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Is Concrete Fire Resistant? 

While nVent PYROTENAX MI cable is the preferred solution for the protection of critical circuits during a fire, there are plenty of buildings that use concrete construction methods as an alternative. This process is the encasement of critical circuitry with up to two inches of concrete.  

This approach has historically been accepted, but the new technical note released by the NFPA shows an evolution in building codes and standards may be about to begin.  

Let’s explore the fire resistance of concrete, and how it compares to fire-rated wiring solutions.  

Why is Concrete an Option for Buildings? 

When designing a building, there are two type of fire systems to keep in mind: active and passive.  

  • Active Fire Protection Systems: Smoke detectors, fire sprinklers and other options to reduce the spread of fire  

  • Passive Fire Protection Systems: Building design and layout, including non-combustible floors, wall and roofs.  

As building design has evolved in the twenty-first century, both active and passive systems need to protect electrical circuitry.  

Concrete as a structure and a material is inherently fire resistant. It’s a non-combustible material with a slow rate of heat transfer, making it a natural choice for building fire protection. In fact, it was once approved for one hour of fire protection by the NFPA. All critical wires and circuitry could be encased in the concrete for a relatively low cost.  

If the question is – is concrete fire resistant? The simple answer is yes, but this does not mean it’s the most optimal material for building fire protection.  

The Evolution of Building Codes  

By 2018, a number of NEC building standards have upgraded from one hour of fire protection to two hours. These included:  

  • Article 695 “Fire Pumps” requires 2 hour protection per 2008 NEC 

  • Article 700 “Emergency Systems” requires 2 hour Protection per 2011 NEC 

  • Article 708 “Critical Operating Power Systems requires 2 hour Protection per 2011 NEC 

  • New Article 728 “Fire-Resistive Cable Systems” in 2014 

  • Article 760 “Fire Alarm Systems” requires 

  • 2 hour Protection per 2005 NEC 

  • NFPA 72 “Fire Alarms” requires 2 hour “Survivable Circuit” and cables must be installed per Article 760 

These updates fell in line with NFPA codes requiring two hours of fire protection applied to emergency power supply generators, elevator circuits, fire pump circuits, smoke venting fans and more.  

As of April 2018, 42 states mandated a minimum two-hour fire rating. This means critical circuits should remain operational in temperatures from 1000°F (537°C) at 5 minutes to 1850°F (1010°C) at 120 minutes.  

How Do Concrete Methods and MI Cable Compare for Fire Protection? 

The main problem with concrete and fire protection, is that you need more inches for more hours of protection. To meet the current codes and standards, most concrete encasements would need to be between three and five inches thick, depending on aggregate used. This means that buildings with one or two inches of concrete are not currently meeting NFPA or NEC code. More concrete leads to less usable space , a critical aspect for modern building design.  

Downside of Using Concrete for Fire Protection in Buildings:  

  • Buildings with one or two inches of concrete are not currently meeting 2 hours of fire protection 

  • More concrete leads to less space savings, a critical aspect for modern building design 

  • Lack of approval or testing in their final installed state, leads to misapplied or inadequate protection  

  • Concrete is prone to  damage  

  • Concrete is not ideal for building retrofits  

Upside of using MI cable for Fire Protection in Buildings:  

  • MI cable is UL/ULC fire rated for two hours of protection 

  • MI cable is Free air rated  

  • MI cable can be installed in tight, or hard to maneuver spaces  

  • MI cable can withstand the impact of a blow, or falling concrete, etc.  

For well over one hundred years, fire safety codes have saved lives and property by promoting best practices in building design. With the availability of fire-rated products, building professionals are better equipped to specify the safest systems.  

For more information on how these codes affect building design, watch our code video series or sign up for our on-demand webinar.