Firefighting Foam: Concentrates, Proportioning & Application

Firefighting Foam: Concentrates, Proportioning & Application

Water alone cannot hold a flammable-liquid fire. Foam answers the hazards that actually burn here — the Limay and Batangas tank farms, LPG refilling plants, diesel gensets under BPO towers, tanker rollovers on SLEX and NLEX, and service stations dispensing ethanol-blended gasoline. The 2019 Revised IRR of RA 9514 adopts NFPA 11, Standard for Low-, Medium-, and High-Expansion Foam as a referenced standard for foam systems, so the application rates below are NFPA 11 figures rather than rates spelled out in the Philippine text itself. Fire Suppression is 30% of the FOE, and foam is examined under "Tools, Equipment and Apparatus."

What Foam Is, and the Four Ways It Suppresses

Finished foam is built in three stages: foam concentrate is metered into water to make foam solution (proportioning), then air is introduced to make finished foam (aeration). Fail any stage and the blanket fails.

1. Smothering / separating. The blanket floats on the liquid, excludes oxygen and separates flame from fuel surface.
2. Cooling. Water in the bubble structure absorbs heat from the fuel and from adjacent hot steel — tank shells, pipework, drum walls.
3. Vapour suppression. The film and blanket seal in flammable vapour. This is why crews blanket an unignited spill: no vapour, no ignition, no flash-back during recovery.
4. Penetrating. The surfactant lowers water's surface tension so solution soaks into baled or deep-seated Class A fuels instead of running off.

Concentrate Families

The polar-solvent rule matters here. Ethanol is water-miscible: it draws water straight out of an ordinary AFFF blanket, which collapses in seconds. RA 9367, the Biofuels Act of 2006, mandates a minimum 10% bioethanol blend (E10) in Philippine gasoline, and DOE Department Circular 2024-05-0014 opened a voluntary E20 roll-out. Every service-station and fuel-tanker spill you meet is therefore a polar blend, and international guidance calls for alcohol-resistant foam once alcohol content exceeds 10%. AR-AFFF lays a polymeric membrane between fuel and foam that ordinary AFFF cannot form.

Proportioning and the Arithmetic

The percentage on the pail is the volume of concentrate per 100 volumes of foam solution: 3% means 3 parts concentrate to 97 parts water. It says nothing about foam quality — a 1% and a 6% concentrate can make identical foam; the 1% simply carries more chemistry per litre and cuts your logistics.

Concentrate volume = solution flow rate × proportioning percentage × duration

Worked example 1 — diesel tanker rollover on SLEX. A tanker sheds a 120 m² pool. The RIRR quotes NFPA 11's hand-held application rates for spill fires as 4 to 8 L/min per square metre; the commander sets 6.5 L/min·m², 3% AFFF, 15 minutes.

• Solution: 120 m² × 6.5 L/min·m² = 780 L/min
• Concentrate: 780 × 0.03 = 23.4 L/min
• Total: 23.4 × 15 = 351 litres

The same job on a 6% concentrate needs 702 litres; on a 1%, only 117 litres.

Worked example 2 — E10 spill. Polar fuels take roughly double the hydrocarbon rate; a common listed figure is 12.2 L/min·m². That same 120 m² pool then needs 120 × 12.2 = 1,464 L/min of solution, and 1,464 × 0.03 × 15 = about 659 litres of 3% AR-AFFF. Assume hydrocarbon numbers on an ethanol spill and you run dry mid-attack.

Worked example 3 — single handline. Take a 45 mm foam handline flowing a nominal 450 L/min (a typical rated flow for that line; confirm the figure for the nozzle you actually carry). Run for 20 minutes at 3%, it consumes 450 × 0.03 × 20 = 270 litres of concentrate.

Expansion Ratio

Expansion ratio is finished-foam volume divided by the solution volume used to make it: 1 litre of solution at 500:1 yields 500 litres of foam.

Wetter low-expansion foam cools better and resists wind and radiant heat; drier high-expansion foam covers vast volumes on little water but collapses outdoors. Blanket durability is measured by 25% drainage time.

Proportioning Hardware

• In-line eductor. A venturi in the hose lay: flowing water creates a pressure drop that draws concentrate up a pickup tube. Cheapest, most common on BFP engines, most often botched. Its flow rating must match the nozzle's; nozzle pressure must not exceed about 65% of eductor inlet pressure or the venturi stalls; keep the hose to the nozzle short (roughly 30 m), the pail no more than about 1.8 m below the eductor, and the pickup tube submerged.
• Around-the-pump proportioner. An eductor in a bypass from pump discharge back to intake — simple, but a pressurised hydrant supply on the intake can overcome the venturi and stop pickup.
• Balanced-pressure proportioner. A separate foam pump holds concentrate pressure equal to water pressure at a ratio controller, staying accurate across a wide flow range.
• Bladder tank. Water pressure squeezes a rubber bladder of concentrate — no pump or power needed; the default for fixed tank-farm, hangar and loading-rack systems.
• Direct injection. An electronic pump meters concentrate against measured water flow; the basis of compressed-air foam systems, which the RIRR requires to be installed to NFPA 11.
• Nozzles. A standard fog nozzle makes unaspirated foam — acceptable for film-forming concentrates, and it gives reach. An air-aspirating foam nozzle or branch pulls air into a barrel to build a thicker, longer-lasting, higher-expansion blanket, and is mandatory for protein, fluoroprotein, most alcohol-resistant and all medium- and high-expansion foams. The RIRR puts it plainly: for unaspirated foam, normal water equipment may be used provided a film-forming concentrate is used.

Application Techniques

1. Roll-on (bounce-off). Direct the stream at the ground just short of the pool so foam rolls onto the surface. Open, level ground only.
2. Bank-down (bank-back). Deflect the stream off a vertical surface — tank shell, bund wall, building face — so foam runs down onto the fuel.
3. Rain-down. Lob the stream so foam falls gently onto the surface. Slowest, but the only option with no backstop or a pool too wide to reach across.

Never plunge the stream into the burning liquid. Plunging drives foam beneath the surface, mixes concentrate into the fuel, splashes burning liquid outward and shreds the blanket you are building; on a tank fire it churns hot fuel and invites frothing. Apply gently and continuously, do not break an established blanket with a straight stream, and re-apply, because blankets degrade under radiant heat and tropical sun. Foam will not stop a pressurised gas or liquid fire; shut the valve.

Current Affairs: the Fluorine Phase-Down

AFFF, FFFP, fluoroprotein and AR-AFFF all owe their film to fluorosurfactants (PFAS). PFOS was listed under the Stockholm Convention on Persistent Organic Pollutants in 2009 and PFOA in 2019, and the Philippines is a party. Internationally the shift is toward fluorine-free foam (F3): the US Department of Defense issued specification MIL-PRF-32725 for F3 in January 2023, and civil aviation authorities are running F3 transitions. F3 forms no aqueous film, so it generally demands aspirating nozzles, higher application rates and stricter technique. What you must not do on the FOE is assert a Philippine deadline. Section 10.5.3.4(F) bans extinguishers containing Ozone Depleting Substances "in accordance with the phase out schedule by DENR" — a halon rule, not a PFAS rule — and no equivalent published BFP or DENR phase-out schedule for fluorinated foam exists as of July 2026. Answer the chemistry, not a date.