BY DAVID F. PETERSON, CHMM
Fine craftsmen produce their products with great precision and quality as a result of their training, experience, and skill with their tools. Consequently, they use and maintain their tools and equipment with the highest degree of care. Much of the same could be said of members of the fire service. Most of us recognize the importance of maintaining our tools and equipment in response-ready condition, but we must also understand when and how to use our tools effectively.
CLASS B FOAM
One tool that seems to be commonly neglected in the fire service is Class B foam.
There are many reasons for this neglect. One is that many responders do not understand Class B, low-expansion foam technology and how it works. It can be confusing and confounding, especially if proper and frequent training is not provided. This is quite often the case. Since foam concentrate is expensive (more than $25 per gallon), many departments do not train frequently enough to maintain responder competency. Additionally, abundant field experience with Class B foam is rare, as flammable liquid releases do not occur often on the home front. As a result, an apathetic attitude may develop. This is dangerous because emergency responders will lack the ability to use this tool safely and effectively when it is needed.
This apathy can also extend to improper maintenance of foam equipment. To ensure that they will operate properly when needed, you must flush thoroughly and inspect portable foam eductors, foam nozzles, and nozzle attachments after use and check for leaks. Check foam concentrate in pails often for signs of degradation. Check onboard apparatus foam systems in the same manner.
Additionally, regularly exercise the ap-paratus foam system to ensure proper performance on the next flammable liquid emergency. Again, thoroughly flush all onboard foam components after using Class B foam.
Finally, replace foam after the manufacturer’s suggested shelf life has expired or the foam has degraded significantly. Signs of degradation include changes in color and viscosity or consistency, which result from exposure to air, ultraviolet light, temperature extremes, and even repeated agitation.
Another reason Class B foam is often overlooked as a tool is that firefighters find the foam concentrate formulas difficult to comprehend and remember. One author even described the use of Class B foam as the fire service’s “Voodoo Science” because of the way many firefighters view Class B foam technology. In reality, applying Class B foam is relatively easy, and you can easily calculate the quantity of foam concentrate you need.
Many quality articles have been written concerning how Class B foam works and when to use it. My intent is not to reiterate what has been written but to offer some suggestions that will make responders more willing to use Class B foam as a suppression tool. Since flammable liquid releases occur with some regularity across the country, it would behoove responders to become competent and confident in the proper use of Class B foam.
CALCULATING FOAM CONCENTRATE NEEDS
Outside of the equipment used in producing finished foam and the proper techniques for applying it, the most perplexing issue for firefighters is calculating the quantity of foam concentrate needed at a spill. The formulas for calculating the quantity of foam concentrate needed are complex, and firefighters may not be able to recall them during an emergency.
Simplified Foam Formula
The following simplified formulas can help you calculate the quantity of foam concentrate needed at any flammable liquid emergency quickly and accurately:
- Area/20 for pure hydrocarbon spills.
- Area/5 for polar solvent spills.
Comprehensive Foam Formula (Complex)
To understand the simple formula, you should have some knowledge of the components of the complete and comprehensive formula and the science behind the formula. The complex formula for calculating the needed foam concentrate at a flammable liquid release is as follows:
Area (of spill) X Critical Application Rate (CAR) X Eduction Rate (ER) X Duration = Foam Concentrate Needed.
Area. This is the amount of space the spill occupies, usually in square feet. Area can be calculated by multiplying the spill’s length by the width. If the spill is in a circle, estimate the length and width to establish a ballpark figure. (To be precise, and this is not a precise science, the area of a circle is 3.14 multiplied by the radius of the spill squared or 3.14r2. Still another method for determining the area of a circle is to multiply 0.8 by the diameter of the spill squared or 0.8d2.)
Critical application rate (CAR). This is the minimum flow of finished foam per square foot needed to extinguish a flammable liquid fire. Underwriters Laboratories (UL) established the CARs for different fuels through extensive testing; they can be found in National Fire Protection Association (NFPA) and foam manufacturer literature. The CAR for hydrocarbon fuels has been calculated to be 0.1 gallons per minute per square foot of the spill area (0.1 gpm/ft2). The CAR for polar liquids, like alcohols, has been calculated to be 0.2 gpm/ft2. Be sure to consult the literature of the manufacturer of the foam you are using for the appropriate application rate. Be aware that alcohol-type concentrate foam may be required for incidents involving hydrocarbons that have been blended with polar solvents such as alcohols and other oxygenated fuels.
Eduction rate (ER). Class B foam concentrate must be mixed with a percentage of water that will produce enough solution to cover the spill or extinguish the flammable liquid fire. For many types of foam, the eduction rate for hydrocarbons is 3 percent (.03) and 6 percent for polar liquids (.06). This means that for every 100 gallons that flow through the nozzle, there will be three gallons of foam and 97 gallons of water and six gallons of foam and 94 gallons of water, respectively. Some Class B foams use 3 percent eduction rates for both hydrocarbons and polar solvents, which simplifies the formula. There is even new foam on the market that is educted at 0.4 percent for both Class A and Class B fuels (how is that for simplicity?).
Duration of application. This is a safety concern addressed in NFPA 11, Standard for Low Expansion Foam, which states that the foam concentrate should be applied at the critical application rate for a minimum of 15 minutes. This safety factor will also encompass weather conditions such as high winds and high temperatures that can affect foam application. The safety factor ensures enough foam to adequately cover the spill or extinguish the fire despite these weather conditions.
“X” factor. This component is not part of the formula, since some fire departments may use nonaspirating nozzles with no aeration capability. It is the aeration expansion ratio produced by the nozzle. If you know the expansion ratio of your nozzle or nozzle attachment, you can add this factor to the formula. For example, some nozzles will aerate, or expand, the foam solution at the nozzle by a factor of 4 (4:1). By adding a nozzle attachment for foam operations, the expansion ratio will be 8:1. This simply means that air has been added to the foam solution to expand it to eight times the original volume. Aerating nozzles and attachments greatly extend your foam supply by covering more of the spill with “finished foam” or aerated foam solution. Most nonaspirating (fog or combination) nozzles produce expansion ratios of between 3:1 and 5:1. Contact the manufacturer of your nozzles for specific expansion ratios.
EXAMPLES UTILIZING FOAM FORMULAS
To reinforce the use of the simplified formulas, review the following examples.
Q. How much foam concentrate is needed to cover a 40-ft 2 40-ft spill of gasoline?
The full formula is Area X CAR X ER X Duration = Foam concentrate needed.
Area = 1,600 sq ft, CAR = 0.1 gpm/ft2, ER = 0.03, Duration = 15 minutes.
1,600 sq ft X 0.1 gpm/ft2 X 0.03 X 15 minutes = 72 gallons of foam concentrate.
The simplified formula is Area/20.
1,600 sq ft
Q. How much foam concentrate is needed to extinguish an alcohol fire that is 20 feet 2 30 feet?
The full formula is Area X CAR X ER X Duration = Foam concentrate needed.
1. Area = 600 square feet.
2. CAR = 0.2 gpm/ft2.
3. ER = 0.06.
4. Duration = 15 minutes.
600 square feet X 0.2 gpm/ft2 X 0.06 X 15 minutes = 108 gallons of foam concentrate.
The simplified formula is Area/5.
1. 600 square feet
Remember, in the above examples the “X” factor was not part of the formula. With a nozzle attachment that has an expansion ratio of 8, your foam supplies will go eight times further, or in the above examples, the required foam concentrate would be 8 times less than what was calculated.
One last concept to realize with foam operations is your limitationsin other words, how big of a flammable liquid spill will your available foam concentrate reserves cover? This spill area can be calculated before an incident by using the following formulas.
For hydrocarbons:
Area = foam concentrate reserve X aeration factor of your nozzle
For polar liquids:
Area = gallons of foam X 8/0.18.
Q. If you have 20 gallons of foam concentrate on your response vehicle and you have a gasoline spill, how big of an area can you blanket with foam?
1. Area = 20 gallons X 8/0.045.
2. Area = 3,555.56 square feet or 59.6 feet X 59.6 feet.
You are limited to an area of approximately 60 feet by 60 feet for hydrocarbon spills.
Q. If you have an ethanol spill and 20 gallons of foam concentrate on your vehicle, what are your limitations in terms of the area you can cover?
Area = 20 gallons X 8/0.18.
Area = 888.89 square feet or 29.8 feet X 29.8 feet.
You are limited to an area of approximately 30 feet by 30 feet for polar liquid spills.
RESPONSE CONSIDERATIONS
When responding to flammable liquid emergencies, be sure to do the following:
- Respond from upwind and uphill.
- Set up hot, warm, cold, and isolation perimeter zones as appropriate.
- Evacuate as necessary.
- Stay out of the product.
- Use full protective clothing.
- Identify the product, and consult the Department of Transportation Emergency Response Guidebook.
- Strive to confine the product to as small an area as possible.
- Determine your actions. If you decide to apply foam, do you have enough to adequately cover the spill? Do you have the type of foam required for the spilled material? If there is fire, is extinguishment the best tactic?
- Consider using air monitors to determine the affected area and the effectiveness of the foam application.
- Reapply foam at safe intervals based on monitoring results and weather conditions.
- If there is no fire, consider removing ignition sources.
- If there is fire, protect exposures.
Knowing your limitations is important because you would be wasting time, effort, and foam if you initiated foam operations on a spill that is larger than one you would be able to cover alone. If the entire area is not covered, the fire may burn back and consume the foam you applied. It would be prudent to wait until more foam arrives before you begin foam operations.
To stay adept at foam operations, you must practice calculating foam concentrate needs and using your foam-producing equipment. Instead of neglecting Class B foam, embrace it as an effective flammable liquid handling tool. Use it with precision and skill in the finest fire service tradition.
References
1. “Handling Flammable/Combustible Liquid Carriers,” Gene Carlson, Fire Engineering, Dec 1995.
2. “Burning Gasoline Tankers: The Best Action May Be No Action.” Peter M. Stuebe, Fire Engineering, Nov 1997.
3. “Responding to Gasoline Releases.” David F. Peterson, Fire Engineering, Apr 2001.
DAVID F. PETERSON, CHMM, a 21-year veteran of the fire service, is a lieutenant with the Madison (WI) Fire Department. Previously, he was a training coordinator for the Regional Level A Haz Mat Response Team. He is the owner of Americhem Safety & Environmental, LLC, a haz-mat training and consulting firm in Janesville, Wisconsin. He is also an IAFF Master Trainer, an adjunct instructor for the National Fire Academy and the Emergency Management Institute, and an FDIC presenter. He is a member of the NFPA Classification and Properties of Hazardous Chemical Data Committee and the founder and past president of the Wisconsin Association of Hazardous Materials Responders, Inc.
