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  • Writer's pictureChas Murrell

FUEL FOR THOUGHT … Aviation Rescue Fire Fighting and the coming cryoplane revolution

The aim of this paper is to apply current Aviation Rescue Fire Fighting (ARFF) tactics against an aircraft fuelled with liquid hydrogen (LH2).

This paper was originally published in 2008 in the Aviation Fire Journal and the PDF is attached below.

ARFF for Cryoplanes
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The demand for commercial jet travel has never been greater than it is now. Aircraft such as the soon to be introduced double deck Airbus A380 powered by aviation turbine fuel, are carrying greater loads over longer distances than ever before. This paper will explore the environmental impact of aviation turbine fuel and why liquid hydrogen is a viable alternative. Furthermore, it will also explore the efficacy of Aviation Rescue Fire Fighting tactics applied to an aircraft fuelled by liquid hydrogen. The need for an Aviation Turbine (AvTur) replacement

In the coming decades, the adverse environmental impact of aviation will become such that an increasingly powerful influence on aircraft design is unavoidable. Environmental impacts will progressively restrict the growth of aviation, except if the adverse impact per passenger kilometre can be significantly abridged as compared to today’s levels (Green 2003) (NASA Glenn Research Center 2002).

Turbine engines produce, amongst other gases, carbon dioxide (CO2). CO2 is a greenhouse gas that most significantly remains in the atmosphere for 50-100 years. The only other emission gas remaining in the atmosphere for a time measured in years is Methane, (8-10 years). The remaining greenhouse gases have lives in the atmosphere measured only in days, weeks or months (Green 2003).

The position of causing burgeoning pollution that the aviation industry

currently finds itself in, is similar in many ways to the position that the car

manufacturing sector found itself in, in the early 80’s. The solution then, as it is now,

is related to fuel (Shauck & Zanin 2002).

In addition to the environmental issue, the issue of dwindling world oil

reserves is also paramount. In 2003, the University of Utah calculated the weight of

pre-historic plant matter that was required to produce all the fossil fuels used in 1997.

The figure arrived at was a staggering 44 million billion tonnes. This figure in 2003

terms, equated to 22 percent of all plants then on the planet (University of Utah 2003).

The eleven nations that comprise OPEC, (Organization of the Petroleum Exporting Countries), aver they can supply oil for the worlds needs for the next 80 years. OPEC currently supplies approx. 40% of the earth’s oil and controls approx. 60% of world reserves. By 2010, Russia is expected to be the 2nd major world oil supplier behind OPEC, with China and Kazakhstan also rising as the major suppliers. Interestingly, world oil production is yet to peak, (Cetron & Davies 2006).

Technological advances have brought to light a new type of aeroplane, known as a cryoplane, that may resolve the environmental and non-renewable resource conundrums. A cryoplane is an aircraft that uses a liquid fuel whose fuel temperature is kept below minus 73 degrees C (College of the Desert 2001). In this case, the fuel is Liquid Hydrogen.

Why Liquid Hydrogen (LH2) ?

Some considerable research effort has already been expended into the blending of AvTur with renewable fuels. This research consists of essentially diluting AvTur with less environmentally damaging fuels such as Biodiesel, Alcohol and even liquefied Bio-methane at percentages of up to 25% renewable fuels. Fuels such as variants of Biodiesel, AvTur itself (Kerosene IGT & TPS), and even Biomass produced hydrogen, still produce CO2 emissions when burnt (Saynor & Bauen & Leach 2003). Notwithstanding, “dilutions” can produce significant CO2 emission benefits with no discernable losses in engine power or economy, at equivalent cost (Shauck & Zanin 2002). However, such blends are not intended as replacements, only emission reducing agents.

If the primary driver of a replacement fuel for AvTur is elimination of CO2 emissions altogether, then Liquid Hydrogen (LH2) generated by renewable resources such as hydroelectricity is currently, the only answer. An adoption of aircraft fuelled by liquid hydrogen is technically feasible and would substantially decrease the adverse impact on the environment by the aviation industry (Birkenstock 1998) (European Commission 2002) (Saynor & Bauen & Leach 2003). The USA gave LH2 its first aviation test by powering one engine of a modified Canberra bomber in 1956 (Birkenstock 1998).

Properties of Liquid Hydrogen (LH2)

Hydrogen is colourless, odourless, flammable and tasteless, and is the most abundant element in the universe (Schmidtchen 2003). Scenting agents such as thiophanes and mercaptans may not be used to add aroma, as they will poison hydrogen fuel cells. A flow of hydrogen from a leak even during daylight, is almost invisible and in a confined area, diminutive leaks only create a diminutive threat of asphyxiation, but may pose a fire risk (College of the Desert 2001).

However, substantial leaks can create a substantial threat since hydrogen diffuses quickly to fill the volume within a confined area. Inhaled Hydrogen can produce a flammable mixture inside the lungs and may also cause loss of consciousness and asphyxiation (College of the Desert 2001).

In comparison with AvTur, LH2 produces 3 times the energy but requires 4 times the volume per kilo of fuel. However, as LH2 is less dense (x 2.6 times) it retains an efficiency advantage over Avtur. Conversely, this reduced volumetric density means that a larger fuel tank is required. In an aviation application, given also that it needs to be stored cold at pressure, current technology dictates that a spherical or cylindrical tank is required (Birkenstock 1998) (Saynor & Bauen & Leach 2003). This requirement means existing designs will require modifications to use LH2 and new designs need to include this requisite (Saynor & Bauen & Leach 2003). Hydrogen has a wider flammability range than AvTur. Notwithstanding that, Hydrogen fires will consume themselves much more rapidly than kerosene (AvTur) fires, making them comparatively ephemeral. Explosive mixtures of hydrogen are easily achieved in enclosed areas, but achieving explosive mixtures in open areas, is almost impossible (Saynor & Bauen & Leach 2003) (Birkenstock 1998). Liquid Hydrogen expands 848 times by volume when transitioning from a liquid to a gas (College of the Desert 2001).

As a general rule, gases can be liquefied by reducing their temperature, a process called liquefaction. Correspondingly, Hydrogen has the second lowest boiling point of all substances (minus 253 degrees C). To reduce the amount of cooling required to achieve liquefaction, pressure may be applied and in the case of hydrogen, up to 1300 KPA can be applied, above which, no further benefit to liquefaction occurs. As a result of such pressure, the boiling point is raised to minus 240 degrees C (College of the Desert 2001). In addition, hydrogen is difficult to contain due to its molecular size which allows it to permeate containers usually considered airtight or impermeable. When liquid hydrogen is exposed to the atmosphere is evaporates very quickly due to its low boiling point and becomes buoyant, raising in the atmosphere due to its low density in comparison to normal air. Conversely, AvTur spreads laterally when liberated from a container and evaporates slowly and during this period, fire risks will exist. The products of Hydrogen combustion are non-toxic, in contrast with AvTur which generates black toxic smoke (College of the Desert 2001). Timelines for change

Airbus estimates as a result of its “Cryoplane” project which concluded in 2003, that full cryoplane technology could be expected in 15-20 years at the earliest (Airbus Deutschland GmbH 2003). Airbus in conjunction with GE Motors (General Electric), plans to test a cryogenic fuel cell in the hold of an A320 aircraft (the Airbus equivalent of a Boeing 737), mid 2007. Similarly, Boeing intends to install a 440W cryogenic fuel cell APU (Auxiliary Power Unit), to power a demonstration aircraft later this year and has been conducting fuel-cell research in Spain since 2003 (Fuel Cell Today 2006).

These estimates and forecasts gel well with other estimates that consider growing world energy needs. It is estimated that world energy needs will increase 40% over year 2000 requirements, to nearly 290 millions barrels of oil-equivalent energy per day, disregarding further efficiencies and conservation measures put into place (Collier 2004). Similarly, the European Commission’s position is that the conversion to sustainable fuels is unavoidable and may well commence as early as 2015 (European Commission 2002). Aviation Rescue Fire Fighting (ARFF) tactics

The review method is to apply current equipment and practices as if a cryoplane had miraculously appeared today and required some form of ARFF intervention. ARFF tactics are derived from a strategy to; “Create conditions under which rescue operations can be mounted”. To achieve this strategy, ARFF tactics are; “The correct deployment of vehicles, personnel and equipment to achieve the strategic plan, having regard to wind, terrain, aircraft type, manning, and vehicles” (ARFF 2006a). Liquid Hydrogen (LH2) Leaks

Wind may affect the ability of LH2 to rise once released. The figure below shows

a comparison between Liquid Hydrogen, Methane and Propane. The quantity of LH2

spilled is 3,000 litres, the equivalent of 1% of the quantity of gas normally carried by

Hindenburg. This spill though still significant and in a wind of approx. 16km/ph,

corresponds to a LH2 downwind danger far reduced from that of Propane - which is

heavier than air.

The possibility that a fully fuelled cryoplane had been on the ground for

sufficient time to allow hydrogen to gasify in its fuel tanks, and thereby raise internal

fuel tank pressure cannot be discounted. This would be dealt with automatically using

a safety valve on the vertical tail to facilitate a controlled release (Birkenstock 1998).

If there were safety concerns with nearby structures, ARFF could provide a (limited

benefit given LH2 behaviour) water curtain, as shown below.

ARFF could expect to see something similar to the below effects for a LH2 release from the highest point atop a cryoplane empennage.

Release experiment at a model tank for liquid hydrogen on the BAM test ground at Horstwalde, (Germany). The white fogs consist of air moisture condensed by very cold hydrogen gas (above the tank) and liquefied air (on ground) occurring as a by-product (Schmidtchen 2003). Photo: BAM, Gollner

In the event that H2 was physically prevented from raising and dispersing, current high pressure (low flow) hose reels could be used where appropriate. In a confined space, positive pressure fans to ventilate affected structures or aircraft could be applied. Current gas detection equipment should be reviewed in the interim to ensure that the LEL (Lower Explosive Limit) warning function is totally appropriate to Hydrogen detection. Furthermore, a hydrogen HEL (Higher Explosive Limit) function should also be included (AFFM 2006b).

In the event of an emergency where an aircraft has to return to the field shortly, or immediately after take off, LH2 may also have an advantage. The MTOW (Maximum Take Off Weight) of the aircraft may well exceed the weight at which it is permitted to land (Getline 2005). Existing aircraft have height and in some cases area restrictions (not over city and suburbs) as to when they can “dump” fuel. This ensures AvTur has time to evaporate and not pose a hazard. LH2 may well eliminate this requirement and add to the safety of an abnormal landing, where the dumping of fuel is desirable for reasons such as outlined. Current jet aircraft if exposed to sufficient damage or malfunction of their fuel systems including their tanks, could result in AvTur leaking. Gravity will cause fuel to find its way to a lowest point. If an opening exists to the outside world, then that fuel will flow and pool on the ground. Depending on the fuel type, weather & topographical considerations, that fuel may remain pooled for minutes, hours, days, weeks or even months (ARFF 2006b). This is quite contrary to physical properties of LH2.

Aircraft such as the Boeing 787 and the Airbus A350 are to be introduced to service within the next 3 years. Both these new aircraft are more “electrified” than previously and are planned to set the standard for future aircraft. That is, they will have electrically operated components superseding pneumatic components to save weight and provide greater and easier serviceability (Norris et al 2005). It is assumed that such electrification will not provide additional sources of ignition.

Liquid Hydrogen (LH2) Fires

The current practice of creating and maintaining a rescue path by laying foam (monitor or handlines), to cover the evacuation area and allow passengers to escape will not become obsolete, but an appreciation of the physical properties of LH2 needs to be gained.

It can be fairly argued that gravity, influences actions to be taken and as such equipment, training and extinguishing agents target this phenomenon. The principle extinguishing method of foam is by smothering the fire. This largely requires existing aircraft fuels to lay in an area where this can be accomplished. If this is not completely the case then secondary agents such as DCP (Dry Chemical Powder) or CO2 (Carbon Dioxide) can be applied (ARFF 2006b).

The aforementioned mainly includes considerations for the control of the primary fire. An aviation fire fighting issue in any event, is that a primary fire may cause secondary fires of the aircraft itself, or exposures (ARFF 2006b).

The Hindenberg took just 60 seconds from ignition to burn the equivalent of 235,000 litres of LH2 (Wikipedia 2006) which, if taken as typical, seems to set a largely unachievable, no notice, ARFF response time. Current response time requirements are from time of notification to time of first effective intervention is no more than 3 minutes to the end of any runway (ARFF 2006a). A study of the LH2 response time issue would perhaps benefit from using the Hindenburg fire as a case study.

Given the short time frames of hydrogen burn off, it appears prima facie that ARFF may have to consider more specific targeting of the implications of a flash fire rather than focusing on primary ground based fire control. In particular, the secondary consequences may include flash or radiated hydrogen burns to passengers, crew or others. In practical terms, it should evolve that ARFF carries large quantities of the latest in burns treatments.

The above photographs impart a very graphic depiction of the fire behaviour

differences between AvTur and liberated H2 gas. The volume of liberated H2

involved is approx. the same as could be expected to be carried in a large four engined

aircraft in LH2 form. In the case of the Hindenburg, it is supposed there would have

been little even modern ARFF crews could have done to intervene during the free

burning phase. Conversely in the DC10 photograph, as a result of a fast response time and fighting an AvTur fire with conventional equipment and conventional agents, direct ARFF intervention saved lives (ARFF 2006a).

It is interesting to juxtapose if this DC10 had been fuelled by LH2 instead of AvTur, then the fire would have then existed in about the orange area above the jet, instead of the area on the ground where the fire is shown. This, and similar incidents may also be worthy of further study on such comparative grounds. Conclusion

Of the need to replace AvTur the evidence is clear on environmental and fossil fuel reserve grounds. Such evidence has been building for a number of years and is becoming ever more prevalent and valid. Of the need to replace AvTur with an environmentally renewable fuel, there too is clear evidence, and we may see the initial introduction of LH2 within the next 20 years. LH2 is the only fuel available that can meet both the performance requirements of the aviation industry and the environmental needs of the planet.

There are a number of ARFF tactical considerations in relation to LH2 powered cryoplanes, and indeed the wider use of this highly flammable but environmentally friendly and limitless fuel supply. This paper has outlined ARFF tactics for dealing with LH2, however, by its very nature, it inexorably broadens the subject scope such that more specific investigation is required. Recommendations

1. An international ARFF working group be formed with all stakeholders, especially cryoplane manufacturers to establish and where possible meet, the needs of all concerned including:

➢ Equipment (IE, Gas detection equipment, Positive Pressure fans, Thermal Imaging)

➢ Tactics

➢ Training of responders and the public

➢ Response times

➢ Burns treatment technologies

2. The Hindenburg fire be examined from an ARFF perspective to see if beneficial information can be extracted, (IE. Types of injuries, propagation etc.)

3. Aircraft incidents involving major fires be examined, to determine likely outcomes had LH2 been the fuel rather than AvTur. References

Airbus Deutschland GmbH 2003. ‘Liquid Hydrogen Fuelled Aircraft – System Analysis’ Final Technical Report. Project funded by the European Community under the ‘Competitive and Sustainable Growth” program 1998-2002

ARFF 2006a. Aviation Fire Fighting Technical Manual. Available Airservices Australia intranet [online] http://avnet/g1/arff/vol4.asp

ARFF 2006b. Aviation Fire Fighting Reference Manual. Available Airservices Australia intranet [online]


Birkenstock, W 1998. Hydrogen Aircraft Fuel Research Plans. [online]

Cetron,MI, Davies,O 2006. ‘Trends Now Shaping the Future – Economic, Societal, and Environmental Trends’, The Futurist, March-April p.38.

College of the Desert, 2001. Module 1: Hydrogen Properties, Rev 0, Hydrogen Fuel Cell Engines and Related Technologies. pp. 1-25.

Collier, MA 2004. The Next 100 Years. [online]

European Commission 2002. Meeting the Challenges In Aircraft Emissions: Commission Looks Into Clean Alternatives To Fossil Fuel. [online]

Fuel Cell Today 2006. [online],1602,7626,00.html

Getline, M 2005. Ask the Captain [online]

Green, JE 2003, ‘Greener by Design’ in Proceedings of the AAC-Conference, Friedrichshafen, Germany, pp 334-342.

NASA Glenn Research Center 2002. Zero CO2 Research Project – Project Objectives. [online] Norris,G, Thomas,G, Wagner,M, Forbes Smith,C, 2005. Boeing 787 Dreamliner – flying redefined, 1st edition, Aerospace Technical Publications International Pty Ltd, Perth WA.

Saynor,B, Bauen,A, Leach,M 2003. The potential for Renewable Energy Sources in Aviation. Imperial College Centre for Energy Policy and Technology. [online]

Schmidtchen, U 2003. Liquid Storage of Hydrogen – Status and Outlook. Federal Institute of Material Research and Testing (BAM) Berlin.

Shauck,ME, Zanin,MG 2002 ‘The present and future potential of biomass fuels in aviation’ Renewable Aviation Fuels Development Centre, Baylor University Waco Texas.

University of Utah 2003. What’s new at the U - Bad Mileage: 98 Tons of Plants per Gallon [online]

Wikipedia 2006. [online]

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