Changing Gears Part 2 - a fire suppression review

by Admin 14. December 2011 07:04

It's snowing in hell

Ahh foam! I can still remember the warm water splashing while Mom poured a capful of that wonderful soapy stuff under the faucet and making the bubbles pile higher and higher. oh, sorry. Wrong blog! Got lost there for a sec.

It's interesting to think that as children we were playing in basically Class A foam. Same basic principles at work there but though it is a bit ironic, we'll revisit that a little later in this article. For our purposes today, we should start at where foam started. Foam has been around for quite some time.

Foam was invented by a Russian scientist, trying to find an effective means of combating large oil fires, in 1902. The original formula was produced by adding dry chemical powders to water and agitating them until they became foam. Now, mind you, this was not the foam that we are accustomed to in this day and age. This concoction had more of a frothy consistency containing carbon dioxide bubbles. This new invention gave way to the chemical engines and, yes you guessed it, the sodium bicarbonate fire extinguisher (which had to be inverted to mix the powder and liquid to activate the reaction). We have ALL seen those "obsolete" extinguishers in flea markets and yard sales. Great timepieces they are. Good for modern firefighting? Not so much. It was found that it took far too much powder agent to fight large fires. This put the practice into history.

Throughout the 1940's, foam began to take a turn away from chemical agents and moved to "natural" products to create the finished foam. Soy-Protein was utilized to create Aerofoam. Animal waste was utilized to construct other foam agents, as well. These were better than their predecessor; however, still had problems with breaking down when exposed to fuels, heat or dry chemicals.

In the early 1960's, Fluoroprotein foam was introduced by National Foam, Inc. This latest development in foam technology had greater heat resistance and blanketing characteristics due to the oil-rejecting, fluorinated surfactant it was produced with. It also worked well when used in conjunction with dry chemicals and would not break down.

During the mid-1960’s, the U.S. Navy developed AFFF (aqueous film-forming foam). The surfactants in this type of agent make it ideal for covering static fuel surfaces. The foam, when aspirated at the nozzle, "bubbles up", rendering the water lighter and capable of floating on the surface of a hydrocarbon fuel. At the same time, the finished foam product drains a film across the liquid surface, sealing it from the air and preventing the fuel vapors from igniting. This is the foam product that most of us have come up using in the fire service. It is still used today and remains carried by most urban fire departments.

In the early 1970's, National Foam made another leap in foam technology by developing "Alcohol-Resistant" AFFF (AR-AFFF). Since alcohol has become so prevalent in fuel mixtures, this is generally the preferred type of foam to be carried by FD's.

While AFFF and FFFP(Film Forming Flouroprotein Foam) had taken care of the issue of fighting fires involving hydrocarbon fuels and other flammable/combustible liquids, nothing had really been done to increase our effectiveness at fighting Class A material fires. Many companies, such as PhosChek, had taken on the burden of creating reliable retardants but little had been done to augment the firefighter's arsenal in regards to the fires we normally deal with.

OKAY, HERE IT IS!! (the "bubble bath" thing)

Then along came Class A foam. Now we had a product to make the job of combating our "daily" fires a little easier. While Class B foams were aimed at making the water"float" on the surface of a liquid (with a lower specific gravity than water itself), Class A foams were designed with a "similar" characteristic.

Class B foams are usually proportioned at 3-6-10 or 20 percent. While in the hose itself, the surfactants mix with water. As this mixture leaves the nozzle, it is aerated (often with an air-aspirating nozzle). The surfactant/water mixture traps the air into bubbles, making the "finished foam" product capable of floating on a liquid surface. Once applied to the intended area, the surfactant drains from the “foamy” mix and creates a “seal” across the liquid surface.

Class A foams are utilized in a much lower concentration of .1-1percent. The goal of such a low concentration is not to make the water float but rather to break the surface-tension of the water, allowing it to "soak" to porous materials making it absorb heat deeper into the burning fuel package. This is basically the "bubble bath". Now, can you make a Class A foam "foam up"? Absolutely. If you aerate the mix it will look very similar to Class B foam. However, it will not last in this state very long. The bubbles of air are very fragile and will quickly burst, creating a milky-appearing mix, which is quite effective on Class A fires but will profit nothing on Class B. It can leave what it is dispensed on with a "slick" coating. This is merely the concentrate sticking to the fuel. We had that same film on us, when crawling out of a bubble bath, as kids.

In more recent years, newer foam agents have been developed which work in a different manner than "conventional" foams, such as AFFF. F500 has made a definite impact on the market. While the foams we are used to using require specific application methods (rain down, roll-on, bounce/deflection), F500 and similar products may be applied in these methods OR by plunging into the burning fuel. How is this possible? The action of F500 is to encapsulate the fuel molecule itself, rendering it unable to mix with oxygen and form a flammable mixture. This product has been utilized to clean pipelines out for just that reason. It takes away the fuel! This is a very good product (as I have used it myself for many years) and has won the favor of many departments in lieu of AFFF, for use on flammable liquid fires.

The Problem With Foam

Well I'd like to say that there is only one but,..there is a couple to consider.

First, foam comes as a concentrate and must be mixed with water somehow. To achieve proper proportioning, a proportioner (or eductor) must be utilized to make this happen correctly. Foam may be batch-mixed for some operations but if a specific effect is desired, the correct equipment must be employed. In conjunction with this problem, nozzles and eductors should be properly matched (gpm-gpm) in order to create the desired finished-foam product. The deployment of a standard eductor is an “added” step in the firefighting process, making it time-consuming.

Secondly, once foam has been employed to create a blanket, extreme care must be taken to not operate “clean” water streams near the blanket. Straight water destroys foam! The air bubbles will become burst or the blanket otherwise disrupted.

Thirdly, foam blankets are susceptible to the atmosphere in which it is applied. Naturally, a foam blanket will deteriorate due to drain-down (when the surfactant and water begin to naturally separate and drain away). The loss of a foam blanket may also be caused by wind, rain, or high ambient temperatures.

Fourth in point, is the fact that foam is still a water-based product. While foam products can assist in making the water lighter or decreasing surface-tension, the surfactants themselves are not the primary means of heat absorption. Water is still the means of taking the heat away. Air is a great insulator (as is proven by current PPE technology), however, when air is heated the molecules increase in activity. This is precisely why hotter air rises. As it rises, the molecules begin to take up more space by spreading apart (if enclosed in a container: i.e.- a bubble, this will also increase internal pressure which will eventually lead to rupture of the vessel or container). Therefore, over time (or if exposed to high heat) foam blankets will begin to break down in this fashion.

Closing

Now since we have covered water already, in the first segment of “Changing Gears”, I would be remiss to not mention that even though we may use less water in the total firefight, we must still flow the correct GPM to absorb the heat we are up against. Foams ARE water-based products and water IS the primary means of absorbing heat. If we miss that point and try to rely on the"foam" to do the work, we may be in for a harder fight than should be necessary. Remember, the "bubble bath" may have been fun but it didn't necessarily get us clean! It just made the process of getting there a little more tolerable.

Foams are and will be a part of the Fire Service for many years to come. As technology improves and our understanding of fire increases, newer products will (and have already) be developed to make our task easier. Foam has been a part of our repertoire for over 100 years. It is an enormous milestone in Firefighting History and has earned its place as one of the best advancements in firefighting technology.

My next installment to "Changing Gears" will be on Dry Chemical agents. I hope that you have enjoyed this segment and learned, at least a little more, firefighting history and how it has "changed gears".

I think I'll go have that "bubble bath" now... Be safe out there!

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Categories: FireIce | GelTech Solutions