested for compliance and yet are also simpler to install. The strategy to finding the best formulation for the intumescent ingredients is to use a core technology that can cover as many different pipe materials as possible. However, sometimes compromises are necessary. Therefore, different systems exist to cover different pipe materials and sizes, covering different opening sizes and burnable pipes vs. cables, cable trays or insulation materials. 

Classic intumescent Firestop solution Hilti CP 643 N / CP 644 for plastic pipes with high performance intumescent inlay and solid housing installed on the wall. 

Besides the technological challenges described in this article, Hilti, with its own research and development, is committed to supply easier-to-use firestop solutions, providing cutting-edge fully integrated and tested systems. Together with unique, professional technical support in many countries, this helps specifiers and installers to correctly select the right systems for the right applications and to correctly specify compliant and tested systems. 

Hilti is the global market leader in firestopping. Our dedication to stringent testing and code developments help make buildings safer today, saving lives and protecting assets, with proven reliability and outstanding service.

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For further enquiry or clarifications, please feel free to reach out to us at my.engineering@hilti.com

Additional technical resources:
On-demand : Fire Protection - Passive Firestop Solution
General Notes, Typical Details & Specification Text
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