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In my limited understanding, neither one really explodes. The petrol one would look like a huge impressive fireball that launches a big black mushroom cloud and

by sfink 3y ago

In my limited understanding, neither one really explodes. The petrol one would look like a huge impressive fireball that launches a big black mushroom cloud and then just burns like crazy. The hydrogen one, if the hydrogen is fairly pure, would be like a big faint blue wispy fireball, not all that impressive. If there were an oxidizer in the mix somehow, it would be rather more explosive.

justinclift 3y ago
Cool, thanks. :)
anon_cow1111 3y ago
The issue with hydrogen is that it has a fairly wide combustion range (meaning the ratio of fuel/air that can burn), I can't remember the numbers but it's several times greater than other common fuels. The other issue with hydrogen is that the combustion happens VERY fast... if you ignite gasoline vapor/air in an open 5-gallon jug, you have a nice rocket that'll fly 50 feet or so. If you ignite hydrogen/air in the same jug, you have permanent hearing damage and shards of plastic embedded in you.
- Taiwan_No_1 3y ago
  [dead]
amluto 3y ago
If the hydrogen is fairly pure and the amount is question is small, then sure: combustion will happen at the hydrogen-air interface. If it mixes with air before ignition, then it can burn all a once, and Wikipedia informs me that “the limits of detonability of hydrogen in air are 18.3% to 59% by volume.”. Yes, it will literally detonate with supersonic flame velocity. I once got to watch some moderately crazy students fill an ordinary party balloon with a stoichiometric mix of hydrogen and oxygen at ambient temperature and pressure. When it was ignited, the result was extremely impressive. No one was injured (because we were all warned to protect our ears and open our mouths and balloons don’t produce significant shrapnel), but the shock wave was not at all subtle. https://en.m.wikipedia.org/wiki/Hydrogen_safety https://en.m.wikipedia.org/wiki/Hydrogen_safety
- ben_w 3y ago
  Why is having open mouths important?
  - adrianN 3y ago
    Less pressure on your eardrums if the shock wave reaches them from both sides.
    - ben_w 3y ago
      Ah. So holding my eustachian tubes open (half way through a yawn) would also be a good idea?
- sfink 3y ago
  My dad did this once. He drained the acid from a car battery and put it in a container with a narrow opening, then dropped in a bunch of zinc galvanized nails. Sulfuric acid + zinc = hydrogen gas. He then stretched balloons over the mouth of the container to inflate them, tied them up, and attached a strip of newspaper to the bottom. Finally, he lit the bottom of the newspaper on fire and let it go. Balloon floats up, makes pretty fireball. We ran into two problems. First, a number of the flames blew out on their way up. No fireball. Second, we ran out of balloons pretty fast. So he cast around for ideas, and decided to fall back on a box of condoms. They held a lot more hydrogen than the balloons. They were also equally likely to go out before blowing up. I always imagined them coming down on someone's lawn, causing no end of confusion. [DO NOT TRY THIS AT HOME! And if you're tempted, there's one thing I left out that's necessary for it to work properly, and the only thing I'll say about it is this warning: https://sciencenotes.org/add-acid-to-water-or-water-to-acid/ https://sciencenotes.org/add-acid-to-water-or-water-to-acid/ ]
  - amluto 3y ago
    That’s not the same thing, though — your dad forgot the oxygen! A balloon full of approximately pure hydrogen makes a nice fireball but doesn’t really explode — the same group that made the exploding balloon I watched also did one of those. The stoichiometric premixed balloon is only 2/3 H2 by volume, so it releases 1/3 less energy, but it’s a whole different experience when the energy is released essentially all at once. Interestingly, there was no noticeable fireball from the premixed balloon. A premixed H2+air balloon probably makes a fine explosion, too :)

by sfink 3y ago

justinclift 3y ago

Cool, thanks. :)

anon_cow1111 3y ago

The issue with hydrogen is that it has a fairly wide combustion range (meaning the ratio of fuel/air that can burn), I can't remember the numbers but it's several times greater than other common fuels. The other issue with hydrogen is that the combustion happens VERY fast... if you ignite gasoline vapor/air in an open 5-gallon jug, you have a nice rocket that'll fly 50 feet or so. If you ignite hydrogen/air in the same jug, you have permanent hearing damage and shards of plastic embedded in you.

Taiwan_No_1 3y ago
[dead]

amluto 3y ago

If the hydrogen is fairly pure and the amount is question is small, then sure: combustion will happen at the hydrogen-air interface. If it mixes with air before ignition, then it can burn all a once, and Wikipedia informs me that “the limits of detonability of hydrogen in air are 18.3% to 59% by volume.”. Yes, it will literally detonate with supersonic flame velocity. I once got to watch some moderately crazy students fill an ordinary party balloon with a stoichiometric mix of hydrogen and oxygen at ambient temperature and pressure. When it was ignited, the result was extremely impressive. No one was injured (because we were all warned to protect our ears and open our mouths and balloons don’t produce significant shrapnel), but the shock wave was not at all subtle. https://en.m.wikipedia.org/wiki/Hydrogen_safety https://en.m.wikipedia.org/wiki/Hydrogen_safety

ben_w 3y ago
Why is having open mouths important?
- adrianN 3y ago
  Less pressure on your eardrums if the shock wave reaches them from both sides.
  - ben_w 3y ago
    Ah. So holding my eustachian tubes open (half way through a yawn) would also be a good idea?
sfink 3y ago
My dad did this once. He drained the acid from a car battery and put it in a container with a narrow opening, then dropped in a bunch of zinc galvanized nails. Sulfuric acid + zinc = hydrogen gas. He then stretched balloons over the mouth of the container to inflate them, tied them up, and attached a strip of newspaper to the bottom. Finally, he lit the bottom of the newspaper on fire and let it go. Balloon floats up, makes pretty fireball. We ran into two problems. First, a number of the flames blew out on their way up. No fireball. Second, we ran out of balloons pretty fast. So he cast around for ideas, and decided to fall back on a box of condoms. They held a lot more hydrogen than the balloons. They were also equally likely to go out before blowing up. I always imagined them coming down on someone's lawn, causing no end of confusion. [DO NOT TRY THIS AT HOME! And if you're tempted, there's one thing I left out that's necessary for it to work properly, and the only thing I'll say about it is this warning: https://sciencenotes.org/add-acid-to-water-or-water-to-acid/ https://sciencenotes.org/add-acid-to-water-or-water-to-acid/ ]
- amluto 3y ago
  That’s not the same thing, though — your dad forgot the oxygen! A balloon full of approximately pure hydrogen makes a nice fireball but doesn’t really explode — the same group that made the exploding balloon I watched also did one of those. The stoichiometric premixed balloon is only 2/3 H2 by volume, so it releases 1/3 less energy, but it’s a whole different experience when the energy is released essentially all at once. Interestingly, there was no noticeable fireball from the premixed balloon. A premixed H2+air balloon probably makes a fine explosion, too :)