Fire protection coating
Fire protection coatings are functional coatings with self-adapting surface properties that reproduce the natural burning behavior of wood. It was recognized that in the event of a fire, a wooden beam is superior to a comparable steel component in that it carbonizes itself and endeavors to transfer this surface behavior to steel structures. The first recipes for this became known in the early 1970s. The technology of reactive fire protection coatings has now become an indispensable component in structural steel construction. Applications in Germany go back to the mid-1970s and in some cases have already completed their first life cycle. A representative example is the new building of the former Federal Chancellery in Bonn , built from 1973 to 1976, in which the steel structure was protected with a fire resistance of 30 minutes (F30).
Technical specifications
If steel beams are heated, they lose their stability and load-bearing capacity from approx. 500 ° C. A building with structural elements made of steel beams would collapse as a result. Uninsulated steel beams reach this temperature in the event of a fire, depending on the fire load , after just 5 to 10 minutes. Steel girders with a fire protection coating , on the other hand , can withstand a fire significantly longer, depending on the coating in the range of hours. There are also appropriate fire protection coatings for wood and other materials.
application
A fire protection coating is usually applied in several layers using the airless method or with a brush. The required layer thickness for profile steel depends on the internal fire resistance of the component and is specified in µm. Usual dry layer thicknesses are between 350 µm and 750 µm for open profiles (F30) and 2000 µm to 3600 µm for open profiles (F90). However, there are currently no building inspectorate approvals for coatings on steel girders with high fire resistance times. In order to achieve F90, fire protection jackets made of approved sheet materials must be provided.
Mode of action
Fire protection coatings ( intumescent layers ) contain a polyvalent alcohol (mostly pentaerythritol ), a nitrogen source (mostly melamine ) and a phosphorus donor (e.g. ammonium polyphosphate ). Ammonium polyphosphate (APP) decomposes at temperatures above 250 ° C to phosphoric acid . This reacts with pentaerythritol to form phosphate esters , which further decompose to form carbon dioxide and residues containing carbon and phosphorus. When exposed to heat, the melamine decomposes into gaseous ammonia , which leads to the expansion of the ammonium polyphosphate residues. This creates a heat-insulating foam that shields the steel beam from fire.
A layer with a thickness of 1 mm can foam up to approx. 50 mm in the event of a fire and thus forms effective heat insulation. The foamed layer consists of microporous "carbon foam". This layer decomposes over time in the course of the fire, which reduces the insulating effect. Some fire protection coatings insulate for over an hour in the event of a fire.
Certification
The fire protection coatings are tested with various standard tests and divided into classes based on the results. Class F 60 means, for example, that a steel beam with this coating can withstand a fire for at least 60 minutes under standard conditions.
Individual evidence
- ↑ Vijay Mohan Bhatnagar: Fire Retardant Coated Fabrics Formulations Handbook . Ed .: Technomic Publishing. 1973, ISBN 0-87762-117-9 .
- ↑ Entry on intumescence. In: Römpp Online . Georg Thieme Verlag, accessed on February 15, 2015.
- ↑ Brigitte Osterath: Plastic that defies the flames . In: ChiuZ . tape 63 , no. 2 , 2015, p. 122-125 , doi : 10.1002 / nadc.201590043 .