Wikipedia:Reference desk/Archives/Science/2024 March 12

= March 12 =

Hydrogen balloon safety
My mom's birthday was recent. We had some people over, brought a few presents, and got a helium happy birthday balloon which I thought was ridiculously expensive for what it was (why? inflation! Heh). It turns out helium itself is quite expensive even in such small quantities. Plus it's a limited and somewhat scarce resource, yada yada.

Hydrogen went out of fashion as a lifting gas after the 1932 Hindenberg explosion, but that was an airship. A 1 foot diameter party balloon would have roughly 1 gram of H2 inside if my math is right. If that gets ignited, is it more of a danger than, say, dropping a lit match by accident? I can imagine a rather loud pop, but would it be enough to damage hearing, blow out windows, or anything like that? There is a standard chemistry class experiment where you have H2 bubbling up from a liquid and put a lit wooden splinter into it and there's a pop, but I guess that would be more like milligram amounts. Thanks. 2601:644:8501:AAF0:4043:7961:893C:EC1 (talk) 02:03, 12 March 2024 (UTC)


 * (Side comment: That was actually 1937.) --142.112.220.50 (talk) 03:03, 12 March 2024 (UTC)


 * It makes a fairly loud pop from when I last did that. I doubt it would shatter windows but it can make your ears ring. Cheers! 🇺🇲JayCubby✡ plz edit my user pg! Talk 02:16, 12 March 2024 (UTC) If you want to use hydrogen, I'd be more concerned about how to safely make it, so don't try it unless you already have most of the materials and are willing to spend a good bit.
 * Electrolysis of water is a good place to start. 🇺🇲JayCubby✡ plz edit my user pg! Talk 02:19, 12 March 2024 (UTC)
 * If the gas is pure H2, igniting it is not more dangerous than igniting the gas of a gas stove. But oxyhydrogen, hydrogen gas mixed with enough oxygen, like one part O2 to two parts H2, will explode with a loud bang and can permanently damage the hearing of bystanders. --Lambiam 09:35, 12 March 2024 (UTC)
 * Classroom demo. --Lambiam 09:45, 12 March 2024 (UTC)
 * ...or burns from the flash fire (Fred Grandy on the set of The Love Boat for example). DMacks (talk) 14:10, 12 March 2024 (UTC)
 * That was a whole collection of balloons, in a confined space, the back of a cab. Literally "in your face". --Lambiam 15:10, 12 March 2024 (UTC)
 * There was no hydrogen explosion in the 1937 Hindenburg disaster; it just burned rapidly, but no bang. Some of the crew up in the envelope were killed by the hydrogen fire, others by lithobraking after the rapid decent or by burning spilled diesel fuel, ignited by the burning envelope. And the flames were the result of the burning envelope and impurities in the hydrogen, as hydrogen itself has an invisible flame. This made hydrogen balloons less popular, but, as our German article explains (de:Gasballon), hydrogen balloons are still used for humans and weather balloons, at least in some countries, like Germany. With proper safety measures and in the hands of professionals, it's safe enough. Amateurs normally use helium, as they might be stupid enough to fill the balloon indoors.
 * So, if this tiny bit of hydrogen in the party balloon is ignited, not much will happen. The pop won't be louder than that of an air filled balloon. If, whilst filling the balloons, you get a leak, then somebody unplugs a phone charger, you may get a big boom, destroying the house. PiusImpavidus (talk) 12:08, 12 March 2024 (UTC)
 * How do you know? Have you tried it? ←Baseball Bugs What's up, Doc? carrots→ 17:54, 12 March 2024 (UTC)
 * "Leaking and uncontained hydrogen led to an explosion that killed four workers and seriously injured a fifth last May at AB Specialty Silicones in Waukegan, Illinois". --Lambiam 07:13, 13 March 2024 (UTC)
 * USCSB did a video for that one. DMacks (talk) 07:19, 13 March 2024 (UTC)
 * Link to USCSB video. --Lambiam 07:25, 13 March 2024 (UTC)
 * Also, "Hydrogen is 14 times as flammable as natural gas and can be ignited by static electricity."  --Lambiam 07:22, 13 March 2024 (UTC)

Fail-safety of the air brakes in the Lac-Mégantic rail disaster
I have been reading the Lac-Mégantic rail disaster article, and what happened with the air brakes doesn't seem to be consistent with what is stated in the railway air brake article.

The Lac-Mégantic rail disaster article says that the air brakes failed because the locomotive was shut down:


 * "Air brakes on the train are supplied with air from a compressor on each locomotive. When a locomotive is shut off, the compressor no longer supplies the brake system with air. An air brake pipe connects to each car and locomotive on the train. When air leaks from the various components, the air pressure drops. If the system is not recharged with air, the locomotive air brakes will become ineffective and provide no braking force."


 * "With all the locomotives shut down, the air compressor no longer supplied air to the air brake system. As air leaked from the brake system, the main air reservoirs were slowly depleted, gradually reducing the effectiveness of the locomotive air brakes. At 00:56, the air pressure had dropped to a point at which the combination of locomotive air brakes and hand brakes could no longer hold the train, and it began to roll downhill toward Lac-Mégantic [...]"

As described above, the air brakes are thus fail-deadly: if power is not available to supply air, the brakes fail. This seems to me to be an atrocious, terrible design which makes no sense, so I started reading the railway air brake article. That article instead says:


 * "Modern trains rely upon a fail-safe air brake system that is based upon a design patented by George Westinghouse on April 13, 1869. [...] In various forms, it has been nearly universally adopted."


 * "The Westinghouse system uses air pressure to charge air reservoirs (tanks) on each car. Full air pressure causes each car to release the brakes. A subsequent reduction or loss of air pressure causes each car to apply its brakes, using the compressed air stored in its reservoirs."


 * "Unlike the straight air system, the Westinghouse system uses a reduction in air pressure in the train line to indirectly apply the brakes."


 * "The Westinghouse system is thus fail-safe -- any failure in the train line, including a separation ("break-in-two") of the train, will cause a loss of train line pressure, causing the brakes to be applied and bringing the train to a stop, thus preventing a runaway train."

This seems to contradict the other article by claiming that Westinghouse air brakes are "nearly universally adopted" and fail-safe. So, what is going on here? Did the train in the Lac-Mégantic rail disaster use a fail-deadly straight air system instead of the fail-safe Westinghouse system? If so, that puts into question the claim that the Westinghouse system is nearly universally adopted and raises the question of why that train did not use the Westinghouse system. If the train did use the Westinghouse system, and that system really is fail-safe, then the loss of power and air should have applied the brakes and held the train in place, unless the Westinghouse system is not really fail-safe.

—SeekingAnswers (reply) 04:29, 12 March 2024 (UTC)
 * It's a difference of short-term vs long-term. Short-term, loss of pressure in the pipe (such as car becoming separated from the engine, or the engine compressor being shut off and the pipe leaking) causes automatic braking using the stored pressure in each car's reservoir. Long-term, there could be enough slow leaks that the system on each car no longer has enough pressure to keep the brakes applied. The air pressure is needed for the actual braking process, not just signaling to apply the brake. Part of the intact system involves replenishment of each car's supply from the compressor. I assume there is some standard for how long a disconnected rail car needs to maintain its braking. DMacks (talk) 08:22, 12 March 2024 (UTC)
 * The referenced TSB investigation summary explains this a bit better. There were automatic (fail-safe) and independent (fail-deadly) brakes.  Both are described in Railway air brake.  Leakage in the automatic brakes was too slow and they had not (yet) applied.  The WP article could maybe be improved here. (edit: fix spelling) Alien878 (talk) 08:35, 12 March 2024 (UTC)

There were three braking systems on the train: the automatic Westinghouse-type train brake, the independent direct air brakes on the locomotives and handbrakes on all vehicles. The Westinghouse brake relies on stored compressed air to actuate the brakes and the pressure in the continuous pipe (the "train line") to keep them off. The stored air will eventually leak, but in normal operation this is topped up from the train line via a valve. A slow leak in the train pipe will cause an ineffective operation of the brakes until the stored pressure has reduced to that of the train pipe; as the report has it: "Due to the slow decrease in brake pipe pressure, no automatic brake application occurred". The direct brakes use compressed air from the locomotive to apply and hold on the brakes; this is independent of the Westinghouse system. Finally the hand brakes are applied by (typically) turning a wheel which screws the brakes on.

The engineer brought the train to a stand using the automatic brakes. He then applied the direct brakes. He applied the hand brakes on the locomotive "consist". The four trailing locomotives were shut down. He then performed a hand brake effectiveness test which should involve releasing all air brakes and gently nudging the loco to ensure that the hand brakes are holding. However he forgot to release the direct brakes, and so the test merely confirmed that direct brakes and hand brakes held the train. The train was then left with the lead loco running, the direct brakes applied and some handbrakes, and the train pipe energised so that the Westinghouse automatic brakes were held off. Following the fire and subsequent shutdown of the lead locomotive the air started to leak out from the direct brakes until eventually the train started to roll downhill. The train did not part until the derailment, so there was no full application of the Westinghouse system, the slow release mentioned above ensured that the Westinghouse brakes remained off.

The full report can be read at Railway Investigation Report R13D0054, but be aware that it is a technical report running to 191 pages! Martin of Sheffield (talk) 11:00, 12 March 2024 (UTC)

Penetrating the time-space continuum
Will it ever become possible to penetrate the time-space continuum? I frequently fantasize about having some national government send a drone back in time to 1916 in order to kill Lenin in the hope that doing this would have prevented the 1917 Bolshevik Revolution and thus secured much better 20th and 21st centuries for Russia in a parallel universe (our real universe would remain unchanged due to the grandfather paradox).

Lenin was quite literally the worst thing to happen to Russia, with his creation of a totalitarian one-party making Stalin's subsequent rise to power much easier (does one think that Stalin would have won any free and fair multiparty elections in Russia in the 1920s?) and with the Soviet Union making Tsarist Russia seem like an extraordinarily mild pussycat in comparison. Tsarist Russia at least nominally allowed opposition parties, even though it tried to weaken them and spy on them, and certainly allowed for free emigration, unlike the Bolshevik regime. And it executed a couple of orders of magnitude less people than the Bolsheviks did. The Bolshevik takeover of Russia wasn't even a good thing for most Bolsheviks themselves, who subsequently got purged and killed by Stalin. How ironic! Creating a monster-state and then personally being devoured by that very same monster-state! 172.56.186.104 (talk) 05:06, 12 March 2024 (UTC)
 * I think you should read our article time travel which talks on the topic covering possibility and paradoxes. Also see Arrow of time, which you are tying to reverse. Using information perhaps it is possible to go into time reversal for very small systems. But the amount required is too colossal to send humans back in time. And changing history is unlikely. It is more likely that you would find out everything you learned about Russia was incorrect, and you would have to make it so that it was incorrect for everyone. Graeme Bartlett (talk) 06:02, 12 March 2024 (UTC)
 * on your claim that "...everything you learned about Russia was incorrect..." 2601:646:8082:BA0:8014:354A:6A03:A76 (talk) 14:09, 13 March 2024 (UTC)
 * What information is needed for time reversal? And what about sending an extremely tiny AI-powered drone back in time, the size of a small flea? 172.56.186.104 (talk) 07:55, 12 March 2024 (UTC)


 * Supposing you achieved that, how would you know? And what makes you think things would turn out any better than they did? ←Baseball Bugs What's up, Doc? carrots→ 06:27, 12 March 2024 (UTC)


 * I've heard it suggested that Trotsky would not have been capable of launching a mass Bolshevik uprising in Russia outside of Petrograd in late 1917 like Lenin was, which in turn would have made it much easier for any Bolshevik uprising that Trotsky would have launched in Petrograd to get crushed. Unless you're suggesting that a non-Bolshevik-led Russia would have become just as bad in due time. 172.56.186.104 (talk) 07:55, 12 March 2024 (UTC)
 * I'm saying (not just suggesting) that there's no way to know what might happen. ←Baseball Bugs What's up, Doc? carrots→ 17:51, 12 March 2024 (UTC)
 * A running joke in the Time Travel sub-genre is that the Time Patrol (or whoever) have to keep foiling attempts by well-meaning temponauts to assassinate Hitler because the outcome would be much worse.
 * It's inherently difficult if not impossible to predict how future history will play out or how an alternative history might have gone, because there are so many interacting factors, but historians (I believe) broadly agree that Hitler was an incompetent military strategist and industrial organiser (see Führerprinzip), and any replacement would likely have been more successful. {The poster formerly known as 87.81.230.195} 51.198.186.221 (talk) 18:18, 12 March 2024 (UTC)
 * Did any other possible alternatives to Hitler (e.g. Drexler, Strasser, Roehm, etc.) have a similar grand vision of global German expansion and/or systematic mass extermination of Jews and other ethnic minorities that he had outlined in Mein Kampf and then seriously attempted to implement, with a large measure of initial success, in real life? 2601:646:8082:BA0:8014:354A:6A03:A76 (talk) 14:09, 13 March 2024 (UTC)
 * Hitler was pretty good at rising to power. He succeeded after about 12 years, which is pretty good for somebody with such extreme ideas in a democratic state. He was not so good at remaining in power. He lost power (along with his life) after just 12 years, rather short for a dictator. Killing him before he rose to power may very well have been beneficial to the world, doing it after he rose to power maybe not. PiusImpavidus (talk) 09:24, 14 March 2024 (UTC)
 * National governments keep sending killer robots back in time to kill inventors of time travel before they make their inventions. We just happen to be on a timeline in which all these missions have been successful. --Lambiam 09:06, 12 March 2024 (UTC)
 * Are we actually certain that nobody turned up to Hawking's time traveller party? :-) NadVolum (talk) 13:00, 13 March 2024 (UTC)
 * As a rule we don't do speculation here. (But I'd remove Woodrow Wilson instead.) —Tamfang (talk) 20:44, 22 March 2024 (UTC)
 * This question is based on the idea that if you travel back in time, you will see whatever you remember being there still there. I've never understood why this idea is so pervasive as a real possibility. It is great for books and movies because it leads to paradoxes that create drama. But, in reality, it doesn't make much sense. For example, if you are driving down the highway and you have some magic machine that lets you jump backwards instantly to a part of the road you were on in the past, the cars that were there when you there previously won't be there. The moved on. It would be an entirely new group of cars. So, if you went back to, say, 1964 to see the height of Beatlemania, you wouldn't see it. They aren't there now. They moved on. It would be an entirely new group of people, if there are any people at all, and they probably won't have a popular group of boys from Liverpool running around the world playing silly songs to screaming fans. 12.116.29.106 (talk) 13:20, 26 March 2024 (UTC)