ConAgra Natural Gas Explosion and Ammonia Release
– Purging Gas Piping Into Buildings – a dangerous practice
Date June 9, 2009. Venue: Con Agra Slim Jim Production facility at Garner, North Carolina. The catastrophic gas explosion at Con Agra had caused a large number of deaths as well as damage to property. The natural gas explosion did not just kill four people but three people were also burnt badly. One more person was amputated and 67 people died because of deadly injuries. An area of nearly 87000 square foot at the warehouse of Con Agra received serious structural damages. Walls and roof also feel as a result of the explosion which could potentially cause many more deaths.  Around 37% of the roof area fell due to the explosion. 60% of it sustained heavy damages and as a result became highly unstable. Con Agra is remained as one of the deadliest cases in industrial history. The explosion damages the large ammonia based refrigeration system of the plant which released toxic anhydrous ammonia gas into the atmosphere. Apart from the site of the explosion toxic ammonia gas was also detected offsite after the explosion. The explosion had released nearly 18000 pounds of ammonia into the atmosphere. During the emergency procedures followed after the explosion, there was release of more ammonia that contaminated the nearby surface waters.
The explosion was lethal. Apart from killing people, it caused economic losses due to damage to property. Following the explosion, the plant’s operations were suspended resulting in huge economic damages. Con Agra was one of the largest regional employers. Once again when operations resumed, hundreds had to be laid off. The ammonia readings recorded by US EPA and DENR showed ammonia readings of 10000 ppm (parts per million) in the discharged water and 150 ppm in the air above it which had killed fish. The accident took place when a new water heater was being installed. The water heater made by Energy Systems Analyst Inc. was a 5 million per hour gas fired water heater. Some weeks before the installation of the water heater a new gas line had been installed.  This three-inch gas line ran along the roof horizontally for more than 120 feet. It then descended into the utility room where the new water heater was. The new and the old gas lines had also been pressure tested after their installation to identify any kind of leaks. A CSB report showed that the after having pressure tested successfully, the workers had purged the gas supply line of air. The purged gases were vented directly outdoors through a hose from the boiler room. This was done to avoid the accumulation of flammable gases inside the building. However, air from the new piping that led to the new water heater had not been purged immediately. There were no uniform guidelines at Con Agra for purging. It did not have any good combustible gas detectors in use either that could provide a warning of any potential dangers.
Whenever a new fuel gas line is applied, it is essential to purge the lines of air. Even the US fuel gas safety codes establish that the new gas pipe should be pressure tested with either air or inert gas before operations are begun. The Con Agra accident brought issues related to gas lines safety to attention. It has left behind a number of lessons regarding gas lines safety. Purging gas pipe lines inside a building is dangerous. It can cause the accumulation of gasses above the lower explosive limit that gives rise to the danger of explosion. Moreover, purging indoors is proper only when purging outdoors is not possible. Odor is not a highly reliable source for detecting the release of fuel gases which was the case in Con Agra explosion. It is proper to use combustible gas detectors. The personnel handling the gas purging operations lasso need to be well trained.