Fire Rated? - Fire Stop? - Fire Safe?

Fire Stopping; Masonry Constructed Cavity Walls

 Cavity Stop Sock          Cavity Stop Sock 2

 Cavity stop sock compression applied between block work.               Cavity stop sock closing the top of the cavity wall.

External Wall Build Up

  • Sand and cement render
  • 100mm Block outer leaf
  • 40mm Un-ventilated cavity
  • Combustible cavity wall insulation
  • 100mm Block internal leaf
  • Internal render

In Construction Terms;

  • What does Fire Rated mean?
  • What is a Cavity Fire Stop?
  • What is Fire Safe?

What does Fire Rated mean? 

Fire rated simply means that there is proof available that the building materials in question were tested and a fire rating was awarded. The fire rating in itself does not automatically ensure that the materials in question are suitable to stop or resist the spread of fire.

Highly flammable building and insulation materials are awarded fire ratings. One of the most common misconceptions in the construction industry is that of a building or insulation material identified as having a fire rating is understood to be fire safe or some kind of fire stop. This is simply not true, it simply means the materials were tested. The fire test will identify the suitability of the building materials not the fire rating.

If you are looking for a fire stop for a construction detail please identify the construction type; i.e. floor, wall of roof buildup identifying each layer and expected fire stop timeline to allow your supplier to provide you with the best possible options. Not all construction details and building types will have a proven fire test.

Fire rating results will range from A1 to F with A1 being the best and F being the worst.

A building material such as stone wool which identifies an A1 fire rating should not be misunderstood and automatically viewed as a fire stop.

Example: Rockwool is a brand; the insulation materials are stone wool. Knauf is a brand; Knauf building slabs are stone wool.

The simplest way to view fire rating results is to think of the fire ratings as exam results.

A1. Top of class, the building materials are non-combustible. The building materials will not add to the fire load of a burning structure. A1 fire rated building materials may be suitable for application as a fire stop or may be applied to resist the spread of fire. Always check with the building material manufacturer or supplier for suitability. Ask for a copy of the fire test. Where no fire tests are available confirm the materials are Class A1 non-combustible. Remember smoke kills first. Check the smoke emmissions test.

B. Could do better, the building materials are combustible. Better than C but not as good as A. In the event of a fire we can't rely on B fire rated building materials for protection against the spread of fire. The building structure surrounding the B fire rated building materials may require additional fire protection. Combustible building materials will add to the fire load of a burning structure.

C. The building materials are combustible, in the event of a fire we can't rely on C fire rated building materials for protection against the spread of fire. Combustible building materials will add to the fire load of a burning structure.

D. Combustible building materials, in the event of a fire we can't rely on D fire rated building materials for protection against the spread of fire. Combustible building materials will add to the fire load of a burning structure.

E. Combustible building materials, in the event of a fire we can't rely on E fire rated building materials for protection against the spread of fire. Combustible building materials will add to the fire load of a burning structure.

F. Combustible building materials, in the event of a fire we can't rely on F fire rated building materials for protection against the spread of fire. Combustible building materials will add to the fire load of a burning structure.

There is also a term used to describe building materials as being of limited combustibility.

I ask three questions here,

1: will a building material of limited combustibility eventually ignite?

2: will a building material of limited combustibility add to the fire load of a burning structure?

3: will a building material of limited combustibility stop or delay the spread of fire?

If the answer is yes, yes and no; don’t take the risk; apply building materials with the A1 fire rating.

 

What is a Cavity Fire Stop?

There are a wide range of stone wool cavity fire stops available on the Irish market suitable for residential buildings. What we have to understand is this; the fire stop will only ever be as good as the surrounding building structure.

What I mean by this is; that if the inner leaf block work and the outer leaf block work is proven to provide 60 minutes fire protection, we can assume the stone wool fire stop when compression applied between the block inner leaf and the block outer leaf will provide 60 minutes fire protection stopping the spread of fire.

We must also understand that if the block work or brick work fails to provide 60 minutes fire protection; the 60 minute fire stop will fail to provide 60 minutes fire protection.

The construction layers must always provide the same or greater fire protection than that of the desired timeline expected of the stone wool fire stop.  

A cavity fire stop for typical masonry constructed cavity walls as described above is generally a building material manufactured from non-combustible stone wool insulation materials. Non-combustible stone wool insulation materials generally identify a Class A1 Fire Rating. Stone wool insulation materials used in the manufacture of cavity fire stops will have a density between 33kg and 45kg per m3 and will be proven by test to provide a range of timelines for fire protection dependent on the size of the cavity and the building structure.

Cavity fire barriers are also known as Cavity Stop Socks or Tcb,s are designed for use in masonry build residential building and are supplied in lightweight polythene sleeves for weather protection prior to installation. The polythene sleeve is a sacrificial layer and will burn away in seconds in the event of a fire.

 

Fire safe is something that will not ignite or add to the fire load of a burning structure. If it ignites it is NOT fire safe.

If a building material in the event of a fire emits toxic fumes it may kill you before the flames get to you.

 

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