Personnel exposed to hydrogen sulphide during maintenance

Subcontractor personnel were exposed to a high concentration of Hydrogen sulphide (H₂S) for a short period during maintenance work in a vessel’s Well Treatment System (WTS) room. The incident occurred during annual maintenance work being conducted on the system's acid filter units. When the upper vent valve on an acid filter unit was opened, the subcontractor supervisor noted a pressure release from the system and a strong smell. The valve was immediately closed, an “All Stop” called, the extraction fan unit turned on and the team exited the room (no alarms were activated).

The subcontractor supervisor notified the company supervisor, who started to suspend the Permit To Work. During this period, the subcontractor supervisor made the decision to re-enter the room and open the acid filter vent slightly to check for pressure. At this point, the supervisor’s personal H₂S alarm sounded and highlighted the presence of H₂S at high concentration (357ppm), and the vessel H₂S alarm in the WTS room also sounded. Personnel evacuated the room and work was suspended. No personnel showed any symptoms nor suffered any adverse health effects.

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