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How fire spreads in the façade?

Modern ventilated rainscreen cladding systems have become one of the preferred choices around the world for high-rise structures, providing design flexibility as well as weather protection. A free flow of air behind the cladding is very important to keep the cavity dry, but this also makes the façade one of the most vulnerable elements of a building in case of a fire.

Colourful facade

Fire resistance is an integral part of the building envelope.

A façade must neither propagate fire, nor allow fire or heat to travel from one area to another (compartmentation) and it should remain structurally intact for a reasonable amount of time when exposed to fire.

That ultimately means that:

  • The separating function between fire cells must be maintained.
  • Spread of flame within the wall must be stopped
  • Spread of fire along the surface of the building façade should be limited.

Why are fire in cavities and air gaps in facades so dangerous?

Due to the “chimney effect”, fire in the air gap behind cladding can spread very quickly. As the oxygen in the air gap is utilised, the fire seeks more oxygen and moves rapidly upwards.

Leap-frog English text

“Leap-Frog”-Effect

Fire spreading only on the outside of cladding is often not that critical, while fire that spreads in the air gap behind the cladding can travel 5-10 times faster in the same time frame due to rapid buoyancy of hot air in the air gap, compared to fire on the outside.

Speed up to 8 meters per minute have been measured. Since the fire is hidden behind the cladding, it is very hard for fire fighters to extinguish it. A flashover in a room may cause fire to break out of a window and the flames and hot gasses escaping through a window opening are sufficient to cause the re-entry of the fire in the room above the storey of fire origin. When this mechanism of fire spread occurs, it has the potential to repeat through the same mechanism to every floor above it. Therefore, this is referred to as the “Leap-Frog”-Effect.

"The “chimney” still allows the flames to reach the next floor level, where windows and other wall penetrations will allow the fire to re-enter the building and maintain the spread of fire".

WHAT IS THE CAVITY IS NON-COMBUSTIBLE?

Even if the cavity itself is fully non-combustible, the extended length of flames created in the “chimney” still allows the flames to reach the next floor level, where windows and other wall penetrations will allow the fire to re-enter the building and maintain the spread of fire.

THE FIREBREATHER CAVITY BARRIER STOPS THE CHIMNEY EFFECT

The Firebreather Cavity Barrier is the only product on the market that has the ability to instantly stop fire from spreading in the air gap behind the cladding in a facade. This makes it possible to use non-combustible materials in the air gap.

Read more about the advantages of the FB Cavity Barrier.

 

 

sECURO fIREBREATHER