Monday Accident & Lessons Learned: Subsea OXYARC Cutting – Risk of Explosion
OPG Safety Alert 227
SUBSEA OXYARC CUTTING – RISK OF EXPLOSION
Location: OFFSHORE : Specialist vessel eg. diving, construction, survey
Type of Activity: Diving, Subsea, ROV
Type of Injury: Explosion / Burn
Subsea Oxyarc cutting utilises an energising current supplied by a welding generator. There is a potential for leakage current to be present in the circuit if industry standard single pole isolation is used. This increases the potential for hydrogen gas to be produced as a product of electrolysis, these can become trapped in pockets inside the oxyarc torch and burning rod subsea. Hydrogen pockets introduce a risk of explosion when mixed with the oxygen.
What Went Wrong?
Common Industry practice is to use a single pole isolation as a break in the circuit and this can result in leakage current still flowing through the Oxyarc torch and Rod while the diver believes it fully isolated.
Corrective Actions and Recommendations:
Double Isolations that perform a complete break in both poles of the circuit should be used between the surface generator and the diver. These will form a more effective and dependable isolation.