Passive fire protection

Steel structures

Steel is a non-combustible material that does not generate smoke or toxic gases when it comes into contact with fire. However, it loses its mechanical properties as its temperature increases and, due to its high thermal conductivity, it causes heat to spread very quickly through its profile.

The required fire resistance on the steel elements is determined on the basis of the type of building and its use.

Two concepts must be clear for the fire protection of steel, namely:


The critical temperature is the temperature at which the structure loses its load-bearing capacity, i.e. the element in question is not capable of performing its structural support function.

The critical temperature of each profile that makes up the project is calculated according to the effect of the actions on the project’s fire situation and the design stress of the profiles based on their applied loads.


The form factor, commonly referred to as massiveness, is the relationship between the perimeter of an element exposed to the fire and its section area.

The section area will always be a constant and intrinsic value of the profile, while the perimeter may vary depending on the different fronts exposed to fire.

Form factor = Hp/A (m-1)

WhereHp is the perimeter exposed to the fire (m) and A is the section area of the steel (m2).

The higher the mass value, the faster the critical temperature (collapse temperature) of the profile will be reached. Therefore, the greater the mass, the thicker the protection should be.

To determine the necessary thickness to be applied on a profile, the following steps must be followed:

  1. Determine the fire resistance dictated by the CTE or RSCIEI depending on the type of building.
  2. Determine the critical temperature.
  3. Determine the massiveness of the profile by using standardized tables or by calculation
  4. Determine the thickness based on the tables obtained according to fire resistance tests.

Perlita y Vermiculita  offers products to ensure the fire protection of steel structures.

Here you will find some of our recommended products to ensure greater passive fire protection: