Northern Natural Gas

Northern began development of its program in 2002 and began integrity assessments in 2003, prior to the Gas Integrity Management Rule being finalized. During 2004 and 2005, Northern implemented a system to identify High Consequence Areas (HCA) based on the impact area of a potential pipeline failure and the surrounding population. Next, Northern performed risk-of-failure calculations to determine, on a relative basis, which HCA pipeline segments had the highest risk of failure. This information was then used to prioritize the HCA segments to determine how best to assess the integrity of the segments and the appropriate order and timeframe to do so. Northern currently addresses the HCA segments by inspecting the line using sophisticated tools that provide information about the integrity of the pipeline, using water to pressure the line beyond its maximum allowable operating pressure to ensure the line can hold gas to the required pressure, rerouting the pipeline around the HCA, or abandoning the pipeline. All of these methods of addressing the HCA provide a safety measure against pipeline ruptures in HCAs.

Northern has identified approximately 400 segments, totaling approximately 125 miles of pipelines as HCA. As of May 1, 2006, Northern has performed an integrity assessment on approximately 80 miles of HCAs and 1,000 miles of general pipelines. Northern will continue to move forward with its program until all HCA mileage is assessed along its system.