What important criteria are missing from recent fire test standards?

Published:  03 November, 2014

The International Civil Aviation Organisation (ICAO) revised their fire test standards recently, with changes to their Level B fire test and introduction of a new higher performance Level C fire test (1). Mike Willson, of Willson Consulting (Tasmania), questions whether a more comprehensive standard could have been delivered. 

Australia has been discussing Standard issues between civil airports, replacing their ICAO Level B approved Aqueous Film Forming Foam (AFFF) with a Level B approved Fluorine Free Foam (F3) largely on environmental grounds.

The Australian Defence Force continues their commitment to military specifications and it is anticipated they will adapt their requirements towards AFFF meeting the US Military Specification Mil-F-24385F (Mil Spec) Standard (4,5), the US EPA PFOA program and local environmental tests defined in Western Australia’s recent Foam Policy, plus general compliance with Australian Def(Aust)5706 (2) (requiring laboratory fire tests  meeting the UK DEF STAN 42-40/2(3), and ICAO level B1 4.5m2 fire test).The Mil Spec only specifies AFFF foams (Fire Extinguishing Agent, Aqueous Film Forming Foam (AFFF) Liquid Concentrate, for fresh and seawater) but other foam types are currently unable to pass, so do not meet their QPL requirements.

In two locations these Australian civil and military organisations share an airport, so there are potential logistics and efficiency considerations that suggest a single firefighting foam agent may make more sense on these shared sites.

Applying a fair evaluation

This becomes complex since the fire test requirements in each standard vary, but perhaps of greater significance is the raft of important secondary performance criteria that these Defence Standards demand, yet which are not present in the ICAO Standard (8).

These secondary criteria are necessary to ensure reliability and consistency of firefighting capability, not only in peaceful Australia, but also war torn theatres around the globe in which Australian troops and equipment may need to operate. Military and industrial standards fire test foams with fresh and usually more challenging seawater. Many civil airports adjoin or protrude into the sea and extended events may require the use of seawater to extinguish potential incidents, yet ICAO fire tests are conducted in freshwater only. Dry chemical is a widely used secondary media for fires involving aircraft, so compatibility with foam concentrates should be a pre-requisite. Perhaps consideration should be given to applying these secondary criteria to civil airports which can also be operating at coastal locations and under arctic, desert, temperate and tropical conditions?

Real life experiences and a broader range of Military end user’s requirements suggest that more than just fire tests need to be considered. The first Qualified Products List (QPL) of approved AFFFs meeting all Mil Spec requirements arrived in 1966 (6). Even 2014 sees only four 6% and five 3% AFFFs on this approved Mil Spec QPL list (7), suggesting it is not easy to meet these standards.

The rationale for these additional criteria is explained within each section below. Most would probably agree they are a benefit for military personnel, but my question is, could they also benefit civilian aircraft travellers, flight crews and Airport Rescue and Fire Fighting (ARFF) services worldwide?

Environmental impacts

Defence Standards adopt a more holistic approach, beyond reviewing fire test performances in isolation. Subsequent impacts when firewater run-off may enter the surrounding environment, water courses, or waste water treatment facility for disposal, are important considerations for any foam usage.  Def(Aust)5706 also requires evidence of persistence, disposal requirements, non-bioaccumulating, and non PFOS-based status.


How poisonous these products may be to fish and other aquatic organisms in lakes, rivers and the sea is measured by aquatic toxicity. Testing in concentrate form simulates a worst-case scenario, such as inadvertent spillage into a waterway from damaged or leaking containers. Placing limits on aquatic toxicity minimises the risk of unacceptably polluting events occurring, during normal use. Toxicity may derive from a range of foam ingredients, including hydrocarbon surfactants (detergents), solvents, foam boosters, film forming additives, stabilisers and others. A fluorine-free product does not guarantee low aquatic toxicity. Often the reverse occurs because higher detergent levels are required and these ingredients are quite toxic to aquatic organisms, including waste water treatment bacteria.


Biodegradability testing identifies how fast or slowly a foam concentrate will degrade in the natural environment, once it has been used on a fire and drains into containment prior to waste water treatment processing, or as a worst case directly into a water body like a pond, river or bay. Placing limits on how fast the agent breaks down, helps control the rate at which oxygen is depleted in the receiving waters. Even with a seemingly benign and non-toxic substance like milk, its biodegradation is very fast by acting as a food for bacteria. Even a small spillage could quickly suffocate fish and other aquatic organisms, even though it is not toxic, causing them to die unexpectedly. Releases into water bodies of seemingly benign products, could cause severe pollution incidents, which acceptability limits are trying to avoid.

Chemical and biological oxygen demand

The amount of oxygen required for any product to degrade completely is determined by its Chemical Oxygen Demand (COD).  This may increase significantly with additional ingredients that contain sugary water soluble polymers (eg Alcohol Resistant AR-AFFF and F3), which in turn act as food for organisms. This could lead to faster oxygen depletion in receiving water bodies.

The oxygen demand required by biological organisms digesting these products is recorded as Biological Oxygen Demand (BOD), defining oxygen depletion speeds, often over a 20 day period. A 65% biodegradability rate is generally acceptable. Too rapid BOD could lead to organisms dying through suffocation, potentially leaving the water body sterile and effectively stagnant.

Interestingly, and perhaps uniquely, Def(Aust)5706 also requires evidence that acceptable foams do not cause temporary incapacitation or permanent residual injury to firefighters during use.

Stability and inter-agent compatibility

Foam concentrates and premix solutions under Mil Spec are stored for 10 days at 65°C to ensure no precipitation, stratification or premature deterioration occurs, prior to physical properties and smaller fire testing. Def(Aust)5706 requires 48 hr testing at 65°C, with -15°C for 1 hr to ensure no separation. It also requires a minimum five-year guarantee for storage in sealed containers between -21°C and +63°C, without deterioration. When mixed with existing in-service AFFF concentrates in bulk tanks, the mixture must still pass the fire tests, with little or no reduction in storage life. This becomes very challenging for viscous AR-AFFF or F3 agents.

In recognition that the preferred foam concentrate may not be available at every location, each Mil Spec QPL 3% listed product must be mixed in equal parts, then pass the physical properties and fire tests satisfactorily. Useful verification that mixing another product into a bulk tank will not harm the existing stock of AFFF foam being used. This QPL also has a refractive index requirement that helps users calibrate their equipment when several compatible QPL agents are mixed together for use.

 This Mil Spec compatibility requirement allows mutual aid groups to utilize foam stocks from partners during emergencies without fear of contamination, or rendering proportioning systems and emergency equipment inoperable, disrupting effective response and incurring additional repair and maintenance costs. An associated economic and logistical benefit derives from having several sources of supply versus a single source situation, ensuring maximum product supply flexibility when operating across different global theatres.

Corrosion testing

Before using most chemicals, assessing whether they pose a general or localised corrosion hazard to military hardware, vessels, aircraft and specific foam-making equipment is advisable before endorsing acceptability. Defence standards require concentrate testing on diverse metals over a period to check whether any pitting or surface corrosion is evident. Mil spec requires a 60-day period using seawater, which maximises the probability of corrosion occurring. Nothing is defined by ICAO.

A complex raft of container testing requirements is usually required to ensure no cracks or leaks during storage and transportation. ICAO has no such requirements.

Variable proportioning

Fire tests frequently use premix solutions for accuracy, yet these rarely reflect real life incident usage when foam proportioning systems are mostly used. Proper maintenance and calibration is often lacking due to resource or cost.  Proportioning equipment accuracy is not always guaranteed, and varies with temperature. Underwriters Laboratories (UL 162) (8) requires acceptable proportioning at the foam’s lowest use temperature to meet ≥85% of its ambient proportioning accuracy. This seems a better way to gain assurance of acceptability, particularly with more viscous concentrates.

Establishing that approved foams can adequately extinguish the fire under ‘rich’ or ‘lean’ induction conditions (particularly when physical damage to proportioning systems during conflict or terrorist situations may occur) would seem imperative. Mil Spec requires fire testing at half strength, and at five times ‘over-rich’, before operational acceptability. This is not the case with ICAO.

Proportioning accuracy

Most measurements require a tolerance to minimise the degree of error during calibration, measurement, or varying viscosity of the foam being used. This is essential for a proportioning device, otherwise the fire may not extinguish. It also ensures verification for measured premix foam solutions. Proportioning accuracy can also be impacted by temperature, the foam’s viscosity or relative thickness. The latest 2014 ICAO Airport Services Manual Chapter 8 (9) now has a new Section 8.1.6 defining an induction tolerance of ±10%.


The viscosity of AFFF foam is generally fluid and Newtonian (ie. does not change with flow or shear rate, remaining constant and independent of pumping or proportioning methods). Concentrate fluidity simplifies proportioning and mixing AFFF uniformly into water. This creates reliable, uniform foam solutions for effective control and incident extinction.

Most AR-AFFFs and F3 products contain water-soluble polymers and polysaccharide gums causing much higher viscosities, typically around 5,000 centistokes at 20°C. Many of these foams are pseudo plastic or thixotropic (sheer-thinning). Their viscosity changes as energy is imparted to the foam, becoming thinner when stirred, yet thicker when stirring stops.  They can behave anywhere between thick wallpaper paste and runny honey, often becoming virtually solid around freezing (0 to -5°C). Consequently they are thicker and flow less easily from the container, under most climatic conditions. Blockage or restricted movement can result from small bore vehicle pipework and proportioning devices, leading to under-induction or no foam concentrate flow, so water alone may be ejected onto the fire. This could cause reduced effectiveness, flare ups, incident escalation and danger to firefighting personnel.

ICAO’s latest edition (9) recognises this in section 8.1.5 by accepting differences in viscosity between foams, and the vulnerability of vehicle pipework to restricted flow. Accordingly it clearly states “The viscosity measurement of a foam concentrate when at its lowest temperature should not exceed 200mm2/s (centistokes). Any higher registration will restrict flow and retard its adequate blending into the water stream unless special precautions are taken. The determination of viscosity for pseudo plastic (thixotropic) liquid type foam concentrates may differ from this method, such concentrates may be utilized following a thorough proportioning test aimed at the agent can effectively be proportioned within the required tolerances using a similar ARFF vehicle system.”

Whilst useful for new build vehicles where larger bore pipework for generally viscous F3 concentrates could be included, this may still cause significant problems trying to “retro-fit” F3 foams into vehicles originally designed for AFFF concentrates. This may result in pipework blockages, under-induction, inadequate mixing, or potentially all combined.

 The US Federal Aviation Administration (FAA) in its 2002 CertAlert (10) warns: “The following problems are associated with the use of alcohol type foams on an airport.  Alcohol type foams are usually not compatible with AFFF currently in use at airports, and ARFF vehicles cannot proportion alcohol foams correctly without changes in the mechanical proportioning systems.  Also, a special additive to the alcohol foam can produce, over time, a scale that can form in and obstruct the metering valves on truck foam systems.” Since nearly all F3 agents behave very similarly to AR-AFFFs in terms of proportioning, these same problems should be expected to apply.

Inadequate mixing

In addition, proportioning viscous concentrates can tend to form globules which fail to mix adequately within the water stream. Induction may occur, but discrete concentrate globules within the water flow tend to sink and coalesce along the bottom of the pipe with clear water flowing above. This failure to mix with the water stream can prevent fire control or extinguishment. Thicker concentrates require more energy at the induction point to achieve uniform mixing into water flows, which may not occur if proportioning devices are primarily designed for Newtonian foam usage. Alternative positive displacement devices can generally rectify such problems.

Portable inductors relying on atmospheric pressure to operate are particularly prone to these under-induction problems because they operate as a ratio of orifice sizes and an orifice sized for Newtonian concentrates will often under proportion with viscous concentrates. Consequently inductors designed with larger bore orifices specifically tailored to the viscosity profiles of polymer-based concentrates with separate “AR” settings usually improve accuracy results.

Test temperatures to reflect reality

Climate zones vary around the world and fuels may be less volatile, and resulting foam bubbles more stable, if colder temperatures are used for testing, so foams will behave very differently in arctic compared to tropical conditions. Surely specifications should not just identify a minimum foam solution and fuel temperature requirement, but a higher ambient fire testing requirement, not only to enable fair comparison, but also to simulate warmer locations, where otherwise foams may struggle to control or extinguish a real fire. Seasonal changes between summer and winter also need consideration, as they may impact on viscosity and proportioning accuracy. I suggest that specifications should require two fire tests to be passed, at perhaps 3°C and 33°C, to better reflect realistic ambient conditions in an emergency.


A comprehensive range of important secondary criteria is required to be met and verified by foam concentrates, as well as fire testing, before generally being accepted for military use. These must provide the necessary flexibility and performance reliability needed during diverse deployment scenarios. This should favour the identification of more robust, flexible and valuable concentrates. It also increases quality assurance, particularly when these products are often required for fast action in demanding and potentially mission-critical situations.

I believe such criteria, if adopted in the civilian sector, would improve fire safety for all civil passengers and emergency responders. Aren’t civil airport incidents equally demanding and mission-critical?

Secondary criteria remain a fundamental and valuable plank of military firefighting requirements. Tougher criteria still favour leading AFFFs as the foam of choice for reliability, flexibility and speedy extinction. Other foam types have been submitted against the Mil Spec (5), but failed to pass or meet the QPL requirements (7). Personal communications indicate the Australian Defence Force are refusing to accept F3 foams at their shared airbases, which is believed to be on the basis they do not perform as efficiently and effectively as their existing Mil Spec AFFFs.  In addition AFFFs reliably pass the former ICAO level B fire test requirement of extinction within 60seconds, where it seems most F3 agents are slower, requiring the revised 120 seconds to achieve extinction after sometimes prolonged edge flickers. A change that will also allow inferior AFFFs, and previously excluded foam types like FP, Protein, other modern F3 to pass, which previously were excluded into Level A.

Surely adoption of these secondary criteria as with military standard testing, plus proportioning scrutiny would be useful in the civilian arena, increasing the resilience and safety of ARFF fire crews; delivering improved reliability of outcomes; and extending current capabilities at civil airports. Wouldn’t that benefit everyone?



1. International Civil Aviation Organisation (ICAO), 2013 – Revised ICAO Fire Test Protocol, Airport Service Manual Doc 9137, Part 1 Chapter 8 Rescue and Fire Fighting. http://www.caainternational.com/docs/default-document-library/revised-icao-test-protocol-july-2013.pdf?sfvrsn=2

2. Australian Government, Department of Defence, 2009 – Australian Defence Standard Def (Aust) 5706 - Foam, Liquid extinguishing: 3 percent and 6 percent concentrate.

3. UK Ministry of Defence, 2002 – Defence Standard 42-40/2 – Foam Liquids, Fire extinguishing (Concentrates, foam, fire extinguishing), ftp://ftp.iks-jena.de/mitarb/lutz/standards/dstan/42/040/00000200.pdf

4. US Department of Defense, 1994 – Military Specification MIL-F-24385F(SH) “Fire Extinguishing Agent, Aqueous Film Forming Foam(AFFF) Liquid Concentrate, for fresh and Seawater”, https://www.wbdg.org/ccb/FEDMIL/f24385f.pdf

5. Australian Government, Department of Defence, Defence Support Group, 2008 – Environmental Guidelines for Management of Fire Fighting Aqueous Film Forming Foam (AFFF) Products

6. Place & Field, 2012 – “Identification of Novel fluorochemicals in Aqueous Film Forming Foams (AFFF) used by the US Military” Environ Sci Technol. 2012 July 3;46(13): 7120–7127. http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3390017/

7. US Department of Defense, 2014 – Qualified Products Database, Mil F 24385F(SH) http://qpldocs.dla.mil/search/parts.aspx?qpl=1910

8. Underwriters Laboratories Inc.,1994– Foam Equipment and Liquid Concentrates, UL 162, Seventh Edition. http://ulstandardsinfonet.ul.com/scopes/scopes.asp?fn=0162.html

9. International Civil Aviation Organisation (ICAO), Airport Service Manual Doc 9137, Part 1 Chapter 8 Rescue and Fire Fighting 4th Edition, 2014.

10. US Federal Aviation Administration, 2002, CertAlert-02-04 Aqueous Film Forming Foams (AFFF) concentrations, restrictions and other user guidelines. http://www.faa.gov/airports/airport_safety/aircraft_rescue_fire_fighting/

The Author

Mike Willson has over 25 years experience in the fire industry across many sectors including aviation, refineries, brigades, bulk fuel storage, much of it involved in flammable liquids as a technical specialist on Class B foams, their application and associated foam delivery systems. He has been deeply involved in their product development and testing for many years, and has co-ordinated several emergency foam responses to major incidents worldwide.  He also has a deep understanding of high volume fluid transfer systems, large capacity monitor systems and the special hazards associated with liquefied gases, particularly LNG.

He was heavily involved in the UK Government’s strategy review on PFOS (PerFluoroOctanyl Sulphonate) and contributed to the European CEN Standards Committee by helping develop the recent fixed foam firefighting systems standard EN13565-2:2009 which involved some ground-breaking work on bund protection, LNG and bulk storage tank protection. He recently contributed to the Fire Protection Association of Australia’s comprehensive Information Bulletin on the Selection and Use of Firefighting Foam.

He provides technical consultancy fire protection advice particularly in the environmental impacts of foams, but also training workshops, system design reviews, site surveys with system upgrade recommendations. He also writes articles on topical firefighting and foam issues. Other work involves business sustainability, energy efficiency and project management of Solar PV systems in Australia

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