Explosive repercussions

Deadly blast raises concerns about gas purging practices

Three days after the Chemical Safety Board recommended strengthening provisions for gas purging, an explosion during purging-related activity killed six workers at a power plant under construction in Middletown, CT. As investigators piece together details of the blast, larger questions are emerging about safety protocols for purging gas lines.

On the morning of Feb. 7, workers at the site of the nearly completed 620-megawatt Kleen Energy Systems LLC plant were engaged in a cleaning procedure called a “gas blow,” during which they sent natural gas through pipes at a high pressure of about 650 pounds per square inch to remove debris, according to CSB. At the time, potential ignition sources were nearby and construction activities were going on inside. The gas, which was vented into the atmosphere at predetermined locations, accumulated in a congested area outside and ignited by an undetermined source.

In the 10 minutes before the explosion, approximately 400,000 standard cubic feet of gas was released into the atmosphere – enough to fill the entire volume of a professional basketball arena with an explosive natural gas-air mixture, CSB said.

At a Feb. 25 news conference, CSB lead investigator Don Holmstrom noted that gas blows used in the power industry are different from the purging activity addressed in the agency’s recommendations to the National Fuel Gas Code, from which power plants are exempt. Purging involves using pressurized gas to displace air or other gases in pipes. Holmstrom said the processes are similar in that gas is applied at one end of a pipe and intentionally discharged into the atmosphere at the other end.

He stressed an “underlying common theme” among the Kleen Energy accident and other purging-related incidents, such as the fatal June 2009 explosion and ammonia release at the ConAgra meat processing plant in Garner, NC. That accident, which was linked to releasing purged gases indoors, prompted CSB to issue the purging recommendations (.pdf file).

“Companies must ensure that flammable gases are not vented into close proximity with ignition sources and workers,” Holmstrom said. “That is a vital safety message from all these tragedies.” Gas blows are common during the commissioning of new or modified gas pipes, yet Holmstrom called the practice “inherently unsafe.” He said CSB is looking into alternatives, such as using air, steam, nitrogen or water to remove debris, or using combustion devices to safely destroy gas. Investigators also intend to determine what regulations, codes or good practices apply to gas blows. At press time, no codes had been identified.

“I think we feel there’s a potential gap in standards,” said Daniel Horowitz, CSB’s director of public and government affairs. That became clear in Connecticut at a committee meeting in March when a state lawmaker asked experts which state agencies enforce safety measures during power plant construction. Reportedly, the response was silence.

“The fact of the matter is gas piping is something that is mostly left up to the installing contractor,” said John Puskar, principal engineer at CEC Combustion Services Group in Cleveland. CEC provides services such as gas piping safety training, interlock testing and inspections to clients, including ConAgra Foods.

Enforcement is difficult because many parties that appear to have jurisdiction do not. The utility company’s authority usually stops at the meter. The building inspector is not required to be present, nor is the licensed engineer or the local fire marshal, according to Puskar. He advocated more training for workers. “The problem is that the average individuals holding tools and performing this work don’t understand those rules,” he said.

Stronger codes

Natural gas is odorless and colorless, so a sulfur derivative called mercaptan is added to make it smell like a rotten egg. But Puskar said over time, people become accustomed to the smell and cannot distinguish between levels of concentration. New gas pipes also can absorb or otherwise neutralize the mercaptan agent.

In its recommendations, CSB urged changing the National Fuel Gas Code (developed by the National Fire Protection Association and the American Gas Association) and the International Fuel Gas Code from the International Code Council to require venting purged gases outdoors and away from personnel and ignition sources. CSB also recommended receiving approval from local officials for indoor purging, using combustible gas detectors to monitor gas concentrations and training workers not to rely on their nose to detect fuel gases.

Jackie Nowell is the occupational safety and health director for the Washington-based United Food and Commercial Workers International Union, which represents about 650 workers at the ConAgra plant in Garner. She said she would prefer no exception for discharging gases indoors.

“Our concern is that unless there is really sweeping change that says no inside venting at all, it all has to be done outdoors, then it will be accepted practice as usual in business and it will just continue,” she said.

In late February, Quincy, MA-based NFPA took steps to revise its code to require discharging purged gases outdoors. Paul Cabot, administrator of the National Fuel Gas Code for Washington-based AGA, noted that it is up to local jurisdictions to adopt the policy. An NFPA spokesperson said 34 states have done so.

More regulations may be coming. The chairman of the House Education and Labor Committee has agreed to host a hearing on the Kleen Energy explosion. And Sen. Chris Dodd (D-CT) called for a national standard for pipeline purging after touring the damaged power plant.