Why common sense must prevail
09 March 2010
If common sense was truly universal, we’d all have it. But from recent findings in the US, this is clearly this is not the case. Would an industrial operator deliberately purge a process line with a flammable gas into an enclosed area containing hot spots and electrical ignition sources? Common sense would suggest not but this operation is surprisingly a standard practice in certain sectors. Last month's accident at Kleen Energy has proved to be a fatal example of this high risk practice.
Gas escaping at Kleen Energy just before the blast
The explosion at Kleen Energy's Middletown, Connecticut plant, which left five dead and 12 seriously injured, occurred during a planned work activity to clean debris from newly fitted natural gas pipes. The US Chemical Safety Board (CSB) inquiry into the incident found that workers used natural gas at a pressure of more than 40 bar to remove debris in the new piping. The high velocity of the gas, known in the natural gas industry as a gas blow is intended to clear obstructions in the pipework.
At pre-determined locations, gas used in the blow was vented to the atmosphere through open ended pipes, located less than 20 ft off the ground. These vents were adjacent to the main power generation building and gas can be seen venting out of the system in a photograph taken a short time before the accident.
CSB investigators have reviewed gas utility records for the morning of the accident. These records together with written pipe cleaning procedures and witness testimony confirm that the gas blows occurred intermittently over the course of the morning. At the same time that gas blows were underway, there were potential ignition sources present in the surrounding area, including inside the power plant building. There were many construction-related activities underway inside the building.
Determining the exact ignition source was not a major focus of the CSB investigation as in most industrial worksites, ignition sources are abundant and efforts at accident prevention focus first and foremost on avoiding or controlling the release of flammable gas or vapours.
Initial calculations by the investigators has revealed that around 400,000 ft3 of gas was released to the atmosphere near the building in the final 10 min before the blast. That is enough natural gas to fill the entire volume of a basketball arena with an explosive natural gas-air mixture, from the floor to the ceiling. This gas was released into a congested area next to the power block building. This congested area likely slowed the dispersion of the gas. The gas built up above the lower explosive limit of approximately 4% in air and was ignited by an undetermined ignition source.
In the days since the accident, companies and safety regulators from around the world have contacted the CSB asking about the circumstances of this devastating accident. Some companies, including a power plant here in the region, indicated that they themselves have been planning similar gas blows as part of commissioning pipes in the very near future.
Industry sources have indicated to CSB investigators that gas blows have become common practice during the commissioning of new or modified gas pipes at natural gas facilities in the US.
A CSB spokesman suggested that the major focus of the investigation was to determine what regulations, codes, and good practices might apply to these gas blows. No specific codes have yet been identified but CSB is continuing its research.
Until an idiot-proof solution can be written, there is an overwhelmingly powerful recommendation emerging from the CSB inquiry which is to avoid the venting of high-pressure natural gas in or near work sites. The gas blow may be common place but as a practice it is inherently unsafe and clearly not common sense.