“Should I order 3% or 6% AFFF?” is one of the most common questions we receive from fire system engineers, procurement teams and site managers before a first-time AFFF order. It sounds like a straightforward question — but the answer matters more than most buyers realise. Using the wrong percentage in a system that is calibrated for the other will result in an under-concentrated or over-concentrated foam solution that fails to meet performance requirements, potentially rendering the entire system non-compliant with NFPA 11 or GB 15308.
This guide explains exactly what the 3% and 6% mixing ratios mean, how they affect system design and foam performance, which model is correct for which application, and what to check before placing your order. For the CA-FIRE product range, the two AFFF models are S-3-AB (3%) and S-6-AB (6%) — both available in stock for immediate shipment from our Fujian facility.
Quick Answer
3% vs 6% AFFF produces identical firefighting performance when each is correctly proportioned. The choice is determined entirely by your proportioning system design — not by fire type, tank size or water supply. Check your proportioner calibration first. If uncertain, contact your system designer before ordering.
In This Article
What Does the Mixing Ratio Mean?
The mixing ratio — 3% or 6% — refers to the volume percentage of concentrate in the finished foam solution. It has nothing to do with expansion ratio, fire class or foam blanket thickness. It simply tells you how much liquid concentrate is added to the water supply before the solution is aspirated into foam.
3% AFFF (S-3-AB)
+
97 L water
100 L foam solution
6% AFFF (S-6-AB)
+
94 L water
100 L foam solution
The proportioning system — whether an inline Venturi proportioner, a bladder tank, a balanced pressure pump skid or an around-the-pump proportioner — is designed and calibrated at the factory to induct concentrate at either 3% or 6%. This calibration is fixed in the hardware: an orifice size, a pickup tube diameter, a valve setting or a metering device that controls exactly how much concentrate enters the water flow.
This is the fundamental point that determines your concentrate choice: the system tells you which percentage to use — not the other way around. Your proportioner manual or system design drawing will specify 3% or 6%. That specification must be matched exactly by the concentrate you order.
Do 3% and 6% AFFF Perform the Same on a Fire?
Yes — when correctly proportioned, 3% and 6% AFFF produce equivalent firefighting performance. The final foam solution — 3 parts concentrate plus 97 parts water, or 6 parts concentrate plus 94 parts water — contains the same effective concentration of fluorosurfactants and foam stabilisers per litre of solution in each case. The finished foam blanket that emerges from the nozzle has the same expansion ratio, the same drainage time, the same aqueous film-forming speed and the same vapour suppression capability.
This equivalence is verified by the GB 15308 and NFPA 11 Annex B foam performance tests, which test the finished foam solution — not the concentrate percentage. A 3% solution produced from S-3-AB and a 6% solution produced from S-6-AB, both correctly proportioned, must meet the same performance criteria to achieve standard compliance.
Common Misconceptions — Corrected
❌
“6% AFFF is stronger / more effective than 3%”
False. Both produce the same concentration of active agents per litre of foam solution when proportioned correctly. The 6% concentrate is simply less concentrated in the drum — it requires twice the volume per litre of solution produced.
❌
“I can use 6% AFFF in a 3%-calibrated system by reducing the proportioner setting”
False. Most proportioners do not have an adjustable ratio — they are fixed at either 3% or 6% by design. Attempting to use the wrong percentage will result in incorrect concentration in the foam solution, compromising performance and standard compliance.
❌
“3% AFFF is more modern / better than 6%”
False. Both 3% and 6% AFFF are current, standard formulations. The 3% format became more common in newer systems because it reduces the volume of concentrate that needs to be stored on site — but neither is technically superior.
How to Choose: The One Deciding Factor
There is only one question that determines whether you need 3% or 6% AFFF concentrate:
What mixing ratio is your proportioning system calibrated for?
Check your proportioner nameplate, system design drawing or original equipment specification sheet.
✅
Proportioner is calibrated for 3%
Order CA-FIRE S-3-AB (3% AFFF). Freeze point −5°C. Minimum operating temperature 0°C. Suitable for temperate-climate installations with fresh or sea water supply.
✅
Proportioner is calibrated for 6%
Order CA-FIRE S-6-AB (6% AFFF). Freeze point −2°C. Minimum operating temperature 0°C. Suitable for temperate-climate installations with fresh or sea water supply.
⚠️
Proportioner calibration is unknown
Do not order until confirmed. Check the proportioner nameplate, original installation drawings or contact the system installer. If the system and drawings have been lost, a certified fire engineer should inspect the proportioner to determine the calibrated ratio before any concentrate is ordered or installed.
Where to Find Your Proportioner Ratio
The proportioner calibration percentage will typically appear in one or more of these locations:
- → Proportioner nameplate — a metal plate stamped or engraved with the flow rate, inlet pressure range and foam percentage. Usually on the proportioner body.
- → System design drawing / fire protection drawing (FPD) — the as-built drawings for the foam system will specify the concentrate type and percentage.
- → Original equipment specification — the original purchase order or equipment data sheet for the proportioner or bladder tank.
- → Bladder tank label — bladder tanks for foam concentrate are usually labelled with the design concentration percentage.
- → Annual inspection report — fire system inspection records should document the concentrate type and percentage used in the system.
S-3-AB vs S-6-AB — Full Specification Comparison
The two CA-FIRE AFFF models differ in mixing ratio and freeze point only. All other performance parameters — expansion ratio, pH, temperature range, fire class coverage and water compatibility — are identical.
On freeze point: The −5°C freeze point of S-3-AB vs −2°C for S-6-AB is a secondary consideration in most installations, as both are above the 0°C minimum operating temperature. However, if your concentrate storage tank is outdoors or in an unheated space in a region where ambient temperatures can approach 0°C, the lower freeze point of S-3-AB provides a small additional margin of safety against concentrate crystallisation during cold nights.
Concentrate Economics and Storage Volume
Even though 3% and 6% AFFF produce identical firefighting performance, there is one meaningful practical difference: a 6% system uses twice the volume of concentrate per litre of foam solution compared to a 3% system. This affects concentrate storage requirements, replenishment logistics and total concentrate cost per system discharge.
This is why modern system designs increasingly prefer 3% AFFF — halving the concentrate storage requirement reduces bladder tank size, concentrate storage tank volume, and the quantity of concentrate that needs to be ordered, stored and eventually replaced at end of shelf life. However, many installed systems — particularly older installations — were designed for 6%, and these must continue to use 6% AFFF.
The concentrate economics advantage of 3% over 6% does not justify switching an existing 6%-calibrated system to 3% concentrate without recalibrating the proportioner. The storage saving is real — but it is irrelevant if the system cannot proportion the concentrate correctly.
Common Ordering and Installation Mistakes
These are the most frequent errors we see when customers order AFFF concentrate for the first time or for a system top-up or replacement:
Mistake 1: Ordering based on tank size or fire hazard size
The percentage has no relationship to the protected area, tank diameter or fire risk level. A 50,000 m³ crude oil tank and a 100 m³ diesel day tank can both use 3% AFFF — if their systems are calibrated for 3%. Order based on the proportioner, not the tank.
Mistake 2: Mixing 3% and 6% concentrate in the same storage tank
This creates an unknown concentration in the system. The proportioner will continue to induct at its calibrated rate — producing a foam solution that is neither 3% nor 6%, and failing to meet performance requirements. Never mix concentrations. If you need to switch ratio, drain, flush and refill the storage tank completely.
Mistake 3: Mixing AFFF with AR-AFFF or other foam types
Never mix AFFF with AR-AFFF, FFFP or any other foam concentrate type in the same storage vessel. Different foam chemistries can interact adversely, causing precipitation, viscosity changes or performance degradation. Systems must be fully flushed before switching to a different foam type.
Mistake 4: Assuming AFFF covers polar solvent fires
Standard AFFF (3% or 6%) does not work on fires involving alcohols, ketones, esters or other water-miscible fuels. If ethanol, IPA, acetone or similar solvents are present at your site, specify AR-AFFF foam concentrate instead.
Mistake 5: Not testing the concentrate after installation
NFPA 11 Annex C requires foam concentrate to be sampled and tested after installation and annually thereafter. The test verifies expansion ratio, 25% drainage time and pH. Simply installing the correct percentage concentrate and assuming it works is not sufficient for compliance — a performance test must be conducted and documented.
Sea Water Compatibility
Both CA-FIRE S-3-AB (3%) and S-6-AB (6%) are formulated for use with fresh water and sea water. Foam performance — expansion ratio, drainage time and aqueous film formation — is maintained when either model is mixed with sea water at normal salinity levels. This makes both models suitable for:
- → Marine vessels (tankers, bulk carriers, container ships, workboats)
- → Offshore oil and gas platforms
- → Coastal industrial facilities using sea water for fire suppression
- → Marine terminals and port facilities
For very cold-climate marine installations where sea water system temperatures fall below 0°C, consider whether the 3% or 6% AFFF is appropriate, or whether an AR-AFFF sea water grade (耐海水-36°C) with a freeze point of −36°C is required for the installation conditions.
Pre-Order Checklist — Confirm Before You Buy
Use this checklist before placing an AFFF foam concentrate order:
If any item cannot be checked, resolve it before placing your order. Contact CA-FIRE at sales@ca-fire.com if you need technical support confirming the correct specification.
📚 Standards & Technical References
- → NFPA 11: Standard for Low-, Medium-, and High-Expansion Foam — Agent selection, proportioning requirements, system design and annual testing (Annex C).
- → NFPA 16: Standard for the Installation of Foam-Water Sprinkler and Foam-Water Spray Systems — Proportioner design, system installation and testing requirements.
- → API 2030: Application of Fixed Water Spray Systems for Fire Protection in the Petroleum Industry — AFFF system design guidance for petroleum storage facilities.
- → ISGOTT 6th Edition — International Safety Guide for Oil Tankers and Terminals — Foam system requirements and AFFF application guidance for marine installations.
Ready to Order? Get a Quote for S-3-AB or S-6-AB
CA-FIRE AFFF foam concentrate ships factory direct from Fujian. 20 L sample orders available for system compatibility testing. SDS supplied on request. Contact our team for project pricing and lead times.