Exothermic reactions can kill, Cavity Barriers can help prevent this.

An exothermic reaction can kill but just what is an exothermic reaction?

An exothermic reaction occurs as a fire develops. As the fuel source is heated, volatile gasses are released until enough heat, combustible material and oxygen are mixed together in the right proportions and ignition occurs.

Once ignition has occurred the fuel source is further heated causing the release or more volatile compounds which turn combust; a chain reaction starts. This exothermic chain reaction will continue until the heat is supressed, the fuel is removed, or the oxygen is depleted. An exothermic reaction is commonly known as a fire.


Installing a Cavity Barrier

There are two ways a correctly installed Cavity Barrier can help stop this process spreading throughout the building;

  • Firstly, the Cavity Barrier should do just what it says; it should act as a barrier within the cavity to prevent the passage of hot gasses (smoke) and fire; a simple requirement that everyone understands.
  • The second way a Cavity Barrier can prevent the fire spreading is to provide an effective barrier to the passage of heat or to insulate; this element of a Cavity Barriers role is less well understood.

Cavity Barriers are typically installed on fire compartment lines within the construction; let’s consider the role of a horizontal cavity barrier upon the line of the floor slab.

Above and below the Cavity Barrier may be combustible materials but what will happen when an exothermic reaction occurs, and fire develops below?

A correctly fitted Cavity Barrier will stop smoke, fire, and heat in the early stages but as fire develops the heat quickly grows below.

Even though the Cavity Barrier is fully filling the cavity and stopping flames reaching the combustible material, heat is rapidly growing.

Once the temperature rises too much, even with the barrier still closing the cavity, the heat causes the exothermic reaction to start above the cavity barrier with the ignition of the combustible material allowing the fire to continue to spread through the cavity. This is where the correct selection of a Cavity Barrier can make the real difference to the overall fire safety of a building.


What does a Cavity Barrier do?

A well designed, developed, and tested Cavity Barrier will not only stop fire spreading through the cavity but will also act as a barrier to heat preventing any combustible material on the ‘non-fire’ side of the barrier from spontaneously combusting in a fire situation.

As a specifier, you need to look deeper than the headline of a performance table on a Cavity Barriers data sheet; does the four-hour performance claimed cover the integrity performance only or both the insulation and integrity performance? For example, some Cavity Barriers currently available will provide 120 minutes integrity but only 30 minutes insulation.

Here at AIM we have always worked with the insulation ratings of our Cavity Barriers. If we claim a 60-minute fire performance, we are using the insulation rating as this is the harder of the two to achieve.

With this in mind you can be confident that, even with combustible materials in the cavity, the AIM range of passive fire protection products will be effective at preventing the passage of smoke, fire and importantly HEAT through the cavities they fill.