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daredevil
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hydrogen:safer than petrol?
hi
i've read that in case of a leakage in a hydrogen powered vehicle,there is less chances of a fire as compared to a petrol powered vehicle.i think
hydrogen powered vehicle should be more risky sinse h2 is highly inflammable and as in the sun there are always explosions happenings(fusion) due to
h2 and O2.what do u think about it?
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Theoretic
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"and as in the sun there are always explosions happenings(fusion) due to h2 and O2."
Bullshit. Inside the sun, thermonuclear fusion is happening, not a bloody chemical reaction!
As for the fire hazard, hydrogen dissipates very quickly and doesn't gather in one place.
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tom haggen
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Hydrogen is safer than petrol in someways, and in someways not. In the event that a compressed hydrogen tank should explode, the shock wave would be
imense. Though after the initial blast most of the energy would travel straight up and out of everyones way. Gasoline however gets over everything
spreading fire everywhere. The fire potential for gasoline is much greater. I'm sure if the compartment housing the compressed hydrogen tank was
lined with some sort of blast proof material(kevlar). Then the shrapnel risk would decrease dramatically.
[
[Edited on 12-10-2004 by tom haggen]
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neutrino
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Here's a very informative site on this. It talks about storing hydrogen as a metal hydride. As for the safety:
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Even opening the tank, or cutting it in half will not release the Hydrogen gas. In addition, you could even fire incendiary bullets through the tank
and the Hydride would only smolder like a cigarette. It is in fact, a safer storage system than your Gasoline tank is. |
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kyanite
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Sorry for being off topic(maybe too off topic) but,
but I have a few questions...
I'm probably wrong, but I've always thought that the hydrides researchers were using were metal hydrides like NaBH4, where it reacted with
water to form the hydrogen. The type they depicted was one that was a chemical/element extreemly reactive enough to react with hydrogen at room
temperature. I have absolutely no clue what it could be...
Thinking about the E Act graph, its got to be something reactive enough to combine, but not reactive enough that some heat from the gas engine would
be sufficient to liberate the H2...
IM SO CONFUSED
Also, where does this hydrogen come from to start with? Hydrogen doesn't just grow on trees you know 
Could someone explain this to me?
[Edited on 12-10-2004 by kyanite]
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Hermes_Trismegistus
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re: H2 safer than petrol
This is a really sticky question.
Technically, all substances are perfectly safe under their "ideal" conditions and assuming rigid borg-like adherance to the handling
protocols.
Unfortunately, in the real world, these scenario's don't occur.
People screw around. Handling hydrogen as a metal hydride might technically be very safe, and as I don't know much about it, I'll stay away
from discussing it, and it would seem unlikely to be practical and financially worthwhile.
In the current system of fairly relaxed controls, a compressed gas especially one that needs to be HIGHLY compressed like H2, is inherently dangerous
and suseptible to mechanical and storage failure.
Liquids are generally a helluva lot safer to transport and work with, by your average workaday doorknob.
you would have to institute strict controls to make h2 gas even reasonably close to as safe. Also, with the extremely high burning temperature of h2,
small accidents might escalate alot faster and alot worse.
Keep in mind that gasoline was considered a dangerous waste by-product for a very long time, and fuel oils like diesel were almost exclusively used.
(fromA brief history of technology)
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rift valley
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Hydrogen is perfectly safe
What could go wrong?
What temperature is the hydrogen stored at (it isn't in a liquid state is it, I doubt it -260 degrees Celsius but you never know)
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Ium
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A common misconception with the fate of the Hindenburg is that is crashed purely because of it's volatile Hydrogen contents. Not so as written in
the investigation report from the air ministry at the time. The conlcusion was that the fire was caused by an electrostatic discharge which ignited
the sensitive flammable alminium paint formulation on the skin of the aircraft, and so up she went.
As the skin disintegrated the tubular bags containing the hydrogen were breached and hydrogen being less dense than atmospheric air quickly dissapated
up into the atmosphere with little destructive combustion taking place within and outside the airship.
The same theory has been verified later on by more in-depth investigations.
Given the volatile nature of the paint, one can make the conclusion that even if the Hindenburg was filled with helium it still would have crashed and
burned with a comparable number of casualties.
Remember that to store a gas in liquefied state it does not necessarily need to be stored at or below it's BP. Pressurisation negates this need.
Why do you think propane can be kept liquid at room temperature in storage tanks without an overpressure explosion?
[Edited on 13-10-2004 by Ium]
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Hermes_Trismegistus
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Not all gasses are created equal.
RiftValley;
It really is often stored at those ridiculously low temperatures. (Depending on the application and process used) Because the cost of transporting it
is seriously reduced (up to 50 times as much can be transported in a semi)
also due in part to the bastard like difficulty of compressing it until liquefaction occurs.
lum;
The aluminum doping used to cover the skin of the hindenburg was flammable, it was often a problem in conventional aircraft, (they mixed
powdered aluminum with a resin). However, the hydrogen obviously had a role in the destructive power and speed with which it burned. Hydrogen burns
hot enough to get even the aluminum spars burning, and that report you are quoting is controversial second only to the inquiry into the kennedy
assasination. It is seen as an attempt to keep the airship industry afloat (helium was a rare gas and unavailable in commercial quantities at that
time)
Helium flotation would have extinguished any fire almost immediately.
Have you ever been near a hydrox torch? It is quite the experience, a flame the size of your thumb radiates enough heat to be felt across the room,
and at arms length, feels like the sun on your face.
also; propane and other fuels are liquefied by lowering the temperature prior to storage and the dynamic process inside the tanks keeps the gas
liquid. Propane likes being liquid. It is a social gas.
Hydrogen, on the other hand is like the school bully and is a asshole of a gas to store, especially as a liquid.
It is cooled below 473 DegC to convert it to the para form, unfortunately as it warms up it converts back to the ortho form releasing a great deal of
heat and gassifying more hydrogen, simultaneously converting more hydrogen to the ortho form...releasing more
heat...etc...etc.....BOOM!.....overpressure explosion.
This nasty ass fly in the H2 ointment is the reason for such complicated and difficult containment devices for hydrogen, and why the affordable H2
motorcycle is a LONG way off.
It is really too bad, I love hydrogen and would love to be able to make a homemade high velocity H2 generator to use in various applications as a
fuel.
Working with quartz tubing and rod on my balcony.....uhhhh!!!....(drooling)
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Ium
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| Quote: |
Hydrogen burns hot enough to get even the aluminum spars burning, and that report you are quoting is controversial second only to the inquiry into the
Kennedy assasination. (Snip)
Helium flotation would have extinguished any fire almost immediately.
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You should understand that in any situation where lives are lost, people look for a cause inline the effect. What sounds more convincing to your
average uneducated citizen?
A) That the Hindenberg disaster was attributed to it's vast amounts of "dangerous and highly explosive hydrogen gas" in the fuselage?
B) That the Hindenberg was destroyed due to the flammable paint igniting and the subsequent fire destroying the craft with little contribution from
it's volatile gaseous content.
These statement almost go tit for tat so to speak. It is easy to back a statement with more universal appeal regardless of it's credibility.
Remember that there was actual scientific testing to back up the second claim while practically no scientific evidence has been published for the
former, only media/public speculation. It should be evident that it is practically only a political argument as to why the former explanation should
be taken over the latter.
To compare the Hindenberg disaster to the JFK assassination is quite a wild extrapolation. Two completely different events that share no similarities
and I'm sure you can see that.
Helium also being a gas lighter than atmospheric air would have dissipated up into the above air before it would put out any large amount of the fire.
That and the lower bottom surface of the skin would have been protected from the extinguishing gas. As soon as the gas had of dissipated the fire
would only have continued it's destruction.
Hydrogen/Oxygen combustion yes can be highly devastating in it's heat output and destructive effect. However, the mixture of hydrogen and air was
far from it's ideal ratios to be of any real destructive effect and it's contribution to the destruction of the craft while visible, was not
necessary to complete its demise.
The hydrogen was not stored intermixed with air due to the higher density, flammability and sensitivity of the gas as you should appreciate.
You will notice from the pictures of the burning balloon that the ensuing fireball, visible due to the partial combustion of the painted fabric
releasing carbon species into the flame, travelled high above. While spectacular, the fireball had little bearing on the continued destruction of the
craft. The end of the craft has already begun it's descent to the ground due to the breach of the contained hydrogen. The fire is still burning
with all its intensity, fueled by the surrounding atmospheric oxygen.
The craft would still have been doomed regardless of the burning hydrogen. The surface area of combustion was great enough to destroy the craft with
relative speed and ease.
As regards to the storage of liquid hydrogen, while it is not necessary to keep it at temperatures below BP to keep it liquid cryogenic cooling is
needed to help absorb any continued heat produced due to compression.
You will notice the vast amounts of foamed insulation attached to vehicles using H2/O2 mixtures destined for space.
The heat threshold to keep hydrogen in liquid form while vast amounts lower than propane, the fundamental processes used to keep gases stored in a
liquefied state are still evident in both. Propane may not need external cooling during storage, it does need it during the compression into liquid
form. Also isolation from elevated temperatures are also needed to prevent overpressurization of the containment vessel. H2/Propane may be scales
apart but I was just trying to explain it in an easy to understand situation.
Hopefully that better projects what I was trying to say. Sorry for the length .
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tom haggen
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To compare the Hindenberg disaster to the JFK assassination is quite a wild extrapolation. Two completely different events that share no similarities
and I'm sure you can see that.
actually I can think of a few things that these 2 events have in common. They are both surrounded with conspiracy theories,
Now isn't it ironic that the greedy oil companies are spreading so much controversy about the dangers of hydrogen cars?
[Edited on 14-10-2004 by tom haggen]
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Ium
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Well I should have added the word physical before the word similarities shouldn't have I . Point being the physical difference is great. Only political points of view can tie the two together. Eg. conpiracy on soforth.
Conspiracy theories are rampant throughout society on many goven topics. Logically to me this only further shows that there is no abstract or
contextual reason to tie the abovementioned events together.
Lol, yes it is quite interesting. Oh well whatever explanation that suits the need.
What is your own opinion of the disaster?
[Edited on 14-10-2004 by Ium]
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Hermes_Trismegistus
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You guys are losing me..
I did compare the inquiry into the hindenburg, with the inquiry into the Kennedy headshot....but not the events themselves....
I am not certain that the two events are related, but I see a clear and direct comparison between two committee’s of politicians, both trying
desperately to make sense of a shocking event. The two committee’s were under massive pressure from all sides and had to come up with answers
quickly, whether or not they were factually accurate.
Couple this with the definite fact that everyone they called to give testimony was (justifiably) concerned with ending up as the sacrificial
lamb…pass the mint jelly please mum…
These descriptions suit both of the committee’s and in the end the “evidence” is so sketchy I don’t think we’ are going to be able to figure
it out across the great expanse of time that now exists.
-------------------------------------------------------
The question comes back to Hydrogen gas…. The fact is; that the definition of fuel makes the possibility of danger inherent.
Energy + compact + portable + fairly easily released = possibility for serious accident.
In the end, it seems that trying to directly compare Hydrogen and a fuel like gasoline is difficult at best, they are entirely different animals. Such
comparisons would only be superficial at best.
And yes; there will probably be mishaps with hydrogen until the bugs are worked out, and people may die. In every other era such accidents were
thought of as minor and acceptable…in the new age of anxiety that we live in….there seems to be a far smaller tolerance for any potential
loss of life.
So it goes.
Hermes.
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tom haggen
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My opinion on the disaster... Well as someone who has had some expirences with Al flash I can say that obviously the Al powder skin had a lot to do
with the combustion. I also can tell by looking at the combustion that some hydrogen was also burned. As someone who loves fire I find this event
quite pleasing to the eye. Unfortunately lives were lost. I also think that some sinister political plot was behind this disaster.
[Edited on 14-10-2004 by tom haggen]
[Edited on 14-10-2004 by tom haggen]
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neutrino
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| Quote: | Originally posted by Hermes_Trismegistus
age of anxiety that we live in…
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It's not an age of anxiety that we live in, its an age of lawsuits. Everyone always suing everyone else.
| Quote: | | Energy + compact + portable + fairly easily released = possibility for serious accident. |
Hydrogen is not so easily released from the hydrides used in hydrogen tanks. Simply opening them won't release the hydrogen, they have to be
heated.
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unionised
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About 2 out of 3 people on the Hindenburgh survived. That's not bad for an accident that destroyed the aircraft.
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JohnWW
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About the Hindenburg airship disaster in 1937: The problem with using hydrogen for buoyancy is not so much its flammability, as the fact that it forms
explosive mixtures with air, the detonation of which does the most damage. The rupture of the hydrogen chambers resulting from the fire started in the
inflammable sheathing initiated by an electrostatic discharge would thus have resulted in explosive combustion of the hydrogen as it was released.
This explosion would have caused further substantial structural damage to the airship, and so releasing further hydrogen.
The progress of the fire and the crash of the airship would have been considerably reduced, if it had been filled with helium, which being inert would
probably have smothered the fire in the parts where it would have been released. It might have even enabled it to be salvaged and repaired.
However, the problem with using helium for airships is its limited supply, being economically extractable only from natural gas (which normally forms
and is contained only in sedimentary rocks) which has somehow come into contact in its lengthy underground storage with rocks containing long-lived
radioactive elements which decay by alpha-emission. Such rocks are usually granite (an igneous rock) containing K, U, Th, or rare-earth metals - or
sedimentary rocks formed from decomposed and eroded granite. This situation is relatively rare, and most of the world's helium comes from natural
gas (mostly methane) wells in Texas, from which it is extracted by liquefaction of the natural gas. The world's supply would probably be
insufficient for a whole new generation of airships in the event that fuel shortages force a reduction in the use of fuel-guzzling heavier-than-air
aircraft. Helium could be extracted from the air (which contains other inert gases) with more difficulty by fractional liquefaction/distillation, but
the amount in air is very small and is continually lost to space due to its low atomic weight.
For a new generation of airships, with the depletion of helium, the only long-term solutions would therefore be to either use hydrogen in small
clustered non-flammable containers so as to minimize the damage possible by explosion if one container was ruptured; or to use the only other inert
gas, neon, that is lighter than air. Neon occurs in small quantities in air from which it is already extracted for neon lighting by fractional
liquefaction/distillation, but because its atomic weight is 20, compared to the average molecular weight of air of 29 and 4 for helium and 2 for
hydrogen, the buoyancy obtainable using neon is much less. Using either hydrogen or neon would thus present substantial design obstacles to overcome.
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Hermes_Trismegistus
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| Quote: | Originally posted by neutrino
Hydrogen is not so easily released from the hydrides used in hydrogen tanks. Simply opening them won't release the hydrogen, they have to be
heated. |
Don't be silly, all fuels must have energy that is fairly easily released, or they aren't used as fuels....
It is part and parcel of the definition of a fuel.
Compare the ease of releasing the hydrogen in hydrides to that of releasing the oxygen in silica and you'll understand why we don't consider
sand a fuel.
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neutrino
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But hydrides aren't fuels; they are simply materials that fuels are stored as. For example, a battery isn't free energy, the electricity
contained within it is. The only way (within reason, of course) of releasing hydrogen from hydrides is by heating. Thus, unlike with gasoline, if the
tank is ruptured, fuel won’t leak out. If it’s heated, however, it will probably burst into flame much like gasoline would.
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Ium
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| Quote: |
The rupture of the hydrogen chambers resulting from the fire started in the inflammable sheathing initiated by an electrostatic discharge would thus
have resulted in explosive combustion of the hydrogen as it was released. This explosion would have caused further substantial structural damage to
the airship, and so releasing further hydrogen.
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John, taking into account my above statement relating to ideal fuel/oxidizer ratios do you still think that the combustion of hydrogen would have been
explosively damaging?
In my own experience hydrogen intermixes with air readily however if the flame front was the cause of the reservior ruptures then I do not see how the
hydrogen would have the timeframe to mix with oxygen to burn in an explosively damaging ratio within the structure. Sure some damage occurred even if
slight, from the ruptures. However combustion conditions were far from ideal in the oxygen starved, hydrogen saturated environment of the balloon.
Considering the use of petrochemicals in flight there have also been many many accidents due to fire. If a fuel leak manages to ignite on an aircraft
it quickly engulfs it due to the fast moving surrounding air providing enhanced combustion which causes further leaking/damage. Considering the use of
aviation as an easy source of travel and so taking it into account that it is thus widespread, there have still been a considerable number of
accidents resulting in the subsequent destruction of the craft. Although it has more to do with the surrounding environment than the use of
hydrocarbon fuels.
I would agree that in practicality, a liquid fuel is still much more desiriable over a gaseous means (is gas at STP) of propulsion/travel. Unless the
situation calls for volatile liquefied gas due to it's higher performance such as in it's use in space vehicles.
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Hermes_Trismegistus
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| Quote: | Originally posted by neutrino
But hydrides aren't fuels; they are simply materials that fuels are stored as. For example, a battery isn't free energy, the electricity
contained within it is. |
GaK! still splitting hairs I see, I wonder if you would come by my lab, the microtome could use a day off!
P.S....Electricity isn't actually "contained" in a battery.
and while a punctured fuel tank leaks gasoline, a broken hydride container leaks hydride...
and it is a broader sense I am trying to convey, having energy available "on tap" so to speak.
A fuel must be stable....but not TOO stable. Similar (but not exactly the same) to the situation with explosives, stable enough for transportation and
handling, yet unstable enough to explode.
For instance, if you were trying to introduce gasoline as a new fuel today, elaborate safety measures would probably be needed, only our historical
use of it, and our resulting familiarity has grandfathered in the relatively simple and dangerous fuel tank in use today.
Fuel of all kinds is, and will always be a balancing act between safety and the other factors.
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neutrino
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The battery thing was a simple analogy. The point was that hydride should contain hydrogen in the case of an accident and prevent it from becoming a
major problem.
| Quote: | Originally posted by Hermes_Trismegistus
if you were trying to introduce gasoline as a new fuel today, elaborate safety measures would probably be needed, only our historical use of it, and
our resulting familiarity has grandfathered in the relatively simple and dangerous fuel tank in use today. |
I wouldn't consider gas tanks to bee too dangerous, but I suppose this can be debated.
As has been pointed out many times, both hydrogen and gasoline are highly volatile and flammable, but gasoline tanks are now reasonably safe. This may
or may not be true of various types of hydrogen tanks now, but this emerging technology will improve to the point of equal or greater safety than gas
tanks today once it comes into wider use. I don’t expect this to take too long, as Iceland is already starting the conversion from gasoline (of
which they have none naturally) to hydrogen (made by abundant geothermal energy).
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mick
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I have ignited a balloon full of hydrogen, it does burn up but if you are not quick it takes all the hairs of your arm.
mick
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IvX
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Just a thought but in many places compresed natural gas is used for bus's.
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neutrino
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The reason people are trying to move away from gasoline is that it, like natural gas, is a nonrenewable resource. It can’t be made by simple
electrolysis from any source of electricity like hydrogen can.
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