Etankfire update

Published:  30 September, 2016

Latest research results for extinguishing large-scale fires involving ethanol; common test standards for foam ’do not really reflect tank fire situations’. Report by Henry Persson and Magnus Bobert, SP Sweden.

Although conducted in 2015 the results of the reduced scale fire tests, which simulate tank firefighting with ethanol, have up to now only been available to the Etankfire consortium of companies that are financially backing the research project.

The goal of this part of the Etankfire project was to evaluate the potential of traditional and unconventional extinguishing media and application techniques for ethanol tank fires.

Two series of fire extinguishing tests in reduced scale were conducted with large amounts of fuel and long preburn times.

Foam application techniques, foam properties and application rates were investigated both with AFFF-AR 3x3 foam and one 3F-AR 3x3 (fluorine free foam). Some tests included alternative extinguishing media such as cellular glass, liquid nitrogen and aqueous vermiculite dispersion (AVD).

In total 29 extinguishing tests were carried out in the first test series using a 0.41m2 fire tray. Fourteen tests took place in the second test series using a 3.14m2 fire tray.

The first tests were used to better understand the various parameters that might influence the extinguishing process. The second tests focused on verifying the extinguishing performance of the most promising tests in the first set, but in a larger scale.

The results from both test series showed that a tank fire situation with an increased depth of fuel, a prolonged preburn time and a slightly higher impact position of the foam on the tank wall might have a severe influence on the foam extinguishing performance.

In several tests the fire could not be controlled at all or it could not be controlled until the fuel was significantly diluted by the foam solution. This was also the case when using a fixed foam pourer on top of the tank; the hot tank wall prevented the foam from sliding gently down to the fuel, resulting in forceful application. The results indicated that the conditions used in the most common test standards for foam, such as EN1568 and UL 162, do not really reflect tank fire situations.

However, the results also showed that fire performance can be improved significantly by adjusting the finished foam properties, for example via higher expansion and/or longer drainage. In these tests, improvement was obtained by increasing the foam concentration compared to the nominal concentration value, which provides more stability and better survival of the foam when landing on the fuel.

Another method to improve the finished foam quality was to use CAF instead of aspirated low-expansion foam. A combination of higher foam concentration and CAF provided the best results. These changes even made it possible to significantly reduce the application rate and still achieve improved performance.

The importance of gentle application is well known when extinguishing water-miscible fuels but these tests also showed that an improved quality of the finished foam can compensate for a more forceful application, and is far more important than the application rate.

In addition, the tests that combined cellular glass with foam resulted in very good extinguishing performance, because the cellular glass layer reduced foam breakdown in the severe direct application (Type III) conditions. Even a moderate layer of cellular glass was found to reduce the burning rate and thereby the heat radiation significantly before the foam application starts.

The full results will be announced at a meeting in Stockholm, Sweden, 26 April, 2017. For further information visit the Etankfire website, http://www.sp.se/en/index/research/Etankfire/Sidor/default.aspx.

Published with the permission of SP Sweden.

Fire reduction was obtained around four minutes after a layer of cellular glass was applied. The fire was then successfully extinguished by using forceful (Type III) foam application. Photo: Magnus Bobert

  • Operation Florian

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