If this was problem related to flammable gasses igniting... it was because the welding going on was in an area that was just above the water level and some heavier than air gas like propane was mixed with the right amount of air to combust when a spark or arc above the ignition temperature of the gas ignite the mixture I was the head of a Hazmat Team for many years. We have not been given enough info to know exactly why this happened but your
OK... again...
Hydrogen and Chlorine mixed. Tested with several different light waves and yet only UV will cause the violent reaction. It is right here in this. No mistake.