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.