Mike Willson, firefighting foam and foam systems specialist, investigates whether airport firefighting foams fit is for purpose under increasingly hot summers

The world is experiencing more frequent and severe summer heat waves, impacting our safety.  Soaring 40-47^oC temperatures across much of Europe, North America, India and Pakistan across to China, Korea, Australia and Japan were experienced during summers 2021 and 2022. Usually restricted to Saharan Africa, Middle East, Mexico, even Central Asia, July 2022 saw Arctic Norway glow in 30.8^oC, while London’s Heathrow sizzled in record breaking 40.2^oC. Heat stress and increased fire volatility are both outcomes facing firefighters.

We rely heavily on firefighting foam fire test approvals like ICAO (International Civil Aviation Organisation) and European Norm EN1568-3 to verify acceptable fire performance under all major credible event conditions being faced during fire emergencies, including hot summers. Such fire testing is routinely conducted in cool 15±5^oC conditions. US MilSpecrequires 23±5^oC but most choose the lower temperatures, gaining a cooling advantage – never elevated around realistic ≥40^oC.levels. Do all foams still work under such elevated conditions? How do we know? It is becoming a significant life safety issue.

Ignitable vapours hover above pooled fuel when Jet A1’s 38^oC flashpoint is exceeded. These vapours are easily lit by burning embers or incandescent materials, potentially causing rapid re-escalation. Rising temperatures increase extinguishment difficulty, with fuel vapours more easily penetrating foam blankets, reducing effectiveness and causing premature collapse, particularly when fuel repelling or vapour sealing additives are absent. Where does this leave passenger safety?

Foam quality

Foundation research by US FAA (Federal Aviation Administration) established that Fluorine-free or PFAS-free foams (F3s) (i.e. without aqueous film formation) showed: “The predominant factor defining firefighting effectiveness is foam quality, which is indicated to rapidly deteriorate through the loss of liquid as it drains from the foam body at elevated solution temperatures.” It concluded: “As the foam viscosity increases, the fluidity decreases, and the foam may become more difficult and time-consuming to distribute uniformly over a burning fuel surface. Therefore, excessively high or low water temperatures are to be avoided.”

Investigations by US Naval Research laboratory in 2015 confirmed that: “Fuel surface cooling by the foam and the resulting reduction in fuel vapor pressure, which depends exponentially on the surface temperature. … the interface cools because the two layers are at different temperatures”. Consequently, higher foam solution temperatures have an exponentially reduced ‘cooling’ effect, making fires harder and slower to control and extinguish. Maximising rapid cooling could be delivering ‘easier approval passes’ – but how does this affect hot summer performances?

NRL extended their work in 2017 finding: “As the fuel temperature is raised, there is a higher concentration of fuel vapours beneath the foam than at lower temperatures. This increased concentration at the foam interface can increase the amount of fuel transport through the foam, increasing the rate of foam degradation … For all experiments F3 degraded much faster than AFFF. …The effect of surfactant formulation is a close second relative to the temperature effect.”

2012 FAA research cautioned against the impact of aircraft composite materials like carbon fibre: “There is also potential for re-ignition of a fuel fire from smouldering fuselage composites.” It referenced US Military graphite/epoxy/carbon fibre composite testing, finding that: “This composite would self-sustain combustion in as little as 2.5 minutes of exposure to an external pool-type fire. … The pool fire was easily extinguished in all tests. However, extinguishment of the composite combustion was not as easy. The surface flames were readily extinguished, but smouldering composite combustion was already established. To extinguish … fire fighters applied a continuous stream of AFFF directly on the composite material. After applying AFFF for 3 minutes or more, the smouldering composite combustion was extinguished.” Do such re-ignition sources further expose F3 vulnerabilities, without vapour sealing additives?

Protocol deficiencies

These findings highlight potential deficiencies in our existing fire test protocols. FAA’s Oct. 2021 Cert Alert raised public safety concerns with Fluorine Free Foams (F3s) due to delayed extinguishment times; failure to maintain fire suppression; incompatibilities with dry chemical and other foam agents, plus firefighter training strategies. FAA’s rigorous testing of nineteen F3s (nine commercially available, ten developmental) at room temperature (around 20^oC) concluded: “Approximately 400 fire tests have been conducted; none passed MilSpec or ICAO Level C”.

Consequently, FAA: “Conducted ICAO Level C tests both outside and inside because of test results.” All F3s tested failed ICAO Level C and MilSpec fire tests indoors (~20^oC) in FAA’s latest USD $5 million ‘state-of-the-art’ fire test facility. They also all failed ICAO Level C protocol when re-tested outdoors under similar conditions. Surprisingly analysis showed these leading F3s had Fluorine levels from 10-87ppm, which could exceed some residual PFAS expectations. 

62% of F3s also failed to extinguish within Level C’s 2-minute requirement, with two failing to extinguish completely. Burn back testing was also failed by 66% F3s tested. All F3s similarly failed MilSpec’s 30sec extinguishment outdoors, only one achieving 38secs, the rest up to 2mins 23secs (also ~20^oC). FAA concluded: “Overall, none of the tested FFF candidates can be considered a direct replacement for AFFF without compromising the efficacy of fire extinguishment.”

FAA and NRL are undergoing extensive scientific research and rigorous fire testing to find adequately effective F3 alternatives to meet these demands, but so far unsuccessfully. So, what happens during hot summers, when conditions make fires even harder to extinguish?

ICAO requires Aircraft Rescue and Firefighting Services (ARFFS) to operationally use 5.5L/min/square metrewhen firefighting with AFFFs, delivering adequate safety under wide ranging operational conditions during credible major fire events, based on a safety factor double the Level B fire application rate of 2.5L/min/square metre(1.56L/min/sq metre for tougher Level C).Is this safety factor adequate for F3s without fuel-repelling or vapour-sealing additives? Reluctance to conduct realistic high temperature F3 competency testing to ICAO Level B, means we still don’t know, potentially placing travellers’ lives under increased risks.

Unnecessary risks

This safety factor covers a range of practical ‘contingencies’ across often unforeseen, diverse prevailing conditions associated with major credible aircraft fires, including: Foam destruction factors like wind, rain, snow, ice, high/low temperatures, updrafts/vortexing; Fuel re-exposure by wind increasing re-ignition risk and sudden flashbacks; Some foam blankets (particularly PFAS-free) are attacked by co-incident dry chemical powder usage; Premature reduction in foam blanket fluidity/effectiveness from low humidity; longer pre-burn times increasing fire intensity; and lower foam blanket quality and greater plunging effects (from non-aspirating/lower expansion nozzles), potentially exacerbated by pressure fluctuations.

Additionally: Temperatures exceeding fuel flashpoints increase vapourisation rates, fire intensity, particularly when pooled on hot concrete runways or tarmac; Under or over-rich proportioning with resultant under-performance (‘too watery’ or ‘over-stiff’ if rich), potentially reducing foam quality or duration; Poor mixing of viscous concentrates, forming inadequately dissolved ‘globules’; Reduced effectiveness from delayed foam activation/response and composite materials; Stability changing with water quality (hard/soft/bore/seawater); and insufficient/inadequate training on foam type; operator errors; exposing foam vulnerabilities (not strengths), eroding effectiveness when insufficiently conservative tactics used.

Shouldn’t these safety considerations be incorporated into ICAO Level B/C fire tests? US MilSpec (2020) includes most considerations, which now risk exclusion in the draft land forces alternative F3 MilSpec, seemingly with ‘watered down’ performance levels potentially exposing not safeguarding lives – it’s key objective. Worrying evidence from a 2016 Dubai Boeing 777 crash in 48^oC conditions, saw the aircraft ‘burned out’ after 16 hours, despite several failed attempts to extinguish using F3s.

So our Regulators, EPA’s, Standard approvals, FAA, Defense ARFFS and the travelling public are left with a major dilemma: Either we ‘force through’ weaker F3 specifications, without providing equivalent current fire protections to save lives in future major fire incidents, or we continue using proven, effective, life protections even when severe conditions prevail (eg. Syria, Afghanistan) or like civilian heat waves of 2021-22, by continue using high purity, short-chain C6AFFFs.

Evidence suggests it’s time for a re-think before exposing many lives to unacceptably increased risk of harm – or do we choose to continue risking the loss of plane-loads of precious lives unnecessarily? The real question that needs to be asked: it that even ethical?

About the author

Mike Willson BSc Hons, MCIM, is a firefighting foam and foam systems specialist with over 35 years’ experience of developing, testing, comparing and reviewing fire performance and environmental impacts of both fluorinated and fluorine free foams, their delivery devices and integrated fixed systems performances. An active member of Fire Protection Association Australia’s Special Hazards Technical Advisory Committee, he provides technical advice to a diverse range of stakeholders to better protect Class B flammable liquids with potentially suitable C6 and PFAS-free (F3) alternatives.

This article was originally published in the January edition of IFSJ. To read your FREE digital copy, click here.