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...


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...


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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.