Foams, powders & gels

- the evolution continues

Published:  01 July, 2005

The environmental impact of firefighting foams has become of increasing concern to both national regulatory authorities and fire services, as well as to manufacturers of the surfactants used and to companies in the fire engineering industry which formulate foam concentrates, following on from the announcement by 3M in May 2000 that they were phasing out fluorosurfactant production based on perfluorooctanyl sulphonate (PFOS) chemistry.

What constitutes a ‘PFOS’ foam?
Two international IFE seminars have been held at the Reebok Stadium in Greater Manchester in the last two years, both concerned with the environmental impact of firefighting foam. The seminar held in December 2004 focussed on a consultative document outlining the UK Government’s risk reduction strategy for PFOS-derived foams published that month by the Department of the Environment, Food and Rural Affairs (DEFRA).
This document and the philosophy on which it is based looks set to become the standard for many other countries in the European Union. The discussion covered not only the environmental issues for the so-called ‘PFOS’ foams but also for those containing fluorosurfactant manufactured by the fluorotelomer process, the alternative to 3M’s now discontinued PFOS chemistry.
There seems to be much confusion in the industry as to what constitutes a ‘PFOS’ foam and what it is that is environmentally damaging.
Perfluorooctanyl sulphonyl chloride (C7F15SO2Cl) was the chemical feedstock or precursor used in the manufacture of 3M PFOS-type fluorosurfactants. These fluorosurfactants degrade in the environment to give perfluorooctanyl sulphonate (PFOS).
The fluorosurfactants themselves can be thought of as containing PFOS in derivative form. Thus it is quite correct to speak of a PFOS foam concentrate, meaning a foam formulation which both contains derivatised PFOS and degrades in the environment to give PFOS, which has been shown to have an unacceptable PBT profile (PBT = persistence, bio-accumulation and toxicity).
Foam concentrate or finished foam does not, however, contain free PFOS unless it has degraded. PFOS has been shown to be widely dispersed worldwide both in man and other animal species, including those with no apparent history of exposure.
Toxic to biological systems
Human serum samples, which are now generally contaminated, contained no detectable organic fluorine compounds prior to the manufacture of these fluorine-containing compounds in the 1940s and 1950s. PFOS bio-accumulates in animal tissues with an accumulation ratio between 6,000 and 120,000, as shown by the Etobicoke incident at Toronto International Airport in June 2000.
PFOS is also toxic to biological systems. The lithium salt of PFOS is an insecticide. PFOS causes disturbances in lipid and steroid metabolism and has also been implicated in human bladder and prostatic carcinoma.
It is also quite correct, although misleading, to say that the fluoroteleomer fluorosurfactant foams are PFOS-free and do not degrade to PFOS, as these foams contain a chemical entity which is similar to PFOS.
Fluorotelomer foams contain, typically, a partially fluorinated tail, such as C6H13CH2CH2-S-, attached to a sulphur atom as part of a sulphonamide. Under appropriate environmental conditions, fluorotelomer foams can degrade to either perfluorocarboxylic acids, C6F13COOH, or the fluorotelomer sulphonates, such as C6F13SO3-, also known as 6:2 FtS or H-PFOS.
Contrary to claims in the trade press and even in the scientific literature, possibly intended to deflect environmental scrutiny from the fluorotelomers, the fluorotelomer sulphonate (6:2 FtS or H-PFOS) is chemically very similar to PFOS and is considered a structural analogue of PFOS by practising chemists. The correct IUPAC name for 6:2 FtS (H-PFOS) is 1H,1’H,2H,2’H-perfluorooctane sulphonic acid. Structural analogues have similar physical and chemical properties which show a progression based on chain length.
High levels discovered on sites
The 6:2 FtS fluorotelomer sulphonate has been found at very high levels in groundwater and to be extremely persistent at old military firefighting training sites.
Indeed 6:2 FtS (H-PFOS) may be even more stable than PFOS itself based on                           the measured groundwater concentrations (Schultz, Barofsky and Field (2004)). Currently we do not know for certain whether fluorotelomer sulphonates also bio-accumulate and are biologically toxic, although their structural similarities with PFOS should produce a high index of suspicion. More independent research is urgently needed to answer these environmental questions.
Another source of confusion concerns the difference in potential environmental impact between foam concentrate or finished foam and their degradation products. There would appear to be a very low risk of toxicity from using foam concentrate or finished foam either to firefighters or the environment, based on the manufacturers’ Material Safety Datasheets (MSDS).
Fluorotelomer surfactants, like all fluorosurfactants irrespective of their means of manufacture, are detergents and as such have acute biological toxicity to aquatic systems. The long-term problem is, however, that              the fluorotelomer environmental degradation products are extremely persistent, surviving in groundwater for at least a decade, and are, as yet, of unknown bio-accumulative capacity and toxicity.
There is no ‘safe’ level for discharge of a substance which will accumulate indefinitely within an environmental compartment and which is of unknown biological activity. It is well nigh impossible to remove a contaminant from groundwater once it is there!
Contaminated run-off issues
All fluorosurfactant foams, whether PFOS or fluorotelomer based, degrade to long-lived organohalogen degradation products. Dispersive use where containment and disposal are not possible, such as firefighting operations, is likely to result in discharge of contaminated run-off to groundwater or controlled waters.
Under List 1 of the UK Groundwater Regulations 1998, discharge to groundwater of organohalogen compounds or materials than can degrade to organohalogen compounds, a category which includes all fluorosurfactants, is explicitly prohibited.
Materials can only be downgraded to List 2 if the Enforcing Authority is prepared to issue a derogation in writing based on a lack of persistence, bio-accumulation and toxicity. Clearly not the case for fluorosurfactants.
The UK regulations are based on the implementation of the EU Groundwater Directive 1979 and all EU member states have the obligation to subsume this directive within their national legislation under the concept of subsidiarity.
Thus uncontrolled discharge of fluorosurfactants and their degradation products to groundwater is not only environmentally irresponsible but actually illegal in the United Kingdom with the possibility of prosecution, and probably also in all other European countries which have incorporated the EU Groundwater Directive.
Problems with foam extinguishers
The manufacture of PFOS-based fluorosurfactants has now been phased out worldwide. There remain, however, large stocks of PFOS foam concentrate held by the petrochemical and process industries, as well as smaller quantities held by municipal fire services.
An often overlooked problem is that of hand-held foam fire extinguishers which, for maintenance purposes, must be discharged regularly and re-filled.
These extinguishers are most frequently discharged by maintenance personnel down car park drains, onto the grass verge or down toilets, without checking first where the surface water is going to or whether they need to inform their local waste water treatment plant.
Indeed, water treatment undertakings may not even be aware of the problem of fluorosurfactants being organohalogens under the Groundwater Regulations! There are a very large number of extinguishers in use representing a very considerable potentially unknown reservoir of PFOS-based foam.
In a sense PFOS foams are history. What remains is to be decided is the way in which the exit strategy will be managed at regulatory level.
DEFRA in the UK is taking a European lead in this respect, having formulated a strategy which, if accepted by other European member states, will result in there being a 5 year derogation period for the phasing out of all use of PFOS-based fluorosurfactants with the ultimate high temperature incineration of remaining PFOS-containing material.
High temperature incineration of the fluorosurfactant residues is environmentally friendly as scrubbing of the flues gases containing hydrogen fluoride (HF) yields calcium fluoride (CaF2), the naturally occurring mineral fluorite or fluorspar originally used as the source of the fluorine atoms.
Whether this regulatory strategy is subsequently applied to all fluorosurfactants, not just those derived from PFOS but also including the fluorotelomers, remains to be seen and will be determined by environmental and toxicological studies in progress.
Risk reduction strategies
What risk reduction strategies are available to fire brigades for reducing the environmental impact of  firefighting foams?
The responsible approach for Procurement Officers is to consider replacing foam stocks, as use permits, with either AFFF and AFFF-AR low-fluorine foam concentrates or even with fluorine-free formulations depending on operational imperatives.
For many municipal fire brigades fluorine-free foam may be a realistic option as a number of these preparations have now achieved full compliance with the test standards and do show performance equivalent to classical fluorosurfactant AFFF, such as Arctic Foam’s RF-6(tm) series or Bio-For(tm) and Ecopol(tm) from Bio-Ex.
As pointed out recently by Ted Schaefer from 3M Australia at the Reebok Seminar in December last year, it is not necessary to have film-forming in order to get AFFF-like extinguishing capability.
Moreover, municipal fire brigades often use firefighting foam under true dispersive conditions under which containment is all but impossible and contamination of the water table all but certain.
In this sort of situation the use of a long-term environmentally ‘clean’ foam - for example, a fluorine-free Class B or a Class A foam - is a natural solution. Real problems remain, however, for the petrochemical and chemical process industry.
Here Class B foams are required with extreme performance capabilities in terms of spreading, burn-back, fuel pickup or foam blanket stability, for large hydrocarbon tank fires, currently only satisfied by fluoro-protein formulations such as Angus Fire’s FP70 Plus(tm). Even then containment of foam-contaminated run-off is necessary in order to protect the environment.
A sea-change towards extinguishing media is needed amongst fire brigades. Rather than the simple choice of water as jets or spray, or the use of a general purpose AFFF-AR Class B foam, brigades should consider the alternatives.
Class A foams may be much more appropriate and much less damaging environmentally, than excessive amounts of water alone for carbonaceous fuels such as wildland fires, structural fires with buildings made predominantly of wood as in the rural United States, or pallets and car tyres.
Class A foams and similar additives, which are usually based on hydrocarbon surfactants or detergents and used at very low induction rates, lower the surface tension of the water and aid penetration of the fuel source, thus producing savings in water usage and run-off volume.
Class A additives & CAFS
Environmental toxicity tends to be low and of an acute but not long-term nature as these materials are normally 100% biodegradable. Even vehicle fires can be effectively extinguished using Class A additives. Water may also be used as high-pressure mist or fog, especially in confined spaces, with an increase in efficiency resulting from much larger droplet surface area.
Compressed air foam systems (CAFS), which also use very low induction rates of Class A additives  - such as those from Schmitz or Hale Products - may provide an environmentally friendly solution. A recent report from the Canadian Research Council has demonstrated that a properly proportioned Class A CAFS system can even approach the performance of an AFFF Class B foam!  For other situations powders may be an appropriate choice, with commercially available products recommended for Class A, B, C and D fires. These may also be used in combination with water or foam nozzles, as sometimes done in the chemical process industry.
Municipal fire brigades often try to avoid having a multiplicity of extinguishing media available on appliances, in order to simplify operational procedures, equipment and training.
To a harassed Procurement and Training Officer a so-called ‘one stop’ foam concentrate would have its attractions, if it could be realised. A recent suggestion in the trade literature that a Class B AFFF-AR fluorosurfactant foam can be used not only for deep-seated hydrocarbon and alcohol fires at 3% but also for hydrocarbon spills at 1%, for training at 1% and as a Class A or wetting agent at 0.8%, is environmentally irresponsible and represents a high-risk strategy for any operational officer.
The fire brigade involved would be liable to prosecution under the UK Groundwater Regulations, or its equivalent, and would not have the protection of the Memorandum of Understanding between the Local Authorities and the Environment Agency unless human life and health could be shown to have been at risk, thus excluding training and most Class A wildland fire or structural building incidents.
Moreover, Class B fluorosurfactants, being both hydrophobic and oleophobic, do not penetrate carbonaceous fuels such as wood nearly as well as made to measure Class A hydrocarbon surfactants and are thus not so efficient.
In addition, most fire service appliances with round-pump proportioning only use one set induction rate, so that a ‘one stop’ foam would be used in practice at only 3%. Simplification of operational procedures is all very well but the ‘one size fits all’ philosophy cannot be applied to extinguishing agents!
The way forward
So if you can minimise or reduce your use of fluorosurfactant-containing foam for fighting fires, without hazarding operational capability, do so by using either low-fluorine or fluorine-free formulations, or even a different extinguishing technology.
Do not disregard the environmental issues of fluorosurfactants to the extent experienced a couple of years ago by the author when it became apparent that fire crews at an international airport in the United States were using a PFOS-containing AFFF concentrate to clean their cars and fire appliances.
You bet it worked well. It is, after all, an effective detergent but somewhat more expensive and environmentally-damaging than kitchen washing-up liquid!

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