Fire protection of steel structures in newly constructed and renovated buildings has already become a standard. Under fire conditions, steel can reach its yield point very quickly, leading to the collapse of the supporting structure. Fire retardant paints, also called intumescent paints, are designed to extend this time, giving people a chance to safely evacuate and the fire brigade to intervene. During a fire, the intumescent paint layer swells, creating a protective foam on the structure.

Fire retardant paint is never applied to a structure as a stand-alone coating. A complete fire protection system consists of three coatings, each of which performs a specific task.

  • primer paint – anti-corrosion protection of steel,
  • fire retardant paint – extending the time it takes for steel to reach its yield point,
  • topcoat – protects the fireproof paint coating against mechanical damage and moisture. In some cases it may be omitted (it depends on the specific intumescent paint, environmental corrosivity class and exposure). The topcoat can be produced in a color selected by the customer from RA L palette .

Both the primer and topcoat must be approved for use in a fire retardant system. The Technical Approval/European Technical Assessment issued for the intumescent paint specifies which specific paints can be used in the fire protection system. These specific products have been tested under fire conditions. The use of an inappropriate primer may result in the entire fire protection system becoming detached from the structure during a fire and not fulfilling its purpose.

The fire protection system is applied to a clean steel or galvanized steel substrate. If there are old paint coatings on the structure of unknown origin, they should be removed. Some systems also allow application to cast iron.

Selection of fire retardant paint for steel structures

Selecting a fire protection system for steel structures is a complex process and depends on several factors. Each of the elements listed below is necessary to select the optimal fire protection system.

Required fire resistance class

The fire rating refers to the additional time that a coating of fire retardant paint is intended to provide before the steel member reaches its yield strength. This class is marked as e.g. R30, i.e. protection for 30 minutes.

The fire resistance class for given building elements is determined on the basis of the table below, which can be found in the Regulation of the Minister of Infrastructure of April 12, 2002 on the technical conditions to be met by buildings and their location. 

fire resistance class of building elements

Steel section massiveness index

The massiveness index of a steel section means the ratio of the perimeter of the section that will be exposed to fire to its cross-sectional area. The unit of the section massiveness index is [  1  m ] . This means that the circumference should be expressed in meters and the cross-sectional area in square meters. These values ​​are usually found in tables for designing metal structures. On the Internet, you can easily find ready-made tables with massiveness indicators for various steel profiles. This is an individual value for each cross-section, so in order for us to be able to prepare an offer for a fire protection system, it is necessary to send us a steel list. Unfortunately, we are unable to calculate the theoretical demand for fire retardant paint based on the total area or weight of the structure.

Example calculations for a normal IPN240 I-beam, assuming that it is exposed to fire on all sides (so-called four-sided exposure):

Cross-sectional area: A = 46.1 cm 2 = 0.00461 m 2
 Circumference: U = 0.884 m

Section massiveness index:
U  A = 0.884m  0.00461m 2 = 191.76 1  m If the same I-beam would, for example, support a monolithic ceiling, then the calculations assume the perimeter reduced by the width of the upper footer. In this case, the section massiveness index will be 168.76 1  m . We proceed similarly if only the footer protrudes from the ceiling (e.g. Klein ceiling). As you can easily deduce, if we want a well-selected system, we should provide detailed data at the inquiry stage. Additionally, the lower the section massiveness index, the thinner the intumescent paint layer, so it may turn out that it will save us money.

If our structure consists of some unusual profiles, it is worth marking it. For example, two C-sections can be welded together, thus creating a closed profile. The thickness of the fire-retardant paint coating is then selected from a different table than for open profiles.

Design critical temperature

The critical temperature means the temperature at which our steel section reaches its yield point and loses its load-bearing capacity. The critical temperature should be provided by the designer.

coating based on the Technical Approval or the European Technical Assessment issued for the intumescent paint. Each of the above-mentioned documents contains tables containing a summary of coating thicknesses.

Steelguard 564 fireproof paint , for open profiles, class R60 and the designed critical temperature of steel in the range of 550-700℃. Returning to the earlier example of the IPN240 normal I-beam, it is easy to notice that depending on the degree of exposure to fire and the section massiveness index, the thickness of the fire-retardant paint coating changes significantly. The thickness of the coating is expressed in millimeters and for a critical temperature of 550 ℃ it ranges from 0.22 mm to 1.62 mm. That is, from 220 to 1620 microns dry.

steelguard561 table fragment

It may happen that a given profile cannot be secured to the required class. For example, the R60 class was adopted and the designer used closed rectangular sections with thin walls. In this case, unfortunately, you have to select other profiles.

Environmental corrosivity class

The environmental corrosivity class is determined according to the PN-EN ISO 12944-2:2001 standard . A detailed description of environmental corrosivity classes can be found in our article "Selection of anti-corrosion painting systems" . For office/service buildings, the corrosion class usually does not exceed C2. The corrosion class mainly serves to determine the thickness of the primer and topcoat layers.

To sum up, in order to choose the best fire protection system for a given steel structure, we will need the following information:

  • list of steel structures (how many linear or square meters of individual profiles)
  • critical temperature given by the designer (if not given, we assume a temperature of 550℃, but please remember that the responsibility always remains with the client)
  • environmental corrosivity class
  • information whether it is black steel or galvanized steel
  • required top color