You have to take it for granted that fluorinated foam concentrates will not remain on the market for long. Environmental considerations doom their use, and they will have to be replaced by fluorine-free foam concentrates (FFF).
For more than 60 years a culture of firefighting has been built based on Newtonian AFFF and later with the pseudoplastics AFFF/AR. With fluorinated surfactants specially designed for aqueous film forming and the resistance against the polar solvents, the extinguishing of liquid fuels was almost resolved, and application rate tables were created classifying fuels by their flash point and water solubility.
The ban of fluorinated surfactants leaves the deck without a joker. We will have to renounce the formation of an aqueous film, rapid extinguishing by spray, thermal resistance and oleophobicity. The fluorine-carbon bond is so strong that it is ideal for fighting fire, but it is very difficult to break. But they are the rules of the game and you have to accept them.
Since, for the moment, it is not possible to put out fires of polar solvents with Newtonian fluorine-free concentrates, we can summarize our problem in two variants: Newtonian FFF to substitute the AFFF (hydrocarbon fires) and pseudoplastic FFF to substitute the AFFF/AR (hydrocarbon and polar solvent fires).
Water immiscible fuels
Fighting hydrocarbon fires with AFFF was relatively easy regardless of the type of water used and the class of fuel to be extinguished. Thus, an AFFF could extinguish heptane, gasoline, JetA1, diesel, hexane, crude oil, etc. fires using fresh or sea water.
When using Newtonian FFF foams, we must consider that seawater reduces the fire performance of the foam produced by fresh water. But much more drastic is the type of fuel. It can happen that a foam with an excellent result in heptane and fresh water does not manage to control the fire of gasoline and sea water – as is the typical application of MilSpec. This Standard also demands to test the foam concentrate at half and several times the nominal mixing ratio, which respectively translates in the case of fluorine-free foam concentrates in slow control, longer extinguishing times and huge contamination due to the big quantity of hydrocarbon surfactants in the foam.
Another big problem is the extinguishing of JetA1 aviation fuel. Good results can be achieved according to the ICAO standard as level B and even C with very poor fire performances in heptane or gasoline fires.
With respect to the IMO standard, although extinguishing is not difficult by gentle application, the burnback resistance of 15 minutes is hard to get in Newtonian low-viscosity products. A similar problem appears in LASTFIRE applications: maybe it is easy to extinguish but the foam has to stay over the fuel for a long time.
In the sprinkler applications of FM 5130 and UL 162, special attention must be paid to the quality of the produced foam since you have to renounce the aqueous film formation over the fuel.
Anyway, progress is still being made to solve all these problems with even better formulations trying to avoid the use of pseudoplastic high-viscosity foam concentrates when the fire to extinguish is based in hydrocarbons.
Water miscible fuels
With these fuels there is no way to get out of the polymers which confer a pseudoplastic rheology and a considerable viscosity.
The complexity is great trying to extinguish this kind of fire because fuels apparently quite similar can behave totally differently in their interaction with the foam produced by fluorine-free foam concentrates. A very typical example is the case of acetone and methyl ethyl ketone. Some ‘good’ FFF products have excellent results in Acetone and even IPA fires, but MEK literally destroys the foam. N-butanol seems to have the same behaviour.
In AFFF/AR it is easier to extinguish IPA fires than Acetone fires, while in FFFs it is the opposite case.
Some firefighting foam manufacturers consider putting in the formulation a lot of polymers (total or semi-hydrated) and so, the resulting foam has a very long drain time (more than one hour). But, to have a lot of water in the foam does not mean lower contamination or better sealing of the vapour coming from the fuel. To get a stable gel coat depends on both formulation and fuel.
It is not advisable to use salts to inhibit the increase in viscosity in the concentrate because they can create considerable corrosivity problems.
We need to carefully study each type of fuel to be sure that we will extinguish the fire by extrapolating the results of the small-scale fire tests. In the pseudoplastic FFF concentrates we must take into account the interaction between the polymer and the surfactants to get the best results.
As we can see, the problem is quite complex and requires a lot of effort – not being reduced to a long series of fire tests and letting statistics take care of providing us a satisfactory solution.
Getting a homogeneous solution of the concentrate in water is easy with the Newtonian FFFs due to their low viscosity, but it can be problematic with the pseudoplastics, some of which require a long stirring time to be ready to extinguish the fire satisfactorily.
Special attention must be paid to the temperature range of the usability of the concentrate.
It is possible that we have to change the application rate of some concentrates for special fuel fires. This seems to have an easy solution: increasing the number of nozzles, monitors, foam chambers or sprinklers.
When you can’t change the application rate you can increase the mixing ratio percentage, i.e. from 3% to 6%. This is also easy.
What we consider risky is trying to maintain the application rate and concentration by using a foam concentrate with problems of gelling, corrosivity, stability, etc.
The absence of fluorine makes the compatibility between two concentrates even more delicate. The interaction between ingredients causes the mix of concentrates to have a very different fire performance in the Newtonian FFFs.
With the pseudoplastic ones the danger is even bigger. Here we find the interaction between surfactants and the polymers. So, the mix of two normal-viscosity FFF pseudoplastic concentrates can achieve a huge viscosity, much bigger than the more viscous of them.
Another question is the compatibility of the foam produced with the chemical extinguisher powder – a simple question in AFFF but not always easy in FFF foams.
Since some of the current standards are designed for fluorinated foam concentrates and we have to move to fluorine-free products, we have only two possibilities: make new standards or edit the previous ones with some reductions in the requirements of the fire performances. We recall the controversy that arose when ICAO changed the extinguishing time from 1 minute to 2 minutes or when the I+A class was established for products that extinguished a heptane fire in less than 90 seconds in the EN-1568-3 standard.
Whatever the final decision is, the demands should be great to ensure proper fire protection. A general pass is always detrimental to the quality of teaching.
After carrying out research on fire extinguishing for more than 40 years, I can assure you that there are no products that are suitable for all applications. Some fires, such as those caused by lithium-ion batteries, are still far from a fast and effective extinguishing method.
If someone tells us that we can substitute fluorinated foam concentrates for non-fluorinated ones with the same effectiveness, they should pass the truth machine test.
As part of its work, VsFocum periodically makes a sweep of the fluorine-free products in the market, and we can assure that all of those analysed have many flaws.
The VsFocum answer
All the research by VsFocum on FFF foam concentrates is based on three criteria in this order: usability, fire performance and environmental respect.
Our catalogue of Silvara products can be divided as follows:
- Newtonians: 0.3% (CORE), 0.5% (ZFK), 1% (I), 3% (III) and 6% (VI)
- Newtonians for Aviation: 1% (K1), 3% (K3), 6% (K6)
- Pseudoplastics: 1×3% (APC1), 3×3% (APC, APC+, AR)
It should be noted that VsFocum was the first company to certify the first 1%, 0.5% and 0.3% Newtonians, the first one for ICAO-B 3% Newtonian and 1×3% pseudoplastic FFF/AR.
Seconds out! The time has come. We must take advantage of the legacy of the AFFF using the devices to produce the extinguishing foam. We must be very careful with foam concentrates that produce aqueous solutions more viscous than the concentrate itself.
It is necessary to know the viscosity-temperature curve to be able to ensure that the dosage is correct. We should know if the foam concentrate to be used is valid for each fuel to be protected. We should continue investigating the synthesis of new fluorine-free surfactants that provide fluidity, oleophobicity and resistance to the polar solvents.
This has only just begun. Much work remains to be done.
LUCK, SIGHT AND FIRE!
For more information, go to www.vsfocum.com