How does a intumescent coating work?
Fire protection coatings are also called intumescent coatings. The term describes their effect well. In the event of fire, temperatures between 120°C and 200°C trigger a chemical reaction in the coating. A foam forms, which conducts heat very poorly (in contrast to steel). The layer thermally protects the steel so that it heats up more slowly. Fire protection coatings are used, for example, in steel construction and plant construction.
Critical temperature for intumescent coatings
Many manufacturers of fire protection coatings specify a critical temperature. This depends on the profile factor A/V (also called U/A). This is the ratio of the surface area exposed to fire (A) to the volume of the component. With both values, users can then read the necessary layer thickness of the coating from tables.
Adhering to the tabulated values does not mean, however, that a fire resistance class is necessarily achieved. It is true that the strength of structural steel decreases at temperatures above 400°C. However, the modulus of elasticity, which is important for stability problems, already drops from 100°C! This means that steel columns, for example, often buckle under their load in the event of a fire.
The critical temperature is often simply set at 500°C without further consideration. This is a genie that has been let out of the bottle and is difficult to recapture. Because each component must be considered individually. Here's an example. A steel column with a height of 20 m (e.g. in a fire wall) is much more at risk of stability (buckling) than a column with normal storey height between 3 and 4 m. Consequently, different thicknesses of coating must be applied.
The most important variable is still the critical temperature. This must be calculated for each component and structure with a fire design. I can do that for you. The required layer thickness can thus be read from the manufacturer's tables. It may even be possible more precise temperature curves than the ISO standard fire must be taken into account. Then, if necessary, a fire protection coating can be completely dispensed with. In certain sectors (e.g. in the chemical industry and in plant construction), other fire room curves may have to be used, such as the so-called hydrocarbon fire curve.