History suggests that each year air travel should see improved safety, but that is not always the case. Changes in aircraft construction materials, firefighting agents and reduced firefighter training, as well as weakened standards and unfavourable passenger practices, could be creating a perfect storm of future tragedies. That impacts us all when travelling on planes.
More near-misses, runway incursions, human errors…
Increasing aviation incidents, human errors, runway incursions, near-misses and poor maintenance are disturbing. It has sparked growing concerns amongst regulators, operators and firefighters about our safety. A near-disaster when a door plug fell out in mid-air (5 January 2024) from a three-month-old B737-9 MAX aircraft, fuels these concerns. Amazingly no one was sucked out of the aircraft, but it forced an emergency landing and US Federal Aviation Administration’s (FAA) grounding of all 171 aircraft of this type for thorough inspection checks of retaining bolts, which reportedly seemed missing.
Of greater concern is the recent devastating runway collision where ferocious fire destroyed a modern A350 aircraft in Japan. It burned for six hours, seemingly unable to be extinguished at Japan’s Tokyo airport (2 January 2024), despite expected use of leading AFFF foams. Miraculously all 379 passengers and crew evacuated safely, although tragically five lives were lost on the smaller Dash-8 plane involved. It was almost a catastrophic disaster. This incident alone sends warning bells about the fire risks and extinguishment challenges of modern composite aircraft. potentially highlighting weaknesses in our expectations from existing firefighting test standards, materials and foam agents. Current fire testing may no longer be fit for purpose in today’s more challenging aviation environment, especially with increasing use of alternative foams, which we know behave differently, requiring slower, more gentle, well-aspirated applications but are prone to sudden flashbacks. It suggests urgent fire-test-standard overhauls may be essential, with greater focus on firefighter training using liquid fuel fires, particularly when transitioning to Fluorine Free Foams (F3s), to ensure life safety is adequately maintained and help prevent future tragedies.
Research confirms composite material use in modern aircraft is growing fast, to reduce weight and fuel costs. A350s have 53% composites, B787s 50%, A380s 25%, even B777s comprise 12% composites, when composite fires are proving harder to control and extinguish. This A350 collision and six-hour fire destroyed the aircraft, reportedly leaving ‘…the severely damaged A350’s wings as the only identifiable pieces remaining of the plane’s charred and broken fuselage.’
Composite materials bring benefits and hazards
Extensive small-scale fire testing shows composite materials are strong, resisting fire longer than conventional aluminium-skinned aircraft. FAA’s 2020 Strategies for Aircraft Rescue and Firefighting (ARFF) confirms: ‘The components of advance composite materials are all affected by fire. Resins and epoxy will burn, particularly in the presence of an aviation fuel fire. … Pooled fuel fires should be controlled first, then burning composites, smoldering composites tend to reflash if not sufficiently cooled.’
US Navy firefighters (2019) found: ‘One of the specific threats of carbon fibers exposed to fire and/or heat can release Methyl Ethyl Ketone Peroxide (MEKP), a liquid catalyst used to accelerate fiberglass curing. It can cause permanent blindness from a single small dose.’ Safety Data Sheets confirm MEKP is a flammable polar solvent liquid, requiring alcohol-resistant (AR) foams for fast, effective, reliable extinguishment. Regular aviation foams whether Fluorine Free Foams (F3s) or AFFFs are substantially attacked by polar solvents, significantly reducing effectiveness. Might this help explain long extinguishment delays in composite fires like this A350? Perhaps we should be using low-viscosity AR foams for composite fires in future, ensuring rapid control and quick extinguishment are maintained?
Europe’s Aircraft Fire Report (2014) found:
Composites are an efficient fire barrier, but:
- The resin warming destroys the cohesion between carbon fibres, which changes the mechanical properties of the composite. A mechanical stress can break the fibres as soon as the first layers of fibres are de-correlated;
- The fast heat penetration in the composite induces an off-gassing of pyrolysis products, potentially toxic (intoxication of the occupants) and flammable (gas ignition) with a potential fire propagation in the cabin after few tens of seconds, …potentially having a fatal effect on passengers and crew survivability.
Concluding: ‘This requires a re-evaluation of the hazards, to reduce the fire incident/accident rate and to increase the survivability of the passengers and crew during accident involving fire.’ Shouldn’t this trigger a review and overhaul of existing firefighting practices and fire test standards, especially when transitioning to PFAS-free foams which behave very differently from faster, more effective C6-AFFFs?
FAA’s 2012 ‘calculating agent quantities’ report also found smoldering composite material difficult to extinguish, potentially re-igniting suddenly and unpredictably during passenger evacuations: ‘It was concluded that fast response by the fire fighters reduced the chance that smoldering fire will be established. Since fire fighters may have to work in close to the aircraft to control the composite fire, they must be aware of potential re-ignition of fuel under or around the aircraft.’
Composites are fast gaining a ‘track-record’ for difficult extinguishment. A small $1.4 billion US Military B2 stealth bomber was destroyed by fire in Guam (2008) after burning for six hours, despite 83,000 gals (314,189 litres) of fire water and 2,500 gals (9,463 litres) of AFFF concentrate being used. Nothing could be saved. A 2019 Defence System Information Analysis Center (DSIAC) Report confirmed two composite ship fires (Norwegian and Indonesian Navy vessels) also both resulted in complete loss: ‘One burned for 24 hours at sea before capsizing, breaking apart and then sinking. …The fires were so intense that on-board firefighting measures were not enough to overcome them.’ The other vessel caught fire from an electrical short while docked during fit-out for sea trials, but the fire-protection system had not yet been installed. Reportedly large and intense fires overwhelmed the fire-protection measures available, so the entire ship was destroyed. How might alternative PFAS-free products behave, compared to MilSpec AFFF usage?
Aircraft take-off and landing performance decreases as temperatures rise
Elevated summer temperatures show decreased aircraft take-off performance. Research in 2023 found: ‘It is urgent and crucial to understand the effects of increasing temperature on the complicated and comprehensive performances of aircraft. As air warms, it becomes less dense. Low-density air conditions further lead to reduced lifts for aircrafts, which significantly influences the maximum take-off weight (MTOW) of an aircraft. The warming air leads to the MTOW reducing and take-off distance increasing.’ Continuing: ‘The take-off distance does not change linearly with temperature but shows a stronger increase with higher temperature.’ Extended take-off distances and reduced aircraft manoeuvrability during landing increase the risk of over-runs and unexpected accidents under more challenging conditions.
Weakening fire test standards – a major concern
We seem to be witnessing weaker aviation firefighting test standards, extended response times and lacking functionality verification under realistic worst-case emergency fire conditions, including composites during hot summers. This includes verifying long-term stability without viscosity increasing, which could cause reduced proportioning accuracy with potentially poorer fire performance over time. We must ensure compatibility and effectiveness of F3s with equipment used and training provided. The new Fluorine Free Foam (F3) MilSpec (MIL-PRF-32725, January 2023) for land-based fresh water (potable) use has a less demanding test application rate, closer to International Civil Aviation Organisation’s (ICAO) Level B, not Level C like existing AFFF MilSpec (MIL-PRF-24385F (SH) amdmt4, Apr.2020). Already industry comments for F3 MilSpec improvement are being sought for revision. Are weakening firefighting test standards reducing passenger, crew and firefighter’s safety?
With such composites evidence to hand, why did ICAO reduce its firefighting foam extinguishing fire performance criteria from 60 to 120 seconds at Level B and C in 2015, when F3s were struggling to pass? Allowing continuing edge flickers, when this was known to potentially re-ignite fuel, and allowing adjacent composite materials to continue smoldering and re-flash areas in which surviving passengers are escaping to safety, seems counter-intuitive. Could it be making life harder for firefighters to facilitate rescues, placing them and escaping passengers in potentially more dangerous situations, particularly when F3s are used? Increasingly ICAO Level B, C and F3 MilSpec fire tests seem inappropriate for today’s more challenging demands.
Important tests missing from ICAO
Currently, ICAO fire tests rely on a single premixed foam concentrate fire test at just 15°C on Jet A1, when summer temperatures globally are reaching over 40°C (104°F) in many places. Jet A1 becomes more volatile above its 38°C flashpoint. ICAO uses a special nozzle, un-representative of typical nozzles widely used in practical Aircraft Rescue and Firefighting (ARFF) use, without any repeat fire test of aged concentrate, proportioning devices to determine acceptable tolerance variation, or compatibility test with co-incidentally applied dry chemical powder (often used with foam for rapid extinguishment of aircraft engine fires). Unlike MilSpec, ICAO also has no fire test using gasoline, relevant for all congested airport car parks (often multi-storey adjacent to terminal buildings) and hazardous set-down/pick-up areas at the heart of most major city airports.
Such extra testing is mandated by MilSpec, so why not ICAO? No fire-test standard currently requires composite aircraft materials, which seems an increasingly important fuel consideration in future.
National Fire Protection Association (NFPA) recommends increased Level B applications
New NFPA 460:2024 includes NFPA 403:2018 recommendation (Annex B.6) for 7.5L/min/m2 (0.18gpm/ft2) application rate for ICAO Level B approved foam use, not the 5.5L/min/m2 widely used. It explains: ‘There has been limited full-scale testing of ICAO C foams, but tests to date have reflected extinguishments on Jet A within 1 minute at ICAO Application rates of 0.992gpm/ft2 (3.75L/min/m2). The 0.13gpm/ft2 (5.5L/min/m2) application rate requirement for AFFF meeting MilSpec in NFPA 403 is 40% higher.’
This raises big questions: Are alternative ICAO Level B/C foams, particularly F3s, still effective at this low 40% safety factor operationally? It’s considerably less than existing double or triple safety factors currently required by ICAO Level B and AFFF MilSpec/ICAO Level C foams respectively? What Level B foam application rate is required to extinguish Jet A1 within 60 secs? Does it allow any safety factor?
NFPA 460 Annex B.6 recommends:
Airports adopting ICAO foam concentrates should evaluate equipment requirements any time a switch to a new manufacturer of foam concentrates is considered.
Therefore, starting with the 2018 edition of NFPA 403, the following application rates by test standard are used:
- Mil-F 24385 and ICAO Level C = 0.13gpm/ft2 or 5.5L/min/m2
- ICAO Level B = 0.18gpm/ft2 or 7.5L/min/m2
- ICAO Level A = 0.20gpm/ft2 or 8.2L/min/m2
Presumably this revised Level B operational rate also applies to the new F3 MilSpec, since it uses a similar test rate of 0.07gpm/ft2 (2.87L/min/m2) on Jet A/A1 (Level B is 0.06gpm/ft2 or 2.53L/min/m2).
This should be of particular concern to regulators, fire-testing standards agencies, aviation and industrial firefighters, when extensive comparative fire testing confirms F3s generally deliver inferior fire performance to C6-AFFFs and may require typically 1.5–3 times higher application rates to extinguish test fires on volatile fuels like gasoline.
Perhaps surprisingly, NFPA 460 endorses response times extended from 2 to 3 minutes, when evidence shows composite materials exposed to exterior heating can quickly create problems inside the aircraft. potentially reducing passenger survivability in a major fire event below 1 minute. Should passengers, crew and firefighters suffer increased risks to life from diminishing safety standards, which may help reduce airport operating overheads?
Combined factors justify fire-test standards overhaul
Challenges from more difficult firefighting, composite materials, hotter summers, adverse heat stress, delays in evacuation from infirm passengers, those with babies and frightened children, disabled or injured during the accident, plus those insistent on accessing overhead lockers, could potentially increase the loss of life. Seconds matter when saving lives.
Composite fuselages could deliver increased toxicity and flammability of smoke in cabins, sudden re-involvement from smouldering composites, excessive firewater run-off, extended foam use (even if non-fluorinated), plus increased disruption and danger to other aircraft, passengers, flight crews and firefighters. We had a miraculous escape in Japan’s A350 January fire. The criticality of urgently addressing these issues in our fire-test standards and firefighter training should not be underestimated in preventing future major aircraft fire tragedies.
Let’s hope new evidence from this Tokyo A350 fire, and improvements to safety standards will help make us all safer when we travel in future.
About 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.
