As you know, steel is not flammable, but its load-bearing capacity is nevertheless greatly reduced when the temperature rises sufficiently. At a critical steel temperature of 500 degrees C, the steel's load-bearing capacity is only half of what it is at 20 degrees. With a normal fire development (time-temperature curve according to ISO 834), it takes approximately eight to nine minutes for the steel to reach 500 degrees.
It is important to ensure that people using a building have enough time to escape in the event of a fire. Fire protection is divided into fire classes according to the consequences of a fire in terms of damage to life, health, social interests and the environment. For example, it must be possible for a fire to burn for one hour in an apartment without spreading to other units in the building.
For load-bearing steel structures, the load-bearing capacity, expressed as R, is crucial. The R value describes how many minutes the steel's load-bearing capacity must be maintained in the event of a fire. We operate with the classes R60, R120 and R180.
Active fire protection
Active fire protection is triggered when a fire breaks out, such as fire alarms, fire doors, door closers, emergency lighting and ventilation systems. But with the goal of ensure that the critical steel temperature in load-bearing structures is a maximum of 500 degrees centigrade, it is in practice full sprinkling that is required. If the building is not designed with an approved sprinkler system, passive fire protection must be used.
Passive fire protection
Passive fire protection is all about insulating the steel beam/column and thus protecting the steel from temperature rise as a result of heat development.
This can be achieved by painting the steel beam/column with fire-retardant paint or insulating it with fire-retardant panels.
Fire retardant paint
In many cases, it is not possible to use insulation mats, for example in facades and other visible structures. Such steel structures are often fireproofed with fire-retardant paint. The paint is applied directly to the steel and swells into a protective layer when exposed to heat.
Isopartner carries the Steelmaster series from Jotun. It comes in three different versions adapted to the environment in which it is to be used and the specified fire class.
Fire retardant boards
At Isopartner, we primarily stock stone wool boards for this purpose. Rock wool can withstand significantly higher temperatures than glass wool, and the boards have a melting point of up to 1000 degrees. This means that a steel structure protected with rock wool will last considerably longer than if it were insulated with glass wool, for example, which has a melting point of around 750 degrees.
The insulation thickness depends on two factors:
- How much of the steel beam is exposed to the heat
- The dimension of the beam. Thicker steel requires less insulation.
The insulation thickness can therefore be calculated by looking at the relationship between Ai (exposed area) and Vs (steel volume) and the critical steel temperature.
Isopartner has two different product ranges designed for fire insulation of steel structures:
What all fire insulation has in common is that it is installed exactly according to the installation instructions, and even small deviations can significantly reduce the insulation capacity and potentially cause major damage.
Advice and guidance
If you need help calculating the dimensions and quantities of fire insulation, please contact us. If you need a more detailed description of materials and methods for fire protection of load-bearing steel structures, we recommend downloading the description from Byggforsk.