Ethanol — Part 1: Physical and Chemical Aspects

This is the first installment of a three-part series about ethanol. The series focuses on physical and chemical characteristics, manufacturing processes and hazards, and firefighter response to ethanol emergencies in transportation and at fixed facilities.

Ethanol, in the context of this series, is denatured ethanol manufactured and used for use as a motor fuel and motor fuel additive. To form a comparison with ethanol, we will first look at more common motor fuels.

Gasoline and diesel fuel, hydrocarbon products refined from crude oil, have been the primary motor fuels for over 100 years. Both are flammable and have physical and chemical characteristics that make them hazardous in use, storage and transportation. These fuels are classified by the U.S. Department of Transportation (DOT) as Class 3 Flammable Liquids and are marked with red placards and labels. Gasoline and diesel fuel are usually shipped in bulk quantities so they will have the United Nations four-digit identification numbers 1203 and 1993, respectively, placed in the center of the placards.

The DOT's 2008 Emergency Response Guidebook (ERG) assigns Orange Guide 128 for both gasoline and diesel fuel. Guide 128 is titled "Flammable Liquids (Non-Polar/Water-Immiscible)" and gasoline and diesel fuel have these characteristics. While ethanol is in the same hazard class as gasoline and diesel fuel, we will discover that the concepts of polarity and miscibility are among the primary differences.

Although gasoline and diesel fuel have some different physical characteristics under fire conditions, they are handled much the same. Firefighters should, however, be aware that those differences exist when dealing with emergencies involving both fuels. Generally, firefighters should know how to deal with gasoline and diesel fuel in a fire or other emergency because they are so common and have been around for so long. In fact, the most common hazardous materials response in most jurisdictions involves these fuels.

Gasoline and diesel fuel are mixtures of hydrocarbon compounds and other additives. For example, a common blend of gasoline contains benzene, n-butane, ethyl alcohol (ethanol), n-hexane, methyl-tertiary butyl ether (MTBE), tertiary-amyl methyl ether (TAME), toluene, 1, 2, 4, trimethylbenzene and xylene mixed isomers. Physical and chemical characteristics will vary depending on the mixtures, which will very likely be different from one manufacturer to another. The mixture listed above has a flash point of -45 degrees Fahrenheit, which is the same for most blends of gasoline and an auto ignition temperature greater than 540°F. Some sources list gasoline mixtures with ignition temperatures in the 800°F range.

Diesel fuel is also a mixture made up of diesel fuel and naphthalene and other additives. Diesel fuel has a flash point greater than 125°F and an auto ignition temperature of 500°F. Diesel fuel is usually harder to ignite than gasoline, but when diesel fuel does ignite, it has a greater heat output than gasoline and therefore may be harder to extinguish. Dry chemical and foam are the most common extinguishing agents, depending on the amount of fuel on fire.

Large-scale use of ethanol as a motor fuel in highway vehicles is fairly new. Hazards of ethanol may not be as well understood by responders as hazards of gasoline and diesel fuel, which are primarily transported by pipeline and with highway transportation vehicles. There is some rail transportation of gasoline and diesel fuel, but it is not nearly the volume as pipelines and highway transportation. Ethanol, on the other hand, is largely transported by rail, supplemented by highway and minimal pipeline transportation. It is classified by the DOT as a Class 3 Flammable Liquid, just like gasoline and diesel fuel, and is marked in transportation with red placards and labels.

The DOT places hazardous materials with similar hazards in the same hazard class because they are dealt with in a similar manner during a transportation emergency. In bulk shipments, the red Class 3 placard for alcohols and denatured alcohol will have the four-digit identification number 1987 in the center of the placard. The number 1987 does not specifically identify ethanol, but alcohols as a chemical family have the same hazards when in manufacturer, storage, transportation and use. As a result, procedures for handling them during an emergency would be much the same.

The 2008 ERG refers to Orange Guide 127 for alcohols and denatured alcohol. Guide 127 is titled "Flammable Liquids (Polar/Water-Miscible)." This is a direct opposite of gasoline and diesel fuel and one of the major differences between these Class 3 liquids. Flammable liquids, whether gasoline or ethanol, are transported in atmospheric pressure containers because they have similar physical and chemical characteristics. The point is that gasoline, diesel fuel and ethanol, while different in some aspects, are quite similar in others. The bottom line is they are all flammable liquids and when on fire will behave much the same. If we understand the physical and chemical characteristics of ethanol, we will find it really isn't any more or less difficult to deal with than gasoline or diesel fuel. What is important is that we need to understand how to deal with the differences.

Ethanol is a member of the alcohol hydrocarbon derivative family of chemicals. All alcohols are flammable and toxic to some degree. Hydrocarbon derivatives get their name from the fact they are hydrocarbons to start with and have other chemical elements added to create a new chemical that has some economic value. Hydrocarbons are made up entirely of combinations of the elements hydrogen and carbon covalently bonded together with single, double or triple bonds. Single-bonded hydrocarbons are the most stable. Double- and triple-bonded hydrocarbons are more reactive and hazardous during an emergency. Hydrocarbon derivatives are hydrocarbons with one or more of the elements oxygen, nitrogen, fluorine, chlorine, bromine or iodine added to a hydrocarbon compound. Ethanol, along with other alcohols, is single bonded with oxygen bonded to a single hydrogen (-OH) added to the hydrocarbon compound. Ethanol is an alcohol with the -OH attached to a two carbon backbone from the hydrocarbon ethane. It is a pure chemical, whereas gasoline and diesel fuels are mixtures of chemicals. Mixtures that form gasoline and diesel fuel include members of the hydrocarbon family.

Alcohols, including ethanol, are members of a hydrocarbon derivative sub-group known as polar solvents. (Polarity is a somewhat complicated phenomenon that we do not have the space to discuss here. Therefore, you will just have to trust me on this one.) Water, like alcohol, is also a polar compound. Water has a molecular weight of 18. Air has an average molecular weight of 29. With a molecular weight of 18, water should be a gas at normal temperatures and pressures. But as we know it is a liquid. It is polarity that lets water exist as a liquid.

Because water and alcohols are polar compounds, they are miscible; that is, they mix when placed together. (There are some experiments you can do at home that will prove this is true.) Because water and alcohol mix, that is one reason why different types of firefighting foam are required for alcohol fires versus gasoline or diesel fires. More on that later. Gasoline and diesel fuels, on the other hand, are not polar compounds and are immiscible in water. When gasoline or diesel fuel are spilled on waterways, water and the fuels form layers and the fuels float on top of water. When chemicals float on the surface of water, they are considered to be lighter than water. Chemical reference sources will sometimes list a specific gravity for a liquid chemical. Specific gravity is the weight of the liquid versus water. Water is given a numerical weight of 1.00. Any chemical with a specific gravity greater than 1.00 will be heavier than water and sink to the bottom if it is not miscible. Chemicals with a specific gravity less than 1.00 will be lighter than water and float on the surface if it is not miscible. Ethanol is miscible with water. If spilled in a water source, it is difficult to clean up. Polarity is a major difference between ethanol and gasoline and diesel fuel. Several physical characteristics of flammable liquids are important in terms of combustion. These include flash point, ignition temperature, flammable range, vapor density and heat output.

Flash point, boiling point and ignition temperature are affected by polarity. Compounds that are polar have a tendency to have higher boiling points and flash points than non-polar compounds with similar molecular weights. Within the parameters of combustion, several things must be in place for combustion to occur. First and most importantly, a flammable liquid must be at or above its flash-point temperature. Flash-point temperature is the temperature of the liquid, not the ambient temperature around the liquid or container. This is an important factor. It could be 32°F ambient temperature outside and a chemical could have a flash point of 50°F. However, if the chemical is in a black container in direct sunlight, it is possible the temperature of the liquid could be above its flash point. It is therefore very important that you know the temperature of the liquid when determining if a chemical could be above its flash point. If the temperature of the liquid is at or above its flash point, combustion may occur.

If any one of the three conditions listed above are not present, combustion cannot occur. However, flash-point temperature is the most important of the three. For combustion to occur at all, first the liquid must be at or above its flash point temperature. Flammable range has to do with the proper mixture of air and fuel that it takes for combustion to occur. Gasoline and diesel fuel have narrow flammable ranges, between 3 and 10. Ethanol, as with other alcohols, has a wider flammable range, from 3.3 – 19. That means that ethanol will burn within a greater percentage of mixtures of fuel and air than gasoline and diesel fuel. The wider the flammable range, the more likely the fuel may burn inside a container.

It would appear that ethanol falls somewhere between gasoline and diesel fuel in terms of its combustible characteristics. Gasoline has flash-point and ignition temperatures of -45°F and greater than 540°F, respectively. Diesel fuel has flash-point and ignition temperatures of greater than 125°F and 500°F, respectively. Ethanol has flash-point and ignition temperatures of 61.88°F and 685°F, respectively. In terms of ignition temperature, gasoline and ethanol are closer than diesel fuel, which means the liquids must be heated to near the same temperature or the ignition source temperature would be close to ignite both liquids.

The major differences between gasoline, diesel fuel and ethanol are polarity and miscibility. This results in different firefighting tactics in terms of foam use with ethanol. Ethanol will mix with water, so the foam used to fight fires involving gasoline, diesel fuel and ethanol must be different to be effective. If you use regular protein foam, AFFF or fluoroprotein foam, it will not work on ethanol fires because the water from the foam will mix with the alcohol and the foam blanket will break down. When fighting ethanol fires, you will need to use alcohol or polar-solvent types of foams.

Another different physical characteristic between ethanol and gasoline and diesel fuel is the color of the flame. Gasoline and diesel fuel burn with a yellow-orange flame. Ethanol burns with a bluish flame that may be difficult to see under certain light conditions. Ethanol fires also give off less carbon, or black smoke, than gasoline and diesel fuel fires.

In Part 2, we will take a tour of an ethanol manufacturing facility and learn about the production process.

ROBERT BURKE, a Firehouse® contributing editor, is the fire marshal for the University of Maryland Baltimore. He is a Certified Fire Protection Specialist (CFSP), Fire Inspector II, Fire Inspector III, Fire Investigator and Hazardous Materials Specialist, and has served on state and county hazardous materials response teams. Burke is an adjunct instructor at the National Fire Academy and the Community College of Baltimore, Catonsville Campus, and the author of the textbooks Hazardous Materials Chemistry for Emergency Responders and Counter-Terrorism for Emergency Responders. He can be contacted at