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Cleaning fire extinguishing systems that have been contaminated by fluorine foam agents

How to clean fire extinguishing systems that have been contaminated by fluorine foam agents? Keeping the entire issue simple and describing it in a few sentences would have been great. However, the issue is more complex and requires some explanations resulting in considerations that must ultimately be decided by every individual system operator.

Extinguishing system with proportioner and foam tank

What is the present situation?

Many older foam-based fire extinguishing systems contain fluorine in the form of poly- or perfluorinated chemicals (PFAS, also referred to as PFC or PFT) that have been produced and used for over 50 years. These are getting more and more into the focus of discussion as they are not degradable in the sewage water and harmful to health. The most common PFC are perfluorooctanoic acid (PFOA) and the perfluorooctanesulfonic acid (PFOS).

The use of fluorine foam agents is more and more restricted.

Since 4th of July 2020:
In the European Union, the maximum PFOA content in foam agents, i.e., the total of all fluorinated compounds, has been newly regulated. According to EU Directive 2019/1021 (POPs Directive) and Directive (EU) 2017/1000, foam agent concentrates containing more than 25 ppb (0.025 mg/kg) PFOA or one of their salts or more than 1 ppm (1 mg/kg, 1000 ppb) of individual PFOA precursors must no longer be brought to the market in the EU.

31st of December 2022:
Foam agents in tanks of fire extinguishing systems may be used; however, not for training purposes; and for testing only if all discharged amounts are contained and disposed of in a professional manner.

1st of January 2023 until 4th of July 2025:
Their use is allowed only if the extinguishing water can be contained completely and disposed of thereafter in accordance with the legal regulations.

4th of July 2025:
no more use is allowed.

The German drinking water directive refers to PFC by use of the equivalent name of per- and polyfluorinated alkylated substances, PFAS. PFOA and PFOS belong to this group. The new regulations on PFAS include two thresholds. These do not apply directly to extinguishing water, but are considered to be a good reference.

  • The total of 20 individual PFAS compounds listed in an appendix to the directive in the amount of 0.1 µg / l or ppb (sum of the PFAS)
  • The sum of all fluorine compounds contained in PFAS (the PFAS family comprises several 1,000 fluorine compounds) in the amount of 0.5 µg / l (PFAS total)

What effects do the thresholds and guidelines have for foam extinguishing systems having been operated with PFC foam agents?

The term 'foam extinguishing system' may refer to a stationary fire extinguishing system as well as to a fire truck or a mobile system.

  • With regard to the guideline, this means that every system operator wanting to switch to a fluorine-free foam agent will have to consider which new fluorine-free foam agent to use in future firefighting operations.

  • After a decision is made, based on extinguishing properties, it must be checked whether the foam agent proportioner, the foam agent suction line, the pipework filled with premix, the hoses, fittings and discharge devices are suitable for the new foam agent. During the evaluation, attention must be paid, among others, to the water and foam agent flow rates, the proportioning rate, the physical properties of the foam agent such as viscosity and temperature behavior, as well as existing and necessary approvals and the suitability of the discharge devices for the new foam agent. Specialized companies, such as FireDos as a manufacturer of foam agent proportioning systems, will be pleased to assist you in analysis and decision-making.
  • In the next step, the PFC or fluorinated foam agent must be completely removed from the extinguishing system and disposed of by a professional specialist company. During the removal, a suitable floor surface must be ensured to prevent spilled foam agent from seeping into the ground.

  • Before adding the new, fluorine-free foam agent, all parts of the system that were exposed to the fluorinated foam agent must be thoroughly cleaned. Even small amounts of the old, fluorinated foam agent remaining inside the system can lead to contamination of the extinguishing water beyond the permitted thresholds during firefighting, system tests or maintenance.

What effects do PFC foam agents have on components of a fire extinguishing system?

Foam agent concentrate can deposit on extinguishing system pipe walls and system components. Incrusted, dry foam agent residues, which are hard to remove, are commonly found.

PFC can be absorbed by plastics and released later on. It is estimated however, that the concentration is very low and can surely be neglected in further considerations. Nonetheless, it is recommended to replace, e.g., seals during the cleaning process. If a system is out of service for cleaning, this is a good opportunity to conduct the corresponding maintenance work and possibly replace worn or old components and seals.

Water that has been used to clean an extinguishing system having been exposed to PFC foam agents must be disposed of as PFC-containing wastewater. This wastewater is subject to corresponding thresholds set by local wastewater regulations. Disposal should be made by specialized companies only that certify law-conforming disposal.

How can PFC-contaminated foam extinguishing systems be cleaned?

During the life time of foam agents in extinguishing systems, the fluorosurfactants adhere to the tank walls, pipe and system components such as fittings, valves and the proportioning device.

In general, various cleaning concepts are available and discussed in the industry. Three methods are presented and compared here.

  • Cleaning with water and thermal disposal (high-temperature incineration) of the waste products (flushing water)
  • Cleaning with water, adsorption of the PFC by means of activated carbon, thermal disposal of the activated carbon (high-temperature incineration) and discharge of the flushing water into the sewer system
  • Cleaning with water that is mixed with additives that bind PFC and create microflocs. The microflocs are removed by filtration. The remaining water is purified using activated carbon and discharged into the sewer system. The microflocs and the PFC containing activated carbon are disposed of thermally (high-temperature incineration)

According to the state-of-the-art of science and technology PFC can only be completely destroyed without the risk of forming fluoro-organic transfer products at temperatures exceeding 1,100°C. Any re-generation of PFC-contaminated activated carbon and any disposal in regular waste incineration plants, that operate only at temperatures of 850°C, should be rejected.

Cleaning with water and thermal disposal

Provided there is no major incrustation, good cleaning results using water can be achieved with stainless steel tanks and tanks made of polyethylene or glass fiber reinforced plastic (GRP), provided that the tank cleaning is carried out very carefully. Cleaning the remaining components of the extinguishing system, such as pipes, fittings, valves and the proportioning device, can prove to be more difficult, as there is no direct access and there is a high probability that deposits are present. Even if the quantities of fluorine contaminated deposits are considerably lower than in the foam agent tank, these can lead to contamination of the new fluorine free foam agent and thus the extinguishing water.

The Bavarian State Ministry of the Interior, for Sport and Integration, the Bavarian State Ministry for Environment and Consumer Protection and the Bavarian State Office for the Environment have developed the guideline 'Environmentally friendly use of fire-fighting foams' in cooperation with representatives of the state fire brigade schools in Bavaria, the fire departments and fire brigade associations. The following passage is from the 3rd edition from September 2019.

The following cleaning procedure is recommended for stainless steel tanks, GRP and polyethylene tanks:

  • Complete draining of the foam agent (dispose of foam agent)
  • Remove foam agent residues mechanically and by flushing with hot (50 – 60°C) water. All pipes and fittings carrying the foam agent must also be flushed. The flushing process is sufficient when the draining water no longer forms foam. The flushing water must be disposed of.
  • The tank, the pipes and fittings carrying the foam agent must be completely filled with water that is as hot as possible. The water must remain in the tank for at least 24 hours. Then the water must be completely drained and disposed of.
  • The tank, the pipes and fittings carrying the foam agent must be completely filled with fresh water that is as hot as possible three more times. The water must remain in the tank for at least 24 hours. The water from these flushes can be fed into the sewage treatment plant via the sewer system, provided that the procedure is carried out carefully. After this cleaning process, the tank can be filled with fluorine free foam agent. This complex cleaning process ensures that the new, fluorine free foam agent is not contaminated with fluorosurfactants from the tank wall.

Even if not explicitly mentioned, it is assumed that the cleaning process also applies to all valves and the proportioning device.

Experience has shown that flushing with three times the system volume is necessary for point 2 to prevent any further foam formation. All water that has accumulated up to this point, plus one more flushing (see point 3), must be disposed of properly, i.e., sent to high-temperature incineration.

The level of contamination of the flushing water in the three other flushing processes is not measured. Even if only with a low probability, it is possible that water with inadmissible PFC concentrations will find its way into the sewer system. It is therefore recommended to have the PFC concentration determined by a laboratory analysis before disposal in the sewer system.

 

Cleaning by means of water and activated carbon treatment and thermal disposal of the same

As in the previous procedure, the system is cleaned by means of multiple flushing cycles with water. The procedures differ in terms of the different disposal methods. Instead of the thermal disposal of the polluted extinguishing water, it is cleaned by treatment in a stationary or mobile activated carbon treatment plant. In the case of high PFC contents, it can be assumed that the activated carbon is heavily loaded, so that regeneration of the loaded activated carbon is no longer possible, requiring its thermal disposal and replacement.

As in the previous procedure, it is recommended that the PFC concentration is determined by a laboratory analysis before the purified flushing water is disposed of.

Cleaning by means of water mixed with additives and thermal disposal of the flocculation products

In this process, a liquid active ingredient is continuously added to the flushing water, which binds the dissolved PFC and flocculates it. The dosage is based on the concentration of the PFC and allows the process to be adapted to the individual circumstances. A filtration unit removes the precipitated microflakes from the flushing water. The filtered flushing water is finally cleaned in a stationary or mobile activated carbon treatment system. The significant reduction in the PFC load of the flushing water results in relief for the activated carbon unit.

An example of the additive process is the PerfluorAd process developed by the German company Cornelsen Umwelttechnologie. The procedure usually consists of the following steps.

  • If required or at the customer's request, sampling or flushing with water (base sample) to determine the basic contamination.
  • Multiple flushes with a PerfluorAd solution. The flakes that form are separated at regular intervals and new PerfluorAd is added if necessary. In the case of severe contamination, it is recommended to let the solution rest in the system overnight.
  • The flushing processes are repeated until there is no more foam formation.
  • After the PerfluorAd cleaning process, a final flush with water is carried out.

A sample is taken, which is examined in the laboratory. If the analysis confirms that the cleaning has been successful, the remaining flushing water can then be cleaned using an activated carbon filter and fed into the sewage treatment plant via the sewer system. The precipitated PCF is sent for professional thermal high-temperature disposal. When cleaning fire engines, waste of approximately 'one teacup' full of thin sludge is produced. When cleaning large industrial fire protection systems, the amount of residual material could be in the range of up to several 100 liters. The quantity depends on the size and contamination of the system.

There is presently no clear guideline from the authorities for the PFC limit values that must be complied with after cleaning, nor is there a defined method for taking samples. Cornelsen has set a limit value of <1.0 µg / l (ppb) total PFAS in the last flush, without this benchmark being legally binding. A 'zero' is always aimed for, which is possible to achieve on specific projects. In the case of a theoretical contamination of fluorine-free foam agent with 1 ppb PFAS, the load on the extinguishing water, at a proportioning rate of e.g. 3%, would be 0.03 ppb, and thus even below the limit value for drinking water.

 

What about the costs of the various cleaning processes?

It is very difficult to compare the costs of the three processes, as all the systems to be cleaned are different and different foam agents with different PFC contents are used in each case.

It can be assumed that cleaning with water and activated carbon is most efficient for small systems due to the high thermal disposal costs. The costs for thermal disposal are between € 450 and € 2,500 per cubic meter, depending on regional regulations. The amount of waste products to be disposed of therefore has a major impact on the overall costs. Furthermore, the transport costs for this "hazardous waste" and the distance to the nearest high temperature incineration plant that accepts the corresponding products must be considered. It has been shown that the disposal of contaminated water can be difficult.

The more complex and larger a system is, the more cost efficient the PerfluorAd cleaning process may be.

In addition to the costs, various other points must be considered:

  • System downtimes
    When using the water methods, the downtimes are specified by the flushing times, including the recommended 24-hour periods, but at least one week of downtime can be expected. With the PerfluorAd process, cleaning can be carried out in a few days. Fire trucks can be cleaned in one to two days in the stationary Cornelsen plant. In both cases, the analysis of the last flushing water is not included. The analysis usually takes a week. A premature refilling of foam agent, before the results of the analysis are available, is based on the experience of the cleaning company and is at your own risk.
  • Amount of water required and to be moved
    When using the water methods, the volumes are specified by the flushing steps and are usually at least 7 system volumes. With the PerfluorAd process, the water can be circulated continuously and only a theoretical requirement of one system volume is necessary.
  • Local conditions
    When using the water methods, it must be ensured that a large amount of hot water between 50 and 60° C can be made available and processed in the system without any problems.
  • Safety of the complete cleaning process
    When using activated carbon for cleaning PFC contaminated flushing water, which will most likely also have a high organic background load, as will be the case in any flushing water, the "safely of the process" must be considered. The point in time of the so-called breakthrough, i.e., the degree of pollutant release of PFC from the activated carbon filter, will occur very quickly with high PFC loads and high organic background loads in the water. PFC can therefore have run out of the activated carbon filter and entered the sewer system without the results of an analytical analysis being available. Since this "breakthrough" is a well-known fact, authorities often require a close monitoring of the drain of the activated carbon system, to be able to examine retained water samples, possibly also long after the cleaning measure. If it is proven that PFCs were introduced into the sewer system during or after the cleaning operation, this environmental offense can be prosecuted accordingly. The advance cleaning of PFC-contaminated water, for example with PerfluorAd, relieves the activated carbon filter stage in such a way, that a spontaneous filter breakthrough is very unlikely to occur.

What does FireDos recommend how PFC contaminated foam extinguishing systems should be cleaned?

As a rule, only those parts of the system that have been exposed to the foam agent concentrate need to be cleaned. If system operators are unsure whether other parts of the extinguishing water system are contaminated with PFC by the premix, it is advisable to take samples from the extinguishing water of various system parts and have them analyzed. In the following, reference is only made to those parts of the system that have been exposed to the foam agent concentrate. The cleaning of other parts of the system would, however, be carried out accordingly, while it can be assumed that less effort will be required, as the PFC concentration in a premix is considerably lower.

In general, all the methods presented are suitable for cleaning foam extinguishing systems. In any case, it is recommended to take a sample from the last flush in order to have the PFC concentration determined by a laboratory analysis.

1 = water motor 2 = proportioning pump 3 = coupling 4 = ball valve 'flushing' 5 = ball valve 'returning / proportioning' 

The following procedures are possible.

  • Cleaning the complete system while installed using one of the methods mentioned above. For this, at least the flushing and proportioning line of the FireDos proportioner on the water motor must be disconnected, so that the flushing water can be circulated. Furthermore, it must be ensured that the water motor is set in rotation during the flushing process so that the piston pump moves, and the flushing water can reach all interior spaces. The ball valves must also be flushed in all positions.
  • Removal of the FireDos proportioning pump and cleaning as described below. Cleaning of the foam agent tank, pipes, fittings and valves using one of the above-mentioned methods.
  • Separation of the system into components (foam agent tank; pipes with fittings and valves; proportioning pump). Cleaning of the FireDos proportioning pump as described below and the other components using one of the methods described above.

Because of the many internal moving parts that also must be moved during a flushing process, FireDos recommends removing the proportioning pump and cleaning it externally. For this cleaning, FireDos has entered into a partnership with the Cornelsen company to have the proportioning pumps cleaned with the PerfluorAd process. This is the only way to ensure that all contaminations in the proportioning pump have been verifiably removed. The FireDos service department takes care of the removal, cleaning, and installation of the proportioning pump in consultation with the company contracted for cleaning the system. All seals are replaced as part of the cleaning process. It is recommended to also replace the seals of the FireDos water motor. This can be done on site during the installation of the proportioning pump.

After the system has been cleaned, the new foam agent can be added and the extinguishing system can be put into operation. In this context, the annual maintenance and the verification of the proportioning rate can also be carried out through the simple return operation of the FireDos proportioning systems, without the generation of premix.

Conclusion

Due to the legal requirements in many countries around the world, PFC-containing foam agents will no longer be approved for use in extinguishing operations in the next years. In some regions, exceptions for installations may be granted, in which it can be ensured that the contaminated extinguishing water can be collected and disposed of. The requirement to replace PFC-containing foam agents means that the extinguishing systems that are contaminated with PFC must be subjected to intensive cleaning. There are several methods that can be used to successfully perform such cleaning. Which method system operators choose will depend on many factors such as system size, system configuration, disposal options for contaminated cleaning water, the proportioning technology used and legal requirements. In any case, FireDos recommends that its proportioning pumps are cleaned separately by FireDos.

In addition to cleaning, special attention must be paid to the future foam agent, since, in addition to the necessary extinguishing characteristics, it must also be ensured that all components of the extinguishing system, especially the proportioner, are suitable for the new foam agent.

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