The lessons of this event fall into five categories: (1) proper in-plant communications during events, (2) proper valve application for use with hydrogen, (3) excess flow check valve set point, (4) heating and ventilation and air conditioning (HVAC) maintenance and flow testing, and (5) hydrogen line routing. The operator is examining ways to improve communications in the plant during events and the training of personnel in reading portable instruments.

As another corrective measure, the operator is examining the use of other types of valves, such as valves with a diaphragm or bellows rather than conventional stem packing, in lines containing hydrogen. The operator is also examining the set point for the excess flow check valves on the hydrogen lines. These check valves are designed to limit the flow of hydrogen in the event of a large leak so that when combined with proper ventilation in rooms with hydrogen lines, hydrogen levels would remain within specified limits throughout the plant.

This plant had HVAC flow balancing problems during the preparation for plant startup. Generally HVAC flow balance is based on the heat loads and the resultant room temperatures under normal and accident conditions. However, this event demonstrates that hydrogen concentrations also may need to be considered to set a lower limit on the ventilation in rooms that contain hydrogen lines.