How clean is clean enough for a legacy foam system?

When an owner drains a legacy foam system, residue can remain in the tank, concentrate pipework, proportioners and hose. Refilling the system brings the new foam into contact with those surfaces, allowing residual PFAS to carry over.

PFAS, or per- and polyfluoroalkyl substances, are found in firefighting foams such as aqueous film-forming foam (AFFF). In Singapore, the National Environment Agency (NEA) sets out the cleaning and acceptance provisions in Version 02 of its industry guideline, dated 27 March 2026.¹

For the owner, the work affects outage time, waste volumes and the evidence needed at completion. An incomplete scope can leave contaminated sections untreated. Poor records can leave the owner unable to demonstrate what was cleaned or how the acceptance basis was met.

Define the scope before the outage

The starting point is an inventory of the equipment that has held foam. Table 2 identifies the systems and parts within the guideline’s cleaning scope, including pipework kept packed with concentrate. The inventory should be checked against the installation so that sections are accounted for before cleaning begins.

The foam history helps the team plan the work. It should identify what each system has contained and where that information is uncertain. Baseline samples can provide a comparison for later results; their purpose and locations should be decided before the old foam is removed.

The owner should also settle the acceptance basis and waste arrangements at this stage. Cleaning produces rinsate, the liquid collected from flushing and soaking, as well as residues and removed components. The programme needs storage capacity, a collection arrangement and a record of where those wastes go.

Apply and record the cleaning method

Section 5.2 requires companies to take all reasonable and practicable steps to clean their systems and equipment. Its hot-water method begins with continuous flushing until no foaming is visible at the outlet, followed by at least three soaking and flushing cycles of 24 to 48 h each.¹

Each soak starts at 50 °C or higher, with the temperature maintained as far as practicable through the cycle. High-pressure washing or surface agitation may assist in removing solidified residue. The work record should show the equipment treated, the cycles completed and the conditions achieved.

Sampling and engineering judgement help determine where effort is needed, which components should be replaced and how the work can be sequenced. These decisions affect the outage and the volume of waste. Any reduction in repeated work must still leave the chosen cleaning method and acceptance basis satisfied.

Keep the two acceptance routes clear

Section 5.3 recognises that some PFAS may remain after cleaning. It provides two acceptance routes: residual PFAS within the Table 1 limits, or cleaning to as low as reasonably practicable (ALARP) using a method described in Section 5.2. Both sit within the requirement to take all reasonable and practicable measures to remove residues.

Footnote 4 explains that systems cleaned using at least the hot-water method, or another method described in Section 5.2, are deemed to meet the ALARP requirement and do not require re-cleaning on that basis. The completion record should identify the route relied on and the evidence supporting it.

Close the work with a usable record

A practical completion file brings together the component inventory, foam history, acceptance basis and cleaning records for each system. It should include baseline and subsequent laboratory results where testing forms part of the programme, together with records of waste collection and disposal.

Where laboratory testing is used, confirm the laboratory’s accreditation and the method’s suitability for the samples. Section 3.1 sets out the accreditation basis NEA accepts and gives a non-exhaustive list of recommended methods. The file should make each result traceable to its system, sample location and collection date.

At handover, the owner should be able to trace each system from its cleaning scope to the work completed, the acceptance basis and the waste records. Any unresolved items should remain identified in that file.

For engineering advice on a specific site, contact Archer.