Intumescent coating, often referred to as intumescent paint, is one of the easiest and most efficient ways to protect load-bearing elements of buildings against fire. Intumescent coating delays the collapse of the structure through insulating the structural elements (columns, beams, floors and roofs) that support the building, thus helping achieve fire resistance levels specified in terms of time. Therefore, it fulfills the highest priority of passive fire protection: preventing the collapse of the building, allowing the time for safe evacuation of people from it and making it safer for the emergency services and rescue team.
Intumescent coating is an increasingly used way of providing passive fire protection to the load-bearing structures, especially structural steel, which is becoming more and more popular in modern architectural design of both industrial and commercial buildings. As a means of fire protection, intumescent coating presents several advantages:
- It does not modify the intrinsic properties of materials, for example, the mechanical properties;
- It is easily processed, and
- Different kinds of intumescent paint can be used on a variety of materials, such as steel, timbers, composite elements and concrete.
How do intumescent paints work?
ntumescent paint is a reactive coating which swells as a result of heat exposure, thus increasing in volume and decreasing in density. Specifically, an intumescent paint is a coating that reacts to heat by swelling in a controlled manner to many times its original thickness, producing a carbonaceous char formed by a large number of small bubbles that act as an insulating layer to protect the substrate.
The purpose of intumescent products is the prevention of the structural collapse of the building, which can occur if load- bearing steel elements reach a critical state.
For steel, this is linked to the critical temperature, defined as the temperature at which the load-bearing capacity becomes equal to the effect of the applied loads (so the steel element is very close to collapse). Critical temperature of steel can vary from 350 °C to 750 °C, depending mainly on the loading scheme, but in most of the cases between 500 °C and 620 °C.
For concrete, critical state is linked to the critical temperature of the reinforcing bars (normally from 350 °C to 500 °C) and to reaching a temperature of 500 °C inside the concrete element.
For wood, critical state is linked to the residual section of the timber load-bearing element after burning.