Part 1
What is the best foam? What are the generic types of foam? What are their strengths and weaknesses? Does brand make a difference? Do you need more than one type? Is there really a "do-everything" foam? Can you use a fog nozzle, or do you need a "real" foam nozzle? Don't feel bad if you've ever wondered about any of these questions. You're not alone! This series of articles is written to help find some answers.
If you read everything that's been written by the manufacturers of foam, and if you study Underwriters Labs (U.L.) and military specifications (Mil Specs), American Petroleum Institute (API) and Federal Aviation Administration (FAA) papers and talk to end users, you'll find a bunch of compromises. As you work your way through this maze of information, you'll find at least eight generic types of what veteran firefighting foam instructor Flynt Josey calls the "foam family". Eleven manufacturers produce 22 variations of the eight foams. The one you choose should be based on head-to-head comparisons in the real world environment in which you operate.
To understand fully which foam is best for a particular purpose, it's important to review the entire foam family. It can be subdivided into three expansion ratios(the ability of the foam solution to hold air in a useable form): 1) low expansion is up to 20:1; 2) medium expansion is from 20:1 to 200:1; and 3) high expansion, ranging from 200:1 to 1,400:1. The expansion ratio is the amount of finished expanded foam that will be produced using the correct nozzle. One gallon of foam solution will make 1400 gallons of finished foam with the correct nozzle and concentrate. In this article series, we'll break the foam family into two primary branches: One is detergent-based, and the other is protein-based, including fluoroproteins.
Each branch of the foam family tree has inherent strengths and weaknesses. Detergent foams, which are always synthetic, are the first branch of the family we'll examine. These foams, known as high-expansion (HiEx), Class A (referring to Class A fires), medium expansion and wildland foams are available in 0.1 percent to 3 percent concentrates. One 3/6% AFFF foam can be used on Class A fires at 0.05%, a truely universal agent. HiEx and medium expansion foams are designed in 0.3 percent to 3 percent concentrates. HiEx and medium expansion foams are designed for flooding areas.
HiEx generally is the last choice for flammable liquid fire suppression when compared to any of the other foam types. However, some manufacturers claim they are effective for flammable liquid fire suppression. In fact, a few are formulated for flammable liquid firefighting. One even has a 2 3/4 percent concentrate, but I've never seen an eductor with a 2 3/4 percent setting.
One of the newest uses for HiEx foam is formation of a vapor barrier for certain hazardous materials, including flammable liquids, in multi-dimensional situations. One manufacturer points out that HiEx is "...the only foam currently available that is compatible or use on acid or alkaline materials." A secondary use for HiEx foams is in flooding of large-area Class A and B fires. A medium expansion nozzle with Class A foam can help firefighters stretch their water supply during overhaul. HiEx is used in some aircraft hangars for filling and extinguishing in large spaces. The main drawback of HiEx foam is its inability to resist heat. Also, if a wind comes up, your protection may end up in the next county.
Nozzles used for application of foam include high-, medium- and low-expansion, and fog nozzles. High expansion foams convert one gallon of foam water solution (concentrate and water combined) into 200 to 1,400 gallons of "expanded foam" when using a high expansion foam generator. Medium expansion nozzles produce 20 to 200 gallons of expanded foam. The end result is far more foam output for the dollar when compared to low expansion foam and fog nozzles. One clip on foam tip will produce low and medium expansion foam. The foam blanket can be a few inches thick or many feet high depending upon need.
Low expansion foam produces 6 to 20 gallons of expanded foam with low expansion foam nozzles. Firefighting fog nozzles make three gallons of expanded foam per gallon of solution. Some of the better automatic fog nozzles can produce up to eight gallons of foam per gallon of solution.
We would all do well to remember that foam aeration is directly related to safety. Burn-back and vapor suppression depends on the amount of air you add; up to a point, the more air you add, the more protection generally offered. The combination of low- and medium-expansion nozzles will provide the greatest flexibility (low-expansion for knockdown and reach, and medium-expansion for vapor suppression and burying the problem).
The main advantage of medium expansion nozzles is that a larger volume of foam is gently applied on the fire. Foams 1,4,5,6 and 8 can be safely and effectively used with low and medium expansion nozzles, and they should be.
Wildland foams are used in wildland firefighting through handlines, dropped from air tankers and sprayed from helicopters using monitor nozzles. This produces a shave- cream-type foam that can be sprayed on vegetation to hold water long term, allowing fire crews to build a line around a fire. It can be sprayed onto houses and other threatened exposures and will resist direct flame contact. Reportedly, it expands the firefighting capability of contract helicopters conducting overhaul on wildland fires by four to five times. Some wildland apparatus uses medium and high expansion foam generators to lay foam lines as fire breaks.
The implications for this foam in structural firefighting are just now being explored by some of America's most progressive departments. Wildland foams allow water tank supplies to go further. They improve knockdown and allow a secure overhaul. The fire should stay down long enough between applications to possibly allow you to run for water. Wildland foams allow your water to stay in place instead of running off.
This type of foam may someday be used on all structural apparatus as a way to reduce water damage and increase fire attack capability, especially in rural areas. This type of foam can be injected into the fire stream using a pump. Compressed air can be injected, producing compressed air foam streams (CAFS) which do not need a nozzle, just a gate valve, to control the line for the ultimate in foam production. Also, wildland foam can be picked up by a venturi eductor with a foam nozzle used to add air. Many departments dump the foam concentrate into the water tank and apply it with a fog nozzle with a clip-on foam tip. That can cause problems with the plumbing. A simple injection system is the best bet.
The second branch of the foam family tree is protein. Proteins were introduced in mid-1930s. They are available in 3 percent and 6 percent concentrates. Protein foams were the first to offer good heat resistance. Hot fuels or hot metal surfaces that destroyed synthetic detergent foams would no longer be a problem. Burn-back resistance is significantly better with protein foam than any detergent foam.
Protein foams will not tolerate fuel mixing any better than detergents, so gentle application is important. Detergent foams offer a quicker knockdown than protein agents. This is because protein foams tend to be stiffer, requiring them to be pushed not sprayed. In other words, they don't flow well.
Protein-based foams can offer a significant advantage over detergent-based foams, however. Under some conditions, detergent foams make certain fuels easier to ignite. For example, a diesel fuel spill might require two to three minutes of direct flame contact to ignite. However, if you spray a detergent foam over the fuel surface and then hold a flame above the fuel surface, it will ignite in as little as five seconds.
This phenomenon occurs because the detergent breaks down the petroleum product, separating the heavier contents from the light ends and, effectively, lowering the flash point of the materials remaining on the surface.
Proteins do not have this effect. Protein foams do require the use of an air aspirating foam nozzle. Detergent foams are most effective when used with a foam nozzle but a fog nozzle can achieve a faster knockdown, but at the expense of safety. (The burn-back time is likely to be much shorter.)
What do the manufacturers of protein foams say about their products? One says, ". . . protein foam is not destroyed by heat. It flows smoothly over the fire's surface to form a protective, cohesive blanket. It acts to extinguish the fire by separating the fire from the fuel, preventing further release of flammable vapors and cooling the area. The foam's water content helps to cool both the fuel and surrounding metal surfaces." Another says protein foam ". . . is a proven, reliable agent for the protection of most hydrocarbon liquid fire risks. Efficient extinction is gained by producing a tough, cohesive, vapor suppressing foam blanket, which has excellent heat stability and burn-back resistance. Of all foam types, well-formulated protein-based foams possess the greatest stability and resistance to hot liquid fuels." Another manufacturer states they have, ". . . good expansion properties and good re-ignition (burn-back) resistance characteristics."
Protein foam is still the only foam that can meet the demanding U.S. Coast Guard shipboard safety requirements. Detergent foam and protein foams were the only choices for flammable liquid fire protection until the mid-1960s and the introduction of fluoroprotein foams and aqueous film forming foam (AFFF). The choice was speed of knockdown with detergents or a safe secure extinguishment with proteins. If you ask the firefighters who have to enter a spill area whether they want speed or safety, you'll probably get one answer: safety.
In 1965, the second branch of the foam family was expanded. Available in 3 percent or 6 percent concentrates, fluoroprotein (FP) foam was the result of efforts to make a better protein foam. Fluoroprotein foam has all the good properties of protein foam, but it flows better across the fuel surface and has much faster knockdown. It is the first foam that can shed fuel. It also allows rough application on the fuel surface. It can even be injected under the fuel surface without fuel pickup.
What do the manufacturers say? One says, ". . . fluoroprotein liquids represent the single most significant improvement in foam technology . . . [Its] improved characteristics include: increased extinguishment ability, increased fluidity, dry chemical compatibility, superior seal-ability and burn-back resistance . . . ." They also report ". . . several advantages over protein foams. Fluoroprotein foams are useful for hydrocarbon vapor suppression and extinguishment of fuel in depth fires . . . ." Another says, "Fluoroprotein foam has become the top choice of the oil and petrochemical industry . . . [It] has the ability to shed hydrocarbons that would cause other types of foam to breakdown."
Fluoroprotein foam was . . . "specifically developed for use . . . against fires in high-risk situations involving bulk storage of hydrocarbon liquids. They were developed primarily to provide optimum foam properties for controlling and extinguishing aircraft crash fires but also [they are] ideal for general use against hydrocarbon spill fires. In refineries, tank farms and wherever low-flash-point fuels, such as gasoline, are stored in bulk, the danger that long pre-burns may build up hot zones in deep fuel layers is ever present. Under such circumstances standard protein foams, however applied, quickly become contaminated with the fuel, burn themselves and are therefore ineffective. In contrast, fluoroprotein is highly tolerant to fuel contamination and controls and extinguishes such fires, forming a secure and lasting blanket.
"Fluoroprotein foam compound is ideal for use against aircraft crash fires, where rapid and lasting control is of prime importance in rescue and life-saving operations," reports one manufacturer. Another manufacturer says fluoroprotein foams provide . . . "control on difficult terrain, clinging to hot metal. [It provides] fast extinguishment, [and also is] effective on gasohol [fires]. Recommended for aircraft crash firefighting and rescue. Fluoroprotein foam has generally the optimum combination of properties for refinery, petrochemical and chemical operations."
Fluoroprotein foam has replaced protein foam in most applications. Still the choice is speed with detergents or safety with fluoroproteins. The main disadvantage of fluoroprotein foams versus detergent foams is that fluoroprotein foam must be used with an air aspirating foam nozzle. Detergents can be used with spray or foam nozzles. The use of a foam nozzle or clip on foam tip greatly improves firefighter safety with all foams with only a slight decrease in the speed of knockdown. You'll almost always spend less money because you'll use less foam concentrate.
Percentage
* Foam concentrate: The raw foam liquid in the foam can used to make foam solution.
* Foam solution: The correct mixture of water and foam concentrate.
* Finished foam: The correct mixture of foam solution expanded with air using a nozzle.
*Expansion ratio: The amount of air added by the nozzle 20:1, 200 to 1, etc.
Foam concentrate percentage is directly related to how much concentrate you need to carry to treat a given amount of water. A 500-gallon water tank would require 30 gallons of 6 percent, 15 gallons of 3 percent, or 5 gallons of 1 percent concentrate. (Note: the larger the percentage, the weaker the concentrate.) A foam educted at two-tenths of 1 percent (0.002) would only require one gallon to treat the tank. The amount of concentrate required is figured by multiplying the water tank capacity by the concentrate percentage. For example, 1,000 gallons x 0.06 percent (6 percent) = 60 gallons. 750 gallons x 0.03 (3 percent) = 22.5 gallons. 2,500 gallons x 0.01 (1 percent) = 25 gallons.
To figure concentrate needs for eductors or foam systems, simply determine the gpm rate and multiply by the percentage of concentrate. A 95-gpm eductor needs 95 gpm x 0.06 (6 percent) = 5.7 gallons of concentrate per minute. Obviously, this is going to be a problem because it takes more than a minute to run to get and open a foam pail. One percent (1 percent) concentrate would be consumed at less than one gallon per minute. So, a five-gallon pail of 1% would last 6 times longer a pail of 6%.
The most common "around-the-pump" foam systems and some self-educting foam nozzles have flows to 750 gpm. That means 750 gpm x 0.06, 0.03 or 0.01 = 45, 22.5, or 7.5 gallons of concentrate per minute. NFPA says you need a 50-minute application rate on a tank fire for a whopping requirement of 50 minutes x 45, 22.5 or 7.5 gallons; or 2,250; 1,125; or 375 gallons of concentrate. One industrial master stream requires 720 gallons of concentrate per minute. (That could cost as much as $14,000 per minute.)
Your choice of concentrate has a direct affect on your ability to pack the needed agent. As a general rule, the engine should carry enough concentrate to treat the entire on-board water supply. If you carry two foam tanks with Class A (structural and wildland) and Class B (flammable liquids) concentrates, the tanks should address the individual concentrate percentages carried.
On a rig with a 750-gallon water tank, you'd need at least 2.25 gallons 0.3 percent Class A(structure or wildand) foam concentrate, and it would be a good idea to carry enough for five to 10 loads of water if you use it all the time. The Class B (flammable liquids) requirement could be from 7.5 gallons to 45 gallons, depending on the concentrate carried. Some departments that have set up for flammable liquid fires like to carry at least two loads of concentrate for sustained operations. ISO wants to see 15 gallons of Class B on the rig and an additional 10 gallons in the station or on the rig. So at least shoot for a 25-gallon Class B foam tank.
The rig with 25 gallons of 1 percent Class B solution is going to fight six times more fire than the unit with 25 gallons of 6 percent. If you carry a dual-rated foam concentrate, such as a 3%/6%, 1%/3%/6%, 0.5%/3%/6% or a 1%/3% the tank should be sized for the highest percentage. So you'll end up with two-or three-load capability on the low end, but only one load on the high end of the percentage. Think ahead. Foam tank selection often lasts 30 years.
AFFF's
Foam is not magic. It can lull you into some very dangerous situations. Your lack of understanding could cost lives, including yours or your crews'. Using foam agents recklessly can lead to some nasty surprises. This is one subject we can all learn more about.
The mid-1960s brought to the fire service a new synthetic detergent foam, AQUEOUS FILM FORMING FOAM (AFFF). This is the fourth member of the foam family. AFFF is available in 1 percent, 3 percent and 6 percent concentrates. One manufacturer produces a 15 percent halon/AFFF.
AFFF reportedly extinguishes fires differently than do protein or fluoroprotein foams. Protein and fluoroprotein foams extinguish by cooling the fuel and hot surfaces, smothering the fire with a cohesive foam blanket, separating the flame from the fuel surface, and suppressing fuel vapors. By contrast, one manufacturer says that three different fire extinguishing mechanisms are employed by AFFF.
"First, an aqueous film is formed, which works to PREVENT the release of hydrocarbon fuel vapors. Second, the layer of foam effectively excludes oxygen from the fuel surface. Third, the liquid content of the foam provides SOME cooling effect. AFFF demonstrates superior extinguishment and burnback characteristics on NORMAL hydrocarbon fuels."
None of the manufacturers explain what a NORMAL hydrocarbon fuel is! One manufacturer gives us a clue by saying the U.S. Naval Weapon Center's AFFF testing concludes that "film formation does not occur on certain hydrocarbon fuels." Has anyone bothered to tell the fire service which hydrocarbon fuels they're talking about? Do we have to wait for the foam to tell us? Another says AFFF is INTENDED for use in air aspirating hardware. It may be used in non-air aspirating hardware "...with SOME DECREASE in certain performance characteristics."
What is "SOME DECREASE" in performance when using a fog nozzle instead of the "INTENDED" foam nozzle? A foam nozzle will provide two to six minutes of burn-back resistance with most AFFF agents. Use a fog nozzle and you'll have only 5 to 7 seconds of burn-back resistance with most nozzles, and as much as 65 seconds with some of the better automatic fog nozzles. The advantage of a fog nozzle is slightly quicker knockdown. The real concern should be firefighter safety!
Remember, without the foam bubble AFFF cannot accomplish two of the three "extinguishment mechanisms" it relies on. It will not exclude oxygen or provide sustained cooling.
If you intend to secure vapors, one manufacturer says, "rapid sweeps of a FOAM NOZZLE over the spill will effectively seal it." The foam bubble is the key to AFFF. Another says, "The foam QUICKLY COLLAPSES to produce a water film barrier that effectively covers flammable liquids and HELPS to control vapor release from volatile liquids. The foams are designed to have a high collapse rate that results in a rapid knockdown of the fire and creates a liquid film barrier that quickly spreads over the surface of the flammable liquid. The film barrier can also be effective in CONTROLLING vapor release from volatile liquids. BUT, since even small breaks in the film can negate ANY containment benefits, it is best to maintain a VISIBLE blanket of foam over the liquid surface at all times. Due to the high collapse rate of the foams, problems may be experienced in sealing against hot metal surfaces and in maintaining an effective barrier to vapor release. Long duration spill situations may require more frequent applications of AFFF foam..."
Another manufacturer recommends Hi-Ex foam for vapor suppression and not relying on AFFF for vapor suppression. Several say, "Unnecessary activity in the spill area should be avoided and repairs to disturbed areas with fresh foam streams should be made as soon as possible."
Should you trust an invisible barrier two ten-thousandths of an inch thick? Some fire fighters say they won't enter a spill until the foam is knee high! That's good advice. Mobil Oil says, "The foam blanket produced should be of such thickness as to be visible before firefighters rely on the aqueous film being vapor suppressant. The film may be present, but because of invisibility it cannot be relied-upon."
Speed or Safety?
The primary advantage of AFFF over Fluoroprotein is a very fast knockdown at low application rates. One producer points out, "Recent comparative tests against AFFF show fluoroprotein foam, when applied at higher rates of application, will extinguish a spill fire IN EQUAL TIME and will provide BETTER burn-back (re-ignition) protection."
Comparative testing supports this. Three-percent (3 percent) fluoroprotein foam costs 23 percent less than 3 percent AFFF to put out the same fire just as fast, but keep it out at least 75 percent longer! Another supplier points out, "For the small fire situations and spills, film forming foams are most effective in terms of agent efficiency. However, when foam application rates are high, all foams can give acceptable extinction times. For larger fires, burn-back resistance and foam stability becomes increasingly important and the protein based foams, including fluoroprotein, have advantages."
Several manufacturers produce a high performance grade of AFFF as well as their "everyday" grade. The better grade AFFF helps to overcome the shortcomings of the low-bid stuff. The foams provide an extra margin of performance and safety. AFFF is the only foam in the foam family with multiple grades. When you go to bid it is a good idea to know what grade you need, and if it does makes a difference. Don't just ask for the cheapest AFFF!
The manufacturers of some AFFFs point out their 6 percent concentrates are faster film formers than their 1 percent or 3 percent versions. A recent FAA status report on current foam fire fighting agents supports this. Recent American Petroleum Institute (API) tests say AFFFs as a whole are "markedly inconsistent" when compared to fluoroprotein and protein foams. The FAA testing points out that 6 percent AFFF's from four major manufacturers will provide 7 percent faster control, 26 percent quicker extinguishment and 14 percent longer burn-back protection than the average 3 percent AFFF. Six percent AFFF will control a fire 3 percent quicker, extinguish 6 percent faster but it's burnback will be 6 percent faster than the average 1 percent AFFF.
When they compared brand against brand, Underwriters Labs (UL), Mil spec., and other approvals did not seem to make any difference. In fact, only six of 18 foams could produce a marginally acceptable spreading barrier. Depending on which brand and percentage of AFFF selected, they noticed a 9 percent to 70 percent difference in control times, 3 percent to 53 percent difference in extinguishment times, and a 23 percent to 51 percent difference in burn-back resistance. It pays to know what you're buying. Another way to read these differences is how much extra foam (money) you'll use to do the same job of a better concentrate. The AFFF with the most listings may not be worth the most money. Other members of the foam family don't have these wide variations in performance.
The greatest advantage of AFFF is said to be its ability to spread very rapidly when compared to protein or fluoroprotein foams. Aqueous film formation is dependent on a fuel surface, especially if you intend to use a fog nozzle. If your fires occur on crowned roadways, the shoulder of the road, railroad sidings, dirt, gravel, sand or grass, be aware of the fast draining nature of AFFF. They will be wicked away by grass, absorbed into the ground or will run off, possibly negating your protection.
This, in conjunction with firefighters breaking the foam blanket while doing their jobs, could result in "ghosted foam." Ghosted foam has visible bubbles that don't provide any protection, or worse yet, the bubbles are saturated with fuel and ready to burn. Nice flat fuel surfaces like we see in a pit fire rarely exist. Most pits and tank fires float the fuel on water. The water absorbs the heat in the fuel-not necessarily something you'll ever find in real life.
It's interesting to note how the foam manufacturers suggest you test your AFFF for film formation. One recommends pouring cyclohexane or cigarette lighter fluid to give a depth of 1/8" into a glass petri dish. "Place dish on black surface and under a lamp if possible so as to aid in observing the film spread. With a ******** dropper CAREFULLY place three drops of premix on fuel surface at center of dish. With aid of reflected light observe the spreading film. After one minute, pass a lighted probe over the surface of the fuel. BE SURE to have a smothering plate handy IN CASE OF IGNITION!"
Current standards allow a FLASH across the fuel surface but not an ignition. How would you like to be caught in a real world flash? Some fire service professionals believe the AFFF standards are written to show AFFF's strengths and not its weaknesses.
Will film formation occur on anything other than cyclohexane or lighter fluid? One way to find out is to substitute gasoline or diesel fuel. Use more than 1/8" of fuel. If the fuel is hot (use an immersion heater) or cold, all of the AFFF may sink to the bottom. Repeat the test by pouring the AFFF on the fuel surface. Notice the word pour. Using an eye-dropper is gentle application, which is rarely possible on the fire ground. Using a drop or two of food coloring in the AFFF premix, it will help you see where the foam ends up.
Another test you can try is to fill a cake pan with diesel fuel. Hold a propane torch with the air holes taped closed to give a visible flame over the fuel surface. Start a stopwatch to see how long it takes to get the fuel to burn. Normally, it should take two to three minutes. Premix AFFF in a spray bottle. In a second pan full of diesel fuel, spray the fuel surface five times with AFFF. Start your stopwatch. In 5 to 30 seconds, depending on the make of AFFF foam you use, you will have ignition. The detergent base of the AFFF spray is changing the ignition characteristics of the diesel fuel. Think about that the next time you apply AFFF on a spill.
If you allow the pans to burn for a few minutes and then put them out with AFFF, and immediately hold a torch over the fuel surface, it will instantly re-ignite.
One final test to demonstrate how quickly your protection drains away is to fill a bottle half-way with premix AFFF and shake it a few times. You'll instantly see the water drain out of the bubbles. It will bring new meaning to the word "drain time."
Chevron Oil points out that, "Mistakes provide valuable lessons for all fire fighters." Let's look at some. A firefighter operating a circular saw in an effort to free occupants of an aircraft that crashed on a golf course in Southern California may have experienced some of the characteristics we've reviewed about AFFF.
Photos and live film footage show firefighters to their knees in AFFF but an ignition still occurred. If there were breaks in the visible blanket, in theory those remaining bubbles would be draining their water to form an aqueous film. This apparently didn't occur, possibly because there wasn't a flat unobstructed liquid fuel surface. Possibly the grass golf course they were working on was wicking away the foam, leaving a ghosted foam in its place.
Or, possibly, as the manufacturer of that foam points out, "With all foams, the foam blanket itself will become saturated with hazardous vapor long before the atmosphere above the blanket has reached the lower explosive limit. This process, in time, renders the foam blanket itself a dangerous source of flammable vapor." At some point all that is needed is an ignition source and all your foam goes up in flames. The sparks from the saw was the ignition source.
It's important to note that earlier we read the manufacturer's warnings about walking through their AFFFs. Four manufacturers recommend foam production using medium expansion nozzles to secure vapors. Simply putting the fire out is only half the job of a good safe foam! Should foam work in the wind and rain? Another points out that one of fluoroprotein foam's main advantages is "control in adverse weather conditions."
Chevron Oil said in a company critique of a well publicized tank farm fire, even though AFFF was successful in extinguishing the fire, "for tank fires fluoroprotein seems to be most effective." During that fire, firefighters standing in a gasoline spill using a fog nozzle set on a wide fog pattern discharging AFFF narrowly escaped serious injury. Their AFFF foam stream broke up the existing foam blanket. Chevron Oil says as a general rule, "if you can't see the foam blanket don't trust it. Don't disturb a foam blanket. Always have a way out. Avoid entering a pool of fuel."
Recent API sponsored research determined that fluoroprotein was superior to any other foam tested, including AFFF, when used to extinguish unleaded gasoline. API says, "AFFF foams were markedly inconsistent. Fire performance was characterized by ease of control and difficulty with final extinguishment." The end result of AFFF was "flicker fires eroded the AFFF foam blanket and flashed around the rim of the tank until the raw fuel became exposed, subsequently leading to sustained burning of the entire tank." Tripling the AFFF concentration did not improve performance.
In API tests AFFFs did not seal against hot tank shell walls as well as fluoroprotein or even protein foams! Once again, the key is gentle application of AFFF with foam nozzles. If gentle application is unrealistic, then fluoroprotein foam is the obvious choice. Mobil Oil says AFFF may be used on storage tank fires provided "that adequate cooling water is applied to the tank shell." Once again the question is speed or safety.
Another recent disastrous tank farm fire points out the hot-fuel high-heat limitations of AFFF. A fire in a diked area of 590 by 295 feet was attacked by a crash truck with AFFF. There was almost immediate burn-back. Fluoroprotein foam was laid down behind it to produce an effective foam blanket and final extinguishment. The product burning was crude oil. Crude oil exhibits the burning characteristics of all products that can be refined from it. Why do we keep making excuses for poor foam performance?
During an aircraft fire in August, 1985, "airport firemen ran out of foam." Using FAA's formula, the aircraft in question required 1,005 gallons of foam water solution to control the fire and 2,010 gallons of foam water solution to extinguish the fire. The airport fire department arrived carrying four to eight times that amount of AFFF. On arrival, airport firefighters were faced with "a burning wing and tail and pools of burning fuel surrounding the aircraft."
What had occurred during an aborted takeoff was the engine exploded, throwing hot metal through the wing fuel tank. The aircraft just happened to come to a stop in front of the airport fire station. "Firemen quickly extinguished the blaze, but while the evacuation was in progress the fire flared again. Foam was directed onto the blaze and also doused several escaping passengers. The fire went out a second time but quickly flared once more. By then the airport fire crew had run out of AFFF and were using hand-held extinguishers in a bid to save the people still in the burning aircraft."
They were dealing with a relatively small airliner, but it is the most produced aircraft of all time. They carried 50 percent more AFFF than required to extinguish the largest airliner. The airport fire crews met the aircraft before it came to a halt. Obviously, this was the ultimate response. "Airport firefighters didn't think anyone would have survived if they hadn't been there so soon." All of this occurred in "less than 120 seconds." The end result was 55 dead. If we don't learn from this experience and others and put what we've learned into practice, how can we avoid repeating them in the future?
What have we learned from these incidents? We have a choice speed or safety. If speed is essential, AFFF and a fog nozzle is the ultimate on some types of fires. One supplier says that in aircraft crash fires, "burn-back resistance is perhaps of secondary importance but should not be ignored, especially for the larger passenger aircraft where rescue of survivors may take some time. The protein-based agents have advantages in this respect, although this will be less evident when spray (fog) nozzles are used since these are not efficient foam makers."
Once again, we are told by the manufacturers to use a foam with the nozzle it was designed to be used with-an air aspirating foam nozzle. Another states, "A spill fire...or an aircraft accident, generally require the use of aspirating foam discharge devices with AFFF agents. The reason for this is that the safety of life is a primary factor, however, burn-back resistance is also a factor, providing time necessary for rescue from the aircraft."
Another warns that conventional AFFFs may be used effectively with properly designed water spray nozzles under some conditions, "although a very unstable foam with relatively poor re-ignition resistance is formed from such devices." Do we want to send firefighters into "a very unstable foam blanket with poor re-ignition resistance?" It sounds like the fire service already has, a couple of times!
According to one large supplier, the U.S. Government (Air Force, Navy, Marines, etc.) use fog nozzles on some crash trucks "based on a conscious decision that the fire will be completely extinguished because of the quantities of AFFF that the vehicles can bring to bear on an aircraft crash." The U.S. government's foam requirement formula is the same as the FAA's. So maybe this "conscious decision" is not one we should emulate.
Two manufacturers wrote their words two to ten years before the 55 people died in the aircraft fire mentioned earlier. If a safe, secure, survivable knockdown is essential, fluoroprotein in conjunction with an air aspirating foam nozzle is the ultimate!
Tests conducted by A.A. Briggs and J.S. Webb of the Fire Research Station in the United ******* concluded, "petrol can reduce effectiveness of some foams." Their testing with "well known brands" showed that "some AFFFs show vulnerability to contamination by petrol, notably where conditions lead to SOME by no means extreme turbulence of application...i.e., they may fail to extinguish petrol fires." AFFF, due to it's detergent base, picks up fuel. As we saw earlier, this is not the case for fluoroprotein foams. In fact, in the petrol tests by Briggs and Webb, AFFF controlled the fires quickly but would not put them out. Fluroprotein would put them out in all cases.
In other cases, control with AFFF was the same or similar to fluoroprotein, but the fluoroprotein would still extinguish the fire much quicker. When compared side by side on trace lead gasoline, it was 41 percent to 88 percent faster than AFFF. Is the key speed of extinguishment AND burn-back protection?
Now that we've taken a look at the three most common generic foam types it's important to ask what makes a good safe foam? One supplier provides a simple summary of the advantages of each type of foam: "PROTEIN; cost-effective, many successful extinguishments, burn-back resistance, water-bearing, seals against hot metal, long-term vapor suppression, non-corrosive, USCG approved, Mil Spec., FLUROPROTEIN; oil resistant, water-bearing, burn-back resistance, seal-ability, long-term vapor suppression, non-corrosive, resists plunging, self-healing, dry chemical compatible, AFFF; quick knockdown, self-healing, aqueous film, Mil Spec., non-aspirating equipment, dry chemical compatible.
A good safe foam should have five characteristics: "1) Flows freely over the flammable surface. 2) Forms a continuous vapor-tight blanket. 3) Resists heat. 4) Resists flammable fuel pickup. 5) Is sufficiently water-bearing to cool and extinguish."
Now that we know what makes a good safe foam, let's grade the three most common foam types. Which types of foam flow freely over the flammable surface? Fluoroprotein and AFFF. Which foams form a continuous vapor-tight blanket? Fluoroprotein and Protein. Which foams resist heat? Fluroprotein and Protein. Which foams resist fuel pickup? Fluoroprotein. Which foams are sufficiently water-bearing to cool (both fuel and metal) and extinguish? Fluoroprotein and Protein. The overall performance characteristics grade for each foam is Protein 60 percent, AFFF 20 percent and Fluoroprotein 100 percent. Until the early 1980s there still were only two choices: speed of detergents or the security of proteins.
Triple FPs
The newest foam type is Film-Forming Fluroprotein Foam (FFFP) introduced in
the early 1980s. The fifth in the foam family, it is available in 3 percent and 6
percent concentrates. FFFP is a protein- or detergent-based foam that has an
Underwriters Laboratory (UL) listing as both an Aqueous Film-Forming Foam
(AFFF) and a fluroprotein. The end result it has the best of the AFFF and
fluroprotein properties.
Protein-based FFFPs don't have the weaknesses of detergent-based AFFFs.
One manufacturer says FFFPs "Provide the knockdown of AFFFs and the
sealability of fluroprotein. It is ideal for use at airports, for spill protection and
municipal fire departments, according to a paper presented to the American
Petroleum Institute by Mobil Corporation's research and development division.
Tests concluded that FFFP foam has substantially faster knockdown than
fluroprotein foam, achieving knockdown almost as quickly as AFFF. FFFP foam
has substantially better vapor suppression than AFFF, with blanket stability
almost as good as fluroprotein foam. The preformance of FFFP on gasohol is
similar to AFFF performance.
FFFP used with a medium-expansion nozzle against low-level controlled-burning
liquid natural gas lasted for 15 minutes, whereas detergent foams lasted three
minutes. FFFPs are the only protein-based foams that can be used with
standard fire department fog nozzles; with AFFFs, safety is compromised. One
supplier says Spray (fog nozzle) application from portable equipment is not
generally recommended as the prime method of attack for major fires where the
security of a stable foam cover is essential. We have to decide if we want speed
or safety.
Making the Decision
Testing at the Fire Research Station demonstrated that FFFP would control
unleaded gasoline just as fast as AFFF; however, AFFF was unable to put the
fire out. FFFP controlled and extinguished fires almost twice as fast as
fluroprotein foam. Leaded gasoline showed similar results: AFFF controlled the
fires in 29 seconds; fluroprotein in 33 seconds; and FFFP in 34 seconds.
Extinguishment times were as follows: AFFF 231 seconds, fluroprotein 164
seconds and FFFP 75 seconds. If speed of complete extinguishment is
important, FFFP is three times faster, and therefore safer, than AFFF. An FFFP
can be subsurface injected at 1 percent even though it is a 3 percent
concentrate; that's the lowest UL application rate. It also is listed at the lowest
rate for hydrocarbon spill fires, as is AFFF.
If absolute speed is a priority, AFFFs are faster at control, but not necessarily at
extinguishment. Where absolute safety is concerned, fluroprotein is the best
choice. If you need both, FFFP is the only choice short of carrying two foams.
Understanding the Technology
With all the talk about the new film technology and so many departments using
FFFP and AFFF to the exclusion of all other foam types, it is important that we
understand the concept. Top-side application on petroleum tank fires and crash
fire rescue applications are different than spill fires where the firefighter is on the
line. Flammable liquid fires should be engineered out, not fought out. However,
with an engine company, you don't have time to engineer the fire out; you must
fight the fire out or wait.
AFFFs and FFFPs do not rely on the foam bubble for knockdown like all other
foams. That is why there is an emphasis on fog nozzles. The sooner the foam
bubbles drain into an aqueous solution, the faster the fuel surface will be
covered. If there isn't a dike or tank wall to keep the foam on top of the fuel, the
foam will run off or sink. Instant reapplication and foam blanket repair is
essential. That is where the foam bubble should come in.
If you insist on subscribing to the concept of non-aspirated foam, then
immediately after knockdown, cover the spill using a medium-expansion nozzle.
In some cases, the application of aqueous foams through fog nozzles may not
secure the fire long enough to lay a safe blanket before a reflash occurs.
Aviation fuels flash in excess of 12 feet per second. Firefighter survival should
not be dependent on an invisible barrier.
If speed is that important, the fog-nozzle aqueous foam lobby has missed the
point. Speed without safety is reckless and irresponsible. If you truly subscribe
to speed above all else, buy the whole concept. The original idea was to use
aqueous foams with simultaneous application of a dry chemical (twin agent)
through the same turret or handline. Testing has shown the best dry chemical
can achieve knockdown as much as 20 times faster than AFFF. There is no
question that twin agents provide the absolute fastest knockdown possible. They
are significantly faster than either agent alone.
The simultaneous application of a dry chemical gives us a three-dimensional fire
attack capability that current foams do not have. The fire service's failure to
employ the three-dimensional agents in conjunction with foam in aircraft spill
fires and those in bulk storage tanks have already resulted in scores of close
calls, deaths and injuries.
Some professionals suggest a two-foam, same-nozzle approach: FFFP or AFFF
fog-nozzle knockdown followed by immediate application of fluroprotein foam
through a foam nozzle, which is more effective than reliance on film formation
alone. Those against it say it isn't convenient and fire trucks don't come
equipped for its use. Now almost every new engine is delivered with two foam
tanks one for Class A and another for Class B agents. It is not all that difficult to
have two Class B tanks. Others want the best of all worlds: They recommend
twin-agent attack with fog-nozzle AFFF or FFFP and immediately burying the
problem with a medium-expansion nozzle.
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