Foam puts out burning fuel — at oil depots, at airports, at chemical plants. There are three kinds in use, and the difference between them is not marketing but physics. Physics decides what a foam can and cannot do.

1. Three kinds of foam, and what each one really is

Fluorinated chemical foam (aqueous film-forming foam, AFFF). It works through an ultra-thin water film that spreads by itself across the fuel surface and seals it. Only fluorine produces that film. On a fuel spill this is the fastest foam there is — here the advertising barely exaggerates.

Fluorine-free chemical foam (synthetic fluorine-free foam, SFFF, or simply F3). It forms no film at all. It puts out fire only through a thick blanket of foam that has to be kept topped up, or the fuel opens again and reignites. The manufacturer admits this itself — in the fine print of the brochure.

Fluorine-free biological foam (protein foam). Also filmless. It suppresses through a dense, heat-resistant blanket. It is made from natural protein, it breaks down in nature, and it does not accumulate in living organisms. It spreads more slowly, but against the hot wall of a tank its structure does not collapse — it holds the barrier.

The whole industry is built around one property — the water film. And that is the first trap: on a large tank fire the film matters far less than a dense, durable blanket. Yet the standards reward the film.

2. Why fluorine was banned

The active ingredient of fluorinated foam is per- and polyfluoroalkyl substances (PFAS). They are called «forever chemicals»: they do not break down in nature and they accumulate in drinking water and in living organisms. They are linked to cancers and hormonal disease.

After the industry switched en masse to fluorine chemistry, cancer cases and deaths rose around the sites where it was used — among firefighters, among the population, among animals and fish. Regulators responded, though very late. In the European Union a regulation amending Annex XVII of REACH imposes a full ban on placing such foam on the market and using it, with a fixed transition deadline. In the United States the Department of Defense is withdrawing fluorinated foam from its sites; the military specification has been rewritten to cover fluorine-free foam instead, and the national environmental authority (Environmental Protection Agency, EPA) has set a drinking-water limit measured in nanograms per litre.

It matters what fluorine was banned for. Not for poisoning here and now, but for persistence and accumulation: its single-dose toxicity is low, but the damage builds up over years and is almost impossible to remove. Keep that axis in mind — «persistence.» It is the axis the regulator acts on.

3. The central misconception: the «green replacement»

This is where the gap between advertising and reality is widest on every axis. Fluorine-free chemical foam is sold as an equal and environmentally safe replacement for fluorinated foam. Take the three promises in turn.

Promise one: «puts out fire as well as fluorinated foam»

Independent fire trials say the opposite. The reason is that certification is run on heptane — a model fuel on which the difference is smallest. On real fuel the gap becomes enormous.

So «no worse» turns into «several times more foam needed» — the moment real gasoline is under the foam instead of laboratory heptane. And even on heptane itself — the fuel where the gap is smallest — the behaviour of fluorine-free foam looks frankly poor.

See the heptane test on video: youtu.be/WMb7aMAOMT4

Promise two: «a drop-in replacement, nothing to rebuild»

Refuted by the U.S. Government Accountability Office (GAO). Fluorine-free foam is a liquid with a different viscosity; it is incompatible with part of the proportioning equipment and cannot be stored pre-mixed. It is not «fluorinated foam without the fluorine» but a fundamentally different foam. For the U.S. military alone the transition was costed at more than 2.1 billion dollars.

Promise three: «environmentally safe»

This is the central promise, and peer-reviewed science refutes it — science funded by the very defence programme that mandated the switch to this foam.

What the studies established:

— Jones et al., 14 aquatic species: at least one fluorine-free foam was more toxic than, or as toxic as, fluorinated foam. The single most poisonous sample was fluorine-free.

— SERDP report ER20-1511 (authors include Ceja-Navarro): five fluorine-free formulations were 8–51 times more toxic than short-chain fluorinated foam, measured by suppression of plant growth.

— EPA, 24-hour test on fish larvae (fathead minnow): the toxicity of fluorine-free foams was orders of magnitude higher than that of fluorinated foam.

— Yeardley et al. (journal Chemosphere): the fluorine-free formulation Angus Fire Jetfoam, at its working 3% concentration, caused 100% mortality of earthworms — the fluorinated foam caused no such kill. The worms wholly avoided soil treated with the fluorine-free foam.

— East et al.: the sensitivity of fish larvae and water fleas to fluorine-free foam was 2–15 times higher than to fluorinated foam.

— Yu and Ceja-Navarro: a direct link proven — the more hard hydrocarbon surfactants a fluorine-free foam contains (sodium lauryl sulfate and diethylene glycol butyl ether), the more poisonous it is.

The conclusion here is calm and hard at once: on equal terms (at equal concentration) fluorine-free chemical foam equals or exceeds fluorinated foam in acute toxicity. In the EPA’s own words: removing the fluorine from a foam does not make it safe for living nature.

4. What stays off the page: the quantity

Now put together two facts that are each already proven.

Fact one. Fluorine-free foam is more toxic per unit of mass (see above).

Fact two. Several times more fluorine-free foam is needed. The only documented field success of fluorine-free suppression of large tanks — a detergent foam, in Poland, on tanks 30–40 metres across — was achieved at an application rate of 24–30 litres per square metre per minute, that is 4–5 times above the NFPA 11 norm.

And here is the point. Not one of the toxicity studies listed above took that multiplier into account. The toxicologists measured the poison «in the test tube,» at equal concentration. How much of this foam actually reaches nature at a real fire lies outside their work.

The total load on a body of water is simple to state: (poison per unit mass) × (volume of foam released). For fluorine-free foam both factors are higher. Both pull the same way — up.

5. The difference over time — and why «biodegradable» does not save the situation

The advertising for fluorine-free foam leans on the word «biodegradable.» Take apart what that changes and what it does not.

— Fluorinated foam: single-dose toxicity low, but the damage accumulates and is almost never removed. It defers and stockpiles.

— Fluorine-free foam: single-dose toxicity high, delivered at the moment of release. Afterwards the foam largely breaks down. It strikes at once, frontally, and several times harder.

And here is the key: the acute poisoning is delivered at the moment of release, before breakdown. The subsequent biodegradation no longer cancels it — the harm is done. «Breaks down in 28 days» does not bring back the fish that died in the first hour.

An objectivity caveat is needed here too. The advantage of fluorine-free foam in degradability is real and significant — persistent fluorine contamination is irreversible and spreads through space, and the regulator’s choice to fight persistence first is not foolish. The honest bottom line is this: it is not «one safe, one dangerous.» It is two different distributions of the same harm across time. Fluorine stretches the damage over decades; fluorine-free delivers it all at once. Whether the total harm from fluorine-free foam is equal or greater — no one has measured that, and we do not assert it.

6. The forgotten foam that actually did the extinguishing

While the argument runs between the two chemistries, there is a third option, usually spoken of as «obsolete and temperamental.» Check it.

The complete world list of documented extinctions of full-surface tank fires runs to thirteen cases. All in the United States, Canada and the Netherlands. And all were carried out with protein foam, by mobile attack at a high rate. Tanks from 29 to 60 metres across. Every kind of fuel — gasoline, crude, fuel oil, ethanol.

Since then, not a single new successful extinction. The large tank fires that followed were not put out.

Why was protein foam pushed out? The reason is not technical but bureaucratic. After the Forrestal aircraft-carrier fire the military specification fixed the criterion of that same water film. And only fluorine produces the film. Through that criterion, fluorine entered the civil standards, and the world was converted to fluorine chemistry. Protein foam was not beaten in a fair comparison — it was cut out by a requirement that in principle only fluorine can meet.

Name the weaknesses of protein foam honestly too: incompatibility with aluminium and copper in storage, a risk of over-enriching water if the concentrate reaches it, sticky residues that have to be washed off. Old bio-foam lost its properties in 2–3 years — but that limit has now been removed by stabilisers, and shelf life exceeds ten years.

7. The root of the whole problem — a single one

All three distortions grow from one place. No certification standard reproduces a real tank fire, and none checks the toxicity of the foam.

A real tank has a surface of 1,256 to 5,333 square metres. The test pan is 4.6. The scale difference is 270 to 1,100 times. Foam is chosen by that pan.

And the second structural failure: toxicity does not enter the certification criteria at all — neither for fluorinated nor for fluorine-free foam. Both earn the certificate on suppression speed alone. That very gap once produced the PFAS catastrophe. And it is now reproducing it anew — through fluorine-free chemistry. The market buys what passes the heptane pan, not what actually puts out a tank and is safe for nature.

8. One proof in numbers: the Orion terminal

The only fully documented extinction of a large tank in the era of synthetic foam also proves that the norms do not work. The Orion terminal, Louisiana: a tank 82 metres across, an area of 5,333 m², nearly 48,000 cubic metres of gasoline.

Now compound the multipliers. The real over-consumption at Orion was 5×. On top of that, fluorine-free foam needs a further 4–6 times more (this is NFPA’s own recommendation for the transition). Together that gives a 20–30-fold norm. No oil terminal in the world holds such a stock, and no mobile equipment can deliver such volumes. The conclusion is blunt: extinguishing large tanks with fluorine-free chemical foam, under the current norms, is physically impossible.

9. What to do about all this

The toxicity problem of chemical foam is not solved. It has merely been renamed. Once the diagnosis was «accumulation of carcinogens over decades.» Now the diagnosis is different — «acute poisoning at the moment of release,» and the foam’s subsequent breakdown does not affect that poisoning. And because the real levels of harm depend on the quantity of foam — increased several times over — and that quantity is not even being studied, at the chemical level the problem is simply being kept quiet.

There are two ways out of this contradiction.

The first — chemical: bio-foam. It resolves everything at once: no consequences for nature and health, almost instant breakdown, good suppression performance. The history of extinguishing large tanks, as shown above, was written by it.

The second — technical: change the delivery itself. If the foam is generated inside the volume with a neutral gas and delivered with very high power and very high precision from minimal distance — without losses along the way — then suppression is achieved with a smaller total mass of agent. And a smaller mass removes both troubles at once: the toxicity and the volume multiplier.

See how it looks on video: youtu.be/eOnmBrO3ljI

We solved both tasks and proved it on real trials on real tanks — more than sixty full-scale tests on tanks 23 and 42 metres across, with a failure count of zero. This is the only field data set in existence for fluorine-free suppression of large tanks.

A third task is solved along the way. By the unambiguous conclusion of the U.S. fire services, existing equipment is not able to deliver fluorine-free chemical foam in the required volume. Our delivery capacity — of the order of 700 litres per second, with a margin up to 1,200 litres per second — exceeds that requirement, and makes it possible to use even fluorine-free chemical foam with no consequences at all. The difference between the two realities can be seen in the photograph below.

References

NFPA / UL Research Foundation, «An Evaluation of the Firefighting Effectiveness of Fluorine-Free Foams» (165 fire tests). U.S. Naval Research Laboratory, 60-second gasoline extinction trials. SERDP programme, U.S. Department of Defense: validation trials and report ER20-1511. Jones et al., toxicity across 14 aquatic species. Yeardley et al., journal Chemosphere (earthworms Eisenia fetida and Dendrobaena veneta). East et al., fish larvae and water fleas. Yu and Ceja-Navarro, hydrocarbon-surfactant toxicity in soil organisms. U.S. EPA acute-toxicity screening (fathead minnow) and «Studying the Breakdown of Fluorine-Free Firefighting Foams.» U.S. GAO, transition cost and drop-in incompatibility. SP Report on the Polish full-scale tank extinctions. Orion terminal incident record (NFPA 11 comparison). EU regulation amending Annex XVII of REACH; U.S. military specification for fluorine-free foam; U.S. EPA drinking-water limit for PFOA/PFOS. Impulse Storm full-scale trials on 23 m and 42 m tanks; test protocol agreed with UL; foam recommended for procurement by the LASTFIRE consortium.