The U.S. Chemical Safety Board (CSB) blamed a February power plant explosion that killed six workers on the practice of clearing natural gas lines called “blow down.” The federal agency said last Wednesday that the use of gas to clear lines is common at gas-fired power plants.

The explosion, at the Kleen Energy Systems LLC power plant project in Middletown, CT, which injured at least 50 workers, occurred during a blow down in early February (see NGI, March 1). The process was used to clean out new fuel-gas piping leading to combustion turbines by directing high-pressure gas through the pipes and out of vents located near ground level, adjacent to the power generation building. The gas accumulated above the lower explosive limit and ignited, causing massive damage to the billion-dollar facility, which was nearing completion.

“Venting any significant amount of natural gas into a workplace is an open invitation to disaster,” said CSB Chairman John Bresland. “With more than 120 new gas power plants slated for completion in the next five years, there is an urgent need to ensure safety during the construction and maintenance of gas piping. The CSB will be considering recommendations to promote safer practices in industries that use natural gas as fuel.”

The ignition source for the blast has not been determined. CSB investigators said the construction site had many possible ignition sources, and that gas blows could also self-ignite if debris ejected from piping impacted other objects nearby, creating sparks — adding to the risk of the practice.

CSB investigators were to present the findings — derived from a survey of 62 representatives from the combined-cycle gas power industry — at professional society meetings in Maryland and Connecticut last week. Thirty-nine survey respondents (63%) indicated that their companies had at some time used natural gas to blow out piping. Only one of those 39 respondents said a flare was used to safely combust the gas prior to venting to the atmosphere, CSB said.

According to the survey, using natural gas to clean pipes remains the most common single practice in industry, employed by 37% of respondents. The other respondents reported using nitrogen, which is nonflammable, or inherently safer alternatives such as air, steam or cleaning pigs. On Feb. 25, 18 days after the explosion at Kleen Energy, CSB stated that natural gas blows were “inherently unsafe” and urged the industry to seek alternatives.

“The industry survey confirms that there are readily available safe alternatives to using flammable natural gas for pipe cleaning,” said CSB investigator Dan Tillema. “At the same time, a disturbing number of companies continue to use natural gas which creates the serious risk of a fire or explosion.”

Bresland said he expected that the CSB would convene a public hearing in Connecticut in late June to consider further recommendations to prevent accidents involving the planned venting of natural gas at workplaces.

©Copyright 2010Intelligence Press Inc. All rights reserved. The preceding news reportmay not be republished or redistributed, in whole or in part, in anyform, without prior written consent of Intelligence Press, Inc.