SAN FRANCISCO – California regulators have ordered Pacific Gas & Electric Co. to lower the pressure on some natural gas pipelines in heavily populated areas to 20 percent below their maximum thresholds.

The California Public Utilities Commission directed PG&E on Wednesday to drop the pressure on pipelines located in the Central Valley, Santa Clara County and the Santa Cruz County coast. The order stemmed from its investigation into the Sept. 9 explosion in San Bruno that killed eight people and destroyed 38 homes.

PG&E said late Wednesday that it already has started lowering pressure on the lines below their maximum allowable operating pressures.

The company also acknowledged it had intentionally increased the pressure on a dozen pipelines temporarily, in some cases going above the limit "by a few pounds."

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Do the terms "maximum thresholds" and "maximum allowable operating pressures" mean the same as "maximum allowable safe operating pressures."  Some of the comments at the end of the article imply that some people view the terms as failure or burst pressures.  Surely pipelines are designed to operate with several factors of safety below burst or weld seam pressure limits.  As gathering and transmission pipelines age wouldn't it make sense to have a schedule to lower operating pressure limits?  What are the gas pipeline pressures taking gas from your well and the pipelines delivering gas to or through your town and neighborhood?