Steel structures without additional fire protection measures often do not offer the required fire resistance class of R30 (formerly F30), which requires sufficient load-bearing capacity for at least 30 minutes in the event of a fire. This requires additional passive fire protection measures for the steel structures, such as cladding, sprayed plaster or fire protection coatings, which are associated with additional costs. The required fire resistance class of R30 can often be achieved by hot-dip galvanizing the steel components. This eliminates the need for additional passive fire protection measures.
Studies have shown that hot-dip galvanizing of category A & B steels can have a positive effect on the component temperature in the event of fire. It is therefore suitable for achieving a fire resistance of R30. The improvement in fire resistance is based on a lower emissivity of the surface of the hot-dip galvanized steels. At temperatures below 500 °C, hot-dip galvanized structural steels only absorb 35% of the radiant energy input, whereas untreated structural steel absorbs 70% of the radiant energy input and therefore heats up more quickly in the event of a fire (see table). Above 500 °C, the heat absorption of hot-dip galvanized structural steels is similar to that of ungalvanized steels, but especially in the initial phase of a fire, galvanized steels of categories A & B show a significantly delayed heating. This means that the load-bearing capacity of the steel structure is maintained for longer in the event of a fire.
| Steel composition according to DIN EN ISO 14713-2 | εm (< 500 °C) | εm (> 500 °C) |
| Category A and B | 0,35 | 0,7 |
| Category C und D | 0,7 | 0,7 |
Classification Categories: A – Low silicon steel, B – Sebisty, C – Sandelin, D – High silicon)
The results of these tests were recorded in DASt027, which is a supplement to the standards DIN EN 1993-1-2 and DIN EN 1994-1-2.
An essential prerequisite for the use of hot-dip galvanized steel for a fire resistance of R30 is proof of suitability by means of a hot-dip measurement in accordance with Eurocode 3 in conjunction with DASt guideline 027. We will be happy to issue you with confirmation that the steel has been galvanized in accordance with DIN EN ISO 1461 and DASt guideline 022. All you need to do is ensure that the steel has a steel composition in accordance with categories A and B of DIN EN ISO 14713-2 and that the results of the hot design (as described above) are positive.
Literature references:
- DASt-Guideline 027
- Gaigl Christian, Mensinger Martin (TU Munich), Fire resistance of hot-dip galvanized, load-bearing steel structures in the event of fire, Report No. 169 Gemeinschaftsausschuss Verzinken e.V.