No the intense heat right at the welding site actually separates the two gasses on a molecular level into Hydrogen and Oxygen creating “Hydroxy” gas, or “Brown’s gas”. It is flamable on it’s own, but in this case it also created Chlorine gasses and added them to the mix. So it created a gas bomb with fuel and an Oxidizer.
Arc welding emits intense UV light. UV light causes Hydrogen and Chlorine combined to have an extremely intense explosive reaction. The Oxygen just added more intensity as an Oxidizer.
I think if they had fan forced fresh air in the top and displaced those gases from the tank it would not have happened.
That is absolutely ridiculous! Water molecules are not broken into hydrogen and oxygen using “intense heat”. They can be broken down through electrolysis. Intense heat turns water into steam it does not break water molecules down. Do a little research on the term electrochemistry and electrolysis.