LEL of a H2/O2 mixture under 5 m water

[papyone]

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.