Appendix
HPL as a façade cladding
HPL-panels are typically made of organic materials. They consist of layers of cellulose fibrous material impregnated with thermosetting resins. During the high-pressure process, defined as a simultaneous application of heat and pressure, the polymer chains are joined (or cross-linked) by intermolecular bonding (thermosets). This produces homogeneous panels that in a fire situation do not soften or drip. Where improved fire retardance is required, the laminate core may be treated with additives, which do not contain halogens, improving its reaction to fire.
Within this paper the scope of the application of such panels are facade constructions, in particular so-called rear-ventilated facades. This type of external wall cladding consists of an external cladding (HPL-panel), mechanically fastened to a subconstruction (usually metal or timber), which is fixed to the external wall of buildings. An insulation layer (mineral wool) is usually also mounted on the external wall.
Between the cladding elements and the insulation layer or the external wall accordingly, there is an air space (rear-ventilation) which shall always be drained and ventilated. The air space is connected to the outside air through supply air openings on the bottom and exhaust vents on the top of the facade or facade sections (e.g. only within one floor) and thus enables a constant exchange of air to transport moisture.
a Façade | b Insulation layer | c Subconstruction | d HPL–Compact | e Transportation moisture | f Rear ventilation
Fire scenarios on the façade
Actual fires as well as a great number of different lab fire tests prove that a fire spread over facades is a danger scenario authority have to deal with. A fire spread over facades may be caused by three types of fire events (see figure 68):
Scenario 1: spread of an external fire onto facade by radiation from a neighbouring, separate building
Scenario 2: spread of an external fire onto facade from a source of fire located next to the façade (for example fire developed on a balcony or fire from a garbage can or a car parked near the façade)
Scenario 3: internal fire that has started in a room inside the building that spreads through openings in the façade (windows, doors, etc.) onto façade.
Considering the most common case, a room fire, it has been discovered that flames reaching the façade show lengths up to 5 metres above the edge of the opening (means two floors above the fire source), regardless of the façade system and the materials used. The flame length depends on the fire load, the size and the geometry of the windows. Subsequently, when the flames reach the outermost layer of the façade, the further propagation of the fire mainly depends on the properties and characteristics (material, geometry, etc.) of the façade itself. Therefore, among the main factors characterizing the fire spread over a façade, there are:
Based on these general fire mechanisms certain requirements concerning fire protection of façades are defined.
