[Papyone]

@Papyone

Is there a reason you do not post the link here?

There is no reason, but I just don’t know if it is allowed or not on this forum.
Here is the link, if not allowed just delete the message.
https://www.academia.edu/40566332/Hydrogen_production_in_underwater_cutting_and_welding

[Enthalpy]

Nice job, well done!

I thought electrolysis would be completely negligible, and water reduction by hot metal would make all the hydrogen. Obviously you were right to investigate this process, as from your graphs if I understand properly, electrolysis does make a non-negligible proportion of the hydrogen.

You seem to suggest that welding is the only operation where the hydrogen concentration can reach the explosive limit. Did you have the possibility to check if the known explosion accidents occurred during welding?

And if this is the case, will you write recommendations for the divers?

[Papyone]

Nice job, well done!

I thought electrolysis would be completely negligible, and water reduction by hot metal would make all the hydrogen. Obviously you were right to investigate this process, as from your graphs if I understand properly, electrolysis does make a non-negligible proportion of the hydrogen.

You seem to suggest that welding is the only operation where the hydrogen concentration can reach the explosive limit. Did you have the possibility to check if the known explosion accidents occurred during welding?

And if this is the case, will you write recommendations for the divers?

Thank you for your message.
Indeed, following the series of tests I have done with a colleague, we can now estimate the quantity of hydrogen that is produced during cutting. As you could read this production is not negligible but the problem that now arises for me is that I do not understand how explosions can take place if gas gets confined in a closet space because it seems that in the majority of cases there is too much unburned oxygen in the rising H2 / O2 mixture.
 In addition, you were absolutely right when you suggested that a lot of the hydrogen would be burned immediately on contact with the flame because since you said that I've been watching in slow motion a lot of cutting video, where it is distinctly seen that many bubbles of gas ignite above the cut. Personally I begin to think that most of these explosion-related accidents are due to the fact that there was probably already a combustible gas (methane, hydrocarbon, or other) present above the diver before he started to cut and that as soon as he starts he sends just enough oxygen in this gas to exceed the LEL of that gas mixture.
Last May, I had also done during a dive in fresh water a series of tests to check the explosiveness of the residual gases and for none of the tests (except welding) I did not obtain an explosion.
Hopefully, I will be able to organize this same series of tests but this time in seawater in a few weeks (indeed an English company and a Russian training centre promised me their assistance.)
Regarding explosion accidents related to welding underwater, in my reference list it does not seem that there have been fatal accidents, but already some divers have reported to me to have been victims of small explosions.
Fortunately, when we weld under water we do not (at contrary to cutting) usually produce a lot of sparks and so to generate an explosion, it would be necessary that the diver welder is very close to the place where his exhaled air and inflammable gasses are entrapped.

[Enthalpy]

You wrote elsewhere that when welding, the resulting gas has a composition within the explosive limits. Did all accidents happen when welding, or also when cutting?

Maybe the gas composition changes from one sheet side to the other, when you cut or weld steel. More oxygen at the torch side, but behind the steel sheet, iron has used up the oxygen, and molten iron droplets make hydrogen by water contact. And maybe cutting slowly leaves an excess of oxygen, while cutting as fast as possible leaves little oxygen. Can this be tested on the ground?

Yes, rotting underwater produces methane, more so in quiet waters like dam lakes, normally not in open shallow seas where waves dissolve oxygen. In a closed volume like a boat hull, methane can accumulate, and oxygen brought by the torch lets it explode. If detailed accident reports exist, they might tell if the explosion was near a closed volume.

Hey the chemists, can rusting produce hydrogen? Fe to Fe₃O₄ and hydroxides is said to happen only if H₂O dissolves some O₂, but does the reaction decompose some H₂O too? Or maybe a subsequent reaction, say from Fe₃O₄ to Fe₂O₃? Problem is, this hydrogen production would be very slow, and hydrogen leaks away so easily.

[Papyone]

Maybe did I write it wrong, but all the lethal accidents happened during cutting operation.
The cutting speed depends on several factors, including visibility (which is often zero), the degree of oxidation of the metal to be cut, but especially the dexterity of the diver. Some divers think that decreasing the flow of oxygen also reduces the risk of explosion, but it seems to be the opposite because less oxygen in the residual gas means then an increase of the percentage of fuel gas.

[Enthalpy]

While is not the main reaction, papers mention that rusting iron produces some hydrogen:
https://www.sciencedirect.com/science/article/pii/B9780408043922500175

The produced hydrogen amount is easily measured. Take steel of typical boat hull composition. To accelerate the experiment, make small chips of the steel, by milling, turning, sawing, filing... so it rusts in few weeks.

Put the steel chips in seawater at several locations that represent known accidents. I feel important to reproduce the water salinity and acidity but also the amount of dissolved oxygen, which depends on the waves, the depth and the concentration or organic materials. To my opinion, measuring and reproducing these conditions on the ground is lengthy and uncertain, so I suggest to experiment in the Ocean directly.

Collect the hypothetical hydrogen in a wide glass part above the steel chips. Something like a salad bowl. The seawater must be able to be renewed at the steel chips, but not to carry the hydrogen away. A piece of cloth maybe.

To carry the produced gas for few days until analysis, a Tupperware must suffice and is less dangerous than glass. Or a plastic bottle, filled with a funnel.

A similar experiment could be done with rotting wood that produces methane in oxygen-poor water, but I suppose data exists already.

[Papyone]

Hello, I suppose that the quantities produced by this process should not be very important, but if we add to this the hydrogen that can possibly be produced by the seaweed that grows in a wreck, we may then maybe arrive at concentrations likely to explode and so this actually seems to be an interesting track that deserves to be studied further.
In this regard, concerning these concentrations (H2 / O2 and or H2 / Air), I could read in a lot of documents that above water the LEL is about 4%, but  once again I did not find anything concerning this limit of explosiveness under water.
As it would surprise me that under water we go directly from a non-explosive concentration (eg 3.5% H2) to a blast (eg 4.5% H2) I’ve decided to make a new series of tests next spring during which I will ignite (under water) some small volumes (10 to 50 ml) of gas mixture (H2 / O2 air) at different concentrations in order to determine a pressure profile and thus determine from what percentage the explosions begin to be felt painfully by the diver.
In this respect and concerning the making of these gas mixture bubbles, I would like to know if as I think it is preferable to first inject the heavy gas (O2) in the test tube and then the light gas (H2), or does it not matter, but also know if this mixture will be homogeneous instantly, or is it better to wait a few minutes before proceeding to the inflammation?

[Enthalpy]

How much hydrogen does rusting steel produce, I have no opinion. The major reaction is between iron and dissolved oxygen, but with many tons or steel compared with litres of hydrogen, a minor reaction suffices. Maybe the acidity of water changes everything. The ability of the hull to retain hydrogen produced over years too, since hydrogen diffuses easily.

Under water, maybe the amount of vapour in the air or oxygen changes the explosive limit of hydrogen. After all, 0.02atm vapour in air are not small compared with 0.04atm hydrogen. Or the inertia of water helps the pressure rise. Unclear to me.

I hope you'll use test containers made of polymer, not glass test tubes. Tupperwares have practical advantages. And I hope that you won't be in the water at that time: if a 10mL hydrogen explosion hurts the ears in the atmosphere, underwater it must harm them. You can use a thin wire to ignite the gas: copper uses not to burn. Take one filament from a stranded electric copper wire
https://en.wikipedia.org/wiki/Copper_conductor#Solid_and_stranded
Use a hot glue gun
https://en.wikipedia.org/wiki/Hot-melt_adhesive
if you need waterproof holes for the ignition line.

I see one reason to blow oxygen before hydrogen: the mix will keep hydrogen-poor all the time. Mixing does take time, preferably with active means, like shaking the gases together with water. It's similar to cigarette smoke mixing in the air.

[Papyone]

No don’t be afraid tests will be made underwater but off course without divers.
Last week I’ve made a first little test in a bucket with 5 ml of a mix containing 30 % of H2 and 70 % of air and tried to ignite it via the current send in a thin copper wire by a 12 volts car battery. The wire melted but without igniting the mixture.
Was the spark too cold or the mixture not homogenous enough (I ignited it immediatly after making) I don’t know?
For the next tests to make sure that the sparks are hot enough we will rather use 2 copper conductors and provoke an arc between them thanks to a 30 volts 150 amps current produced by welding maschine.

[Enthalpy]

30V make a very short arc if any, difficult to obtain with electrodes at a fixed distance. Normally, you'd have a transformer to create like 10kV, as in a car ignition. But here, water would just short-circuit the 10kV side, preventing the creation of the high voltage, that's why I didn't suggest it.

I know no explanation for melting Cu not igniting oxygen+hydrogen. This mixture uses to ignite around 500°C and copper melts at 1000°C. Possibly the energy input was too small for hydrogen as the wire melted instantly, but I didn't expect that. You might try in air with a few different series resistors, keeping the value that melts the wire after a perceivable time.

A filament lamp with broken bulb is also efficient, and tungsten doesn't burn in oxygen. I feel it less convenient than a thin copper wire.

Mixing the gases goes rather quickly, think of tobacco smoke, and you don't need a perfect 30% mix for boom. 5% somewhere suffices. Good mixing is more important near the flammability limit.

Please be very careful with car batteries and wires and short-circuits. They can provide hundreds of amps, letting explode wires much thicker. A friend of mine, excellent experimenter and engineer, nearly lost a finger when he shorted his battery with his wedding ring. No trace of the ring, and surgeons found little more than the bone left. For your setup, a thick LR20 1.5V alkaline battery should suffice, without resistor.

[billnotgatez]

From WIKI
https://en.wikipedia.org/wiki/Hydrogen#Combustion

Hydrogen gas forms explosive mixtures with air in concentrations from 4–74%[16] and with chlorine at 5–95%. The explosive reactions may be triggered by spark, heat, or sunlight. The hydrogen autoignition temperature, the temperature of spontaneous ignition in air, is 500 °C (932 °F).[17]

I always thought the range was 4-95% for air.
I am thinking it still is very burnable over that range in air.

I have read several historical accounts where steam and iron were used to create hydrogen in great quantities. But, those accounts did not go into specifics. While doing searches I found where they used iron, steam and coal to create hydrogen.

[Papyone]

Hello everyone,
A few months ago I posted a few messages concerning the underwater accidental H2/O2 explosion where I said that I was planning to make a series of tests during which I will ignite (under water) in a strong steel tank some small volumes (10 to 50 ml) of gas mixture (H2 / O2) at different concentrations in order to determine a pressure profile and thus determine from what percentage the explosions begin to be felt painfully by the diver.
Due to the Covid theses tests have been postponed several times but finally they will be made next week.
To establish that profile curve I will for each explosion measure the ejection distance of a small inox rivet (see picture).
But when this will be represented into a graph I find that setting this distance in the y-axis will not be very representative and I will therefore prefer replace it by an kinetic energy value in joules thanks to the formula : KE = 1/2 * mv^2
Also, and this is the reason why I come again to you, is that I would like to calculate the potential energy before each explosion of these small volumes of gas mixtures at their different percentage.
As I already explained in other messages, I have only very little knowledge in chemistry and therefore I try to find answers via internet but I’m not very sure that my deductions are correct.
For instance I’ve find that 11, 2 litres of pure hydrogen has a potential energy of 142920 J.
Am I therefore correct to say that 1 ml will be equal to 142920 / 11200 = 12,76 J
I also suppose that this is valid for pure H2, and then what about the value of for instance a 50 ml mix that contains only 20% of H2 and 80% O2.
Is it possible to calculate this in a more or less easy manner?
Thanks in advance for your help.