What will your main challenges be using SFFF firefighting foams?

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Date August 03, 2022
Date August 03, 2022
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The first issue is that SFFF chemical formulations can vary widely by manufacturer. Each manufacturer’s SFFF agent formulation may be significantly different from other producers, even proprietary.

Think about that for a minute — when looking at legacy AFFFs, there were differences in various manufacturer’s formulations — but most of the features and benefits were about the same. Essentially, they could be considered as a “class” of agents, with minor variations amongst themselves.

When in the market to buy 50 gallons of AFFF, you could receive bids from several different reputable manufacturers, decide on one, and have a level of certainty that the product would be at least somewhat comparable and close in fire suppression performance to the other producers’ products.

When discussing new SFFF agents, this is not necessarily so. At least for the immediate future, most F3 formulations, by each manufacturer, are likely to have significant chemical differences and may provide different firefighting results.  

Proportioning Differences

Beware, when changing to new F3 foam agents, they may not be a “drop in” replacement for AFFF.

That means that if we safely drained, flushed, and disposed of existing AFFF concentrate stock onboard a fire apparatus, we may not be able to simply refill the foam concentrate reservoir with SFFF agent, and have effective proportioning. The viscosity and chemical properties of the SFFF foam concentrate may (or may not) be compatible with the foam proportioning device. There have been scattered reports of firefighters having trouble using existing eductors to dispense F3 agents. 

Application Rate Changes

Note that foam solution application rates may need to increase when transitioning from legacy AFFF to new SFFFs.  “Application rate” is expressed in terms of gpm of foam solution per square feet of flammable liquid fuel surface.  Here is an example:  when combating a burning Type III Gasoline Blend (15% Ethanol) spill fire, the application rate required from a major foam agent manufacture is as follows:

Using their legacy AR-AFFF: a 0.15 gpm/sq. ft. application rate is required. 

Using their new SFFF: a 0.22 gpm/sq. ft. application rate is required.

That’s a 47% increase in application rate required.

So, if looking at using a 95-gpm in-line Eductor with their legacy AFFF, the 0.15 gpm/sq. ft will yield capability to extinguish a 633 sq. ft. fuel surface or a 25’ x 25’ fuel surface area.

Since new their new SFFF requires a 47% increase in application rate, to come close to matching the above 25’ x 25’ hazard capability, a higher gpm eductor needs to be deployed.

Using a 125-gpm eductor with SFFF at 0.22 gpm/sq. ft., it will yield capability to extinguish a 568 sq. ft. fuel surface or a 24’ x 24’ fuel surface area.

As the example demonstrates, moving away from a 95-gpm eductor and using a 125-gpm with SFFF is essential to come close to having the same fire suppression capability with this SFFF agent. 

Differences in Finished Foam Application

We previously discussed that SFFF foam applications are considered somewhat of a downgrade from the use of legacy AFFF. Why is that so?

The benefits of AFFF application on burning flammable liquids are many — it is more than just a one-trick pony. Features of AFFF include an invisible aqueous film that speeds ahead of the finished-foam blanket, acting to knock down flames and spread the foam blanket across surfaces and around objects. Several other mechanisms are also at work, including the foam blanket acting as a physical barrier to slow or stop vapor release from the flammable liquid surface.   

With SFFF foam agents, there are far fewer elements or features of fire suppression at work. The primary method is the foam blanket providing a barrier between the fuel and atmosphere. All important is the finished-foam quality generated by the nozzle, which directly affects SFFF agent performance.

What is the ideal finished foam quality for firefighting?