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Specialty Chemistry Forums => Chemical Engineering Forum => Topic started by: Papyone on December 23, 2018, 11:28:44 AM

Title: Underwater accidental hydrogen / oxygen explosion
Post by: Papyone on December 23, 2018, 11:28:44 AM
Hello everyone,
First of all I want to inform you that I’ve not much knowledge with chemistry because my job was commercial diving. I’m now retired, but still very concerned about the security of my former colleagues and therefore I come to you with what some of you will maybe find a weird question, but which has some great and even vital importance to us.
One of the current things a commercial diver does is cutting steel underwater. Therefore we use a short thermal lance that works about the same way as a welding rod except that the lance is hollow to allow the passage of pure oxygen. Due to the DC current we use, as well as the heat of the flame (+/- 5500°c) we have electrolysis phenomena of the water that produce an explosive mixture merely composed of H2 and O2. For commercial divers, the formation of such gas mixture sometimes presents a lethal risk if it cannot escape freely to the surface and a lot of accidents did happen with deadly consequences.
Up to now, we were convinced that during the cutting process the percentage of hydrogen that was produced was situated above the H2 L.E.L which if I’m correct is situated around 3.9%
But, recently following another deadly accident it was decided to make a few cutting tests (6) to recover a few samples of residual cutting gasses for analysis and after seeing the results, I must say that I’m very astonished to see that the percentage of hydrogen present is much lower than this L.E.L of 3.9.
As for instance, the average values that the laboratory has measured are:
H2 0.0167% / O2 93.5% / N2 5.49% / CO 0.113% / CO2 0.855%. 
What is very confusing is that even with such a low hydrogen proportion we are confronted to explosions even if the trapped volume of gas is small (a few cubic centimetres).
So my question is: Why do explosions happen with such a low hydrogen %?
Does the combination of all these gases change the LEL of the mixture?
Sorry for that long description.
I also ad here a picture to help you to understand my question better.
Thanks in advance for your help.
Title: Re: Underwater accidental hydrogen / oxygen explosion
Post by: Papyone on December 23, 2018, 05:07:04 PM
Hello everyone,
First of all I want to inform you that I’ve not much knowledge with chemistry because my job was commercial diving. I’m now retired, but still very concerned about the security of my former colleagues and therefore I come to you with what some of you will maybe find a weird question, but which has some great and even vital importance to us.
One of the current things a commercial diver does is cutting steel underwater. Therefore we use a short thermal lance that works about the same way as a welding rod except that the lance is hollow to allow the passage of pure oxygen. Due to the DC current we use, as well as the heat of the flame (+/- 5500°c) we have electrolysis phenomena of the water that produce an explosive mixture merely composed of H2 and O2. For commercial divers, the formation of such gas mixture sometimes presents a lethal risk if it cannot escape freely to the surface and a lot of accidents did happen with deadly consequences.
Up to now, we were convinced that during the cutting process the percentage of hydrogen that was produced was situated above the H2 L.E.L which if I’m correct is situated around 3.9%
But, recently following another deadly accident it was decided to make a few cutting tests (6) to recover a few samples of residual cutting gasses for analysis and after seeing the results, I must say that I’m very astonished to see that the percentage of hydrogen present is much lower than this L.E.L of 3.9.
As for instance, the average values that the laboratory has measured are:
H2 0.0167% / O2 93.5% / N2 5.49% / CO 0.113% / CO2 0.855%. 
What is very confusing is that even with such a low hydrogen proportion we are confronted to explosions even if the trapped volume of gas is small (a few cubic centimetres).
So my question is: Why do explosions happen with such a low hydrogen %?
Does the combination of all these gases change the LEL of the mixture?
Sorry for that long description.
I also ad here a picture to help you to understand my question better.
Thanks in advance for your help.
Title: Re: Underwater accidental hydrogen / oxygen explosion
Post by: Enthalpy on December 24, 2018, 10:56:00 AM
Welcome, Papyone!

Of the measured gases, only H2 and CO can burn, and both concentrations are very far below the explosion limit. No interaction known to me, nor do I expect any.

Explosions must result from other conditions than the measured composition. The dangerous conditions may not happen every time.

I don't see how an electric arc would produce significant hydrogen by electrolysis. The evolved hydrogen must burn immediately under these conditions, before any amount accumulates. That's even more the case if (?) you use AC current. But surprises happen.

A different scenario? From the item being cut or welded, or from the tools, metal still hot reacts with water when or where no oxygen is present, and produces metal oxide and hydrogen. If hydrogen accumulates in something like a sunken hull, it can detonate.

Still an other hypothesis: methane produced by bacterial decomposition of organic material already accumulated in a place where the diver adds oxygen. The mix can deflagrate.

In case (?) these explosions occur where hydrogen or oxygen accumulates, away from the tools, a solution would be to cap the operation site with a funnel and a pipe to evacuate the gas to the surface.
Title: Re: Underwater accidental hydrogen / oxygen explosion
Post by: Papyone on December 25, 2018, 03:55:15 AM
Already thank you for your reply. I will comment more on it in two days. ;)
Title: Re: Underwater accidental hydrogen / oxygen explosion
Post by: Papyone on December 28, 2018, 06:51:10 AM
Hello enthalpy,
Here I’m again with a few more information concerning our cutting process.
To do what you see on the photo, we use a rod that needs about 150 Amps to create the electric arc which ignite the rod and once ignited such a rod burns during about 50 seconds and consumes about 250 litres (at atmospheric pressure) of pure oxygen per minute.
To limit the electrocution risks we always use DC current.
Concerning the formation of hydrogen by electrolysis we can see that it happens in salt water, because when we start a new job we have to make a polarity test to verify if the cutting torch is correctly connected to the negative pole of the welding group.
Therefore we need to use a bucked of salt water into which we approach the extremity of the electrode at close proximity of the earth clamp. Once the current is on, we can see that a lot of bubbles travel in the water from the clamp towards the electrode (test illustration on the photo).
In most commercial diving schools and manuals they tell the divers that this phenomenon (electrolysis) continuous during the cutting process, but apparently from what I have found during my research on the net this is not really the case.
If I’m correct, thanks to a Faraday law it is possible to calculate the theoretical value of the electrolysis flow generated during the consumption of the rod.
For instance by using one of his formulas I’ve learned that whatever the voltage, 1 ampere will produce 0.209 l of oxygen and 0.418 l of hydrogen, or a total of 0.627 l of gas per hour.
Knowing that when we are cutting, the thermal rod will burn for about 50 seconds with an intensity of 150 amperes, I’ve calculated that this amount of gas mixture would be produced.
(0.627 / 3600) x 150 x 50 = 1.3 l of O2 / H2 mixture
This amount of gas will actually be produced as long as the tip of the electrode does not touch the workpiece but and at contrary to what is often taught to the divers as soon as we start to cut, a large part of the current will pass directly through the electric arc and in this case only the leakage currents located at the periphery of the arc (and therefore still in contact with the water) will be able to create the electrolysis of the water.
I guess therefore that the production of our explosive mixture is not due electrolysis.
Going through the web, I’ve also learned that if water is brought into contact with a very high heat source greater than 2200 ° C, it will start to split into their atomic components hydrogen and oxygen.
At the same temperature of 2200 ° C about 3% of the water surrounding the heat source is decomposed into hydrogen and oxygen, and that this percentage of dissolution increases sharply when the temperature increase. As the combustion temperature at the extremity of our rod is close to 5534 ° C (10000° F) I ‘ve tried to find out  how much water is then decomposed, but unfortunately up to now nobody has given me an answer. 
Do you by chance know how to calculate this amount?
Anyway, I suppose that most of the hydrogen produced in our cutting comes from the heat and not from the electricity.
Concerning the production of methane by bacterial decomposition of organic material you are quite correct. In the latest accident that happened in Japan this was the cause (methane accumulation in a sealed sheet pile tube).
The use of your funnel would be difficult to install in most situation, but anyway thanks for the suggestion. Just to let you know that one of the first things a diver learns when he starts to cut is to make sure the residual gas can escape freely to the surface.
If not, they are taught to make vent holes above their cut or if not possible the must then vent the cut with air.
But unfortunately this is not always done correctly and accidents continuous to happen (35 in the latest forty years).
(https://www.chemicalforums.com/proxy.php?request=http%3A%2F%2F&hash=03ee70165653ed1fcf3a617a5e4320ea)
Title: Re: Underwater accidental hydrogen / oxygen explosion
Post by: Enthalpy on December 28, 2018, 04:41:50 PM
Hi,

150A is the current when the user puts the rod in contact with the other electrode for ignition. It would be extremely difficult to pass this current through seawater, needing huge flat electrodes very near to an other and using deadly voltages. In industrial electrolysis, the current per cell is but bigger, with optimized shapes and solutions as concentrated as possible, not seawater. So as soon as the user separates the rod from the counter-electrode (does he?), the current must drop to a low value, maybe 0.1A or 0.01A.

In electrical engineering, I learned that electrocution is more probable with DC. I can't confirm it first-hand (so to say) as I never had an accident with 240V DC and have zero desire to try. Videos I saw of thermal lances on land used a 12V car battery to ignite the rod, and this may be a reason for DC. Spectacular.

I too would say that any current flowing in an underwater arc is inefficient at electrolysis. Most current flows through the vapour without producing hydrogen nor oxygen.

I didn't quite understand: I imagine that you need current to ignite the thermal lance, but thereafter none is needed. Or is it a different use, maybe when welding with current instead of cutting with oxygen and heat?

If the rod and the counter-electrode are separated by 0.1m or more after ignition, and the voltage is a few volts, any current flowing through the water would be small, like 10mA, and produce very little hydrogen.

Yes, heat decomposes water partly. This could be computed by hand or using software like Propep. At 5500°C it's efficient. However, hot oxygen and hydrogen recombine immediately to form water as soon as the temperature drops. As bubbles go away from the lance, they just make water back. I don't imagine a production of hydrogen by this process. It's the very problem that prevents production of hydrogen from concentrated sunlight.

To my eyes, the credible process is that the hot metal (Fe, Al...) reacts with water to produce hydrogen and metal oxides and hydroxides. This can happen at the outer surface of the lance, near the hot tip, where no oxygen can burn immediately the hydrogen. One potential parry would coat the lance's outer face with thick oxides and hydroxides stable to heat, so water can't reach quickly the hot bare metal.

Experiments aren't too difficult: use a lance horizontally in a tub, observe if gas appears at the outer face near the tip, then collect and analyse it.

The cut parts (hull...) too can produce hydrogen once or where the lance and its oxygen aren't any more but the metal is still hot. And possibly a better candidate: sparks of liquid metal ejected to the water where no oxygen is present. Or biological material attached to the hull: it gets hot at some distance from the oxygen, and its pyrolysis can produce a mix of flammable gases.
Title: Re: Underwater accidental hydrogen / oxygen explosion
Post by: wildfyr on December 28, 2018, 06:13:45 PM
I too think its the very finely powdered (or even gaseous?) metal in the 0 oxidation state that is the most suspicious flammable thing around. Its a matter of surface area. A chunk of Fe and Zn 1 cm3 is not very flammable, but the same amount that has been reduced essentially to nanoparticles is an entirely different story.
Title: Re: Underwater accidental hydrogen / oxygen explosion
Post by: Papyone on December 30, 2018, 02:08:49 PM

 Videos I saw of thermal lances on land used a 12V car battery to ignite the rod, and this may be a reason for DC. Spectacular.

Yes, heat decomposes water partly. This could be computed by hand or using software like Propep. At 5500°C it's efficient.
Experiments aren't too difficult: use a lance horizontally in a tub, observe if gas appears at the outer face near the tip, then collect and analyse it.

Hi again,
If it is true that a thermic rod can be lit with a 12 volt battery we seldom use that method under water because most of the time when we have a cutting job we cut during many hours a day and therefore we use a dc generator or an inverter. Also as you have probably seen on your video, above water it is possible to cut the current once the rod in burning. Under water this works also but most of the divers prefer to cut hot (current on) because the quality of those rods vary a lot and some of them extinguish easily once the current is of.
Thanks again for your explanations that confirm that the majority of the H2 is effectively produced by heat and not by the rod current. I will try to convince the few big commercial diving organization to make a few more gas analysis in order to find out what really kills so many divers.
Concerning the water decomposition by heat, could you give me an example on how to compute it by hand?
Title: Re: Underwater accidental hydrogen / oxygen explosion
Post by: Enthalpy on December 31, 2018, 06:53:13 AM
Computing an equilibrium by hand takes some training and time. I've run Propep on water at 1 atm (but 1+1 atm at 10m depth would change little) and varied temperatures. Here are molar fractions:

  H    H2    H2O    O    OH    O2
0.14  0.18  0.42  0.06  0.14  0.59 at 3000°C
0.58  0.06  0.01  0.29  0.05  0.14 at 4000°C
0.66  0.01   ppm  0.33  0.01  0.1% at 5000°C
0.66  0.1%   ppm  0.33  0.1%   ppm at 6000°C


- It's complicated, and here I didn't even include Al nor Fe. Hand computation is half-way reasonable with 2 or 3 possible compounds at most.
- The amount of H2O that really reaches 5000°C is essentially decomposed, more to atomic H and O than to H2 and O2.
- But when the bubble cools down, everything recomposes snappily and fully to H2O. I expect no H2 production by this process.

But where should water be heated to that temperature? If it's by contact with hot metal, then the reaction is to oxidise the metal, not to decompose water by heat.

----------

Where does the permanent current pass? Is it within the lance, through oxygen, between the outer and some inner electrode? I still can't imagine 150A through seawater.
Title: Re: Underwater accidental hydrogen / oxygen explosion
Post by: Papyone on January 02, 2019, 04:15:11 AM
Enthalpy,
I‘ve another question.
Making a gas analysis is quite a difficult and probably expensive operation and therefore I suppose some diving organisation may be reluctant to do it.
But I was thinking to ask some colleagues to make a flame test above the residual gasses that are reaching the surface (for instance by holding a gas burning torch above the bubbles that are coming up).
What would then happen if the residual gas contains less than the 3.9% H2 L.E.L?
What would happen if the residual gas contains more than the 3.9% H2 L.E.L?
Title: Re: Underwater accidental hydrogen / oxygen explosion
Post by: Enthalpy on January 02, 2019, 12:57:36 PM
I would not make the test over a diver. Instead, collect the gas, for instance by filling with water a container, the letting the gas bubble into its wide opening. Move the closed container to an other location, and try to ignite. Prefer a plastic container, not glass nor metal - something like a Tupperware. Prefer a petrol engine spark plug and coil to ignite the gas from distance, or use a trail of flammable liquid.

The boom test tells you more directly whether the gas can make boom, rather than sub-details about a composition from which you may attempt deductions. And because it's faster and cheaper, you can test more varied situations, which is probably the key to finding the cause. My bet is that explosive mixtures form only under rare conditions, that's why the cause is still unknown.

Maybe methane is already present in the seabed from rotting vegetables, and the diver releases it by walking?
Title: Re: Underwater accidental hydrogen / oxygen explosion
Post by: Papyone on January 02, 2019, 03:49:26 PM
Ok I will ask some colleagues to do something like that. Thanks for the tip and explanations.
Title: Re: Underwater accidental hydrogen / oxygen explosion
Post by: Enthalpy on January 04, 2019, 04:52:02 PM
I've run propep on hot Fe2O3 (and also on hot Al2O3), and
I suggest to experiment that on the ground. No depth needed, no suit - but a tub full of water, steel plates, thermal lances and some sort of explosion-proof wall. Operate behind the wall with a long lance, try some combinations of plate thickness and oxygen throughput, observe in a mirror, collect the gas. If some flue gas can detonate with air or is fuel-rich, it's the explanation.
Title: Re: Underwater accidental hydrogen / oxygen explosion
Post by: Papyone on November 02, 2019, 11:43:32 AM
Hello Enthalpy
Thanks to all your replies I’ve finally made a series of tests to calculate the production of hydrogen by electrolysis and thermolysis and have published the result in a document.
If you are interested by it send me a message with your email or another address where I can send you the link to download it (for free).
Regards
Francis
Title: Re: Underwater accidental hydrogen / oxygen explosion
Post by: billnotgatez on November 03, 2019, 09:23:16 PM
@Papyone

Is there a reason you do not post the link here?
Title: Re: Underwater accidental hydrogen / oxygen explosion
Post by: Papyone on November 04, 2019, 03:00:33 AM
@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
Title: Re: Underwater accidental hydrogen / oxygen explosion
Post by: Enthalpy on November 05, 2019, 06:30:15 PM
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?
Title: Re: Underwater accidental hydrogen / oxygen explosion
Post by: Papyone on November 07, 2019, 11:32:00 AM
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.


Title: Re: Underwater accidental hydrogen / oxygen explosion
Post by: Enthalpy on November 11, 2019, 12:07:15 PM
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.
Title: Re: Underwater accidental hydrogen / oxygen explosion
Post by: Papyone on November 16, 2019, 12:11:01 PM
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.
Title: Re: Underwater accidental hydrogen / oxygen explosion
Post by: Enthalpy on November 28, 2019, 10:56:34 AM
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.
Title: Re: Underwater accidental hydrogen / oxygen explosion
Post by: Papyone on December 02, 2019, 12:24:54 PM
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?
Title: Re: Underwater accidental hydrogen / oxygen explosion
Post by: Enthalpy on December 03, 2019, 11:36:01 AM
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.
Title: Re: Underwater accidental hydrogen / oxygen explosion
Post by: Papyone on December 04, 2019, 11:24:25 AM
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.
Title: Re: Underwater accidental hydrogen / oxygen explosion
Post by: Enthalpy on December 05, 2019, 11:54:16 AM
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.
Title: Re: Underwater accidental hydrogen / oxygen explosion
Post by: billnotgatez on December 10, 2019, 05:55:43 AM
From WIKI
https://en.wikipedia.org/wiki/Hydrogen#Combustion (https://en.wikipedia.org/wiki/Hydrogen#Combustion)
Quote
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.
Title: Re: Underwater accidental hydrogen / oxygen explosion
Post by: Papyone on September 21, 2020, 06:28:10 AM
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.