CSB moves on gas purging code

Author : Paul Gay

09 February 2010

US industry will soon be subject to a revised set of operating regulations following a Chemical Safety Board (CSB) public meeting in Raleigh, NC, which approved the wording of two urgent safety recommendations on gas purging safety. The draft recommendations, which were approved as presented without amendment, urged the National Fire Protection Association (NFPA), American Gas Association (AGA), and the International Code Council (ICC) to strengthen the fuel gas code provisions.

Damage inside the ConAgra plant

The board of the CSB is to be commended for its forthright actions and the detailed report that came up with these important recommendations, which were drawn up following a CSB investigation into the catastrophic natural gas explosion at the ConAgra Slim Jim production facility in Garner, North Carolina, last June. The disaster left four dead, three with critical life-threatening burn injuries and another victim with an amputation. In all 67 people were sent to hospital.CSB investigators found that the explosion was caused by the accumulation of significant amounts of natural gas that had been purged indoors from a new 120 ft piece of pipework during the startup of a new water heater. During pipe purging, workers feed pressurised gas into a pipe in order to displace air or other gases so that only pure fuel gas remains in the piping when it is connected to an appliance such as a water heater or boiler.The board is rightly concerned that companies across the US continue to purge pipes indoors. This practice will be changed if the recommendations made by the investigation are adopted. Currently, the codes of the NFPA and ICC do not require gases to be vented outdoors or define adequate ventilation or hazardous conditions, nor do they require the use of combustible-gas detectors during these operations. This will surely change with the CSB recommendations.Commenting on the recommendations, CSB investigations supervisor Donald Holmstrom summarised: "Purging flammable gases into building interiors is a recipe for disaster. At ConAgra, we determined the accident would not have happened had the gas been vented safely outdoors through a hose or pipe"The recommendationsThe CSB urges the NFPA and AGA to enact tentative interim and then permanent changes to the National Fuel Gas Code. These would require that purged gases be vented to a safe location outdoors, away from personnel and ignition sources.In cases where outdoor venting is not possible, companies would be required to seek a variance from local officials before purging gas indoors, including approval of a risk evaluation and hazard control plan. The recommendation would also require the use of combustible gas detectors to continuously monitor gas concentrations; the training of personnel about the problems of odour fade and odour fatigue; and warnings against the use of odour alone for detecting releases of fuel gases