Fighting an Ethanol Tank Fire Presents Unique Challenges
One obvious consequence of increasing ethanol blends, both in Europe and the U.S., is that the volume of bulk ethanol transported, handled and stored will increase dramatically in coming years, creating new risks and challenges for fire protection and response. The increasing diameter and volume of storage tanks is also making any potential firefighting operations a significant challenge. Experience in tank firefighting involving ethanol or other water miscible fuels is very limited, and those few tank fires that have occurred have resulted in burnout rather than extinguishment. Some critical differences between fighting fires involving petroleum-based products and ethanol need to be better understood.
What Makes Ethanol Different?
The most important differences in terms of fire performance between ethanol and gasoline concern flammability properties, burning behavior and extinguishment methods.
In a closed vessel or a tank, pure ethanol forms flammable fuel vapors at a temperature range of about 12 to 40 degrees Centigrade (12 to 104 degrees Fahrenheit while gasoline needs to be below about minus 20 C for such formation. Ethanol blends have a flammability range between pure ethanol and gasoline, depending on the specific composition. As a result, the possibility for flammable conditions in a storage tank, and thereby the risk for ignition, is greater for ethanol than gasoline.
A very important and related issue is that the burning behavior of a large-scale ethanol fire might be significantly different from a petroleum fire. Experience from small-scale fires shows that radiation is significantly lower from an ethanol fire compared to gasoline. There are indications, however, that the opposite may be true in a large-scale fire. Such observations were made during a 200 square-meter fire-test series conducted in Sweden using a mixture of acetone and ethanol. Measurements showed that the heat flux from the acetone/ethanol fire was about twice that of gasoline at this scale, although gasoline produced a significant higher heat radiation in small-scale tests. The reason for this is probably that a large-scale gasoline fire generates large amounts of smoke that tend to block the visible parts of the flames, thus reducing the heat radiation. The acetone/ethanol fire was almost free from smoke, and the associated heat radiated was therefore not dissipated by smoke. This is likely to be true for pure ethanol fuels. Indeed, such observations were made during a 2004 Port Kembla ethanol tank fire in Australia. One consequence of this phenomenon could be an increased risk for escalation and complexity in firefighting operations due to higher heat exposure of personnel and equipment.
The most important difference from a fire-extinguishing perspective is that ethanol is a water miscible fuel. Some data concerning foam firefighting of ethanol fuels and other water miscible products is available, even for reasonably large-scale scenarios, but they all represent spill fires. Early in the1980s, SP conducted a large test series using methanol where approximately 80 tests were conducted ranging from 0.25 square meters (0.29 square yards) to 50 square meters using a fuel depth of about 200 millimeters (7.8 inches). In the large scale acetone/ethanol tests mentioned above, two extinguishing tests were performed using an average fuel depth of about 150 millimeters. In 2006, a series of small-scale tests (0.6 square meters) were conducted to investigate the influence of low blending of ethanol in gasoline on existing firefighting capabilities. Approximately 30 tests were conducted with between 2.5 to 10 percent ethanol blends, using both gentle and forceful foam application.
A series of fire tests were also conducted in the U.S. in 2007 by the Ethanol Emergency Response Coalition. Tests were conducted both on E95 (denatured ethanol) and E10 using several types of foam concentrates. The tests on E95 showed that the requirements of UL 162 were only fulfilled when using an AFFF-AR and a Type II application, which is a gentle application shown in the accompanying photo where the foam is first bounced on the ground.
Similarly, existing test standards for alcohol-resistant foam concentrates (ISO 7203-3, EN 1568-4, UL162, etc.) all employ thin fuel layers and short pre-burn times—spill fires. Even spill fires pose serious firefighting issues and the general conclusion from various large-scale tests and standard test methods, is that the use of alcohol resistant (AR) foams is a fundamental requirement to obtain extinguishment of water miscible fuels. The tests have also shown, however, that even AR foams will fail unless gentle foam application onto the burning fuel surface can be achieved.
As tank fires are usually extinguished using large capacity foam monitors, gentle application is not possible and therefore extinguishment cannot be expected. Furthermore, a tank fire will present a more severe situation compared to a spill fire due to the large fuel depth, as the dilution effect from the fire fighting foam will be limited. In most situations, the pre-burn time will also be longer than that expected in a spill fire, thereby increasing the temperature of the fuel and creating hot steel surfaces making extinguishment even more difficult.
Clearly, existing test data, both from large-scale tests and in performance according to standardized tests, cannot be immediately extrapolated to tank fire scenarios. In response, SP Fire Technology and the Swedish Petroleum Institute have developed a research project on ethanol tank firefighting called Ethanol Tank Fire Fighting, or Etankfire.
The goal of the proposed tank fire research project is to develop and validate a methodology for firefighting of tank fires containing ethanol fuels and to determine the large-scale burning behavior of ethanol fuels. The results will form a platform of knowledge to ensure adequate investments for the fire protection of ethanol storage facilities. To achieve the goal, it will be important to better understand the challenges in fighting tank fires presented by the increased depth of fuel, the longer pre-burn time and the difficulty in achieving a gentle application of the foam when compared to better-understood spill fires.
Based on the results of initial laboratory tests, the most promising extinguishing methods and media will then be selected for further evaluation and verification at larger scales. Questions regarding the burning behavior and heat radiation from ethanol fuels will primarily be investigated in the large-scale tests.
Stakeholder Input Sought
The project idea was presented in April at a meeting in France to the Lastfire group. Two additional public workshops are planned, the first on June 28 in London. The second will be held in the U.S. with a date and location yet to be determined. Interested representatives from various organizations, companies and agencies will be given the opportunity to obtain more detailed information about the project goals and plans and to influence the planning process as we progress.
A steering committee will be formed by those willing to participate in the funding of the tank project that will participate in the final detailed planning, including the choice of venue for the large-scale tests.
Author: Henry Persson
Research Project Leader SP Fire Technology,
SP Technical Research Institute of Sweden
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