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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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 robert.burke@att.net.