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papyone

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  1. Good evening everyone, I'm here with a weird question about the explosion under water of a mixture of explosive gases. To cut under water the divers use among other equipment mini thermal electrodes that work a bit like a welding electrode, except that these thermal electrodes are hollow to allow the sending of pure oxygen. By electrolysis effect as well as by the heat of the flame (+/- 5500 ° C) the water decomposes into hydrogen and oxygen. For commercial divers, the formation of such gas mixture sometimes presents a lethal risk if it cannot escape freely on the surface. If I am not mistaken, in theory the explosive limit of this H2 / O2 mixture is between 3.9 and 95.8%. When the gases remain confined, we frequently observe the explosion of small amounts of gas (2 - 5 cc) with mixtures which different proportions. Thus, during a few cutting operations between 3,5 and 5 m deep, gas samples were recovered and analysed. Surprisingly, while the entire profession was convinced that hydrogen concentrations in residual gases were within the lower and upper limits of explosion, it was found that these values were much lower. 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% Therefore my question is: how can we have explosions underwater with such low hydrogen values. Does the combination of all these gases change the LEL? As the vaporisation of the water around the flame something to do with the H2 LEL modification? Thank you in advance for your help.
  2. Hello everyone, Thanks for approval in this forum. My question concerns the cutting of metals. Whether by gas cutting torch or thermal lance, all manufacturers recommend using oxygen with a purity of about 99.5%. They also specify that the performance of the cutting will decrease by about 25% per missing percentage and they place the limit at which it is no longer possible to cut around 95% oxygen. I recently did tests with ultra-thermal electrodes (models that are used under water but which works on the same principle as the conventional 3 m oxygen lance) and I still managed to cut on the surface with a mixture oxy / nitrogen 70%. Hence my question: Given the difficulty I had to cut at the surface, I am convinced that if we use such a mixture to cut under water at shallow depth it would not work properly. But when would it be if we did this test at about 132 m depth? There we would again have a PPO² equivalent to 99.4% oxygen at atmospheric pressure and therefore equal to what is recommended by manufacturers. So I would like to know if at this depth and with such a mixture (70%), the thermal electrode would cut normally. FYI, in practice this will never happen, but it is a question that is currently running on a commercial dive forum and for now nobody can answer it. So thank you in advance for your help.
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