Equipment Decontamination and Replacement of Legacy Aqueous Film Forming Foams

Summary

Many users of Legacy C-8 Aqueous Film Forming Foams (AFFF) are considering changing to foams to minimize release of PFOA, PFOS and 8:2 FTS. Modern C-6 AFFF and fluorine free foams (FFF) are replacement options. FFF is preferable from an environmental perspective, but current FFF formulations are inferior in firefighting characteristics to legacy C-8 AFFF and modern C-6 AFFF. In replacing the legacy C-8 foam, equipment decontamination is recommended. The process should be carefully planned and PFAS contaminated residuals properly managed.

Background

Legacy (AFFF) used for firefighting are a significant source of poly-, perfluoroalkyl substances (PFAS) in the environment. Key PFAS from these foams are discussed below:

• Perfluorooctanoic acid (PFOA) and Perfluorooctanesulfonic acid (PFOS), which are long-chain C8 PFAS, have been the initial focus of regulatory criteria setting and some states have enforceable drinking water standards ranging from 8 to 70 nanograms per liter (ng/L). In 2022, the U.S. Environmental Protection Agency (EPA) issued lifetime drinking water health advisories of 0.0004 and 0.020 ng/L for PFOA & PFOS, respectively, and the EPA is expected to propose enforceable maximum contaminant levels (MCLs) for PFOA and PFOS in the near future.
• 8:2-fluorotelomer sulfonate (8:2 FTS) is another long-chain C-8 PFAS that is currently not regulated in drinking water but readily transforms into PFOA.

AFFF is applied to fires via firefighting equipment. This includes fire extinguishers, firefighting vehicles and fixed systems (e.g., foam gun systems used to contain fires around tanks and fuel storage areas and foam dispersing systems). AFFF concentrate is placed in these devices and foam is generated by mixing the concentrate with water/air under pressure using specialized nozzles.

With current and expected regulation, many entities are exploring the process to replace their legacy AFFF (C-8) with other short-chain AFFF (C-6 fluorotelomer sulfonates) or fluorine free foams (FFF). This requires removal of the legacy AFFF and decontamination of the firefighting equipment. Cost analyses indicate that it is generally much less expensive to decontaminate firefighting equipment than it is to replace it. However, some replacement foams may differ in density/viscosity, which may require replacement of pumps, valves and/or nozzles, which would increase the decontamination costs. Very small systems and fire extinguishers would likely be less expensive to simply replace.

TRC reviewed processes and data from industrial decontamination efforts and papers/reports and studied research conducted by the Department of Defense Strategic Environmental Research & Development Program/Environmental Security Technology Certification Program (SERDP/ESTCP) to develop recommendations.

Legacy AFFF Properties

Properties of legacy AFFF that make it very effective for fire suppression include:

• The ability of the AFFF to form a thin, but stable, film on the water interface that smothers the fire. This film also prevents reignition
• Viscosity and density similar to water, allowing for easy pumping and dispersal

Replacement Foams

There are two options available to replace legacy AFFF concentrate. (1) Modern Fluorotelomer AFFF, also called C-6 foam, uses short-chain fluorotelomer sulfonates and (2) Fluorine Free Foams (FFF) that use a variety of fluorine free organic surfactants. The table below compares these replacement options and legacy AFFF.

Replacement Foams Versus Legacy AFFF
Characteristics	C-8 Legacy AFF	Modern C- 6 AFFF	FFF
Environmental Concerns	High environmental concerns. Contains PFOA/PFOS or compounds that may transform to these compounds.	Uncertain environmental concern. Does not contain or transform to PFOS/PFOA. Can transform to perfluoroheptanoic acid (PFHpA) that is regulated in several states.	Very little environmental concern associated with PFAS but foam contains higher concentrations of hydrocarbon surfactants that could pose a risk if released to surface water. Overall concerns much lower than C-8 Legacy or C-6 AFFF.
Effectiveness of Suppressing Fuel/ Chemical Fires	Excellent	Comparable to C-8 Legacy AFFF	Inferior to C-8/C-6 foams
Ability of Foams to Prevent Fire Reignition	Excellent	Comparable to C-8 Legacy AFFF	Inferior to C-8/C-6 foams
Compatibility of Foams with Existing Firefighting Equipment	Fully Compatible	Highly compatible. Similar density and viscosity to C-8 Legacy AFFF	Low compatibility. Most have high viscosity and greater density. Existing pumps, valves and nozzles may need to be replaced.

From an environmental perspective, FFFs are preferential because of the uncertainty of the toxic characteristics of shorter chain C-6 PFAS compounds. In terms of fire suppression, modern C-6 fluorotelomer AFFF performs comparably to that of the C-8 legacy foams. FFFs may have utility for sites with isolated chemical fire hazards where longer extinguishing times are acceptable. However, most chemical fires will require replacement foams with extinguishing characteristics that C-6 fluorotelomer foams exhibit. There is substantial investment into the development of FFF, so it is possible that improved products will be available in the future. When switching foams, check for compatibility to existing pumps, valves and nozzles.

Foam Removal and Decontamination

Foam removal and decontamination should be carefully planned. This includes estimating waste volumes (AFFF concentrate, flushes and rinsates), worker protection, sufficient storage capacity for residuals, leak minimization processes and eventual management and disposal of collected residuals.

The first step for replacement is removal of the legacy foam from the equipment. The foam can be removed via drains at low points in the system, and the removal should be carefully managed to minimize accidental releases.

There are currently no existing requirements for the decontamination of firefighting equipment at the federal level. TRC recommends that decontamination be conducted because residual C-8 foam in the system could result in mixing with the replacement foam and the subsequent release of C-8 PFAS to the environment when the new foam is applied. After draining the entire system of AFFF concentrate:

• Conduct a foam flush, which is a rinse, or series of rinses, until foaming is no longer found in the rinsate.
• Remove and replace disposable elements like bladders and hoses.
• Consider conducting detailed, focused cleaning of valves, elbows, flanges and other elements that may be resistant to the flushing process or removing and replacing these.
• Conduct triple or quadruple rinse to remove the majority of legacy PFAS contaminants. Each rinse should recirculate from 45 minutes to 1 hour before discharging and collecting.
• The foam flush and rinsate water could be treated onsite to reduce the volume needed for disposal. Potential treatments include granular activated carbon (GAC), ion exchange (IX) or foam fractionation (FF).
• Take care to minimize any leaks or accidental releases of the foam flush/rinsate. Collected rinsates should be stored with secondary containment prior to treatment or disposal.
• Laboratory analysis of the final rinsate is an option, but is often not practical because of the need to return the firefighting equipment to service. Further, there are no established standards or advisories to meet.
• Contaminated residuals (AFFF concentrate, rinsates, spent treatment media, etc.) should be managed appropriately.

Studies have shown that legacy PFAS can partition on surfaces in the firefighting equipment, including stainless steel materials. These can be released over time, causing “rebound.” If this is a concern, consider the following:

• Commercially available additives can be used to improve the AFFF decontamination.
• Solvents like methanol/ethanol or non-foaming surfactants could also be used to enhance decontamination efficiencies, although added solvents must be considered in the evaluation of disposal options.
• For legacy C-8-based foams, heated water can be used to improve the mass transfer from the surfaces to the rinsate water.

Flushing Process Options

Disposal of Residuals

Responsible disposal of the residuals should be conducted.  As part of the planning process, discussed in the Foam Removal and Decontamination section, volumes of residuals should be estimated as part of the planning process and these estimates can be used to estimate disposal costs. Approaches for residuals management include incineration and landfilling with onsite methods under development.  TRC can assist with making appropriate selections.

How Can TRC help?

If changeout of C-8 foam is desired, then TRC can assist in recommending a suitable foam replacement and develop plans for foam removal and equipment decontamination. TRC can assist in finding a quality contractor to conduct the foam removal and equipment decontamination and can develop plans to manage residuals from legacy foam removal and equipment decontamination. Contact our experts below to learn more.