Ethanol: It's Not What You Think it is, or is it? - Part 2

During our research we found a number of sources that had incorrectly reported E85 has more volatile properties than gasoline at 32 degrees.


Before discussing E85 firefighting tactics, a quick review of some terms concerning the property of chemicals is in order.

It is the properties of ethanol compared to gasoline that drives the difference in our response and tactics.

When dealing with volatile liquids it is important to understand how each behaves. In our case as firefighters we are concerned with its volatility under "normal fire conditions" and as it is being extinguished (in most cases with water).

Properties of E85 and Gasoline
Although there are many properties of E85 and gasoline, boiling point, flash point, upper explosive limit and solubility are the ones that best illustrate the difference between the two fuels:

Boiling Point: Defined as the temperature at which it can change its state from a liquid to a gas throughout the bulk of the liquid at a given pressure. Remember "at a given pressure." The lower the boiling point, the more volatile the substance.

Flash Point: Is the lowest temperature at which a liquid or solid gives off enough vapor to form a flammable air-vapor mixture near its surface. The lower the flash point, the greater the fire hazard; in other words, the temperature needs for ignition decrease with the flash point.

Upper Explosive Limit: Is the highest concentration of a chemicals vapor in air which will burn or explode upon contact with a source of ignition.

Lower Explosive Limit: Is the lowest concentration of a chemicals vapor in air which will burn or explode upon contact with a source of ignition.

Solubility : Is the measure of how much of a given substance will dissolve in a liquid in this case water.

E85 Versus Gasoline
Properties................ Ethyl Alcohol.......Gasoline
Boiling Point.................173° F...............102° F
Solubility......................Miscible..............Insoluble
Flash Point........................55° F.........-45° F
Upper Explosive Limit......19%.............7.60%
Lower Explosive Limit.......3.30%.........1.40%
Visible Flame....................Yes...............Yes

The above chart, using the properties discussed earlier, will help identify the volatility (its willingness to evaporate into a gas) of each liquid. This is important since all combustion requires the burning material pyrolize (simply put, turn to gas) before it burns.

Ethyl Alcohol's boiling point is over 70 degrees higher than gasoline. Meaning that as the temperature increases, gasoline will convert to vapor more rapidly. Vapor is more flammable than a liquid. In this category, gasoline is the more volatile or flammable substance.

Perhaps the most important property of these two liquids is flash point. Recall that Flash Point is the lowest temperature at which a liquid or solid gives off enough vapor to form a flammable air-vapor mixture near its surface. Low flash point is an excellent indicator of volatility. In the case of E85 versus gasoline, gasoline produce enough vapor for flammability a full 100 degrees cooler than E85. Again, gasoline is the more volatile substance.

Although it is clear that gasoline is more volatile than Ethyl Alcohol, the biggest difference between the two properties is that one is soluble in water and the other is not. Why should a fire officer or firefighter care if ethyl alcohol is soluble or not? Solubility in this case being how much E85 or gasoline will dissolve in water. It is of major concern since water, foam or a combination of the two, are the only methods we have of fighting fire. In other words, in water gasoline will not completely dissolve allowing a film to form. The ethanol component of E85 (and a small amount of gasoline) will dissolve in water which affects the film formation.

Based on the differences, fires that involve gasoline will require foam since gas floats on water. Water will dilute the E85 and foam will smother the fire just as it does with gasoline fires. However, given the fact that ethanol is water soluble, foam will deteriorate more rapidly in E85 than with gasoline.

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