Determination of sediment in foam liquid is a critical quality-control test that quantifies the insoluble solid matter that settles out of fire-fighting foam concentrates during storage and service. Excessive sediment can block proportioners, valves, and nozzles, distort dosing accuracy, and ultimately compromise fire suppression performance. This article explains the technical principles, applicable standards (ISO 7203, EN 1568, GB 15308, UL 162), typical sample types, laboratory determination methods, and practical applications of sediment testing performed by accredited third-party laboratories.
Technical Overview
Fire-fighting foam concentrates — including protein foam (P), fluoroprotein foam (FP), film-forming fluoroprotein foam (FFFP), aqueous film-forming foam (AFFF), alcohol-resistant (AR) variants, synthetic deterdent-type foams (S), and medium- or high-expansion foams — are formulated chemical products designed for long-term storage in fixed fire protection systems, mobile apparatus, and portable extinguishers. Over time, storage, temperature fluctuation, and chemical aging can cause insoluble matter to separate from the liquid phase and accumulate as sediment.
In the context of foam liquid testing, sediment is defined as the insoluble, non-foaming solid matter that settles out of the concentrate under gravity or centrifugal force. Common sources of sediment include:
- Precipitation or crystallization of formulation components, such as hydrolyzed protein solids, inorganic salts, or stabilizers, particularly after exposure to low temperatures or prolonged storage;
- Chemical aging, polymerization, or degradation reactions within the concentrate;
- Corrosion products and particulates released from storage tanks, drums, liners, or piping;
- External contamination introduced during filling, transfer, or sampling operations.
Controlling sediment is essential for fire safety. Sediment can settle in storage tanks and be entrained into proportioning equipment — bladder tanks, balanced-pressure proportioners, in-line inductors, and sprinkler or monitor nozzles — causing blockages, inaccurate proportioning rates, non-uniform foam concentration, and degraded foam properties such as expansion ratio, drainage time, and film formation. In severe cases, excessive sediment can disable a foam system precisely when it is needed during an emergency.
Sediment determination is a mandatory test item in major product specifications, including the ISO 7203 series, the EN 1568 series, GB 15308-2006 for foam extinguishing agents, and UL 162, and it supports service-life assessment within inspection regimes such as NFPA 11 and NFPA 25. Accredited third-party laboratories routinely perform this determination as part of batch release, certification, and periodic in-service condition monitoring.
Testing Samples
Samples submitted for sediment determination cover the full range of foam concentrate families and service conditions. Typical sample categories include:
Fresh (As-Manufactured) Concentrate
Samples taken from production batches or newly delivered containers, used to verify conformity of the product at the point of manufacture or supply. These tests confirm formulation homogeneity and stability before the concentrate enters service.
In-Service and Stored Concentrate
Samples drawn from foam storage tanks, bladder tanks, drums, or pails installed at petrochemical facilities, fuel terminals, aircraft hangars, warehouses, and marine systems. These determinations assess whether storage conditions have caused unacceptable sediment formation over the service life.
Aged or Temperature-Cycled Concentrate
Laboratory-conditioned samples that have undergone accelerated aging at elevated temperature, or repeated freeze–thaw and high–low temperature cycling, in order to simulate long-term storage and extreme climatic exposure before sediment measurement.
Premix Solutions
Premixed foam solutions held in charged portable extinguishers, vehicle tanks, or piped premix systems, where dilution with water can accelerate precipitation and sediment formation.
Concentrates of Different Chemical Families
Protein-based and fluoroprotein concentrates, which contain hydrolyzed protein macromolecules with a comparatively higher tendency to deposit solids; AFFF, FFFP, and modern fluorine-free synthetic concentrates; alcohol-resistant concentrates containing polymeric stabilizers; and medium- and high-expansion concentrates — each evaluated against the limit applicable to its product standard.
Testing Items
Sediment determination is usually requested as a single parameter or as part of a comprehensive physicochemical conformity assessment. Core testing items include:
- Sediment content of the concentrate as delivered, determined by centrifugation and expressed as volume percentage (% v/v);
- Sediment content after accelerated aging conditioning, to evaluate long-term stability;
- Sediment content after temperature cycling (freeze–thaw resistance and heat exposure);
- Sediment content of stored premix solutions;
- Complementary parameters commonly tested alongside sediment, including pH, density, viscosity, surface and interfacial tension, expansion ratio, 25% drainage time, film formation and sealing behavior, corrosion characteristics, and extinguishment and burnback fire performance tests as required by the governing product standard.
Testing Methods
Centrifugation Method (Primary Standard Method)
The universally applied approach follows the procedures specified in ISO 7203, EN 1568, and GB 15308. The sample is conditioned to the specified laboratory temperature and transferred into calibrated conical centrifuge tubes with graduated tips. The tubes are then centrifuged at the rotational speed and duration mandated by the applicable standard, driving the insoluble solids into a compacted layer at the tube tip. The volume of the settled sediment is read directly from the graduations, and the sediment content is calculated as the ratio of sediment volume to total sample volume, expressed as a percentage. Determinations are typically performed in duplicate or triplicate, with the mean value reported.
Sample Conditioning Prior to Determination
Where the test objective is stability assessment, the sample is first subjected to standardized conditioning — elevated-temperature accelerated aging, or repeated freeze–thaw cycles — as defined by the product standard. The sediment content is then measured on the conditioned sample and compared with the specification limit, revealing whether storage stress has destabilized the formulation.
Gravimetric and Diagnostic Confirmation
For research, shelf-life studies, or failure investigations, the sediment may be isolated by filtration through a pre-weighed membrane filter, dried to constant mass, and weighed to obtain a mass-based result. The recovered solids can then be characterized by analytical techniques such as optical and electron microscopy, infrared spectroscopy (FTIR), X-ray diffraction (XRD), or elemental analysis, allowing the laboratory to identify the origin of the sediment and support root-cause analysis of blockages or non-conforming product.
Result Expression and Acceptance Criteria
Results are reported as sediment content in percent by volume, together with the test method, conditioning history, measurement uncertainty, and a conformity statement against the specified limit. Many low-expansion synthetic, film-forming, and fluoroprotein concentrates are limited to a sediment content on the order of 0.25% by volume in international and national specifications, while certain protein-based products and certain specifications permit somewhat higher values. The applicable limit must always be verified against the governing standard and the manufacturer's product data sheet.
Applications
Sediment determination in foam liquids serves a wide range of quality, safety, and engineering purposes:
- Factory quality control and batch release testing by foam concentrate manufacturers;
- Third-party certification and conformity assessment against ISO, EN, GB, and UL product schemes by accredited third-party laboratories;
- Periodic inspection of installed foam systems, including annual or periodic foam concentrate testing recommended under NFPA 25 and equivalent local regulations;
- Fire protection management at petrochemical plants, fuel storage terminals, tank farms, loading racks, and process units;
- Aviation fire protection, including hangar suppression systems and aircraft rescue and firefighting (ARFF) vehicles;
- Marine and offshore fire protection systems, where concentrate condition must be demonstrated to classification and flag-state requirements;
- Shelf-life studies, storage-condition qualification, and evaluation of concentrates after freeze, heat, or contamination events;
- Root-cause investigation of proportioner malfunction, nozzle clogging, or degraded foam performance;
- Procurement acceptance testing and supplier change qualification for end users and engineering contractors.
FAQ
What exactly is sediment in a foam concentrate?
Sediment is the insoluble solid matter that separates from the foam liquid and settles during storage. It may consist of precipitated formulation components, degradation products, corrosion particles, or external contamination. Because it does not dissolve back into the concentrate, it can accumulate in equipment and interfere with proportioning and foam generation.
Which standards govern sediment determination?
The principal specifications are the ISO 7203 series (low, medium, and high expansion foam concentrates), the EN 1568 series, GB 15308-2006 for foam extinguishing agents, and UL 162. These standards define the centrifugation-based procedure and the maximum permissible sediment content for each product family, and testing is conducted by accredited third-party laboratories.
What sediment level is considered acceptable?
Many international specifications limit sediment to approximately 0.25% by volume for low-expansion concentrates, while some protein-based products and certain specifications allow higher values. The exact limit depends on the governing standard, the concentrate type, and whether the sample is tested as delivered or after aging conditioning, so the applicable specification should always be confirmed.
Can a foam concentrate with excessive sediment still be used?
Exceeding the sediment limit is a non-conformity that must be taken seriously. In some cases the manufacturer may approve filtration or reconditioning followed by complete re-testing, but sediment often signals deeper chemical instability. Replacement of the charge is frequently the safest and most economical course of action, and any decision should be based on a full laboratory assessment and manufacturer consultation.
How often should in-service foam concentrate be tested?
Industry practice, including guidance in NFPA 25 and similar inspection regimes, calls for periodic testing of stored foam concentrate — commonly annually or at defined multi-year intervals depending on the product and local regulation — and additionally after abnormal events such as freeze exposure, over-temperature storage, contamination, or partial system discharge.
What factors can influence the test result?
Representative sampling, sample temperature, container handling history, centrifuge calibration (relative centrifugal force and time), tube graduation readability, and any aging or temperature-cycling conditioning all affect the measured value. Standardized laboratory procedures and calibrated equipment are therefore essential for reliable, comparable results.