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).