Survival Tip 7- Class B Foam: Dilution Ratios and Applications Rates
By Steven De Lisi
There are several types of Class B foam concentrates available for use by first responders. These include concentrates referred to as protein, fluoroprotein, and aqueous film forming foam (AFFF).
Protein and fluoroprotein foams generally produce relatively thick foam blankets while AFFF foams often produce a thinner, more fluid blanket. This characteristic of AFFF usually allows for a quick knockdown of a fire as the foam spreads more rapidly across the burning fuel surface, yet this same feature may not be as effective in preventing re-ignition as are the thicker protein and fluoroprotein foams.
While most foam concentrates are intended for use on “nonpolar solvents” that will not mix with water, such as hydrocarbon fuels including gasoline, diesel fuel, and jet fuels, some are intended for use on “polar solvents,” or flammable liquids such as alcohols that will mix with water. First responders should be aware that the 2004 Emergency Response Guidebook (ERG2004) refers to foam for polar solvents as “alcohol resistant” foam and foam for nonpolar solvents (such as hydrocarbon fuels) as “regular foam.”
All foam concentrates are intended to be diluted, or proportioned, at varying percentages with water as determined by their manufacturer. Dilution ratios of 1%, 3%, and 6% are found most often. Once a foam concentrate is mixed with the appropriate amount of water, the result is usually referred to as a foam solution.
For example, 3% foam means that every 100 gallons of foam solution will require 3 gallons of foam concentrate diluted with 97 gallons of water. Using the ratio of 3%, 15 gallons of foam concentrate diluted with 485 gallons of water will produce 500 gallons of foam solution.
A foam concentrate with a dilution ratio of 1% means that 1 gallon of concentrate is diluted with 99 gallons of water. Using this lower ratio, only 5 gallons of foam concentrate would be diluted with 495 gallons of water in order to produce 500 gallons of foam solution. Some AFFF foams are referred to as 3% / 6% meaning that the foam can be used at either dilution ratio, depending upon the type of application.
For example, a manufacturer of foam concentrates may recommend a dilution ratio of 3% for fires involving nonpolar solvents and a higher dilution ratio of 6% for use with polar solvents.
The minimum application rate determines the rate at which a foam solution is applied to the surface of a flammable liquid spill, usually measured in gallons per minute per square foot of spill surface. These rates provide first responders with information regarding not only how much foam concentrate and water is needed to control and extinguish a fire, but also the minimum nozzle flow rate required when applying the foam solution.
Rates discussed here apply only to spill fires involving flammable liquids, defined as a spill that is not contained in a dike with an average depth that does not exceed 1″, and that is bound only by the contour of the surface on which it is lying. As stated earlier, the dilution ratio of foam is determined by the manufacturer of the foam concentrate used while minimum application rates are available from the National Fire Protection Association (NFPA) Standard 11, entitled Low, Medium, and High-Expansion Foam, and are dependent upon the type of foam concentrate used.
For example, when using AFFF foam for non-diked spill fires, the recommended minimum application rate is .1 GPM per square foot of spill surface. Other types of foam, such as protein and fluoroprotein, require higher minimum application rates of .16 GPM per square foot of spill surface.
With knowledge of minimum application rates, how much foam concentrate and water would be needed for certain size spill fire? Furthermore, what would be the largest spill fire that first responders could likely extinguish with the foam concentrate and water carried on their apparatus?
As an example, when using AFFF foam, remember that the minimum application rate is .1 GPM per square foot of spill surface, so that a 600 square foot spill fire would then require the application of 60 gallons of AFFF foam solution (600 multiplied by .1) for every minute of application. But how many minutes of application are required?
According to NFPA 11, first responders attempting to extinguish a spill fire should be prepared for a minimum discharge time of 15 minutes. Therefore, this same scenario would now require a minimum application rate of 60 GPM for 15 minutes, or a total application of 900 gallons of AFFF foam solution. First responders could easily meet the minimum recommended application requirements from NFPA 11 using apparatus with a 1,000 gallon water tank.
However, because foam solution is a product of water and foam concentrate, the question then becomes, “How much concentrate is needed?” That answer depends upon the dilution ratio of the concentrate used.
If using a 3% foam concentrate, remember that every 100 gallons of foam solution will require 3 gallons of foam concentrate diluted with 97 gallons of water. With the above scenario that requires 900 gallons of foam solution for 15 minutes of application, first responders would then need 873 gallons of water (97 x 9, or 97 gallons of water for every 100 gallons of foam solution) and 27 gallons of foam concentrate (3 x 9, or 3 gallons of concentrate for every 100 gallons of foam solution). Table 1 provides a summary of these calculations.
Table 1
Requirement for 3% AFFF Foam Concentrate and Water
to Extinguish a 600 Square Foot Spill Fire
1. .1 GPM / sq ft x 600 sq ft = 60 GPM of foam solution (application rate)
2. 60 GPM x 15 minutes (*) = 900 gallons of foam solution (total amount of foam solution)
3. 900 gallons of foam solution x .03 (3% concentrate) = 27 gallons of foam concentrate
4. 900 gallons of foam solution x .97 (97% water) = 873 gallons of water
(*) Minimum discharge time required by NFPA 11 (2005 edition)
First responders should know that any attempt to extinguish a flammable liquid spill fire that exceeds their capabilities (either in terms of water, foam concentrate, or application rate) could result in them being unable to gain control of the fire. Survival Tip 8 will provide guidance for preplanning foam fire suppression capabilities in order to avoid this problem. When determining the appropriate dilution ratios and application rates for Class B foams, be smart, be safe, and remember, everyone goes home!
Discussion Points
1. Determine the type(s) of foam concentrate used by your department.
2. Determine the dilution ratio(s) and minimum application rate(s) for each type.
3. Contact a representative from your department who is a member of your community’s Local Emergency Planning Committee (LEPC). Request to know if there are any locations in your community that use, store, or manufacture “polar solvents,” and if so, the quantities involved. Are these commodities also known to be transported through your community on highway or rail? Does your department have “alcohol resistant” foam concentrates available?
National Fire Protection Association, Standard 11, Low, Medium, and High-Expansion Foam (2005),
Section, A.5.8.
Ibid., Table 5.8.2.2.
Ibid.
Ibid.
For information on Steven DeLisi’s book Hazardous Materials Incidents: Surviving the Initial Response
go to: store.pennwellbooks.com/hamainsuinre.html
Steven M. De Lisi is a 26-year veteran of the fire service and is currently Deputy Chief for the Virginia Air National Guard Fire Rescue located at the Richmond International Airport. De Lisi is a Hazardous Materials Specialist and chairman of the Virginia Fire Chiefs Association’s Hazardous Materials Committee. He is also an adjunct instructor for the Virginia Department of Fire Programs and a former member of the NFPA committee on hazardous materials protective clothing. De Lisi began his career in hazardous materials response in 1982 as a member of the HAZMAT team with the Newport News (VA) Fire Department. Since then, he has also served as a Hazardous Materials Officer for the Virginia Department of Emergency Management and in that capacity provided on-scene assistance to first responders involved with hazardous materials incidents in an area that included more than 20 local jurisdictions
