On-Site Gasohol Blending Breeds Widespread Extinguishing Problems
John E. Bowen
Most people know that gasohol is a blend of gasoline and alcohol but, beyond that, what is this new fuel? What problems will it generate for the fire service? Can we handle these problems with today’s techniques and equipment or are new fire fighting methods going to have to be developed quickly?
Let’s tackle these questions one at a time. First, what is gasohol? Gasohol is a mixture of unleaded gasoline and an alcohol, usually but not always ethyl alcohol, or ethanol, as it is sometimes termed. Methyl alcohol (methanol) or isopropyl alcohol (isopropanol) can be substituted for the ethanol.
So, before we can define gasohol precisely, we must define unleaded gasoline. The octane rating of gasoline, a measure of its knocking properties, must be increased for it to be used in today’s autos. For decades, tetraethyl lead (TEL), and occasionally lead or tetramethyl lead, was added to gasoline for this purpose. Lead is a deadly poison, though, and a potentially serious environmental pollutant. Also, lead is destructive to the platinum catalyst used in emission control devices on late model vehicles. Thus, these late-model vehicles are designed to accept only fuel containing no lead—gasoline from which TEL and related compounds have been omitted.
The requirement for high octane gasoline remains, however, so a search was conducted for other chemicals that would raise the octane rating just as the discontinued lead compounds did. Tertiary butyl alcohol (TBA) was found to serve this function well and today TBA is the most commonly used antiknock chemical additive. It is being added to gasoline at concentrations of 7 to 10 percent.
Methyl tertiary butyl ether (MTBE) is also an effective anti-knock agent. It, too, is used at concentrations of 7 to 10 percent. There is presently some research being conducted on use of TBA and MTBE in combinations totaling 15 percent.
When you drive into a service station to purchase unleaded gasoline, you’re actually buying a blend of gasoline and TBA, MTBE or both. This is what we know as unleaded gasoline. As an interesting aside, unleaded gasoline is also likely to contain significant amounts of some aromatic hydrocarbons such as xylene, toluene and cumene.
Witches’ brew
Returning now to the definition of gasohol, we begin to see that it’s really a witches’ brew of unleaded gasoline, alcohol, TBA, MTBE, etc. The ethanol that is used is 198 proof (99 percent pure) and would be prized for human consumption so the United States government mandates that it be denatured (made unfit for human ingestion) by addition of 4 percent methylisobutyl ketone. So, yet another chemical is added to the brew.
The gasohol being marketed presently in Texas, Louisiana, Hawaii and several midwestern states contains 10 percent denatured ethanol—one part alcohol to nine parts of unleaded gasoline. There is nothing particularly sacred about using 10 percent alcohol. It could just as well be 15 or even 20 percent. There would still be no major engine adjustments necessary. By adjusting the carburetor and compression ratios, though, pure ethanol could be used. In fact, this is being done on a small scale in Brazil and the midwestern United States.
From the fire fighter’s viewpoint, unleaded gasoline and gasohol present problems that have seldom occurred before. Previously unknown chemicals will be brought into your first-due district. You likely know little about their fire potentials, vapor densities, lower and upper explosive limits, etc. Furthermore, do you have any idea how to extinguish fires in spills or tanks of TBA, ethanol, methylisobutyl ketone and so on?
Perhaps you’re thinking that these chemicals are apt to be used mainly in refineries and bulk storage tank farms. Don’t be too secure in this assumption. There are eight manufacturers of ethanol in the United States and 16 plants make TBA. Fifty-five more plants produce other gasoline additives—corrosion inhibitors and anti-freeze agents. These materials must be transported to the blending site by rail, truck and ship. The final products must then be moved to the neighborhood service stations.
Gasohol blended locally
Furthermore, gasohol cannot be stored for long because it absorbs water readily. When the critical water tolerance (the maximum amount of water permissible in the blended fuel) is exceeded, phase separation occurs. The alcohol-water layer has a higher specific gravity than gasoline, so the former sinks to the bottom of the tank and the gasoline floats on it. When this happens, we no longer have gasohol.
Gasohol, therefore, must be blended as close to the consumer as possible. Local distribution centers are now going to have a tank of ethanol on hand. There are going to be pipes running from this tank to the loading rack. Actual blending will likely be done right in the tank truck. This necessity for onsite blending will bring alcohol storage to many towns and villages across the nation. With ethanol storage comes a new problem for fire fighters—how do you extinguish it?
The same question holds true for TBA, methylisobutyl ketone, MTBE and each of the other chemicals that we’ve mentioned. How do you attack and extinguish a spill or tank fire in one of them? How can you prevent a spill from igniting?
Additive properties
Let’s consider first the properties of the pure additives that will concern fire fighters (table I). Four of these chemicals are alcohols, namely methanol, ethanol, isopropanol and TBA. Being alcohols, these are polar liquids, a very significant fact as we’ll see shortly. These alcohols have several other properties in common also. Each is a highly flammable liquid at normal atmospheric temperature. Although these alcohols are not subject to spontaneous heating, each will ignite when contacted by oxidizing materials. The vapors of each are heavier than air and pose a moderate explosive threat. Fortunately, none of these materials is dangerously toxic.
Methylisobutyl ketone is not an alcohol, but it is a flammable polar solvent liquid nonetheless. Its properties are much the same as those of the alcohols, though (table I).
Low-molecular-weight ethers, such as MTBE, are polar substances, too, but less so than the alcohols. Thus, they should in theory be less destructive to foams than other polar solvents. Ethers are extremely volatile, though, and the resultant high vapor pressure may make it difficult to effect a foam seal against hot metal surfaces. More about this later, however.
So, what do we do when summoned to an alcohol, ketone or ether fire? These are polar solvents, remember, so conventional protein, AFFF and fluoroprotein foams will not be effective. Instead, we must use one of the specialized alcohol-resistant, or polar solvent liquid, foams.
Two types of PSL foams
There are two general types of polar solvent liquid (PSL) foams. One is a modified protein foam, but this is being phased out slowly by the manufacturers. Let’s look at the second type, the modified AFFF which we’ll call PSL-AFFF. Several manufacturers produce these alcohol-resistant foams in the United States, but each of them is a modified AFFF. Thus, the designation PSLAFFF refers to this general type of foam concentrate and not to a specific brand name. These are the only foam concentrates available today which will extinguish alcohol, ether and ketone fires.
PSL-AFFF concentrates contain a polymer which precipitates out of the foam blanket to form a layer over the fuel surface, thus effectively separating fuel vapors and oxygen. The PSL foams will extinguish hydrocarbon fires as well as polar liquid ones, but the technique of applying PSL-AFFF to hydrocarbons is somewhat different than that of conventional AFFF.
PSL-AFFF may be applied to burning hydrocarbons with either air-aspirated or non-aspirated nozzles. Further, it can be applied to the hydrocarbon via topside or subsurface methods. Consult the manufacturers’ literature, though—the reeommendated application rate for a given PSL-AFFF may differ for PSL and hydrocarbon fires.
When a PSL-AFFF is used on a polar solvent fire, it must be air-aspirated. There is no choice about this if maximum effectiveness is to be achieved. Furthermore, PSL-AFFF must be applied topside to a polar solvent liquid fire. Even the alcohol-resistant foams are destroyed when immersed in the liquid. Thus, they cannot be applied via subsurface injection.
Swedish technique
Swedish fire fighters have developed a technique that permits injection of PSL-AFFF into the bottom of a fuel tank, a technique known as semi-subsurface injection. It hasn’t received much attention in the United States yet, but generally here is how it works. The foam is pumped into a pipe on the bottom of the tank. The pressure ruptures a seal and pushes a plastic tube to the surface of the burning fuel. The tip of the tube burns off, gently releasing the foam to extinguish the fire.
PSL foams must he applied gently to the burning fuel. In the case of an alcohol spill fire, for example, direct the foam stream at the ground in front of the fire. Bounce the foam onto the fuel surface. For topside application to a tank fire, deflect the foam off the opposite side of the tank. Failure to apply the foam gently will cause the foam to lie mixed with the PSL fuel, thus destroying the blanket before it can extinguish the fire.
Another problem is caused by the high viscosity of PSL-AFFF concentrates, a much greater viscosity than that of standard AFFF. The viscosity of the concentrate is such that standard in-line proportioned with 5/8-inch diameter pickup tubes may not be able to supply the concentrate fast enough to achieve a 3 percent application rate in a 60-gpm or greater stream. The foam that you actually get at the nozzle may be only 2 or 2.5 percent.
If your proportioner is continuously variable from 3 to 6 percent, set it at 3.5 or 4 percent. For those proportioners that cannot be varied, it may be necessary to replace the small diameter pickup tube with a larger one, e.g., 1 1/4 -inch diameter, for use with PSL-AFFF. Do be aware of this problem and check the pickup tube frequently when using PSL foams. Different makes of PSL-AFFF may differ as much as 10fold in their viscosities, so this problem may occur with one concentrate but not with another.
Apply alcohol-resistant foams to fires in pure PSL additives at rates of 0.15 to 0.20 gpm/ft2 of surface area. Methyl, ethyl and isopropyl alcohols are among the most difficult of the polar liquids to extinguish and require a high application rate.
The radiated heat from a PSL fire will be much greater than that from an equal volume of burning hydrocarbon. This may magnify exposure problems as well as accelerate thermal destruction of the foam. And don’t forget that there is no visible flame when methanol burns!
Fire in an MTBE bulk storage tank requires topside application of a PSL-AFFF even though MTBE is not as polar as the alcohols. Ethers are not as foam-destructive as alcohols, but even their limited destructiveness dictates use of a PSL-AFFF.
Ethers are much more volatile than alcohols, though. For example, the vapor pressure reaches 400 mm at 112°F, 146° F and 186°F for methanol, ethanol and isopropanol, respectively. The corresponding temperature for MTBE is 106°F.
MTBE vaporizes rapidly at fire temperatures, resulting in very high vapor pressures. The high vapor pressures make it difficult to maintain a foam seal at points where the liquid touches hot metal. The expanding vapor continuously disrupts the blanket. This problem can be readily eased by supplemental cooling of the metal surfaces with hose streams, a procedure that produces quick control of the fire.
PSL-AFFF is effective in securing either hydrocarbon or polar solvent spills before ignition occurs, forming excellent blankets with lengthy drain-off times. The foam blanket will also significantly reduce the potential toxic and environmental pollutant effects because evaporation is greatly decreased.
Let’s briefly summarize the information presented thus far. Remember, the TBA and MTBE being added to gasoline to produce the unleaded product are polar liquids, as is the methylisobutyl keton used to denature ethanol for use in gasohol production. The alcohols themselves are also polar. Therefore, the only effective extinguishant for fires in these pure liquids is a polymeric polar solvent foam, a PSL-AFFF concentrate. No other foam will do the job! And, remember when using PSL-AFFF products that conditions of use and application methods differ from those for conventional AFFF.
Amount of foam needed
Let’s give some thought to the final products now, the unleaded gasoline and the gasohol. Spill fires of unleaded gasoline containing up to 10 percent TBA or MTBE can be extinguished with any foam—protein, AFFF, PSLAFFF or fluoroprotein, applied at 0.2 gpm/ft2. At this rate, spills of 10,25 and 50-foot diameters will require the application of 16,100 and 400 gpm of foam, respectively. Don’t underestimate this requirement when you make the initial attack.
PSL-AFFF is the extinguishant of choice for subsurface injection into tanks of burning unleaded gasoline. It must be air-aspirated and applied at a rate of 0.10 to 0.15 gpm/ft2. Thus, 50 and 100-foot-diameter tanks require 200 to 300 gpm and 800 to 1200 gpm, respectively.
PSL-AFFF applied topside at 0.15 gpm/ft2 is also very effective on tanks of burning unleaded gasoline. Fluoroprotein foams will do the job under these conditions, too, but the application rate must be increased by 33 percent.
Gasohol spill fires up to 1 inch deep can be extinguished with AFFF if the alcohol content of the blend is 20 percent or less. It is likely that more foam will be required than if PSL-AFFF were used, though, because of alcohol-induced AFFF destruction. PSL-AFFF must be used if the alcohol content of the gasohol blend exceeds 20 percent. It is suggested, however, that a PSL-AFFF be used on all gasohol fires regardless of the alcohol percentage. Apply the foam at 0.2 gpm/ft2.
Gasohol tank fires must be attacked from the top, pending further progress in alcohol-resistant foam technology. PSL-AFFF and fluoroprotein foams will both extinguish the fire, but the latter must be applied at a higher rate—i.e., 0.15 gpm/ft2 for PSL-AFFF vs. 0.2 gpm/ft2 for fluoroprotein foam.
Securing gasohol spill
How can you secure a gasohol spill to prevent ignition? The PSL-AFFF foams will certainly work, as will the fluoroproteins. Protein foam and the AFFFs may do the job, but this depends on the specific brand of foam and also on the source of the unleaded gasoline. Some combinations give excellent results. With others large tears and blisters quickly appear in the foam blanket. Thus, plan to use a PSL-AFFF or fluoroprotein for handling gasohol spills.
It has been suggested in various articles recently that gasohol fires could be extinguished by initial phase separation followed by conventional (non-PSL) foam attack. We’ve mentioned that addition of water beyond the critical tolerance to gasohol will cause phase separation. Alcohol is almost infinitely soluble in water and the specific gravity of water being greater than that of gasoline (1.00 vs. 0.66 to 0.69), the wateralcohol phase will sink to the bottom of the storage tank or spill. “Pure” gasoline will float on the surface.
Theory has it that a sweep of the burning gasohol surface with fog streams will cause phase separation. You would then be confronted with a gasoline (not gasohol) fire that could be extinguished with AFFF, protein or fluoroprotein foam.
There are some rather obvious problems with this technique, though, and further study is definitely need. For instance, it certainly cannot be done to a full storage tank—there’s no place for the water to go. If attempted on a gasohol spill fire, it would be all too easy to start the fire flowing. Lastly, the water absolutely must be stopped before foam application begins. Otherwise, the foam blanket would be disrupted quickly.
Phase separation with water is therefore not recommended as a firefighting technique for gasohol fires at this time. Our knowledge of potential undesirable effects is inadequate.
Carry flammable placards
Before we bring this discussion to a close, though, two more factors must be mentioned briefly. First, unleaded gasoline and gasohol shipments will be placarded as flammable liquids. No further identification of the product is likely to appear on the vehicle. The incident commander must obtain this information from the shipping papers, i.e., the shipping order, bill of lading, cargo manifest or waybill.
The product involved in the fire or spill must be specifically identified before any control measures can be taken. Thus, it is critically important that the commanding officer promptly obtain this information. Failure to identify the product correctly can negate all further actions.
Secondly, the fire attack procedures detailed in this article supplement basic tank and spill fire-fighting procedures. They do not replace the standard sizeup and tactical procedures for fires in flammable liquid fuels.
Finally, know where polar liquids, unleaded gasoline and gasohol are stored, sold and used in your area. Pre-plan for these emergencies. Transportation incidents are another story. They cannot be pre-planned. Remember, though, to try to identify the product immediately.
