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Hydrogen-Powered Aircraft == Anti-Terrorist Device? 701

Posted by Cliff
from the safer-usually-means-better dept.
maladroit asks: "Today on NPR's Talk of the Nation/Science Friday , Harry Braun of the Phoenix Project said that a hydrogen-powered airplane would not have produced the fire and intense heat that brought down the World Trade Center towers. Is this true ? What are the other advantages and disadvantages of hydrogen fuel ? Details on the Phoenix Project's website are a bit sketchy, but I'm sure the Slashdot crowd has some answers (and Richard Dean Anderson jokes)." Sounds like a good theory, it doesn't account for the hostage aspect, but it would prevent the use of aircraft as cheap bombs. Would there be any drawbacks? How much would such a refit cost for your average commercial aircraft?
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Hydrogen-Powered Aircraft == Anti-Terrorist Device?

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  • by Red Aardvark House (523181) on Wednesday October 03, 2001 @02:00PM (#2384266)
    The fuel made the explosion worse, but anything the size of an airplane hitting a building at 350+ MPH will do some serious damage.

    Electrical fires can still result from such an impact.
    • by Anonymous Coward
      It's not the size, it's the mass that counts. Airplanes are not very massive for their size. Truth be told, both WTC 1 and WTC 2 survived the impact. It was the fire that weakened the steel. Had there been no fire, there would have only been a couple hundred killed.

      Note: part of the reason the fire at WTC was so devistating was that the do-gooder environmentalist whackos stopped the use of asbestos from being used to fireproof the steel columns which supported the structure. The building's chief design engineer is on record as saying that any large fire above the 70th floor would cause failure of the structure due to pancaking caused by lack of adequate fireproofing on the support columns. He said this before the building was ever occupied.

      • Note: part of the reason the fire at WTC was so devistating was that the do-gooder environmentalist whackos stopped the use of asbestos from being used to fireproof the steel columns which supported the structure.

        Guess what? Asbestos is much more dangerous than terrorism. It just kills you slower, and allows some corporation to profit from your demise.

        The building's chief design engineer is on record as saying that any large fire above the 70th floor would cause failure of the structure due to pancaking caused by lack of adequate fireproofing on the support columns.

        Either this is a lie, or faulty design played a part in the collapse. You don't have to be an engineer to figure out that the lower the fire, the more likely the collapse due to the increasing weight on the affected area.

        • by hexx (108181) on Wednesday October 03, 2001 @02:31PM (#2384561)
          Either this is a lie, or faulty design played a part in the collapse. You don't have to be an engineer to figure out that the lower the fire, the more likely the collapse due to the increasing weight on the affected area.


          The use of asbestos was banned (or cut back severely) after they had already insulated floors -10 through 70. That's why it is more dangerous on 70+.

        • Guess what? Asbestos is much more dangerous than terrorism. It just kills you slower, and allows some corporation to profit from your demise.

          Heh. I don't guess you know that there are many different TYPES of asbestos [asbestoslitigation.com], and not all of them are considered a serious health risk.

        • You don't have to be an engineer to figure out that the lower the fire, the more likely the collapse due to the increasing weight on the affected area.
          But if the fire is low enough (and cool enough) the firefighters can get to it and put it out before it causes catestrophic weakening of the support structure.
        • by saider (177166)
          You don't have to be an engineer to figure out that the lower the fire, the more likely the collapse due to the increasing weight on the affected area.

          The upper floors are lighter than the lower floors because they do not need to support the whole building. They make them lighter by using fewer materials. Fewer materials means that the upper floors are weaker. Granted they are under a lighter load, but they are still weaker.

          If you want to make them stronger, then you need to increase the weight. If you increase the weight, then you need to beef up the lower floors. This adds expense to the system.

          The other issue is that fuel fires cannot be adequatly handled by a water based sprinkler system. WTC's fire suppression (and most other buildings) was never designed to suppress a liquid fuel fire. They are principally designed to suppress solid fuel fires like a filing cabinet or an electrical fire.

          The building was not poorly designed. It survived long enough to allow 15000+ people to escape. Sure we learned some lessons, but I doubt that liquid fuel fire suppression is going to make it into the building codes.

          Would asbestos have saved the day? I do not know. It may have given the occupants an extra 15 minutes to escape. But the main issue was not the fire itself, but the unanticipated fuel type.
      • by mz001b (122709)
        Note: part of the reason the fire at WTC was so devistating was that the do-gooder environmentalist whackos stopped the use of asbestos from being used to fireproof the steel columns which supported the structure. The building's chief design engineer is on record as saying that any large fire above the 70th floor would cause failure of the structure due to pancaking caused by lack of adequate fireproofing on the support columns. He said this before the building was ever occupied.

        Can you provide a reference for this statement? There are other fire-proofing materials aside from asbestos that are used to coat steel columns.

      • by jmauro (32523) on Wednesday October 03, 2001 @02:36PM (#2384610)
        Asbestos has no chance against the heat generated by a fuel fire. Asbestos is good for things like paper fires which burn at 400-500 degrees. At the temprature the main fire was buring at asbestos, steel, and concret melts and vaporize. Asbestos coating would of just put another thing in the air.

        Besides asbestos is not an environmentilst issue, its a heath issue. For what asbestos did there are better ways of doing it. If you'd like me to cover your house in asbestos than feel free. But don't come complaining when you get cancer from it, or other lung problems.
        • asbestos (Score:3, Insightful)

          by Silver A (13776)
          Besides asbestos is not an environmentilst issue, its a heath issue. For what asbestos did there are better ways of doing it. If you'd like me to cover your house in asbestos than feel free. But don't come complaining when you get cancer from it, or other lung problems.

          Asbestos in solid form (like insulation) is perfectly, 100%, safe. Until it starts to crumble and asbestos dust starts to fly around. The preferred treatment for a house with old asbestos insulation is to encapsulate it - not remove it. Removal will get more of it flying around the building than sealing it in place.

      • by gclef (96311)
        Asbestos would not have helped in this case. See the analysis at cryptome for reasons why:


        Asbestos junk science [cryptome.org]

        Basically, the fire was way too hot for asbestos to handle, even if it had been used. Nice try.

  • by cryptochrome (303529) on Wednesday October 03, 2001 @02:03PM (#2384294) Journal
    Well at the very least, hydrogen is a renewable intermediate energy source, unlike the oil used to formulate AvGas these days. And presumably it would be less polluting as well. Both excellent reasons for gradually making the switch, but I don't really see how it would make a plane less of a bomb. The synopsis claims it's safer in an auto crash (presumably because it disperses rapidly), but would that necessarily apply to an airplane? Sure, it wouldn't have burned in the WTC as long, and possibly not as hot, but H2 being a gas wouldn't it have been more explosive?
    • One of the main problems with Hydrogen as a fuel is that it is really just an intermediate energy source.

      There are no naturally occurring terrestrial sources of H2, so we have to manufacture it. The 2nd law of Thermodynamics says that any time we use energy to create energy, we're losing some energy. So the question is -- where does the energy to create the hydrogen come from?

      Oil? We're back to the same pollution problems we had before, plus we'd use MORE oil than just burning it as a jet fuel.

      Nuclear? That's probably the best solution, but we'd have to build new plants to create the energy, and then deal with the waste.

      Wind or Solar? They are clean, but aren't economically viable yet. Who wants to pay $10,000 for a coast-coast flight?

      Hydrogen doesn't really make economic sense yet, since most of the sources we could use to make it are either too expensive or are easier to use directly, without converting to hydrogen in the middle.

      Then there are the storage problems. Hydrogen is a very low energy fuel, so the planes would have to carry a MUCH larger volume of it in order to achieve the same energy content. For airplanes, greater volume = greater energy costs.

      How many people could a conventional 747 carry, if it was fueled by hydrogen - 4? 5?

  • by torpor (458) <jayv@@@synth...net> on Wednesday October 03, 2001 @02:03PM (#2384295) Homepage Journal
    Whoa, someone's trying to crash a blimp into the Sears tower!

    *BOOOOIIIINNNGGGGGG*

    Well, there he goes again...

    *BBBBOOOOIIIINNGGGG*

    And again ... Sheesh. This is getting boring.

    Change the channel.
  • low energy density (Score:5, Interesting)

    by mr.ska (208224) on Wednesday October 03, 2001 @02:03PM (#2384297) Homepage Journal
    Yes, hydrogen-powered aircraft won't be a terrorist threat. As soon as they're off the ground, they'll need to land for refuelling.

    It's the same reason why automotive engineers are having such a big problem getting hydrogen-powered cars economically feasible (apart from the storage problem). Compared to gasoline, hydrogen has an abominally low energy density. What does that mean? To get the same amount of energy on-board, you'd need to carry many times the amount of gas in hydrogen. That means either HUGE fuel tanks, or severely curtailed range. Not being an aerospatial engineer, I can't comment about the former, but the latter just won't fly (pardon the pun) with commercial carriers. "Yes, we can get you from New York to Los Angeles. You have seven brief layovers for refuelling..."

    Interesting idea, but not practical. If you're still worried about planes flying into buildings (it's been used once, if they're smart they'll now switch tactics) maybe installing fire-suppressing foam (like the systems they have in McDonalds' in the kitchen) on tall buildings to smother any high-temperature fires that break out.

    A simpler method may be simply to install nose radar in *all* sizable airplanes, and automatically engage the autopilot when flying within 1000m of an object (building, mountain, etc.) to avoid it. We have the technology, folks.

    • by TheTomcat (53158) on Wednesday October 03, 2001 @02:24PM (#2384494) Homepage
      A simpler method may be simply to install nose radar in *all* sizable airplanes, and automatically engage the autopilot when flying within 1000m of an object (building, mountain, etc.) to avoid it.

      How would a plane equipped suchly ever land?
    • by geekoid (135745)
      How much liqued hydrogen does one need to equal the useable energy in 1 gallon of jet fuel?

      what is the weight difference between the two.

      Interesting idea, but not practical. If you're still worried about planes flying into buildings (it's been used once, if they're smart they'll now switch tactics) I see your point, but this is liking saying they'll never use a truck bomb again because they used them before. If we leave them the opportunity, they or someone else will do it again.

      actually, just putting in solid cockpit doors(and using them) would stop this.

      the auto pilot would need to engage at a least a mile to have any real use. and thats only if the pilot is doing something that the uto pilot can recover from.
    • by alpinist (96637)
      A simpler method may be simply to install nose radar in *all* sizable airplanes, and automatically engage the autopilot when flying within 1000m of an object (building, mountain, etc.) to avoid it. We have the technology, folks.

      As a pilot, I feel I should respond to this suggestion. Anytime you take control of an aircraft from the pilot you are going to have serious problems in certain situations. Let us say you install some sort of "terrain avoidance" system. Sounds like a good idea, nobody can fly too close to objects, as the aircraft will steer away from them.

      Now say we have a 757 in distress. Upon takeoff, the number one engine disassembles itself, and in the process renders the flaps and ailerons on the left side useless. Now we have a plane near stall speed, at low altitude with reduced control. Perhaps there is enough speed and power to take the plane around and put it back on the runway. Keep in mind we are dealing with a fully fueled and loaded aircraft. If in bringing the craft back around, the terrain avoidance system decides it is too close to a line of buildings or a ridge, what does it do? Turn away? A sharper turn increases the stall speed of an aircraft. Stall a 757 at low altitude, and it is in the ground. Does it pull up? Again, it could easily stall a slow moving, fully loaded aircraft. Or if the pilot's only option is a "controlled crash" in a nice big flat field, does the avoidance system again try to prevent that?

      There are countless other situations where such a system could cost lives. In addition, if the system went haywire mid-flight, can the pilot override it? If the pilot can override it, so can a trained hijacker. Even on autopilot, you can grab the yoke and push the plane around. Somehow, I don't think anybody would feel happy with a system that is capable of completely ignoring the pilot's input.

      The problems in such a system outweigh the benefits. And frankly, I doubt we'll ever see commercial airplanes used as missiles again.

    • by twitter (104583) on Wednesday October 03, 2001 @05:28PM (#2385717) Homepage Journal
      You are correct, liquid hydrogen is not as practical a fuel right now.

      Public concern has been so missdirected. Airplane fuel, crypto, nuclear power plants, give me a freaking break! It's like all the anti-technology trolls are having a field day with the national press. There is no way to think of all of the devious things people can do, and no way to block them all without crippling eveyone's ability to do anything.

      Wanna kill lots of people? Let's see, how can we do that? How about blowing up a train load of chlorine tanks in a major urban area? How about a distributed fire bomb attack? A few timers and gassoline containers placed here and there over a few months can light up something that no one could stop. How about hijacking a truck load of fuel and another full of fertilizer? Drive it into a tunnel, into a parking garage, a crowded football stadium and boom. Why not break a gas main in the food court of a very large mall? Then there are the traditional targets, dambs and what not. Hey, that was easy, all the gaurds were at the airport waiting for yesterday's strike.

      What are you going to do about it? Stop making plastics? Outlaw possesion of more than ten gallons of fuel? Make farmers go back to manure? Fuel everything with liquid hydrogen? Why not safe and dependable rubberband power? Right.

      I'm not having a good day. Does it show?

  • by astroboy (1125) <ljdursi@gmail.com> on Wednesday October 03, 2001 @02:03PM (#2384298) Homepage
    And like all fuels, is highly reactive. It's main safety advantage over hydrocarbons is that, since hydrogen really wants to be a gas at STP, it won't `pool' like oil would if you were to spill it. This means, given a spill, a lot of it would just waft away rather than their being a contained region of fuel to catch fire.

    This is good news, to be sure, but a plane crash is clearly not the same as an oil spill. How the burning would proceed would depend completely on how the fuel was contained in the plane, and what happened to the containment. Clearly, it has the potential to burn just as hot as hydrocarbons -- it has to contain the same amount of energy as the jet fuel, 'cuz the plane still has to fly.

    Since, as far as I know, no one is even remotely close to building plane-engine-type hydrogen-powered engines (fuel cells are about as close as its gotten) discussion about relative safety is all going to be wild speculation.

  • by franknagy (56133) on Wednesday October 03, 2001 @02:03PM (#2384299) Homepage
    Hydrogen burns very hot but (1) it requires mixing with considerable air to produce an explosion and (2) being very light it tends
    to burn "up", i.e. to rise. The plane would be
    fueled with liquid hydrogen at 20 degrees K
    (only Helium liquifies at a lower temperature) and would evaporate quickly into a gas. Unlike the current JPx fuels, the hydrogen disipates rapidly and would stick to stuff and burn. The hydrogen would burn and disipate rapidly and
    leave behind only those pre-existing materials which have been ignited.

    One problem is that even liquid hydrogen is very light (very low density) and so requires very large tankage. The Shuttle's external fuel tank is mostly a hydrogen tank (something like 80% of the volume?) with a surprisingly small liquid
    oxygen tank at the top. I have seen a liquid hydrogen bubble chamber being filled and marveled at the droplets of liquid hydrogen entering the chamber and just floating down (drifting really, not falling like water droplets do).
  • by jridley (9305) on Wednesday October 03, 2001 @02:05PM (#2384322)
    Point one: don't bring up the Hindenburg unless you know what you're talking about. The Hindenburg disaster was NOT initiated by a hydrogen explosion, it was improper maintenance and a highly flammable skin. In reality hydrogen *is* safer than liquid fuels. Think about it, if you were trapped in a wrecked car, would you rather have hydrogen leaking 10 feet from your head, or gasoline? Keep in mind that pure hydrogen in a tank can not explode, there's no oxygen. I'll take hydrogen any day.

    Point two: Hydrogen is NOWHERE NEAR dense enough to use as an airliner fuel. You'd need all the room in the entire ship including the cabin taken up with hydrogen tanks, and then some, in order to fly cross country.
    • Pure hydrogen, methane, alcohol or gasoline in a tank will not explode. Nothing in a tank alone will explode, because all explosions and fire require oxygen. Unfortunately on this planet oxygen makes up about 20% of the atmosphere so there's a lot around.

      If we were on Neptune which has a methane atmosphere, we'd probably worry about oxygen slipping out and the explosions that would result from that.

  • Well, ONE problem (Score:5, Informative)

    by NMerriam (15122) <NMerriam@artboy.org> on Wednesday October 03, 2001 @02:06PM (#2384332) Homepage
    This might prevent some of what happened on the 11th, but you still have the kinetic energy of a 200-ton plane with 60,000 lbs of thrust hitting the target at 500 mph.

    It wasn't the jet fuel that rammed the plane all the way THROUGH tower two on live TV. It might not have burned hot enough to cause the tower collapses, but having hydrogen fuel wouldn't have made the planes bounce off the towers, either...
    • Re:Well, ONE problem (Score:3, Interesting)

      by jeffy124 (453342)
      It wasn't the impact that took the towers down, it was the fire that followed (which is why hydrogen as jet fuel is being discussed).

      The towers were able to withstand the impact of the jets just fine, as they were designed to. It was the burning of the fuel that softened the support columns that ran vertically through the building. When those support columns became too soft, they fold. The sheer weight of the building above the soft spot caused the collapse.

      That's why Tower 2 fell first - the plane hit near the 70-80th floor or something. Tower 1 was hit at the 103rd, meaning the columns there had to soften up a lot more than Tower 2's columns before they collapsed.

      The idea of using hydrogen as jet fuel is that it burns at a much lower temperature. Hence if a hydrogen powered jet were to strike a sky scraper, firefighters would have a large amount of time to put the fire out and engineers time to build up support to save the building as a whole.

      One place this did happen was (IIRC) in the 1930s. During heavy fog, a twin engine biplane rammed the Empire State Building. Granted it's a much smaller plane, but it still caused a fire, just not as large as a few weeks ago.
  • by TrumpetPower! (190615) <ben@trumpetpower.com> on Wednesday October 03, 2001 @02:07PM (#2384345) Homepage

    ...but it would prevent the use of aircraft as cheap bombs.

    I wrote about this [slashdot.org] the day after the attack:

    Something I just thought of a little while ago, to help me gain some perspective on what happened:

    A Boeing 767-400ER [boeing.com] [boeing.com] has a maximum takeoff mass of a shade more than 200,000 kg. It has a typical cruise speed of 840 km/h.

    Using our favorite formula for kinetic energy, that comes to about 5.6 billion Joules, or between one and two tons of TNT.

    Or, in other words, just the force of that much mass at that speed is about the same as a WWII blockbuster bomb. Add in some twenty thousand gallons of jet fuel...and I still can't wrap my mind around that much destructive force.

    And I thought cars on the freeway were deadly!

    May such magnificient machines never again be used for such awful, awful purpose.

    b&

    • It has a typical cruise speed of 840 km/h

      The plane wasn't moving at top speed. It is reasonable to assume they were going much slower to give them more maneuverability.

      Or, in other words, just the force of that much mass at that speed is about the same as a WWII blockbuster bomb

      While there was certainly a lot of kinetic energy, it was focused in a less than ideal (for the terrorists) way. It was quite successful at knocking out the central supports, but the support beams at the sides remained generally intact. It was the fire that eventually weakened these beams and caused the collapse.

      More specifically, there isn't that much of a link between raw energy and destructive power. A much smaller amount of energy could've toppled the towers if it had been placed correctly. Conversely, a suitcase nuke would do magnitudes less damage if it was detonated at or below ground level versus several hundred feet in the air.

  • Very true... (Score:5, Insightful)

    by supabeast! (84658) on Wednesday October 03, 2001 @02:07PM (#2384347)
    A hydrogen powered plane's fuel tanks would have blown up all at once. The reason the WTC attacked worked is that airplane fuel is sticky and burns slowly when there are massive amounts of it, so it got all over the inside of the building and generated insane amounts of heat over time, starting other fires, etc. Hydrogen would have just blown up, with a small explosion and a lot of fire at impact, but little other damage.

    Hydrogen is unlikely to be seen as a viable fuel, however, because for so many years it was believed that the Hindenburg was destroyed because of the hydrogen that held it aloft. Even now that the truth is known (The Hidenburg went down because the skin was painted with powdered aluminum, AKA rocket fuel, and when the mooring line grounded arcing electricity caught the aluminum on fire.), it is rarely spoken of because so many sources still quote hydrogen as the source of the explosion.
  • Challenger (Score:5, Informative)

    by Artagel (114272) on Wednesday October 03, 2001 @02:07PM (#2384348) Homepage
    The space shuttle Challenger had a fair bit of hydrogen. It blew up just fine.

    Now, as to continued flame, that's a different matter. It is unlikely that the hydrogen would act as an effective fuel to continue the fire for much after the initial impact.

    The fundamental energetics of hydrogen combustion suck compared to fossil fuel combustion.

    Hydrogen comes into its own more in the context of things like fuel cells. I don't think that the high demands of take-off powering would be well met by fuel cells. Cars can take longer to accelerate on a highway for instance with less loss of functionality. Either the airplane gets off the ground by the end of the runway, or it doesn't. The ability to abort a landing and lift off again is an important safety consideration.

    The reason the site is short on details is that anyone who can make hydrogen work better than fossil fuels will make billions in the first year. It's a fantasy for anything but fringe applications. (Compare the Motorola fuel cell story today. Even that is methane-based, not hydrogen.)

    Looks like our journalist at NPR had to fill a slot by deadline and went with what he could get to fill it.

  • Bad idea.. (Score:4, Interesting)

    by cmowire (254489) on Wednesday October 03, 2001 @02:10PM (#2384366) Homepage
    First, you would have a hard time refitting an existing aircraft to be hydrogen fueled. I'd rate it as impossible. You need fuel lines that can handle cryogenic temperatures. You need to replace the whole fuel-tank assembly. You need to replace the entire engine. Along with that, a lot of other systems and fluids will need to be changed.

    The fuel tank sizes need to be changed. Hydrogen has a LOT of energy, but it's not especially dense.

    You'd also have to change the current petrol-based fuel distribution system. Might I mention that, despite the Hindenberg disaster being more related to the design of the craft rather than the use of hydrogen, hydrogen is much less safe to deal with than petrol-based fuels.
    Plus, there are exactly zero hydrogen fueled aircraft in existence. This is for a reason. During the cold war, some pretty intelligent folks tried to make it work, and failed.
    It IS somewhat likely that hydrogen would avoid the exact circumstances that brought about the world trade center crash. But there are problems.

    For one, the aircraft will have a nasty tendancy to explode. One of the reasons why the Chalenger disaster was so bad was because the entire hydrogen tank, filled with liquid hydrogen, evaporated very fscking fast, blowing the top and bottom off the tank and atomizing it. Then it burned very quickly.

    Hydrogen is very light. So in the case of massive fuel leakage, most of the hydrogen would float upwards and leave the area relitively quickly. If you can keep it from forming a fuel-air-explosive.

    I consider that more of a way for scientists to get more funding for hydrogen experiments than anything else. Sure it might be nicer if you crash into a building, but there's so many other things that can go horibly wrong. The only hydrogen powered craft in existence are rockets, which do not have anything CLOSE to an airliner level of reliability. There are not any production-grade hydrogen-powered jet engines.
    • First, you would have a hard time refitting an existing aircraft to be hydrogen fueled. I'd rate it as impossible.

      Well, this was discussed as well on the NPR show. The cost of refitting is a few hundred thousand dollars per plane ... in other words, peanuts compared to the cost of the plane in the first place, and a small added cost over the lifetime of the airframe if the cost could be stretched out. One of the reasons it would be relatively inexpensive is that you take the entire plane apart every few months for inspections anyway, and things like fuel tanks get replaced every few years during overhauls. Or so they said.

      You'd also have to change the current petrol-based fuel distribution system.

      Yup, you would... but there are already widespread distribution mechanisms for refrigerated, compressed gasses; that is, this is a well understood, solved problem, not a show stopper.

      One of the reasons why the Chalenger disaster was so bad was because the entire hydrogen tank, filled with liquid hydrogen, evaporated very fscking fast,

      The reason the challenger disaster was so bad was that the shuttle carries its oxidizer with it, not just that the hydrogen evaporated quickly. Combustion requires both fuel, oxidizer, and heat; violent explosions require a very large supply of readily available oxidizer. That just isn't available in the type of system being discussed here since the oxidizer has to come out of the air.

      If you can keep it from forming a fuel-air-explosive.

      Since the planes wouldn't be carrying oxidizers, this borders on the ridiculously unlikely. FAE's work because a small amount of liquid fuel is atomized and dispersed over a large volume BEFORE the combustion is begun. That wouldn't happen here, as the fuel would begin burning as it disperses.

      I consider that more of a way for scientists to get more funding for hydrogen experiments than anything else.

      The guests on the show were not pie in the sky academics (like me :-), but engineers at commercial establishments that are actively attempting to implement these technologies in the near future. This isn't basic scientific research stuff, it is well understood, applied engineering research at this point.

  • Hydrogen has some drawbacks as a fuel, in general, though is also has some advantages. (I don't really understand them that well, but I do know they exist.) In terms of crashes, a hydrogen-fueled plane that crashed would explode all at once - once the fuel tank was ruptured, all the fuel would either burn quickly or blow away, rather than continue to provide fuel for the fire as avgas does.

    A hydrogen fueled 747 crashing into the WTC would likely have caused a bigger explosion on impact, but the resulting fire wuoldn't have stayed so hot for so long - if the building didn't collapse right away, it may not have collapsed at all.
  • The problem with hydrogen is not so much the flammability (though that is an issue for automotive fuel cells), but the pressurization of the gas in order to have enough to fuel flight.

    In a topic a while back, the idea that if you took a compressed cylinder of H2 to a field, and shot at it with a bullet, it would be unlikely that you'd cause the cylinder to explode; however, because of the rate at which that gas will escape, the cylinder will suddenly have a huge amount of kinetic energy in a random direction. If you ever saw the crap flick 'Chain Reaction', at one point Keanu axes off the top of a cylinder, using the reverse force to push a multi-ton slab of concrete away from his escape route. While that does approximate real life, typically a damaged cylinder can break through brick walls and do tremendous amounts of physical damage before it's exhausted. And this is the stuff that's common in most academic settings.

    Imagine the amount of H2 gas you'd need to power a 747 from NY to LA. Sure, you can compress it to maintain the same volume, but the higher the amount of compression, the thicker you'd need to make the fuel storage, which means more mass to fly, which means more fuel in order to accelerate that mass. If you go too thin, then a small amount of wear can lead to gas vent; I very much doubt that a pilot would be able to steer a plane effectively if it was venting a large amount of expanding gas.

  • by kisrael (134664) on Wednesday October 03, 2001 @02:12PM (#2384395) Homepage
    Project Phoenix??? You would think they could choose a more reasuring name for hydrogen powered aircraft, given people's perceptions!

    Of course, by now it's also [projectphoenix.com] a [hud.ac.uk] bit [wisc.edu] of [sbu.ac.uk] a [sloanweb.net] cliché [seti.org]...
  • by Steffan (126616) on Wednesday October 03, 2001 @02:12PM (#2384401)
    I've read a few things here which only help to spread the myths about hydrogen. Here are some of the common misconceptions and why they are untrue.

    1. Hydrogen is extremely explosive - Hydrogen is not *extremely* explosive. It can be explosive, but it needs a certain amount of oxygen in order to explode.

    2. The Hindenburg explosion was caused by the hydrogen. - It is widely believe that the explosion was caused by the flammable fabric covering of the ill-fated airship.

    3. Myth#1 is why we don't have Hydrogen-powered cars - Actually, the biggest problem is that hydrogen is, for lack of a better term, sparse. (Opposite of dense). It's difficult to package a sufficient amount of it in a reasonable volume. There is ongoing work to change this by combining it / embedding it in other materials or packages, i.e. Carbon nanotubes.

    4. Hydrogen is hazardous flammable substance - Because of its being the lightest (least dense) gas, a hydrogen fire will bascially burn in an upward direction. In addition, the gas will dissipate quite rapidly - imagine what would happen if you 'spilled' some Helium - it would just float straight up, even if it was on fire. Hydrogen does the same.

    5. The fire was not a significant part of the tower collapse - While the kinetic energy of a fully loaded 757 / 767 cannot be ignored, if that was *all* there was, the towers would be standing today, and probably repairable as well. The collapse was caused by the extremely hot (1500+ degree) fires burning long enough to weaken the steel structure. The beams were rated for 1 hour of fire resistance. They held for at least that long, and then gave way, causing the 6 million lb. floor to fall and begin the domino effect.

  • Retrofitting the thousands of commercial jets in use with new engines simply isn't practical.

    As it stands, the terrorists have already blown their wad with reference to planes - they likely wouldn't use them in a subsequent attack - there are still plenty of transportation systems (land, sea) that are still wide open and completely insecure.

  • by -=OmegaMan=- (151970) on Wednesday October 03, 2001 @02:18PM (#2384451)
    The main thing that will most likely prevent planes from being used as cheap bombs is the fact the four planes were already used as cheap bombs.

    I don't see the recent security clampdown going away anytime soon.

    Just my opinion.
    • Yup, and taking away everything including people's tweezers means that only someone insane enough to not understand their odds of success would attempt to perform a copy-cat crime.

      While the terrorists who crashed into the Pentagon and WTC were ruthless, they seemed to understand their chances of success very well. The next terrorist act (assuming there will be another one) will most likely be as difficult to see coming as this one was. And, in retrospect, it will probably seem just as easy to prevent, if only we'd been looking in the right place.

  • This topic comes up a lot especially in alternative fuels discussions. This is the info that I have. It may not be 100% accurate, though.

    Issue 1: Hydrogen is a gas, which means that you need to compress it in order to get enough fuel onboard. Fuel equipment now has to deal with the increased pressure. This adds expense and weight to whatever it is you are building. Weight is bad for airplanes. Liquid petroleum fuels are very dense and do not need pressurized containers. Thus a full load can be carried without the need for bulky equipment.

    Issue 2: The economy is designed to handle liquid fuels. Gasses are handled, but in much smaller quantities. Changing the infrastructure to deal with handling gasses is probably the most prohibitive part of using gaseous hydrogen as a fuel. And don't bother with liquid hydrogen. The handling issues associated with that are worse than compressed gas (insulation, boil-off vents, etc).

    On the plus side, hydrogen is well suited to gas turbines and jet engines. Clean and efficient. It's just a bitch to store and handle.

    When someone makes room-temperature liquid hydrogen, that'll be the day we all switch.

  • by iabervon (1971) on Wednesday October 03, 2001 @02:23PM (#2384492) Homepage Journal
    First of all, hydrogen isn't all that explosive. The Hindenberg situation was different from this situation in two ways: it was coated in rocket fuel (not known to be explosive at the time), which airplanes would not be, and it used the hydrogen for lift (lighter than air gas), rather than just for fuel.

    Having a hydrogen-powered airplane would have been far preferable to a hydrocarbon-powered one, because the hydrogen, being a gas, would have gone out of the buildings. Sure, it would probably have gotten to places that the liquid fuel didn't, but much less of it would have burned, because it would have diffused to essentially normal conditions pretty quickly (there's hydrogen gas in air, remember). Sure, it would have left the building pretty effectively on fire, but such buildings are rated to be able to withstand a fire fueled by the stuff normally found in them for long enough to put the fire out and evacuate the building.

    On the other hand, just switching the fuel is beyond our current technology. Jet engines are rather carefully-designed devices, and you can't just switch the fuel in them without changing a lot. And we don't yet have the fuel tanks and support systems for hydrogen; it needs to be kept under high pressure in order to fit in the airplane, and that means something strong, and designed for high fuel and low fuel situations, which will be heavy. Gas just needs a container that doesn't leak, since it's a liquid anyway.

    Furthermore, the support systems for hydrogen-powered stuff aren't nearly as well in place; no big generation plants, no suitable fuel trucks, and so forth.
  • a hydrogen-powered airplane would not have produced the fire and intense heat that brought down the World Trade Center towers...

    Reminds me of the adage "If frogs had wings, their asses wouldn't smack the ground when they land". There is a 0.00000000000000000% chance that future terrorist attacks will share any implementation details with the WTC attacks. This is just yet another example of someone trying to capitalize on the general populace's temporarily inability to think rationally. He may as well take out a full page newspaper ad, complete with a statement condemning "the cowardly attacks" by those "hiding in the shadows" augmented by a picture of his product's packing, or offer up a national I.D. card so that American Citizens can be more heavily identified.

    I think the problem--and the solution--lies in our foreign policy. Will the Pashtuns, about to recieve aid from the West, be the next ones to bite us in the ass?

  • by nanojath (265940) on Wednesday October 03, 2001 @02:30PM (#2384547) Homepage Journal
    The blimp issue is not relevant. It is a completely different issue because of the storage and combustion dynamics involved. Hydrogen is flammable and potentially explosive. Compressed in a tank, it is generally viewed as a low explosion risk. This is because hydrogen needs to be well-mixed with oxygen to explode. This has been supported by experimental vehicle crash research. However, if a tank is ruptured, there is an ongoing fire/explosion hazard as hydrogen is released and mixes with oxygen in the air. But you would be much less likely to see the instant giant flame-ball you saw in the WTC crashes. There is ongoing experimentation with fixing hydrogen on some kind of solid substrate. There have been some promising storage experiments with graphite and carbon nanotube materials. Potentially these techniques could make hydrogen fuel much less vulnerable to fire.


    I don't know how feasible powering a plane with hydrogen is - I sort of follow hydrogen energy news and don't recall ever coming across any prototype jets or prop planes. I don't know that hydrogen could power a jet sufficiently. Storage methods (tanks etc.) are heavy, possibly too heavy for economical flight. I question whether this is a realistic scenario or just wild speculation.


    The big problems with hydrogen are cost, lack of a production infrastructure, lack of a distribution infrastructure, difficulty of storage, and the unlikllihood of a widespread manufacture of any kind of hydrogen vehicle lacking resolution of all these other issues. Making a plane fly on hydrogen would certainly not be a simple "retrofit". This would be a transition from a liquid to a gasseous fuel with totally different combustion characteristics.


    Hydrogen is clean to burn either chemically (fuel cell) or through combustion and simple (if not easy or necessarily efficient) to generate, and therefore may become a valid way to transform renewable forms of energy into a storable fuel, and to make energy from conventional fuels more efficeintly and cleanly. But I doubt very much it will be the fuel of choice in planes any time soon

  • by trcooper (18794) <coop AT redout DOT org> on Wednesday October 03, 2001 @02:30PM (#2384552) Homepage
    While hydrogen would not have burned like the jet fuel, I'm not sure it's practical in airliners because of the huge distances they travel. Hydrogen as a fuel doesn't provide a lot of bang for it's volume.

    What really gets me is the possibility that abestos could have delayed the colapse for up to 4 hours longer. They stopped spraying asbestos in the buildings above the 64th floor becase NYC banned it. They were wetspraying, which was a technique used to eliminate asbestos from getting in the air. While we'll never know how long if any those building would have stayed up, the belief at the time was that asbestos would provide 4 hours longer before the girders melted, hopefully giving time to evacuate the building.

    Asbestos, much like hydrogen has been demonized, somewhat unfairly. While there is no argument that it is not dangerous, there can be safe ways to utilize dangerous materials. Unfortunately people jump on these bandwagons too quickly to make informed decisions.

    I remember when they removed asbestos from my elementary school, the teacher told us that dust from the ceiling tiles was asbestos, probably exactly what she thought. In actuality, it was normal dust, and the asbestos was covered by fiberglass and foil insulation, and was harmless, until they started scraping it all off that is...
  • perhaps it would have prevented WTC from collapsing, but they still could of flown into it.
  • Given identical planes, it's going to take the same amount of energy to move it from one place to another. Changing from a high-energy fuel like gasoline to a low(er)-energy fuel like hydrogen just means that you are going to have to carry proportionally more fuel. If you release all that chemical energy in a short period of time, you are still going to have a big fsck'ing fire. Granted, gasoline and hydrogen combust at different rates, so instead of slow-burning fire with lots of heat, you get a fairly cool detonation with lots of blast effects. Anything that releases a large amount of energy in a short period of time is going to do a lot of damage to anything nearby.



    A hydrogen-powered aircraft would almost definately have to use liquid hydrogen as a fuel, as it's very unlikely that you could fit enough compressed gaseous H2 into an aircraft's fuel tanks. Liquid H2 is a bitch to handle and expensive to produce.


    Also, remember that aircraft engines have to have a VERY high power/weight ratio. If your engines + fuel are too heavy, you don't have any payload capacity. It would be very difficult to build an air-breathing hydrogen motor that was suitable for aviation. It seems likely that any H2 powered craft would also need an oxidizer in order to generate enough power to carry a meaningful payload. This means carrying LOX (Liquid Oxygen) or some other oxidizing agent -- rocket fuel, in other words. Oxidizers are corrosive, explosive, and very nasty to handle; not somthing you want on a passenger aircraft. A planeload of H2 + O2 would probably make a far better weapon than one full of gasoline.



    It's a nice idea on the surface, but I don't see hydrogen being a replacement for gasoline in aircraft anytime soon. The power requirements are just too high to get away without an oxidizer, the fuel would be expensive, and refuelling would be a logistical nightmare. It's an entirely different engineering problem than powering a ground vehicle -- for which a hydrogen-powered fuel cell IS a viable power source.

  • in most parts of the globe, it's still wednesday, but many of those people are asleep. Some people are in thursday already, but it's definitely not friday where the show is produced (U.S.)....?
  • The main advantage to hydrogen is that it would disperse if there was a leak.

    The main disadvantage is that its density is horribly low, even when liquified.

    Why not use propane instead? It too will disperse (though it'll drift down instead of up), and it can be stored at a density approaching that of gasoline.

    If you want something that won't pool, ethane will work, though that's harder to liquify by pressure alone. It's about as dense as air, and so will just tend to spread out if released.

    Methane would drift upwards, but you'd need a cryogenic tank to hold liquid methane. Much higher energy density per unit _volume_ than liquid hydrogen, though.
  • Here we go... (Score:4, Informative)

    by blazin (119416) on Wednesday October 03, 2001 @02:45PM (#2384686) Homepage Journal
    Ok, after reading this article and many of the replies, I have come up with some observations.

    First, the planes would be using liquid hydrogen, not gaseous, so all the comments about needing to compress the gas, or contain the gas, or the gas not having as much energy as jet fuel need to read the damn article!

    Secondly, there are about a zillion different opinions based on guesses and I didn't see a single person who was qualified (at least no one say why they were qualified) to say what would happen when the plane hit a building. It's all just a bunch of speculation.

    Third, we know what caused the Hindenburg to explode. About half the messages are saying that it wasn't the hydrogen, it was the coating. It should also be noted that the Hindenburg was not filled with liquid H2 so the comparison again is not really valid.

    What I'd like to see is someone who works with H2 in a liquid form to post their thoughts on what would happen based on their own observations and experiments with liquid H2. The closest I saw was one individual who talked about seeing the drops of H2 liquid just kind of floating downwards instead of just falling like water.

    The other point is that I saw many posts saying how H2 contains a lot of energy, and others saying it contains very little. Logic would say that one of those is wrong. Once again, I would like to see someone who knows what they are talking about post something and include either a reference or a credential, or something to compare H2 and jet fuel in regards to energy density.

    I guess this is slashdot, I'd just like to see more people that do know what they are talking about post and less people that think they know what they are talking about claiming that they do... But again, this is slashdot, so I cannot expect much different.

    <-- end rant...
  • Perhaps someone knowledgable can comment on whether Millenium Cell's [millenniumcell.com] hydrogen on demand [millenniumcell.com] system might be potentially useful in aircraft? According to their web site, the hydrogen stored using this system is safely non-flammable.


    I'm also interested in reasons why this system might be practical or not practical in automobiles, if anyone feels like going a bit off topic ;^)

  • Not a chance (Score:3, Informative)

    by Galvatron (115029) on Wednesday October 03, 2001 @02:57PM (#2384767)
    How much would such a refit cost for your average commercial aircraft?


    The simple answer is way the Hell too much. The airline industry (and the leasing industries associated with it) operate on very tight profit margins. Just look at how disasterous the last month has been for the airlines. They are NOT going to be paying to design, much less paying to install, an entirely new type of engine. The bill would be trememdous!


    My father runs a small aircraft leasing business, and basically the industry, which already had a glut of aircraft, is looking at total and utter devestation. This is an industry where every time the government imposes new noise level limits for aircraft, firms go out of business by the dozens. His firm is small enough to find a way through it, and well diversified besides, but the firms that own most of the aircraft that the airlines fly, firms like GE Capital, are going to take huge hits. There simply will not be any money available for refits, and barely enough to meet government mandated maintainence checks, much less a project of this magnitude.

  • Hydrogen Fuel Safety (Score:3, Informative)

    by Chris Y Taylor (455585) on Wednesday October 03, 2001 @04:36PM (#2385402) Homepage
    There safety of hydrogen as a fuel source depends on how it is stored in the aircraft.

    One method of storing this is just to store it as a compressed gas. This is not a very efficient way to store it, and it will have considerable negative impact on the range and or cargo capacity of the aircraft. In other words, air travel would get a lot more expensive and more rare. Not likely to happen. This method would also be dangerous because a rupture of a compressed hydrogen storage tank would release a lot of energy just from the bursting of the pressurized tank. The hydrogen would then be mixed with the surrounding air in a potentially VERY explosive combination, much like an FAE bomb. It is unlikely that a large portion of the hydrogen cloud would have the right fuel/air mixture to explode, but even a small percentage would be a big explosion. In an open area a large portion of the hydrogen might escape without burning, but in an enclosed area like the WTC, a large portion of it would probably still have burned. No benefit to using this method, and a lot of negatives.

    The Hydrogen could be stored in a metal hydride. Basically the hydrogen is "soaked up" into metal like water soaking up into a sponge. Amazingly you can get quite high hydrogen storage densities with this method, even higher than storing it as a compressed gas. It will be much less of a fire hazard than conventional jet fuel. The hydrogen will not come out of the metal-hydride "sponge" all at once; so even if there is a fire it will be a small but long fire instead of a big, quick one. This method will be even safer because of the fact that the planes will never leave the ground. Metal-hydride may give good storage densities for automobiles, but the fuel tanks would be way too heavy to use on an aircraft.

    The third method is cryogenic storage, as either liquid or slush hydrogen. This method gets the best storage densities as hydrogen storage goes; but it is still a lot less dense than normal jet fuel. That means you still need much bigger fuel tanks to get the same range. This might not be more expensive (and might even be cheaper) because of possible engine improvements. But you have the problem of handling a cryogenic fuel, which adds to costs (and the possibility of a ground crew injury). Then you have the problem of where to put the fuel. There isn't enough room in the wings to put all the fuel there, like is done with normal jet fuel. One possibility is to put it in the fuselage, but that is VERY dangerous because you now have the double threat in a crash of killing the passengers with cryogenic hydrogen before they have a chance to be killed in the resulting fire. Putting the extra tanks out on the wings makes sense from a structures point of view because you have shorter load paths, and would get the cryogenic fuel somewhat further away from the passengers; but it still would not eliminate the fuel as a risk. Yes a puddle of liquid hydrogen WILL burn. As the liquid boils it mixes with the air, creating a flammable mixture. As the mixture over the puddle burns the heat increases the rate of boiling of the puddle. This is actually not too different from what happens when a puddle of non-cryogenic fuel burns. Will it be less of a fire hazard? Maybe. A hydrogen fire will not emit as much thermal radiation, which seems safer; but for the same reason it is invisible and therefore harder to fight (a problem that might be solved with trace impurities). In an open area a hydrogen fire will dissipate more quickly and cover less area, but that doesn't apply to the WTC case because it wasn't in an open area and hydrogen might have actually been worse because of the possibility of explosion instead of just fire. I also wonder what that high a volume of cryogenic hydrogen would have done to the steel structure upon impact; the huge temperature swings from ambient temperature to cryogenic to a hydrogen flame might have caused the collapse to happen sooner. In a normal crash that happens in an open area hydrogen is theoretically safer, but modern jet fuel is not as explosive as most people believe, thanks to evolutionary refinements in its composition and I have not seen any full up aircraft tests (such as have been performed with modern jet fuel) that assesses the added hazard of storing large volumes of cryogenic fuel in a passenger aircraft.

    On the plus side, hydrogen powered aircraft could have smaller (possibly cheaper and more quiet) engines. They would not pollute as much (though they still generate NOx). Despite the extra tankage, the aircraft might even be lighter and cheaper. It is possible, therefore, that a fleet of hydrogen-powered airliners might be cheaper to buy and operate than a fleet of normal ones. Or at least it would be if you didn't have to factor in the capital cost of rebuilding the entire fuel production, fuel transport, and refueling infrastructure. But of course you do. If something (a huge terrorist campaign or a sudden shortage of oil) were to wipe out our current fuel infrastructure and we had to rebuild it from scratch, then we might want to look at hydrogen again. Until then it will take a revolution in fuel storage density, hydrogen production and transport technology, or some new super hydrogen-only super engine to justify junking a fuel infrastructure we have already paid for.

    This is not a new idea. Hydrogen has been considered as an alternate fuel in airliners since at least the 1970s. There are good reasons why it has not been adopted.

    Bottom line, for now liquid or slush hydrogen is the only practical storage method for large aircraft. Even then, the storage densities of Hydrogen suck. Fire hazards are safer, but it almost certainly would not have prevented the WTC collapse (it might even have hastened it). The added hazards of cryogenic fuel (especially if stored in the fuselage) may more than make up for the reduced fire hazard. Like so many other technologies, it offers the tantalizing potential for reduced costs; if only we didn't have an already-paid-for infrastructure that supports the current technology of choice... but we do. If you are building a scramjet then it is probably worth the effort to put up with the extra tankage and the cryogenics and the custom fuel infrastructure. If you are building a passenger jet, then you are just asking for more cost with only incremental benefits that have yet to be demonstrated in full up testing. If the gov't wants to help this along, they could have an X-plane program to demonstrate full up development of a hydrogen cargo plane or bomber (the engineering would be similar enough to a civilian airliner for lessons to carry over), then slam one of the planes into the ground in a simulated crash when the program is over to get data on the actual safety of large hydrogen powered aircraft. Until then, the technology will (rightly) lie dormant until something makes it more economically attractive (i.e. a more efficient use of resources).

    References: Hawkins, W.M. and Brewer, G.D., "Alternate Fuels Make Better Airplanes: Let's Demonstrate Now," _Astronautics_and_Aeronautics_, Sept. 1979
    Raymer, D.P., _Aircraft_Design:_A_Conceptual_Approach_, AIAA, 1992

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