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Hydrogen-Powered Aircraft == Anti-Terrorist Device?
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?
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.
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The Hindenburg's problem wasn't that it was full of hydrogen; it's the fabric the outer covering was made of that did it in.
Please read up on these things before spouting retardedness.
- A.P.
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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?
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Whoa, someone's trying to crash a blimp into the Sears tower!
... Sheesh. This is getting boring.
*BOOOOIIIINNNGGGGGG*
Well, there he goes again...
*BBBBOOOOIIIINNGGGG*
And again
Change the channel.
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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.
Mr. Ska
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.
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).
Dr. Frank J. Nagy Fermilab Computing Division Authentication and Directory Services Group
Actually, the Hindenburg burned due to a special treatment applied to the canvas, which made it highly flammable. Add to that the diesel fuel for the engines, and your real culprit is > dead dinosaurs, aka fossil fuel. According to reports I have read, hydrogen will, essentially, evaporate and disperse immediately, since it is the lightest element in the whole big Universe.
Mmmmmm... Bold, yet refreshing!
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.
The "Impact did not bring down the WTC, the super heating of the steel infrastucture did
each "cube" of the building was designed to withstand a certain amount of pressure, when the ones that were superheated colapsed, it increased the pressure on the lower cubes that they could not handle it, thus they collapsed, thats why the building fell straight down and not fall over when the plane hit
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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...
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I wrote about this 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] 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&
All but God can prove this sentence true.
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.
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.
> belive the explosion only had to weaken the metal substructure for the buildings to fall
Nope. The intense heat of the burning jet fuel weakening the structural steel is what supposedly caused the buildings to ultimately collapse.
The structure was designed to withstand temperatures of a 'normal' fire for something like two hours. The intense heat of the burning jet fuel caused the steel girders to weaken and collapse in much less time.
But think about it. If the impact of the planes were enough to bring down the towers, shouldn't they have toppled over right away?
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.
Gentoo Sucks
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 a bit of a cliché...
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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.
It wasn't hydrogen burning.
From the DOE H2 website:
Its called "Walking". There is no possible way you can take down buildings with this new form of travel.
What if you are carrying luggage packed with C4? Or one of these "suitcase nukes" that I keep hearing about?
If these attacks had taken place at street level, even more people would have died.
Huh? Wouldn't H and H20 fall at the same rate? Or is the chamber not evacuated? Or do I need more coffee before posting?
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Bullshit. Jet fuel is simply slightly better refined kerosene, basically diesel. High flash point, relatively cool burning. It's about like charcoal lighter fluid, doesn't go poof!
Why do I know? I'm a general aviation pilot. As such, I'm pretty close to jets frequently, and I've asked the fueler monkeys.
On to the topic. I'm not sure why hydrogen isn't used for jets, other than the fact that it's a bitch to store and transport. I'd think it'd be an ideal fuel for just about everything, since in it's pure form the only burn by-product is water.
BTW, the Hindenberg got smoked mainly because of the aluminum-oxide paint on it's exterior surfaces. Think solid fuel rocket.
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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.
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The additive you refer to was placed into a jet that was deliberately crashed. The wing was severed in the process in a very spectacular manner, resulting in a tremendous fireball. At once the test was deemed a failure before any of the data was analyzed. Since it was 'expensive', the fireball produced all the justification the airlines needed to kill the project.
Unfortunately, when the data was analyzed, it was shown that the metal skin of the aircraft survived. Seats made of that cushy foam junk survived the fire. In fact, most of the damage to the plane (mind you it was missing a wing...) was soot, not intense heat. The test was a spectacular POSITIVE result, not a blatant failure... how many fires currently result in nothing left of an airplane?
Of course, show anyone the video with a 'fireproof' substance in a tremendous fireball moments after impact and they'll say it's a failure, regardless of the fact that the metal skin of the aircraft, usually the first thing to 'melt', survived. Illogical? Yes. Political? Probably. Good Science? No.
Hindenburg exploded because its envelope was coated in the same chemicals that Morton-Thiakol uses in the Space Shuttle's solid rocket boosters.
It doesn't matter if I've eaten Taco bell or not, wearing boxers soaked in rocket fuel is a bad idea.
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.
The Hindenburg's demise was not a result of an initial hydrogen-fueled explosion.
It caught fire because of the way the airship was designed, and how it dissipated the electrostatic charge that built up on the outer skin.
The ship's skin was a series of panels that were stitched (not really, more like tied) together. When the landing lines are lowered, the charge in these panels are supposed to flow through the entire skin of the airship and down the landing lines.
Because of poor design/construction, some of these panels retained their electric charge because of poor contact with their surrounding panels. The voltage between the charged panels and the non-charged panels was great enough to produce a spark.
BUT... the spark did NOT ignite the hydrogen.
The spark ignited the SKIN.
Since the skin had to be reflective to reflect heat, the germans coated the skin with a mixture that contained aluminum oxide powder.
Sound familiar? Aluminum oxide powder is used as solid rocket booster propellant in the space shuttle.
It was the fire on the skin that ignited the hydrogen cells. Hydrogen burns clear, and is barely visible in daylight. The initial fire on the airship was orange-red.
- Ben
These fuel cells will carry water or hydrocarbons. They will split the hydrogen out as it is needed
This got an "insightful" moderation???
It takes more energy to split hydrogen from water, than you get back by running the fuel cell on the hydrogen. This makes sense in some situations, for example a solar-power application where you can build up a supply of hydrogen when the sun's shining and then convert it back to electricity at night. It's like a storage battery, and as far as commercial aviation is concerned it'd be about as useful as a cargo hold full of lead-acid batteries.
As for splitting the hydrogen out from a hydrocarbon as needed, well, wasn't the whole point of the exercise to get rid of the hydrocarbons so that they wouldn't cause high-temperature fires in a crash?
Maybe there's a compromise, like using methane to power the jet engines (probably don't even need a fuel cell). Methane is a lot more volatile than traditional jet fuel, so it might disperse more quickly in a crash situation [and no jokes about the smell please; pure methane is odorless]. However this probably isn't economically viable.
But... I would imagine a full size jet liner weighing how many tons dry, would still be enough of an impact at over 400 mph to bring down the WTC.
Untrue. NPR had an interesting interview with a structural engineer the evening of the eleventh. His professional opinion was that the force of the impact was insignificant in comparison to the weight that the steel structure had to hold up every day. The plane simply disintegrated. The fire was what caused the collapse.
Remember that infrastructure was designed to support thousands (millions?) of tons constantly, and it was able to support those top floors for a considerable amount of time after the impact. The only thing heavy enough to collapse the WTC was, well, the WTC. Without the fire, the towers would have stood and the loss of life wouldn't have been anywhere near as great.
This
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
It Is the Nature of Information to Transgress Artificial Boundaries
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...
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Buildings eventually come down. Hopefully it's a controlled process after a long and useful life, to make way for a new building; or it may be due to natural or man-made disaster. When the inevitable end comes, you do not want a large building falling over sideways (IIRC, this was the objective of the WTC truck bomb several years ago); you want it to collapse in on itself.
So it's not a question of designing ot to collapse - it's designing how it will collapse when the time comes.
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Unfortunately, I think people forget that hydrogen-fuelled jet airliners would likely use liquid hydrogen as its fuel.
Unlike hydrogen gas (which burns relatively safely), liquid hydrogen when it ignites will do it with a force that makes a dynamite explosion seem like a minor event. If the planes that crashed into the World Trade Center were fuelled by liquid hydrogen, the initial fuel explosion would have so much kinetic force that the building would have collapsed right there and then.
If I remember from the Challenger explosion, when the solid rocket booster leak ignited the fuel in the external fuel tank the force of the explosion was equivalent to a 1 kT tactical nuclear warhead. That's why liquid hydrogen must be handled with extreme care.
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...
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.
Quick point: We don't pump crude oil into our aircraft. It's refined, and Thermo applies there too.
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No trees were killed in the creation of this post. However, many electrons were inconvenienced.
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.
"The question of whether a computer can think is no more interesting than that of whether a submarine can swim" -EWD
> Hydrogen as safe alternative fuel... Um... Hindenburg, anyone?
Two points: the Hindenburg burned because of the envelope, not the hydrogen (see the many posts explaining this), and the Hindenburg used diesel fuel for power, and hydrogen for lift.
> No, it wouldn't burn for a sustained time, like jet fuel did,
> but it would burn even more violently, hence causing more initial
> injuries. In fact, a more violent explosion mith have collapsed
> the towers right away, and those 10,000 or so folk wouldn't have
> had the chance to escape like they did.
Not likely a problem. Most of the experts consulted believe that the sustained fire is what caused the collapse of the buildings. As the videos show, the force of the initial explosions was mostly external anyway (remember that huge fireball?) so even if the force of the hydrogen was significantly more powerful (which it wouldn't have been, for reasons below), the extra force would simply have thrown debris farther, not done much more damage. It's very likely that if the planes used to hit the WTC towers had been hydrogen powered, they'd still be standing. In addition to not having burning jet fuel all over the building (which actually trapped people in the floors directly below the impact, by running down the stairwells), the force of the explosion would tend directly out along the impact vector, then upward. The rapid expansion of the hydrogen as it escapes the tanks tends to inhibit explosive force (increase in volume means decrease in temperature and pressure), so the extra force gained by the fact that hydrogen burns very efficiently is offset.
> Then there's the issue of storage... wouldn't high-pressure
> crtyogenic fuel tanks be prohibitively heavy for an aircraft?
Yes, they are, and that's why hydrogen fuel cells aren't more popular. Once that problem can be solved (materials scientists have been working on this for a long time, mostly for space vessels) hydrogen has a chance against fossil fuels, but not until then.
Virg
The WTC towers were constructed with, essentially, redundant substructures. The exterior supporting beams, placed only 1 meter apart rather than the normal 6, could support the entire weight of the building without the internal supporting structure (which, of course, could support the full weight itself). While tower number 2 may have collapsed from the hit it received (it fell rather quicly after being hit), the prevailing theory is that at least tower 1 required the intense heat of the fire to weaken the remaining support before falling. Even if the hydrogen tanks ruptured and the Hydrogen ignited, you'd only have one hell of a flash fire, leaving only normal combustables in the building and on the plane burning after a few seconds. This could have allowed at least one of the buildings to have remained standing, and very possibly allowed those trapped above the impact point to make their way down.
Just how easily aircraft can be retrofitted with Hydrogen engines or electric/fuel-cell based power I've no idea.
When people talk about Hydrogen powered aircraft, they are talking about using rocket engines, not fuel cells. Using hydrogen as a fuel pretty much dictates that you need to use an oxidizer as well, as there is not enough free oxygen in the atmosphere to get the energy levels required for flight. Liquid Oxygen is nasty stuff; you don't want to get it anywhere near a flame.
Also, fuel cells don't have a high enough power-to-weight ratio to get an airplane off the ground. To move an airplane (or a car, for that matter) you need KINETIC energy. Fuel cells produce ELECTRICAL energy. In order to convert the electrical energy into kinetic energy, you need an electric moter. Electric motors are nowhere close to having the kind of efficiency needed for an aircraft engine.
Why is it that the proponents of "one nation under God" are so eager to get rid of "liberty and justice for all"?
The Challenger didn't run on pure liquid hydrogen, but on a special compound called Hydrazine ( H2NNH2), which is VERY explosive (and corrosive too if I remember correctly) and extremely reactive. It will never make a safe commercial fuel for airliners, if for no other reason than manufacturing and safe storage costs.
To make things more interesting, it's also highly toxic (hydrogen - h2 - is not).
Osha comments on it as:
1.1.2. Toxic effects (This Section is for information only and should not be taken as the basis of OSHA Policy.)
Hydrazine is a severe skin and mucous membrane irritant in humans; in animals, it is also a convulsant and a carcinogen. In humans, the vapor is immediately irritating to the nose and throat and causes dizziness and nausea; itching, burning, and swelling of the eyes develop over a period of several hours. Severe exposures of the eyes to the vapors causes temporary blindness lasting for about 24 hours. Recurrent exposure to hydrazine hydrate has been reported to cause contact dermatitis of the hands without systemic intoxication.
In humans, hydrazine is absorbed through the skin, by inhalation, and orally; systemic effects include weight loss, weakness, vomiting, excited behavior, and convulsions; the chief histologic findings are fatty degeneration of the liver and nephritis. (Ref. 5.6.)
Of course hydrogen still reacts well in the presence of oxygen, but unlike hydrazine, requires a spark or other catalyst to start cumbustion.
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Don't forget that the SR-71 was developed from a lot of work that went into designing a hydrogen fueled aircraft.
Yes, one of the more entertaining parts of Skunk Works, IMHO, is the section where Ben Rich talks about his research and experimentation with liquid hydrogen.
~Philly
A witty saying is worth nothing - Voltaire
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
I didn't realize that 1800 to 2000 C was relatively cool .
-- @rjamestaylor on Ello
You made just realize something -- I'd much rather have a hydrogen tanker or hydrogen pipeline rupture, than have an oil tanker or oil pipline rupture. Think of the millions, possibly billions, of dollars saved by avoiding the many costly clean up operations we've seen in the last 20 years.
-Paul Komarek
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?
Friends don't help friends install M$ junk.
A little knowledge is a dangerous thing.
There are a lot of people on Slashdot that know a little bit about the science and technology outside their area of expertise.
What amazes me is the belief by so many people that the experts and specialists who work in these fields must be idiots who cannot see the obvious solutions that seem to occur to the "brilliant" outsiders that reside here at Slashdot.
A little hint people. If it is a completely obvious solution, then at least one of the "experts" has probably also thought of and analyzed it. If a completely obvious solution has not been implimented then it is probably because there is some subtle problem with it that is beyond your ability to forsee.
"Of course there are better methods (eg putting in water supply) but just a thought."
Due to a combination of dilution and the effect of clorine, attempting biowarfare attacks against a water supply is not very effective.
But you are right, there are better methods. They tend to involve generating aeresols, usually with a moving or area source. That is the reason for the worry over cropdusters.
The way I heard it a lot of the hydrogen (which being lighter than air tends to travel straight up rather quickly if not restrained in some way) escaped en route to the upper atmosphere instead of burning.
I see even classic Slashdot is now pretty much unusable on dial up anymore.
The plane itself is not yet feasible, but for cost reasons, not scientific. It can be built, but it'd be too costly to operate at this point. As to the solar engines, I'm assuming you're discussing solar collectors, although I must have missed any mention of it in the discussion. They do clog up the landscape, insofar as anything visible does, and they can take up a lot of area, but if it's properly built, it's very un-shiny from the sky. Since the point of a reflecting solar collector is concentration of the light, all of the mirrors catch light from the sun and direct it toward the collector in the center, like a radar dish. From above, you'd just see a hundred different views of the collector.
Virg