In an effort to prevent fires and explosions caused when natural gas is used to clean or purge gas pipes of debris, air or other substances, typically during facility construction and maintenance, the U.S. Chemical Safety Board (CSB) in a 4-1 vote last week approved a list of “urgent recommendations” for the Occupational Safety and Health Administration (OSHA), the National Fire Protection Association (NFPA) and others.

Among the recommendations is to require “the use of inherently safer alternatives such as air blows or pigging with air in lieu of flammable gas.”

The CSB investigation was triggered following the Feb. 7 natural gas explosion at the Kleen Energy power plant in Middletown, CT, that caused six deaths and multiple injuries (see NGI, Feb. 15) and the June 9, 2009 natural gas explosion at the ConAgra Foods Slim Jim plant in Garner, NC, that killed four workers and injured 67.

The accident at Kleen Energy occurred during the planned cleaning of natural gas piping during the commissioning and startup phase of construction. The CSB said natural gas was forced through large piping that was to fuel the plant’s large electricity-generating gas turbines, in an operation called a “natural gas blow.” This gas was vented directly to the atmosphere from open pipe ends that were less than 20 feet off the ground and were located in congested areas adjacent to the power generation building.

Earlier this year the CSB said the use of natural gas to clear lines was common at gas-fired power plants despite being dangerous (see NGI, May 24). The 620 MW Kleen Energy combined-cycle baseload plant had been expected to begin operation this summer.

Investigators obtained gas company records showing that some 2 MMcf of natural gas was released to the atmosphere during gas blows on Feb. 7 — enough, the CSB calculated, to provide heating and cooking fuel to a typical American home every day for more than 25 years. The gas found an ignition source and exploded.

CSB’s approved recommendations urge OSHA to pass regulations that would prohibit the use of natural gas for pipe cleaning, the cause of the explosion at Kleen Energy, and would prohibit the venting or purging of fuel gas indoors, the cause of the explosion at the ConAgra Slim Jim plant. “Both explosions resulted from releases of natural gas during the installation and commissioning of new piping that led to gas-fired appliances,” CSB said.

In testimony last week at a field hearing before a subcommittee of the U.S House of Representatives Committee on Education and Labor, held in Middletown, CSB Board Member John Bresland said there is a “significant gap” in the current gas safety standards for general industry and construction, “a gap that threatens the continued safety of workers at facilities that handle flammable natural gas.”

On of the recommendations directed at the NFPA urges the code-development organization to enact a tentative interim amendment as well as permanent changes to the National Fuel Gas Code that addresses the safe conduct of fuel gas piping cleaning operations. Under the CSB draft recommendation, NFPA would be asked to remove key exemptions in the code for natural gas power plants and for high-pressure gas piping and to require the use of inherently safer alternatives to natural gas blows. CSB investigators determined that compressed air is a feasible and economical alternative to using natural gas for pipe cleaning.

Other approved recommendations would seek related safety improvements from Connecticut and other states, the leading gas turbine manufacturers, the American Society of Mechanical Engineers and the Electric Power Research Institute.

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