Water alone has no business in a flammable liquid fire; it does not stay on a hydrocarbon surface. Foam builds a barrier. But which foam? That question has been reopened by PFAS restrictions.
Three families
- AFFF (Aqueous Film Forming Foam): uses fluorinated surfactants to form a thin aqueous film on the hydrocarbon surface (NFPA 11 3.3.11.2). Fast knockdown, but it contains fluorine compounds (PFAS).
- AR-AFFF (Alcohol Resistant AFFF): for polar solvents (alcohols, ketones, ethers), and also usable on hydrocarbon fires (NFPA 11 3.3.11.1). Its polymer forms a protective layer on the fuel surface that stops the alcohol absorbing the foam.
- F3 (Fluorine-Free Foam; SFFF in NFPA 11): formulated not to contain PFAS (NFPA 11 3.3.11.8). It works through a mechanical foam blanket.
Comparison
| Criterion | AFFF | AR-AFFF | F3 |
|---|---|---|---|
| Hydrocarbon fire | Very good | Very good | Good (application discipline is critical) |
| Polar solvent (alcohol) | Ineffective | The only correct choice | An AR-type F3 is needed |
| Knockdown speed | Fastest | Fast | Slightly slower |
| Burnback resistance | High (film) | High | Depends on blanket integrity |
| PFAS content | Yes | Yes | No |
| Waste management | Difficult and costly | Difficult and costly | Standard waste |
| Typical concentration | 1, 3 or 6 percent | 3 or 6 percent (NFPA 11: 3–10 percent) | 1, 3 or 6 percent |
| Cost | Low | 30–50 percent higher | Moderate to high |
| Regulatory outlook | Being restricted in the EU | Being restricted in the EU | The transition target |
Which foam for which fire?
| Risk | Suitable foam |
|---|---|
| Petrol, diesel and fuel loading islands | AFFF or F3 |
| Ethanol, methanol or acetone tanks | AR-AFFF or AR-type F3 |
| Whisky or raw spirit in oak casks | Alcohol-resistant foam mandatory (AR-AFFF or AR-type F3) |
| Aircraft hangars | AFFF or F3 (low expansion), or high-expansion foam |
| IBC and drum storage | Foam-water sprinklers plus bunding |
| Oil-filled transformers | Water spray; foam usually not required |
The critical distinction: polar solvents. Alcohols, ketones and ethers absorb the foam and collapse the blanket. Standard AFFF is ineffective on such a fire; an alcohol-resistant type is mandatory (NFPA 11 5.2.4.3.1). High-strength spirits in oak casks fall exactly into that class.
What to watch in a C8 to F3 conversion
Converting an existing system to F3 is not simply changing the concentrate:
- The pipework is flushed. If PFAS residue stays in the system, the new concentrate counts as contaminated too. NFPA 11 4.4.1.1 prohibits mixing different types of concentrate in storage, so the tank is also emptied and cleaned.
- The dosing is recalibrated. F3 has a different viscosity and surface tension; the proportioner is calibrated from scratch.
- Nozzles and expansion ratio are verified. F3 may require a higher expansion, and the existing nozzles may not suit.
- The certificate is renewed. An EN 1568 certificate is issued for the concentrate, nozzle and ratio together; changing one puts the validity of the others in question.
- Waste disposal is planned. The C8 concentrate removed is hazardous waste and cannot go to the sewer.
Turkish context
PFAS restriction in Turkey is not as sharp as in the EU; but facilities exporting to the EU, and refineries and terminals in international insurance portfolios, are already planning the F3 transition. Choosing F3 on a new system avoids the cost of flushing and replacing the whole system five years later. For existing AFFF stock, the most common approach is use until the shelf life expires, then controlled disposal.
Frequently Asked Questions
Why is standard AFFF not used on an alcohol fire?
Polar solvents such as alcohols, ketones and ethers absorb the foam and collapse the blanket. An alcohol-resistant (AR) foam is mandatory on such a fire (NFPA 11 5.2.4.3.1); standard AFFF is ineffective.
Does F3 fully replace AFFF?
In most hydrocarbon applications yes; knockdown is slightly slower and application discipline more critical. On polar solvents an AR-type F3 is required.
What does converting an existing AFFF system to F3 require?
Flushing the pipework, recalibrating the proportioner, verifying the nozzles and expansion ratio, renewing the certificate, and disposing of the removed C8 concentrate as hazardous waste.
Are sprinklers sufficient for Class I flammable liquids?
Generally not for extinguishment. A Class I liquid has a closed-cup flash point below 37.8 °C (100 °F) (NFPA 11 3.3.20.2 and A.3.3.20.2). FM DS 7-14 (3.4) states that water will not, in general, extinguish fires in liquids with flash points below 93 °C, while sprinklers and water spray provide cooling and protect the structure. Where extinguishment is the goal, foam-water sprinklers or an independent foam system are needed, together with drainage and containment in every case.
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Download MEP Calc on the App StoreThe EN 1568 series (fire extinguishing foam concentrates). NFPA 11 Standard for Low-, Medium- and High-Expansion Foam. FM Global DS 7-14. EU PFAS restriction legislation. Product selection must always be verified against the manufacturer's certificate.