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Die Feuerwiderstandsdauer von ungeschützten Stahlbauteilen lässt sich durch den Einsatz reaktiver Brandschutzsysteme (RBS) signifikant erhöhen. Durch den profilfolgenden Auftrag der Brandschutzbeschichtung und die hierfür erforderlichen geringen Trockenschichtdicken, welche in der Regel nur wenige Millimeter betragen, können neben den brandschutztechnischen Anforderungen auch die an die Stahlkonstruktion gestellten gestalterischen Ansprüche erfüllt werden. Kommt es zu einem Brand, schäumt das reaktive Brandschutzsystem auf und bildet eine thermische Schutzschicht um das Stahlbauteil aus. Dadurch wird die Erwärmung des Stahls verlangsamt und der Festigkeitsverlust infolge Temperatur wird verzögert. Die Verwendung von reaktiven Brandschutzsystemen auf Stahlbauteilen wird durch Zulassungen geregelt. In Bezug auf den durch die Zulassung geregelten Anwendungsbereich von reaktiven Brandschutzsystemen auf zugbeanspruchten Stahlbauteilen haben sich in den vergangenen Jahren verschiedene Änderungen ergeben. Der nachfolgende Beitrag gibt hierzu einen aktuellen Überblick und beschreibt die Hintergründe, welche zu den neuen Regelungen geführt haben. Ferner erfolgt in diesem Zusammenhang ein Ausblick auf noch zu untersuchende Fragestellungen, welche bisher noch nicht durch die Regelungen in den Zulassungen abgedeckt werden. Bei den nachfolgenden Ausführungen handelt es sich um einen Auszug des Beitrages für die 18. EIPOS-Sachverständigentage Brandschutz.
This paper is intended to be the first study to discuss the fire suppressing performance of the four most common extinguishing media under the same reproducible conditions. The tests were performed in bench-scale and used standardized 5A wood cribs as well as a miniature extinguishing system with a liquid flow rate of 1.4 lmin−1. The tests results present a consistent overview of the fire suppression efficacies of water, water with a foaming agent, nozzle-aspirated foam and compressed air foam. Depending on their jet types, the cooling capabilities of the extinguishing media water and water with a foaming agent were compared to the cooling capability of a full Jet of wet, general and dry foams. The results show that compressed air foam suppressed fire most effectively under the test conditions. Because of the convoluted crib structure, water and water with foaming agents used from a distance are more effective in the form of a full jet rather than a spraying jet. At close range, spraying jets multiply their effectiveness. A slight difference can be observed in the cooling performance of extinguishing foams that use foaming agents from different manufacturers. The paper establishes a link between the foaming agent's cooling capability and its wetting power by relating the results of wood crib fire tests according to DIN EN 3–7 and findings from laboratory immersion tests compliant with DIN EN 1772.
Recent bus fires in Europe, such as the bus fire in France 2015 with 43 fatalities and the bus fire in Germany 2017 with 19 fatalities, show that these fires can be very hazardous and time for escape can be too short. Recently, several fire safety measures came into force for busses. Engine compartment suppression systems will be mandatory for all busses in Europe. This is a big step in fire safety as about 80 % of fires start in the engine compartment. However, in several recent bus fires a time of less than 5 minutes has been reported from detection of the fire to a fully developed fire. As normally many people are on board of a bus, a bus fire is not comparable to fire in a home. Especially for people with reduced mobility or for fires after a collision the available times for escape are too short. When the fire service is on scene the transition to a fully developed fire might have happened already. Passengers who are not able to escape in this short period of time mostly cannot be rescued by the fire service even with quick response times because of the dramatic fire development. Fires that do not start in the engine compartment but develop in the cabin are rarer but extremely dangerous because fire and smoke spread very rapidly. The reason for the fast fire and smoke development in the cabin are the materials which are used. Over the last tens of years materials in busses had major developments. The amount of plastic in the cabin has grown significantly. In a modern coach the biggest fire load often is not the fuel anymore but the interior materials.
Bus fire safety is mainly regulated by ECE regulations R 118 and R 107. A comparison with European standards for trains shows that for trains, in contrast to busses, a holistic fire concept exists. Fire scenarios as well as escape scenarios and passenger behaviour are taken into account, resulting in fire safety regulations on a high level compared with bus regulations. In contrast to regulations for train materials no limits for heat or smoke production are given for bus materials. Larger heat release values promote more rapid fire spread. Also smoke production and toxicity are key factors in fires. The smoke reduces the visibility in the case of fire, and together with the toxicity of the smoke can make escape from the vehicle impossible. Figure 1 shows the remains of the bus from the recent severe bus fire in Germany in 2017.
As a result of experience with real cases and results from research projects we think it is necessary to develop a holistic fire safety concept for busses as it exists for other transport means like railways. The fire safety concept should include vehicle configuration and design as well as areas of use, e.g. use in cities, use in long-distance traffic on motorways and use in tunnels.
Bare steel constructions are often integrated in modern buildings. Intumescent coatings are widely used to protect the steel from heating up too quickly in a case of fire. As the functionality of intumescent coatings decreases with the impact of weathering processes, it is important to understand the mechanisms of material degradation to maintain long durability. The weathering-induced degradation behavior of a water-borne intumescent coating was examined, and the weakest points of the formulation were identified by a systematic approach. Resulting from this investigation, adjustments to the formula were made, leading to improved weathering resistance.
Whereas the degradation of flame retardant polymers has been discussed since decades, only more recently, the lifetime of the flame retardancy itself becomes an important factor, e.g. for cables used as building products. In this work, several kinds of accelerated artificial ageing tests are performed simulating different environmental exposures and thus highlighting different degradation mechanisms: artificial accelerated weathering, climatic chamber, water immersion, salt spray chamber, and autoclave test. The durability is expected to be different for different flame-retardant materials. Thus, various sets of halogen-free fire-retarded polymers were investigated: ethylene vinyl acetate (EVA) with aluminum hydroxide (ATH), boehmite and synergists, ester-based and ether-based thermoplastic polyurethane (TPU) with melamine cyanurate (MC), aluminum diethylphosphinate (AlPi), and boehmite, and glass fiber reinforced polyamide 66 (PA66) with AlPi-based mixtures.
Intensive degradation of the surface was observed, e.g. yielding discoloration and yellowing, EVA showed cracking when weathered. Changes in chemical structure was investigated by ATR-FTIR. The flammability was investigated with the cone calorimeter, UL-94 classification, and oxygen index (LOI). The flame retardancy of most of the materials studied degraded only slightly for the investigated exposure times. EVA/ATH achieved an improved LOI due to flame retardants agglomeration at the surface. Sets of materials, based on EVA and TPU, were also investigated as cable jackets. While flame retarded EVA exhibited no dripping during burning, TPU flame-retarded with MC cables showed pronounced melt-dripping. Cone calorimeter tests were carried out using cable rafts as well as our self-made cable module test, simulating a vertical bundle of cables at the bench scale. The comparison of different fire tests, different exposure conditions, and different materials carved out the specific degradation phenomena with respect to each of these parameters.
Most of this work was supported by the IGF Project (18926 N) of the Fördergemeinschaft für das Süddeutsche Kunststoff-Zentrum e.V., supported by the AiF within the framework of the program “Förderung der Industriellen Gemeinschaftsforschung (IGF)” of the German Federal Ministry for Economic Affairs and Energy based on a decision of the Deutschen Bundestag.
Nowadays, various polymeric materials are used in E&E applications with sufficient flame retardance by adding rather different flame retardants. It doesn’t matter whether cables are used outdoor or are installed indoor as building products, the weathering exposures such as UV radiation, humidity and variation in temperature occur and influence the flame-retardant property. Recently, the lifetime of the flame retardance itself becomes an increasingly important factor. In this work, several devices were used to perform accelerated artificial ageing simulating different environment exposures.
The comprehensive and global understanding of the durability of flame retardance in dependence on the weathering or ageing conditions is still a matter of discussion. Therefore, the weathering resistance of various halogen-free fire-retarded polymers was investigated in this work. Polymeric systems with different kinds of fire retardants were chosen, including various fire retardant mechanisms. Ethylene Vinyl Acetate (EVA) blends with high amounts of inorganic flame retardant such as aluminum hydroxide (ATH), boehmite and synergists, which mainly dilutes the polymer resin work as heat sink and cooling agent, and enhance residue formation was examined. Thermoplastic Polyurethane (TPU) was modified with melamine cyanurate (MC), which mainly acts by changed melt flow and dripping behavior as well as fuel dilution. Additionally, aluminum diethylphosphinate and boehmite are induced as assistant flame retardant. Furthermore, glass fiber reinforced Polyamide 66 (PA) was investigated containing different kinds of aluminum diethylphosphinate based flame retardant mixtures, which acts by flame inhibition and additional char formation.
The degradation of the surface was analyzed after the different weathering conditions. Most of the specimens exhibited an intensive material degradation at the top surface accompanied by a distinct discoloration, e.g. getting darker or showing yellowing. The weathering of the EVA samples lead to numerous cracks (already) after 4000 h. The corresponding changes in the chemical structure was investigated by ATR FT-IR for all materials.
The flammability was investigated by cone calorimeter, UL-94 burning chamber, and oxygen index (LOI) using plate and bar specimens. The flame retardance of most of the materials studied degrades only slightly or were rather stable for the investigated exposure times. Interestingly, also some opposite results were found. EVA modified by different inorganic flame retardants such as ATH achieved higher LOI after exposing in the humidity chamber and the accelerated oxidation under water in the autoclaves. It is suggested that the particle size of ATH and boehmite plays an important role, when these flame retardants agglomerate at the surface during accelerated weathering.
Both materials, EVA and TPU, were also investigated as cable jackets. While EVA modified with inorganic flame retardants exhibits low-smoke and non-dripping fire behavior, TPU flame-retarded with MC yields cables with pronounced melt-dripping. Cone calorimeter tests were carried out using cable rafts of the size of 100 mm * 100 mm as well as our self-made cable module test, which simulates the vertical full-scale test of a bundle of cables at the bench-scale. Both methods were used to investigate the weathering resistance of the flame retardance in cables. The results of the cable module test for the flame-retarded EVA cables were only slightly affected even when a long time hydrothermal ageing was carried out. This is because of inorganic residue which just delays the fire growth but does not extinguish. However, for the flame-retarded TPU cable jackets, the cable module test exhibited an accelerated fire spread and a melt-dripping behavior which was promoted by weathering exposure.