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Offline Eric A. Taylor

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More hydrogen lies on Naked Scientists
« on: 23/06/2010 10:28:36 »
Yet again I need to correct something on the properties of hydrogen. It was stated on The Naked Scientists that hydrogen is safer than gasoline (petrol). This is patently untrue! All fuels have a fuel/air mixture at which they will burn. Gasoline has a very narrow range, hydrogen will burn from 5% to 95%. But the real danger of hydrogen come from HOW it burns. The classic Hollywood exploding car almost never happens in real life. Gasoline burns with a lot of heat, but it burns slowly enough that you can usually get out of the way. Hydrogen does explode, that's where the real danger is. Also gasoline is a liquid at room temperatures, hydrogen is a gas. This means that hydrogen is much more difficult to store. It's molecules are extremely small which means all your seals need to be very very tight. This would mean that you'd be unable to store the car in an enclosed space (like a car garage). If you have an accident that causes a failure of the fuel cell the car WILL explode, likely killing everyone in the car, any nearby bystanders and likely cause damage to buildings. No I'm sorry to break it to you. Hydrogen is very dangerous.

The Hindenburg was mentioned, but what wasn't said was that most of the visible flame was from the fabric and paint of the airship's covering. Hydrogen burns with a very light blue flame, not visible in daylight, and would not be visible in the film of the Hindenburg disaster.


 

Offline Bored chemist

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« Reply #1 on: 23/06/2010 19:21:04 »
OK, I will get a road tanker full of liquid hydrogen and spill it onto the surface of a small lake, half an hour later I will go down there with a lit match. (This experiment has been done as a publicity stunt, but many years ago so I doubt it's on youtube)

If you think gasoline is safer you do the same thing; you go first.

The fact is that any energy storage system is, by that very fact, dangerous.
 

Offline tommya300

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« Reply #2 on: 23/06/2010 23:35:16 »
  BC makes an understandable point, that hydrogen dissipates rapidly. Like any compressed flammable gas, all have a potential of being explosive. Liquid gasoline vapors ignite, and will show some path to a delayed, abrupt explosion.

Now even though hydrogen dissipates almost instantly, the chances of the build up of concentration is less then rare with respect to the vapors of gasoline.
Although for any flammable, there is still chance of an ignition.
Since you can not smell, taste, or see hydrogen that is where the hazard sits. Propane needs the stinky odor added, holds the same safe guards.
Hydrogen does have a short delay from ignition to explosion, even if it burns colorless to a faint blue, it is a short viewing.
There are not enough of fuel cells out there being used over a long duration to be compared in statistics. A dime on a dollar says, like anything being manufactured, quality control will slip, it is Murphy’s Law.

The only way to detect hydrogen safely is with an electronic snifter.
That also may needed to be certified because it is electronic and that imposes a spark hazard.

Not getting on a soap box, all this is conveying my thoughts.
The reason hydrogen is looked at as an alternative, is that it burns efficiently giving a waste product as only water.

As long as the hydrogen is made using a non flammable energy source, other than that, the effort is self defeating. We will still need the petroleum for the making of these other devices to make the hydrogen.
 Depending on which characteristic in comparison will dictate which is more dangerous, I say both are!
« Last Edit: 24/06/2010 00:24:16 by tommya300 »
 

Offline Geezer

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« Reply #3 on: 24/06/2010 08:55:44 »
Er well, if we happened to have all this hydrogen floating around, one thing we could do with it would be to combine it with atmospheric CO2 to produce synthetic "gasoline", or other hydrocarbon fuels.

The problem with this approach is not the release of CO2 (there is no net CO2 increase) but there is an increase in heat energy to the atmosphere.
 

Offline Eric A. Taylor

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« Reply #4 on: 24/06/2010 15:54:22 »
OK, I will get a road tanker full of liquid hydrogen and spill it onto the surface of a small lake, half an hour later I will go down there with a lit match. (This experiment has been done as a publicity stunt, but many years ago so I doubt it's on youtube)

If you think gasoline is safer you do the same thing; you go first.

The fact is that any energy storage system is, by that very fact, dangerous.

Ok apparently you didn't read my post very carefully. Hydrogen EXPLODES!!!! with quite a lot of energy. Your "experiment" shows how ignorant you are about the way fire behaves. Lets try an experiment that is a bit more realistic. Place a car with a liquid hydrogen fuel tank that is say, 1 year old. This is enough time for seals in the fuel system to develop leaks. Let the car sit over night and in the morning go out and light a match. I think we should use your house, okay?

Lets try another experiment. Take a car with a liquid hydrogen tank and crash it with enough force to rupture the fuel tank. I wonder how many tiny car parts you'll find after?
 

Offline Eric A. Taylor

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« Reply #5 on: 24/06/2010 16:05:10 »
  BC makes an understandable point, that hydrogen dissipates rapidly. Like any compressed flammable gas, all have a potential of being explosive. Liquid gasoline vapors ignite, and will show some path to a delayed, abrupt explosion.

Now even though hydrogen dissipates almost instantly, the chances of the build up of concentration is less then rare with respect to the vapors of gasoline.
Although for any flammable, there is still chance of an ignition.
Since you can not smell, taste, or see hydrogen that is where the hazard sits. Propane needs the stinky odor added, holds the same safe guards.
Hydrogen does have a short delay from ignition to explosion, even if it burns colorless to a faint blue, it is a short viewing.
There are not enough of fuel cells out there being used over a long duration to be compared in statistics. A dime on a dollar says, like anything being manufactured, quality control will slip, it is Murphy’s Law.

The only way to detect hydrogen safely is with an electronic snifter.
That also may needed to be certified because it is electronic and that imposes a spark hazard.

Not getting on a soap box, all this is conveying my thoughts.
The reason hydrogen is looked at as an alternative, is that it burns efficiently giving a waste product as only water.

As long as the hydrogen is made using a non flammable energy source, other than that, the effort is self defeating. We will still need the petroleum for the making of these other devices to make the hydrogen.
 Depending on which characteristic in comparison will dictate which is more dangerous, I say both are!


Please think about this for a second. Gasoline need a spark or flame to ignite. Hydrogen will ignite from the friction generated by the rush gas. While a leaking pressure vessel gets cooler inside the take the gas rush out the hole generates heat at the lip of the hole. Hydrogen ignites very very easily. Gasoline is much harder to light.
 

Offline peppercorn

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More hydrogen lies on Naked Scientists
« Reply #6 on: 24/06/2010 16:25:09 »
Doesn't the podcast expressly mention that the new materials being developed can trap hydrogen molecules at very much lower pressures than a straight-forward 'tank'?
Also, I understand that the material has to go through some form of low heating cycle to release the hydrogen bound up in it.

Although this doesn't remove all the safety concerns it should dramatically reduce the risks.
 

Offline BenV

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« Reply #7 on: 24/06/2010 18:15:00 »
Doesn't the podcast expressly mention that the new materials being developed can trap hydrogen molecules at very much lower pressures than a straight-forward 'tank'?
Also, I understand that the material has to go through some form of low heating cycle to release the hydrogen bound up in it.

Although this doesn't remove all the safety concerns it should dramatically reduce the risks.

I think that was the point, really.  Prof. Bennington was making the point that a tank of compressed hydrogen is indeed very dangerous, and that's precisely why we need to develop high density, low pressure means of storing it.

 

Offline Bored chemist

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« Reply #8 on: 24/06/2010 20:38:16 »
"Please think about this for a second. Gasoline need a spark or flame to ignite. "
I thought about it for more than a second and I realise that diesel fuel is harder to light than gasoline, but you don't need a pilot light or a spark plug in a diesel engine.
I came to the conclusion that your assertion is wrong.


"Ok apparently you didn't read my post very carefully. Hydrogen EXPLODES!!!! with quite a lot of energy. Your "experiment" shows how ignorant you are about the way fire behaves."

FFS I'm a chemist; do you really think I don't know about hydrogen?
Hydrogen does not explode unless you have roughly a star's weight of it.

On the other hand, mixtures of hydrogen and air will explode if (and only if) there is an ignition source.
The energy required to ignite hydrogen is very low- much less than for most fuels, but you still need an ignition source.

Your post is the one that shows ignorance.
Liquid hydrogen spilled on a lake will flash boil. The resulting gas, being much less dense than air, will diffuse and dissipate upwards.
After a relatively short time there simply won't be enough left to burn.

All this talk of liquid hydrogen is a bit of a red herring.
Nobody would seriously consider putting a liquid hydrogen tank in a commercial car.
The hydrogen storage systems that are being developed are more sensible.

Incidentally, the liquid nitrogen tanks at work are something like 20 years old and they still work just fine.

Nobody would be stupid enough to try to keep a liquid gas tank (N2, O2, Ar He H2 Ne, or whatever) in an enclosed space because they always outgas.
Your talk of waiting a year until the car's fuel tank gets leaky shows that you don't understand how they work. They start off leaky; it's part of the design.

Anyway, as I said before, any fuel tank is a potential bomb; the question is how easy is it to set off.

My personal opinion is that they should be looking at methanol or some such as a fuel.

The really big problem with hydrogen is that we simply don't have a lot of it.
There are no hydrogen mines.


 

Offline Geezer

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More hydrogen lies on Naked Scientists
« Reply #9 on: 24/06/2010 21:44:06 »
Anyway, as I said before, any fuel tank is a potential bomb; the question is how easy is it to set off.

My personal opinion is that they should be looking at methanol or some such as a fuel.

The really big problem with hydrogen is that we simply don't have a lot of it.
There are no hydrogen mines.




Right! And honking big batteries are probably just as bad. It's hard to think of any form of energy storage that does not have intrinsic dangers.

I suspect fuel cell vehicles are more "boutique" forms of transportation than anything else. "Plug-in" hybrids might well turn out to be a dead end too.

There is nothing fundamentally wrong with hydrocarbon fuels. Actually, for vehicles, hydrocarbon fuels are probably the only things that have sufficient energy density to be realistic.

There are two issues with hydrocarbon fuels.

1) They create local pollution problems, but that can be largely eliminated with a bit of technology (it's already far better than it was 50 years ago)

2) Depending on the source of the fuel, they might increase atmospheric CO2 levels. However, if the fuel is not derived directly or indirectly from a fossil fuel, there is no net change in atmospheric CO2.

There is some danger that we are "throwing the baby out with the bath water" here. It's not the fuel that you burn in your car that's the problem. It's the source of the energy that produced that fuel that is.

 
 

Offline kenhikage

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« Reply #10 on: 14/09/2010 11:43:22 »
I registered just to note the irony of a flame war starting over this topic.
 :P
 

Offline Bored chemist

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« Reply #11 on: 14/09/2010 20:02:00 »
I registered just to note the irony of a flame war starting over this topic.
 :P
LOL
 

Offline chris

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« Reply #12 on: 14/09/2010 21:19:02 »
Very good, Ken
 

Offline Geezer

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« Reply #13 on: 15/09/2010 01:32:45 »
Inflammatory comments of this nature are hardly likely to resolve the argument.
 

Offline Bored chemist

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« Reply #14 on: 15/09/2010 20:26:52 »
True, not a cat in hell's chance.
 

Offline Geezer

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« Reply #15 on: 15/09/2010 22:24:59 »
True, not a cat in hell's chance.

That's only adding fuel to the fire.
 

Offline kenhikage

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« Reply #16 on: 16/09/2010 10:02:57 »
True, not a cat in hell's chance.

That's only adding fuel to the fire.

The fires of Hell or the flame war?

I wish this thread was actually about what is "lying on (top of) naked scientists," hydrogen or otherwise.;)
 

Offline Geezer

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More hydrogen lies on Naked Scientists
« Reply #17 on: 16/09/2010 18:18:13 »
That's a good point. I can't imagine why hydrogen would tend to lie any more on naked scientists than it would on naked politicians.

Perhaps politicians are more repulsive?
 

Offline kenhikage

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« Reply #18 on: 17/09/2010 16:50:37 »
Quote
Perhaps politicians are more repulsive?

Yeah, I believe that's a constant.
 

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