Handling large-scale ethanol fires
Global production and consumption of ethanol fuels has increased significantly over the last decade. Fuels such as E85 bring new risks and challenges from a fire protection and fire fighting perspective. Experiences from past fires in storage tanks containing ethanol reveal a knowledge gap that a Swedish industry research project aims to address.
According to figures from the US Energy Information Agency (EIA), global fuel ethanol production has increased almost fourfold between 2002 and 2012, from about 378 000 barrels per day to over 1.47 million. Yet experience from past fires in storage tanks containing ethanol suggest a lack of knowledge and fire fighting tactics to successfully conclude an extinguishing operation. Despite the use of large amounts of water and foam, all known ethanol tank fires have ended up in a total “burn-out” completely destroying everything, including the tank itself.
In 2012, “ETANKFIRE”, a Swedish industry research project on ethanol tank fire fighting was launched. Initiated by SP Fire Technology, a division within the SP Technical Research Institute of Sweden, together with the Swedish Petroleum and Biofuel Institute (SPBI) the project seeks to provide a knowledge platform to ensure proper investment in fire protection of ethanol storage facilities. The project aim is to develop and validate a methodology for fire protection and suppression of storage tank fires containing ethanol fuels. The first phase of the project investigated the large-scale burning behaviour of various ethanol fuel mixtures. The results have been published in the report “ETANKFIRE-Experimental results of large ethanol fuel pool ﬁres.”
Two series of free burning tests with ethanol fuel mixtures were conducted, one in laboratory scale with a pool area of 2.0 m2 and one in large scale with a pool area of 254 m2. In both series the burning rate, flame height and heat flux as a function of distance from the fires were measured and the effect of these parameters on the size of the fire area was investigated. Two fuel mixtures were used in the large-scale tests, E97 (97 percent ethanol denatured with 3 percent gasoline) and commercial E85 (85 percent ethanol with 15 percent gasoline). The measurements from E97 and E85 were compared to both calculated data with fire hazard predictive modelling software used by the petroleum industry and some previous experimental data from large-scale gasoline fire tests.
Higher heat exposure
The laboratory scale tests showed increasing heat flux with increasing proportion of gasoline in the fuel. However, in the large-scale tests, the E97 and E85 fuels emitted the same radiant heat. In addition, the heat exposure towards the nearby surrounding is approximately 2-3 times higher for both the E97 and E85 fuels compared to calculated and experimental data on gasoline. The difference declines with increasing distance but it is still about a factor 2 higher at distances of 30-40 m. The radiative fraction, the ratio of radiant to chemical heat release, as a function of the fire area will probably have a larger influence on E85 compared to E97 due to the higher content of gasoline.
– It is likely that a larger E97 fire would generate a higher heat flux compared to a similar E85 fire and the difference between the two would increase as the fire area increases, which would be an additional consideration for E97 storage, remarked Henry Persson, SP Technical Research Institute of Sweden, Fire Technology and one of the authors of the report.
The results from the 2012 free-burning tests demonstrated that the heat flux from a larger ethanol fire is much higher than from a gasoline fire.
– The risk of fire propagating to adjacent tanks or other objects is very high unless an effective cooling operation is carried out. Now that we have a better understanding of what to expect in a large-scale ethanol fire the next step in the project is directed at solving the problems involved in extinguishing a storage tank fire, said Persson.
Phase two of the project zeroed in on tank fires. The tests, which were completed in December 2015, were divided into two test series, the first with a tray of 0.72 m diameter and the second with a tray of 2 m diameter.
– In contrast to existing testing methods, our tests were intended to better imitate the conditions of tank fires by using a more ‘storage tank-like’ tray with thicker sheet metal, longer pre-burn time, and, above all, greater quantities of fuel. In the larger tray, for example, just over 1 400 litres of fuel was used, said Persson
The tests with the smaller tray studied looked the influence of various factors, such as the depth of the fuel, pre-burn time, and different foam types such as low or medium expansion foam and compressed air foam (CAF) and application methods. Some tests were performed using other types of extinguishing agents, for example nitrogen and cellular glass. In all, about 25 different tests were performed. For the larger-scale test series, the most promising conditions from the initial series formed the starting point, so as to be able to verify the earlier results and gain additional knowledge.
The test results are being compiled in a report soon to be made available to members of the ETANKFIRE consortium and, according to Persson, will assist in drafting recommendations to how an extinguishing operation for an ethanol tank fire should be planned and executed.
– Though I cannot reveal any details yet these will include, for example, which type of foam is suitable for use, the properties that the formed foam must have, the required application rate, and other factors which have a bearing on the tactics of an extinguishing operation, said Persson.
The next objective for the ETANKFIRE project is to carry out tests on a ‘real‘ scale once additional funding to perform the tests has been raised.