On April 15, 2010 at approximately 4 p.m., the quiet neighborhood of Calhoun, GA, 65 miles north of Atlanta, was rocked by an explosion. The force of the blast blew out windows within a quarter-mile radius and could be felt up to two miles away.
Fortunately, no personal injuries were reported, but eight neighboring homes were destroyed and nearly 60 other homes were damaged. Insured losses from the event were calculated by the Georgia Insurance and Safety Commission to be in excess of $6 million.
Four certified fire and explosion investigators employed by AGL Resources Inc., the parent company of Atlanta Gas Light, responded immediately to assist state and local authorities with the investigation. In addition to the more than 100 neighborhood residents and dozens of police and fire officials (including the Georgia Insurance and Safety Fire Commissioner himself, who was then a leading gubernatorial candidate), many members of the Atlanta and Chattanooga, TN media arrived on the scene and began speculating about the source of the natural gas that fueled the explosion. Atlanta Gas Light’s investigators recognized the importance of the task at hand.
“When our team arrived onsite, we immediately set out to preserve the scene for a thorough investigation into the origin and cause of the explosion,” said Bryony Hodges, senior litigation counsel at AGL Resources. “We knew we had to determine whether a leak occurred on our system. We had a massive scene to process, but we wanted to work efficiently, while giving our regulators, local authorities and the affected community as much information as possible.”
An Atlanta Gas Light first responder discovered in the blast debris—39 feet from its original location on the side of the home—the gas meter with the advanced metering infrastructure (AMI) gas module still intact. The meter’s location was documented, and the meter was preserved and logged into evidence by Atlanta Gas Light’s investigators.
Working with a key piece of evidence, representatives of Atlanta Gas Light, the Calhoun Fire Department, the state Fire Marshal’s office, the Georgia Public Service Commission, various insurance companies, and numerous origin and cause experts gathered at AGL Resources’ headquarters five days after the incident. They watched as Itron, the AMI provider, demonstrated a data download of the previous 40 days of time-synchronized hourly data from the memory in the recovered gas module.
In 2009, when Atlanta Gas Light Co. began deploying the latest-technology gas modules, they had a goal of improving operational efficiencies. Now, just months after installation of the first of these gas modules, Atlanta Gas Light recognized another benefit of this new technology: The gas modules were useful in providing an additional source of data to assist the investigative process after the major incident.
Data As Historical Record
The hourly data from the AMI gas module showed a major increase in gas flow on the day of the incident, from 9 a.m. to 4 p.m., relative to the home’s typical flow rate over the last month of less than 50 cubic feet per hour (CFH).
The flow rate peaked at 2422 CFH and showed a seven-hour time period of excessive flow through the 400 class meter that was metering at 2 psi inlet pressure.
Excessive hourly gas flow through the meter in the seven hours prior to the explosion was undeniably proven by the historical data downloaded from the gas module.
This definitive hourly consumption data, coupled with Atlanta Gas Light’s extensive testing of the gas lines serving the home and surrounding area, enabled the company to release a statement on April 22, 2010 that its lines outside the home did not cause the explosion.
“The data resolution we pulled from the Itron meter module was very telling in what led up to the explosion, so much so that if we assumed a constant flow rate through the meter for the full seven-hour period, it indicates that gas flow was wide open within the home starting at 9:20 a.m. and that the explosion occurred at 3:39 p.m., which was within one minute of when the explosion actually happened,” said Thom Burruss, chief investigator for AGL Resources and a nationally recognized origin and cause expert.
Proving The Cause
Atlanta Gas Light’s investigators, along with state and local officials and more than 50 origin and cause experts and engineers, participated in a nearly two-week investigation in June 2010 that involved a thorough grid search of the scene. These investigators and experts documented an open pool heater line that all investigators and experts concluded would provide gas flow into the residence consistent with the hourly data recovered from the gas module. Deputy Chief Terry Mills of the Calhoun Fire Department was quoted as saying, “I’ve never been involved with anything of this magnitude before. It was kind of like CSI.”
In August 2010, the state Insurance and Fire Safety Commissioner concluded that the cause of the blast was arson and publicly confirmed Atlanta Gas Light’s conclusion that no failure had occurred on its lines. He subsequently instructed the state Fire Marshal to pursue a criminal investigation. The homeowners’ insurance company has filed a Declaratory Judgment action against the homeowners seeking a ruling that the arson exclusion in their policy disclaims coverage.
“After the Calhoun experience, our investigators, regulators, and the origin and cause experts working in our service territory recognize the value of the data provided by the gas module,” Hodges said. “This technology effectively demonstrated that the source of the leak was downstream of the meter and foreclosed any migrating gas theory that could have been used against us. Through our investigative efforts, Atlanta Gas Light was able to demonstrate that it had no liability for this incident.”
A Comparative Event
Before this gas module technology was developed, Atlanta Gas Light was sued following an explosion at a customer’s home that resulted in two deaths. In the hours before the explosion, two HVAC technicians had been in the crawl space under the home working on the furnace. Atlanta Gas Light’s investigators and experts conducted a thorough investigation and opined that the HVAC technicians left the furnace gas line uncapped and that uncapped line was the source of the gas that filled the crawl space, causing the home to explode. Attorneys and experts representing the HVAC company’s owners countered that migrating gas leaks from small leaks on service lines at the neighboring residences provided the fuel source.
“Had the investigators and experts had AMI gas data for the specific home, they would have had a timeline of gas flow into the home, and our theory of excessive flow between the time the HVAC technicians left and before the explosion occurred would have been conclusively established early on in the process,” Hodges said.
“As it turned out, nearly five years of litigation turned into a battle of the experts in which our theory ultimately prevailed, but not without a fight. Our experience in that lawsuit is one of the reasons why I was happy to have Itron’s new gas module on the meter in the Calhoun incident. The transparency and accuracy of the hourly data removed any doubt that our hypothesis that the leak was downstream of the meter was absolutely correct,” he said.
Collecting Hourly Meter Data
The AMI gas module reads the gas meter at the top of every hour. It stores the latest 960 synchronized hourly reads, equal to 40 days of data (40 days times 24 hours per day). Each hour, the oldest interval drops off as a new interval is read, ensuring that the most current 960 data points are available. The time-synchronized hourly data can be collected with a mobile collection system, as in the case at Atlanta Gas Light, or with a fixed network system. The hourly interval data is helpful in characterizing a consumer’s natural gas usage with historical profiles. The profiles enable utilities to reconcile bill inquiries in real time and to generate load studies and projections.
Atlanta Gas Light has been able to validate its hypotheses as part of the origin and cause analysis of specific events by analyzing gas flow data from an AMI gas module. The availability of this data source has, in some specific cases, reduced Atlanta Gas Light’s exposure to litigation and liability costs.
Janet Penz is product line manager, gas endpoints, for Itron. She is responsible for the marketing and product development of gas endpoints and has been with Itron for 14 years. She can be reached at firstname.lastname@example.org.