On September 9, 2010, in San Bruno, California, a high-pressure natural gas transmission line ruptured. A 28-foot-long section of the 30-inch diameter pipe broke away resulting in two open ends of the pipe. This resulted in two jets of natural gas discharging from the open pipe ends. Within seconds the gas ignited resulting in a large fireball that transitioned into two interacting jet fires. The shut-off valves in the pipeline nearest the rupture site were approximately ¾ of a mile from each open end. These were both manual valves and it required about 1.5 hours for operators to close these valves and shut down the jet fires. The explosion and fire resulted in 8 fatalities, many injuries, and destroyed dozens of residences.
ESi was retained to assess the impact automatic shutoff valves might have had in reducing the effect of the explosion and fire.
ESi used state-of-the-art software to model the flow rate of gas from each open end of the pipe , to model the size and intensity of the jet fires , and to model the angle of the jets discharging from the pipeline). A model of the natural gas transmission pipeline network across the San Francisco Peninsula was used as the basis for estimating the gas pressure and flow rate throughout the system due to the pipeline rupture. The calculations were calibrated using SCADA data of pressure and flow rate at various locations in the network. The gas flow rate from the open ends of the pipe and geometry of the pipeline and the hole in the ground made when the pipeline ruptured was used to estimate the angle of each gas jet discharging from the open pipe ends. These results were then usedto estimate the size of the fireball or jet fire at various times after the pipe rupture.
Video and photographs of the jet fires and the fire damage patterns were used to compare the estimates from these calculations and to tune the models to best match the observed consequence of the explosion and the jet fires.
Once the calculations were calibrated or tuned, various cases were run to evaluate the effect of closing shutoff valves at various times during the incident.
The calculations showed that the gas flow rate was very high right after the rupture, then decreased rapidly as the pipeline near the rupture depressurized. The gas flow rate from the two open ends of the pipe after 5 minutes was less than 25% of the initial gas flow rate. The size of the initial fireball and ensuing jet fires within the first 30 seconds were significantly larger than the size of the jet fires after 5 minutes. The conclusion was that much of the damage, fatalities, and injuries were due to the initial fireball and the first several minutes of the jet fires. The estimated time for automatic valves to sense the pressure loss due to the rupture, fully close, and then for the remaining gas in the pipeline segments to blow down, was 5 minutes or longer. Therefore, automatic valves would not have been able to avoid the most serious damage and fatalities.
Short summary:
ESi analyzed the release of natural gas from a transmission pipeline that ruptured in a neighborhood of San Bruno, CA. The rupture resulted in a massive jet fire that destroyed dozens of homes and resulted in eight fatalities. ESi used state-of-the-art software to model the gas release rate and the resulting jet fire to match the fire shown in videos and the fire patterns observed after the fire was extinguished. This computer model was then used to analyze various scenarios for closing valves to shut off the gas flow.
