MIKE BAKER Associated Press Writer — October 5, 2009 RALEIGH, N.C. (AP) — Federal safety officials warned workers around the country Friday not to clear natural gas lines indoors after an explosion at a Slim Jim snack factory that killed three people.

The U.S. Chemical Safety Board said in a new safety bulletin that the June explosion at the plant underscored that gas lines being worked on should not be emptied, or purged, indoors.

Investigators believe contractors installing a water heater vented natural gas inside the building, leading to the blast that injured dozens who were working at the ConAgra Foods Inc. plant south of Raleigh. Omaha, Neb.-based ConAgra has announced that about 300 employees will be laid off due to the explosion.

Officials suggested that workers vent gases to a location outdoors and use detectors to monitor gas levels, among other recommendations. They said if purging outdoors is not practicable, all nonessential personnel should be evacuated from the building.

The Associated Press reported last month that the safety board voted down a proposal issued by its staff that would have distributed recommendations for state, national and international regulators to strengthen gas code guidelines. Two board members had argued that code writers should be the ones to decide on any new written rules, not the safety board.

North Carolina later voted to enact emergency changes to its code that adopt the new safety suggestions.

"I strongly commend North Carolina for taking immediate action to protect workers following this tragic explosion," said John Bresland, the safety board's chairman, in a statement Friday. "I urge code officials around the country to review the new safety bulletin as well as heed the positive steps taken by North Carolina."

The United Food and Commercial Workers International Union, which represents several hundred workers at the ConAgra site, criticized the safety board for not recommending strong new standards.

"By not recommending urgent standards on fuel gas purging they leave the lives of thousands of workers at risk," said Jackie Nowell, occupational safety and health director for the UFCW. "If the CSB continues to fail America's workers by not taking a stronger stand for safety, it's time for change at the CSB."

Current national safety codes, developed by a committee convened by the National Fire Protection Association and the American Gas Association, says gas purges "shall not be discharged into confined spaces or areas where there are sources of ignition unless precautions are taken." The safety board's warning includes a number of safety suggestions that are much more specific.

Other accidents linked to gas line purges include a May 2008 incident during the construction of a San Diego hotel that injured 14; an August 2007 explosion at a hotel in Cheyenne, Wyo., that injured two; and an explosion at a Porterville, Calif., school that burned two plumbers in November 2005. The Chemical Safety Board also said a 1997 explosion at a fitness center in Cary that injured six was linked to purging.

Federal officials expect the full investigation to be finished in 2010.