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In der Vergangenheit führte die Bundesanstalt für Materialforschung und -prüfung (BAM) zahlreiche Tankbrandversuche mit und ohne Sicherheitseinrichtungen durch. Dabei stellte sich heraus, dass Gastanks mit nicht ausreichend dimensionierten Sicherheitseinrichtungen bei einer äußeren thermischen Belastung innerhalb von 6 bis 10 min in Form eines BLEVE (Boiling Liquid Expanding Vapour Explosion) versagen können. Um die Feuerwiderstandsdauer eines Tanks zu erhöhen, besteht die Möglichkeit, den Tank u. a. mit einer sog. reaktiven Brandschutzbeschichtung zu versehen. Bei einer Temperatureinwirkung ab ca. 200 °C (produktabhängig) beginnt die Schicht aufgrund einer thermochemischen Reaktion aufzuschäumen. Die Tankwand wird dabei temporär vor einer weiteren schnellen Erwärmung geschützt.
How can the risk of a BLEVE be reduced? That is the main question based on different research projects. In various large scale fire tests fire protection coating systems were used of different manufacturers. The degree of the coating as well as the layer thickness and the processing were varied. These experimental configurations were partly tested with and without pressure relief valve. The pressure relief valves were not protected again the thermal Load from the test fire. The ambition is to find a minimum of the thickness from the fire protection coating witch delay a BLEVE up to 90 minutes. Here are given the most interested configurations of tanks in fire and a description of the test-rigs.
Liquefied propane gas (LPG) tanks in a fully engulfing accidental fire experience a fast increase in internal pressure. The result is often a Boiling Liquid Expanding Vapor Explosion (BLEVE) that can result in a large fireball and flying debris over a radius of more than 100 meters.
In the last 30 years BAM has carried out more than 30 real scale fire tests on propane storage vessels across three test sites. The primary research goal was to identify systems that can delay or prevent a BLEVE. Early studies started with water deluge systems, and have since moved on to consider alternative protection systems.
It has been shown that an unprotected vessel fails within 10 minutes or less. Tests with different oil and propane fueled fires have given an overview on possible real accidents involving full-engulfing scenarios. LPG tanks of various sizes (2.7 m³, 3.6 m³, 4.8 m³, 6.7 m³) were used with different filling levels. Numerous protection systems, ranging from active systems like water systems to passive thick- and thin-film layers. Also, the degree of thickness of these layers was variated. Pressure relief valves (PRV) have also been investigated, both alone and in combination with protection systems.
This paper gives an overview of the work performed by BAM in the field of BLEVE prevention of protecting system since the last 30 years. It has been shown that e.g. with a full applied coating degree on the tank with and without PRV can be reached an exposition in a test fire scenario a duration of more than 60min. For partly coated tanks with and without PRV the duration time is like an unprotected vessel. Furthermore, it could be shown that the active water system also protects with technically correct design.
Im Rahmen eines Versuchs sollten die Versagensgrenzen eines mit Fluessiggas gefuellten Eisenbahnkesselwagens bei Unterfeuerung ermittelt werden. Untersucht wurden die Auswirkungen eines Unfallfeuers auf einen mit Fluessiggas teilgefuellten Waggon sowie die Konsequenzen, die sich hieraus im Falle eines brandbedingten Berstens hinsichtlich Truemmerflug sowie Druck- und Temperaturbelastung fuer die Umgebung ergeben. Beschrieben werden der Versuchsaufbau, die Versuchsdurchfuehrung sowie wesentliche Ergebnisse und Konsequenzen aus dem Versuch. Unter anderem wird festgehalten, dass durch das Zerbersten des Behaelters mit schlagartiger Verdampfung und anschliessender Zuendung des Fluessiggases Auswirkungen hervorgerufen werden koennen, die im Brandfall in relativ kurzer Zeit eine ernsthafte Gefahr entstehen lassen, und denen durch geeignete sicherheitstechnische Massnahmen begegnet werden sollte.
Fire Tests with LPG Vessels
(2002)
The results and execution of many full scale fire engulfment tests on 3.6 and 4.85 m³ LPG tanks, protected with thin sublimation and intumescent coatings, mineral wool with steel jackets, vermiculite coatings and water spray systems, are presented.
Additional furnace tests with coated steel plates have been carried out to optimize the necessary coating thickness.
Similarly, an overview of the test conditions for the recognition based on technical rules and BAM requirements for fire protection systems of LPG tanks will be shown and explained.
When the internal pressure reaches the vessel bursting pressure a violent tank rupture, fragmenting of the shell and spontaneous release of the content are the consequences. In case of LPG this event is called "boiling liquid expanding vapour explosion (BLEVE)" with expanding fireball as an additional severe consequence.
For this reason the sufficient fire protection of LPG vessels is an important item.
The tests demonstrated sufficient vessel safety during 90 minutes of a full fire engulfment.
It will also be shown that the examinations and results are transferable to bigger tanks.
The transferability of the test results is illustrated by diagrams which show the dependence of the coating thickness against the shell thickness of the tank.
All tested tanks were equipped with pressure relief valves (PRVs) and partially filled with propane.
Fire Tests with LPG Vessels
(2002)