Underwater Cutting and Welding

An arc will burn underwater, which surprises people, because water conducts heat away fast and ought to quench it. It survives because the arc boils the water around itself instantly and then burns inside its own steam bubble — the same self-sustaining trick as the oil circuit breaker, where the arc creates the conditions it needs to continue. That makes underwater welding and oxy-arc cutting genuinely practical for salvage and repair. It also makes them among the more dangerous jobs anyone does, for a reason that has nothing to do with the heat: the arc electrolyses water into hydrogen and oxygen, and if that mixture collects under an overhang it becomes an explosive pocket waiting for the next spark.