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

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The issue of cleaning fire extinguishing systems that have been contaminated by fluorine foam agents is more complex and requires some explanation, resulting in considerations that must ultimately be decided by every individual system operator.

What is the present situation?

For over 50 years fire extinguishing systems have used foam concentrates that contain fluorine in the form of poly- or perfluorinated chemicals (PFAS, also referred to as PFC or PFT). It has been found that fluorine is not degradable in the sewage water and is harmful to health. The most common PFCs are perfluorooctanoic acid (PFOA) and perfluorooctanesulfonic acid (PFOS). In recent years the maximum fluorine content in foam agents has been widely regulated in various countries with differing thresholds for differing fluorine chemicals. Please check with your local authorities what regulations apply within your region of operation.

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 guidelines, 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 happy 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 tanks and pipe walls and other system components. Incrusted 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 absorbed concentration is very low and can surely be neglected in further considerations. Nonetheless, it is recommended to replace seals, for example, during the cleaning process. 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 lifetime of an extinguishing system fluorosurfactants in foam agents adhere to the tank walls, pipes 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 high-temperature incineration of the flushing water.
  • Cleaning with water, adsorption of the PFC by means of activated carbon, high-temperature incineration of the activated carbon 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 through 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 2,000 °F. Any re-generation of PFC-contaminated activated carbon and any disposal in regular waste incineration plants, that operate only at temperatures of 1,560 °F, 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 following cleaning procedure is recommended for stainless steel, GRP and polyethylene tanks:

  1. Complete draining and disposal of the foam agent.
  2. Remove foam agent residues mechanically and by flushing the tank, all pipes and fittings, with hot (122–140 °F) water. The flushing process is sufficient when the draining water no longer forms foam. The flushing water must be disposed of.
  3. The tank, all pipes and fittings must be completely filled with water that is as hot as possible. Keep the water in the tank for at least 24 hours, then drain and dispose of.
  4. The tank, all pipes and fittings must be completely filled with fresh water that is as hot as possible three more times. Keep the water in the tank for at least 24 hours each time. The water from these flushes can be fed into the sewage treatment plant via the sewer system after consulting with the sewage treatment plant management.
  5. Fill the tank with fluorine-free foam agent.

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 the flush from point 3, must be disposed of properly, i.e., sent to high-temperature incineration.

It is recommended to have the PFC concentration of the flushing water determined by a laboratory analysis before disposal in the sewer system.

Cleaning with water, activated carbon treatment and thermal disposal

As described in the previous procedure, the system is cleaned by means of multiple flushing cycles with water. Instead of the thermal disposal of the polluted extinguishing water, it is cleaned by treatment in an 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 with water mixed with additives and thermal disposal of the flocculation products

In this process, an additive is added to the flushing water, which binds the dissolved PFC and flocculates it. The dosage is based on the PFC concentration 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 can be reused and is finally cleaned in an activated carbon treatment system. The significant reduction in the PFC load of the flushing water results in relief for the activated carbon unit. The cleaning procedure usually consists of the following steps:

  • Flushing with water to determine the basic contamination (base sample).
  • Apply the additive to the flushing water and flush it multiple times with the solution. The flakes that form are separated at regular intervals and new additive is added as necessary.
  • The flushing process is repeated until there is no more foam formation.
  • After the cleaning process with additives, a final flush with water is carried out and the contamination is determined. If the analysis confirms successful cleaning, the flushing water can be cleaned using an activated carbon filter. The precipitated PCF is sent for professional high-temperature incineration.

When cleaning fire engines, waste of approximately “one teacup” full of PFC sludge is produced. When cleaning industrial fire protection systems, up to several 100 quarts of waste may be produced.

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.

What about the costs of the various cleaning processes?

It is very difficult to estimate the cost of cleaning. It can be assumed that cleaning with water and activated carbon is most efficient for small systems due to high thermal disposal costs ($10 to $15 per gallon). The transport costs for “hazardous waste” and the distance to the nearest high-temperature incineration plant that accepts PFC waste must be considered. The disposal of contaminated water can be difficult.

The more complex and larger a system is, the more cost efficient the cleaning process with additives may be. In addition to costs, various other points must be considered:

  • System downtimes – when using the water methods, the downtimes are specified by the flushing times, but at least one week of downtime can be expected. With the additive process, cleaning can be carried out in a few days.
  • 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 seven system volumes. With the additive 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 122 and 140 °F can be made available and processed in the system without any problems.

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. The requirement to replace PFC-containing foam agents means that the extinguishing systems that are contaminated with PFC must be replaced or 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 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.

For additional information on how to clean a FireDos proportioner after usage with fluorinated foam agents, please click here.

For general information about FireDos proportioners please visit: firedos.com 

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