Fire Testing Ethanol Fuels
In 2005, the U.S. Energy Policy Act established initial targets for introducing renewable fuels, among them ethanol.
NFPA Journal®, March/April 2008
By Guy Colonna
For use as a fuel, pure ethanol is transported from the ethanol plant where it is manufactured to blending facilities where it is denatured, or rendered unacceptable for human consumption, by mixing it with a small amount of hydrocarbon, usually gasoline. Two blends are currently used in the United States as motor vehicle fuel: E10, a 90 percent gasoline and 10 percent ethanol mix that can be used in all vehicles manufactured since the early 1980s, and E85, a 15 percent gasoline and 85 percent ethanol mix that can only be used in specially outfitted vehicles.
Ethanol vapors are heavier than air and disperse rapidly. Fuel ethanol mixes with water, but it separates at higher concentrations. And ethanol is less toxic than gasoline or methanol; pure ethanol contains no carcinogens. In 2006, the ethanol industry produced 6 billion gallons of ethanol, which was blended in 46 percent of the U.S. gas supply.1
As an alcohol, ethanol presents certain fire hazards. It has a flash point of 55oF (12.8oC), while gasoline’s flash point is -45oF (-42.8oC) and E85’s ranges from -20oF to -4oF (-28.9oC to -20oC), and it has a wider range of flammable limits than gasoline. For first responders, this means that, during a release of the typical ethanol/gasoline blend, one can expect the fuel to behave like gasoline: It is heavier than air, as noted above, and can produce vapors and form flammable mixtures in air under most ambient conditions.
The author is aware of news accounts of 25 fires involving ethanol since 2000, including fires at ethanol plants, ethanol storage facilities, and ethanol transportation in all modes, including road, rail, and water. These incidents highlight the problems first responders face when pure ethanol catches fire.
In 2006, the U.S. Department of Transportation (DOT) issued an alert recommending the use of alcohol-resistant foam for ethanol and gasoline fuel mixtures. The alert directs responders to the DOT Emergency Response Guide (ERG) for response actions, particularly Guide 127, Flammable Liquids Polar/Water-Miscible.
To help responders deal with such fires, the Ethanol Emergency Response Coalition (EERC) was formed in 2006 to investigate those emergency response issues associated with bulk distribution and storage of ethanol-blended fuels. Members of the EERC include ANSUL, the Independent Liquid Terminal Association, Industrial Fire World magazine, the International Association of Fire Chiefs, and the Renewable Fuels Association, organizations involved with alternative fuels, scientific testing, bulk-fuel distribution and storage, first responders, and key fire service organizations.
In February 2007, the EERC conducted a series of 43 individual performance fire tests on denatured ethyl alcohol, ethanol that was denatured with 5 percent gasoline, and gasohol, defined by the American Petroleum Institute (API) as regular unleaded gasoline with up to 10 percent by volume ethyl alcohol. The purpose of the test program was to evaluate the effectiveness of various foam concentrates and other water additives on these two types of fuels.
Fire testing protocols were based on the methods established for topside and sprinkler testing outlined in the seventh edition of UL 162, Standard for Safety—Foam Equipment and Liquid Concentrates. UL 162 establishes fire test protocols for applying agent to the fire by various techniques using specified application rates. An application rate is defined as gallons per minute (gpm) of unexpanded foam solution flow divided by the fire area. For example, a 50-square-foot fire using a flow rate of 3 gallons per minute would have an application rate of 0.06 gpm/sq.ft.
UL defines the application of the agent directly to the surface of a burning liquid fuel as a Type III application, a technique that allows for the agent to plunge into and submerge in the fire. A Type II application is a fixed discharge applied to a vertical surface, allowing the agent to flow down onto the burning surface, providing a more gentle application with minimal plunging or submergence. UL classifies Type II and Type III applications as "topside" fire tests. Generally, Type III applications are used for hydrocarbon fuels, while Type II applications are used for polar solvent/water-miscible fuels such as ethanol.
Sprinkler application of the agent allows for testing from either air-aspirated or non-aspirated sprinklers, as would be found in fixed protection for loading racks or other fuel transfer areas. For both topside and sprinkler tests, UL 162 requires not only successful extinguishment but also a level of resistance to re-ignition and burn back, typically called burn-back resistance.
The following generic foam concentrates and water additives were evaluated: alcohol-resistant AFFF (AR-AFFF); Class A foam; regular AFFF, an emulsifying agent; regular fluoroprotein; and alcohol-resistant film-forming fluoroprotein (AR-FFFP). Where possible, 3 percent versions of each agent were used.
The test results
Only the alcohol-resistant products, AR-AFFF and AR-FFFP, were capable of extinguishing the fires in the topside fire tests, and they could only successfully extinguish Type II fires. The ARFFFP required a higher application rate to attain extinguishment than did the AR-AFFF. Of these two agents, only the AR-AFFF could also pass the burn-back resistance portion of the test.
AR-AFFF passed all the topside fire test requirements of UL 162 , but only when using a Type II application method. Only the AR-AFFF was also capable of passing the sprinkler test with non-aspirating sprinklers.
Only AR-AFFF and regular AFFF extinguished the Type III fires at the recommended UL test rate of 0.06gpm/sq.ft. An increased application rate was required for the AR-AFFF to pass the burn-back portion of the test. Regular AFFF did not pass the burn-back requirement even at an application rate as high as the NFPA minimum application rate for spill fires of 0.10 gpm/sq.ft.
AR-AFFF passed sprinkler testing on gasohol using non-aspirating sprinkler heads, and regular fluoroprotein foam passed the test with air-aspirating sprinkler heads.
As expected, we can see that denatured ethyl alcohol fires can only be extinguished with alcohol-resistant foams. All other foams or water additives are ineffective because the foam blanket is destroyed when it strikes the surface of the fuel.
Alcohol-resistant foams must be applied to ethanol fires using Type II application techniques. For responding emergency services, this means directing the foam stream onto a vertical surface and allowing it to run down onto the fuel, rather than applying it directly to the surface of the fuel. Direct application to the fuel surface will probably be ineffective unless the fuel depth is extremely shallow—no deeper than one-quarter inch or less.
Gasohol fires can be extinguished using conventional AFFF or AR-AFFF, but increased application rates may be necessary, especially for gaining prolonged burn-back resistance. A Type III direct application may also be used with gasohol.
Non-aspirating sprinkler may be used with AR-AFFF for both ethanol and gasohol to protect against fires at loading racks and similar facilities. All other foams proved to be ineffective at the application rates tested. Use of regular fluoroprotein foam through air-aspirated sprinklers at standard design rates proved effective on gasohol fires but not on denatured ethanol fires.
Overall, AR-AFFF proved to be the most effective and versatile agent tested. It was the only agent that was successful in all fire test scenarios.
Source: The Petroleum Equipment Institute, PEI Journal Online, October 23, 2007.
Guy Colonna is assistant vice-president of NFPA’s Fire Protection Applications and Chemical Engineering Division.