An unplanned shutdown of the hydrogen supply system occurred, affecting the hydrogen furnaces in the plant. The apparent cause was an inadvertent valve closing, which was contrary to the written procedure.

A preventative maintenance activity was being conducted on the hydrogen gas system. Shortly after starting that work, various hydrogen gas users notified the emergency response personnel that the hydrogen supply safety alarms sounded, indicating an interruption of the hydrogen gas supply. As a result, the hydrogen furnaces shut down. This shut down is an automated process which injects an inert gas (nitrogen or argon) to prevent the introduction of oxygen and its mixing with any hydrogen gas. All shut downs functioned as designed. As a precautionary measure, fire protection personnel manually checked the furnaces for the presence of oxygen. Only residual oxygen was found.

Simultaneously, while the hydrogen furnace users were reporting the supply interruption, the on-shift utility operator notified the facility’s hydrogen systems engineer of a flow valve alarm condition. The maintenance craftsmen immediately realized that valves were operated out of sequence while the above referenced maintenance activity was being conducted.

The direct cause was a deficiency in procedures that did not include consequences of failing to follow the procedure and the immediate actions to be taken in the event of error. The contributing cause was determined to be a training deficiency, since no formal records indicated who had received the necessary maintenance training. Additionally, the training was insufficient in that it did not cover system safety controls. The root cause was determined to be personnel error in that the craftsmen performing the preventive maintenance task did not follow the established written procedures.

Incident Date
Aug 05, 1993
  • Piping/Fittings/Valves
  • Valve
Damage and Injuries
When Incident Discovered
Lessons Learned

Diligence needs to be practiced when performing assigned work tasks. To guard against complacency, it is necessary to emphasize adherence to established procedures, including appropriate reviews of preventive maintenance instructions (PMI) and related on-the-job training (OJT). Another lesson learned was that the craftsmen need to be familiar with the total system safety controls. They did not realize, for example, that the furnaces would automatically purge hydrogen with an inert gas for safety reasons in the event of a flow interruption. Had they known this, they would not have been in a hurry to correct the error and turn the hydrogen back on. The hurried action caused an immediate surge in the flow, and in turn caused the excess flow valve to shut. This compounded one error into two errors. They should have stopped when they initially made the error, and notified the hydrogen system engineer.