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Firefighting When Airplanes Are Loaded With Hydrogen Fuel

Thu, Mar 20, 2008 — David Evans

Briefs

Liquid hydrogen (LH2) may be a viable alternative to kerosene as an aviation fuel, but the new fuel poses challenges to Airport Rescue and Fire Fighting (ARFF) assets, argues Joseph Murrell, the senior fire commander for Australia’s Launceston Airport.

Writing in the current issue of the Aviation Fire Journal, the digital magazine of worldwide aviation fire protection, Murell argues that the combination of environmental pollution and dwindling petroleum reserves spell the end of global reliance on oil-based fuel. Technological advances suggest a new type of airplanes, dubbed the cryoplane, as a solution to the twin conundrums of environmental pollution and non-renewable resources. A cryoplane uses liquid hydrogen, stored cold at pressure, in an insulated tank, to power the engines and the auxiliary power unit (APU). As LH2 is less dense than kerosene, larger fuel tanks are required, which affects aircraft design (see concept below).

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Four liters of liquid hydrogen are required to store the same amount of energy contained in just a single liter of kerosene. The necessarily large volume of fuel will require large cylindrical holding tanks for super cooled liquid hydrogen. Tanks on top of the aircraft are one possible solution for large passenger aircraft.

Source:http://ec.europa.eu/research/growth/gcc/projects/in-action-cryoplane.html

The fuel would be produced by a variety of means, but is considered a viable option (see box below)

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Hydrogen can be produced from water by electrolysis. The cost of the electrolysis plant is small compared to the electricity consumption and distribution costs. Locating the electrolysis plant at the airport would minimize distribution cost to about $15 per gallon (estimated 2020 price).

Source: www.iccept.ic.ac.uk

Liquid hydrogen is seen as a means of reducing the aviation contribution to carbon dioxide (CO2), which is a major greenhouse gas. Burning hydrogen produces mainly water, and premixing promises a significant reduction in nitrous oxide (NOx) emissions compared to kerosene engines (see below).

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CO2 emissions will continue to rise, albeit at less than the projected increase in air traffic. However, hydrogen fuel offers the industry a real breakthrough.

Source: Airbus

Liquid hydrogen poses new challenges for airport firefighters. Liquid hydrogen, leaking from a fuel tank, evaporates quickly because of its low boiling point, rising in the atmosphere due to its low density in comparison to normal air. Kerosene, on the other hand, spreads laterally when liberated and evaporates slowly, thereby increasing the fire risk. Burning kerosene also produces black, toxic smoke, whereas the products of burning LH2 are non-toxic.

Fire tests earlier this decade at the University of Miami amply demonstrate the relative hazards of hydrogen versus a petroleum-fueled automobile. The heat in the hydrogen-powered car never rose above 67˚F while the petroleum-fueled car was consumed by the fire (see photo below).

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A graphic display of the different behavior of hydrogen and conventional fuel fires. From a leak in the hydrogen tank, the hydrogen rises and burns off with little damage, whereas the leaked gasoline pooled under the car, where the resulting conflagration destroyed the vehicle. Similar effects could likely be expected for an aircraft.

Source: www.evworld.com/article.cfm?storyid=482

Consider the impacts on ARFF if a cryoplane miraculously appeared today, Murrell writes. He divides the hazards into LH2 leaks and LH2 fires.

LH2 leaks

Wind may affect the rising of LH2 once released. “In the event that [hydrogen] was physically prevented from raising [sic] and disbursing, current high pressure (low flow) hose reels could be used … In a confined space, positive pressure fans to ventilate effected structures or aircraft could be applied,” Murrell writes.

If an aircraft has to return to the airfield shortly after takeoff, LH2 may offer an advantage in terms of dumping fuel. Kerosene-based fuel cannot be dumped over built-up areas, as it must evaporate while falling so as not to pose a hazard. Liquid hydrogen, on the other hand, will evaporate and rise. LH2 would thus “enhance the safety of an abnormal landing” by allowing for greater flexibility as to the altitudes and locations where fuel dumping could be accomplished.

On the ground, kerosene fuel will flow out of the lowest point where a leak may have sprung and will pool on the ground where, if exposed to an ignition source, it can be ignited. LH2 will rise, thereby obviating the hazard posed by a spilled pool of fuel.

LH2 fires

The present practice of creating a rescue path by laying down a blanket of foam to cover the evacuation and allow occupants to escape will not become obsolete, but the physical properties of LH2 need to be taken into account.

Recall that the 1930s era airship Hindenburg gained its lift from hydrogen gas. When that gas was ignited by static electricity or lightning during the landing approach in New Jersey, the fire that destroyed the airship took just 60 seconds to consume all of the hydrogen aboard. Presently, ARFF units must respond from the firehouse to the end of the runway in three minutes.

Given the short time of hydrogen burn off, the implications of a hydrogen-based flash fire need to be considered. Specifically, a hydrogen fire may be limited to the ruptured fuel tanks located above the aircraft, rather than spilled fuel below the aircraft, which may argue for more mast-mounted schnozzles and such to spray fire suppressant at the elevated level of the fire. The intense heat created  by a hydrogen flash fire, and the prospect of flash burns to passengers and crew, means that ARFF responders will need to carry large quantities of the latest in burn treatments.

Given the likely use of LH2 in aviation within the next 20 years, Murrell recommends that an international ARFF working group be formed to assess the training and equipment implications for fire fighting. As a first order of business, he recommends that aircraft incidents involving major fires be examined to assess the likely outcome if LH2 had been the fuel instead of kerosene. (For his full article, ‘Fuel for Thought – Aviation Firefighting and the Coming Cryoplane Revolution,’ see www.aviationfirejournal.com; Murrell e-mail: joe.murrell@airservicesaustralia.comThis e-mail address is being protected from spam bots, you need JavaScript enabled to view it )

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The vision for an environmentally-friendly aviation industry in the future: liquid hydrogen passenger planes on the ramp.

Source: Airbus

Thoughts on Fighting Hydrogen Fires

From Joe Murrell, Air Services Australia

•Training of firefighters. Given the flame characteristics (you could actually walk into a hydrogen flame without seeing it), we need to practice using our thermal imaging cameras (TIC’s) to be aware of the physical properties of a hydrogen fire, such as vertical movement up to 65 feet per second and little radiated heat from the flames. In many cases, hydrogen is safer than a number of gas fuels.

The other side of the coin is to educate fire fighters away from the picture of the airship Hindenberg and provide them with knowledge based on the facts, not what their perceptions might be.

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When the Hindenberg, filled with hydrogen gas, caught fire in 1937, the airship was destroyed, but 62 of the 97 persons aboard survived the conflagration. Photo: Navy Lakehurst Historical Society

•Fire fighting chemicals. My best guess is that ARFF won’t need additional chemicals than what we carry now. But considers that DCP (Dry Chemical Powder) works primarily by intercepting free radicals causing flame propagation to cease. How well does the current range of DCP work when applied to a fuel that has no carbon atoms in it? Do we need to find new powder? Same with foam; do the properties of liquid hydrogen (LH2) require a different foam? We need to get together as an international community and study these things.

It would be nice in a utopian world if we could come up with an international standard for fire fighting and leak tactics for LH2 and hydrogen generally, given the (hopefully) sprawl of hydrogen across the globe in the near future. My guess is that unless we get together now and put some resources into finding the best techniques, remove our misconceptions, develop new equipment, and so forth, then we’ll be forced to do it AFTER there has been some kind of disaster.

(Murrell, e-mail Joe.Murrell@AirservicesAustralia.comThis e-mail address is being protected from spam bots, you need JavaScript enabled to view it )


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