The explosion also caused the deaths of two technicians, two volunteer firefighters and severely injured several others, according to CSB investigators.
Investigators released their preliminary findings on Feb. 15 after completing initial interviews with witnesses who saw the explosion occur at the Little General Store.
Technician Unable to Stop Leak
Jeffrey Wanko, lead investigator for CSB, reported that on the morning of Jan 30, a technician from a contractor working with Thompson Gas was at the Little General Store preparing to switch the station's propane service, when propane started flowing out of one of the tanks. According to Wanko, the technician could not stop the flow.
"It was an uncontrollable release and the technician was unable to stop the flow," Wanko said.
Wanko said that at 10:40 a.m., the technician made the first 911 call. Two EMT responders arrived in an ambulance, joined by two volunteer firefighters who arrived in separate vehicles. About the same time, a second technician also came to the store.
The store was in the process of evacuating employees and shoppers when the explosion occurred, although investigators were told employees had not left the building at that time.
The fire department dispatcher then received a report of a large explosion at 10:53 a.m., 13 minutes after the first 911 call reporting the propane release.
The four victims who were killed - the two technicians and two firefighters - were located in the area near the two tanks next to the building. Of the five victims who suffered serious injuries, four were inside the store and the fifth was in the parking lot.
No Rupture, Cracks in Tanks
CSB reported that after examining the two affected propane tanks, investigators did not find any obvious cracks or ruptures. More tests will be made to confirm this.
CSB will be inspecting and testing the tanks and tank components to determine why there was an uncontrolled release, the agency said.
The agency emphasized that the findings were preliminary and that more interviews will be conducted. Wanko said CSB investigators have not been able to talk to the victims, who still are recovering in the hospital.
"We have more witnesses to interview who may shed more light on events during the morning the propane service turnover was to take place," Wanko said. "Please understand we do not have all the answers at this early date and we are not in a position to speculate on causes or unknown details at this point."