Large Spill Ignites After Unattended Tank Overflows
—photos by Richard A Cowan, Stockton F. D., IFPA
More than 18,000 gallons of gasoline overflowed a storage tank and ignited during a pipeline transfer in Stockton, Calif. Fire fighting operations lasted over 15 hours.
The tank’s capacity had been miscalculated. Rather than an assumed capacity of 10,000 barrels, the tank held only 7600 barrels. Since it already held a measured 2034 barrels, a simple transfer of 6000 barrels was planned to bring the tank to an expected 80 percent full. Instead, 434 barrels were spilled onto the ground.
The incident began just after 5 p.m. last Feb. 12 at the Arco Bulk Oil Terminal. Unleaded regular gasoline was to be transferred from a Southern Pacific pipeline to storage tank 2. The proper valves were opened. Then, contrary to Arco company policy, the responsible employee left the scene to make a delivery far from the terminal.
After two hours of pumping, the tank reached its capacity.
No one noticed
Gasoline began overflowing from around the external floating roof and from vapor vents around the top of the tank. The spilled fuel spread inside the dike for approximately 10 minutes. High-level alarms had been installed on the Arco tanks, but they never worked properly and had been out of service since last fall. Legal action was pending between the alarm installer and Arco prior to the overflow.
The fact remains, however, that there was no one on the Arco premises to hear the signal and secure the valves and pumping operation even if the alarm had been functional.
As a result of the overflow, a rich fuel-air mixture began to engulf the entire facility. The atmosphere on the eve of the incident—threatening rain, high humidity, no wind—helped hold the flammable vapor cloud low to the ground instead of dispersing it.
At 7:42 p.m., a citizen knocked on the door of a fire station about 3/4-mile east of the Arco facility and reported a large fire in the direction of the tank farm. The company officer picked up the fire phone direct line to the communications center to report the incident and his response to the fire.
Upon ignition, the ground shock and explosion was felt by residences more than a mile north and south of the Arco terminal. Consequently, the communications center was soon engulfed with telephone reports. As the first-alarm assignment was being readied for dispatching, the four-man company first notified, Engine 1 responded ahead of the initial broadcast and verified its response via radio.
Others dispatched at 7:44 were Engine 2, Truck 2, Paramedic Unit 2 and Battalion Chief 1. Immediately after the first dispatch, the captain of Engine
1 requested a second alarm.
Upon arrival, Engine 1 backed down Washington St. in front of the main body of fire and prepared to drop two
2 1/2-inch hose lines and AFFF equipment. At this moment, a second explosion occurred, sending a huge fireball toward the Engine 1 crew and apparatus.
A close call
Sections of 8-inch steel fuel lines had ruptured and thrown fuel, fire and steel fragments over the tank farm and engine company. Up to 300-pound pieces landed 250 feet away, almost completely flattened by the explosion. A large section came to rest approximately 10 feet from the Engine 1 crew members. They abandoned their position until the rumbles of the explosion and the volume of fire subsided, then went back to their original attack position.
Battalion Chief 1, arriving at 7:48, witnessed the explosion and fireball and requested a third alarm. This alarm along with the second alarm sent Engine 6, Engine 5, Truck 3, Medic 3, Engine 3, Engine 9 and Battalion Chief 2 to the fire. The volume of fire continued as hoselines, AFFF equipment and heavy stream appliances were placed in operation.
A fourth alarm was requested by the battalion chief at 7:49. This sent Engines 10 and 4, Truck 4, and Medic 4 to the fire. All of the pumpers totalled 13,500 gpm capability on the fire scene. Approximately 80 fire fighters were on the scene wihin 10 minutes of the initial fire reports.
Off-duty shift recalled
The large response required to fight the fire left the outlying fire stations vacated until off-duty response could be achieved. The Stockton Fire Department implemented its mutual aid agreement with the adjacent fire districts. The city stations were manned with pumpers and personnel from both Eastside Rural Fire Protection District and County Club/Tuxedo Fire District, along with Stockton call-back fire fighters.
During the fire at the Arco tank farm, there were seven unrelated fire calls and 14 rescue or ambulance calls. This activity was handled by returning off-duty personnel and mutual aid companies.
Flange gasket failure
As the manpower increased, heavy stream appliances were placed in operation at the terminal. With the application of AFFF, we noticed a definite change in fire intensity; we were gaining control. Fire fighters were sent into the diked area under protective hose lines and AFFF applications to secure intake valves on the unleaded tank. This had to be accomplished due to the failure of flange gaskets on the valves. A flange gasket failure on the unleaded gasoline tank was letting gasoline bypass the flange, where it continued to burn intensely.
Approximately 8000 gallons of water per minute were being applied to the involved area to cool surrounding tanks and the fire area. Due to the volume of water application, the liquid depth within the retaining dike area was filling rapidly, presenting the threat of an overflow.
Portable pumps were placed in operation to transfer water and contaminants to a dry ground area well away from the tank farm. Unnecessary heavy stream operations were reduced to cut down the total flow of water and give the portable pumps a chance to reduce the water level in the retaining wall area. This was feasible because the AFFF had formed a good seal over the entire spill. The only visible flames were coming from the areas of gasket flange failure and inspection plate gasket failure on both the premium and regular fuel tanks located south of the overfilled tank.
Displaced fuel with water
The volume of fire had been reduced substantially. Fire fighters were moving into the main body of the fire with AFFF lines while heavy stream application continued on other leaking gasket failure areas. Chief James T. Clifton, who responded and took charge of fire suppression operations approximately nine minutes after the first alarm, requested information from a representative of the Southern Pacific pipeline pumping station.
According to the engineer, the request by Clifton to reverse the flow of fuel back to Southern Pacific tanks was not possible because of a check valve in the 8-inch fill line to the burning fuel tank. Backflowing the fuel would require bypassing the check valve. This could only be done with a 2-inch bypass line. The decision was made to start the bypass and backflow operations in hopes of reducing the fuel level within the burning tank. If water could then be pumped into the tank, taking advantage of the liquid density differential between water and fuel mixtures, it could settle to the flange failure area at the bottom of the tank. The fire would go out.
After four hours of reverse pumping operations, and with the fires still burning around the failed valves and flanges, personnel were sent to the top of the fuel tank to take a stick measure of fuel depth. The fuel level was determined to be 6 feet below the top of the tank.
At this point Engine 6 was dispatched to the Southern Pacific transfer station on Navy Dr. where the backflow operation was taking place. Engine 6 connected two 2 1/2-inch hose lines 200 feet in length to a hydrant on the Port of Stockton water system. Water was pumped into the same fill line that had been used earlier for the fuel transfer between Southern Pacific pipeline and Arco. At the request of on-site personnel at Arco, Engine 6 pumped at 100 psi back to Arco.
After 30 minutes of pumping, the operation was halted and another stick reading was taken on the tank. The fuel level had risen 3 feet. Engine 6 continued pumping for another 20 minutes and then held for another reading.
The second stick reading showed the tank to be within 6 inches of the top. Within 50 minutes of pumping water into the tank we had raised the liquid level 5 1/2 feet. It took another 30 minutes before the water bottomed out in the fuel tank and began to flow into the broken flange area, extinguishing the fire at the flange.
Protected by the continual application of AFFF, a crew was sent into the area to replace the flange gaskets and place a collar on the flange to stop any additional fuel leakage. Other small fires continued during this operation, but were controlled by AFFF hand lines. This system was employed in all the remaining leaking valves and inspection plates.
The fire was officially out just after 11 o’clock the next morning, although fire personnel remained on the scene in case of a possible reflash for 69 hours after extinguishment. They had used 5315 gallons of AFFF.
Stockton Fire Department arson investigators believe that the ignition source was the telephone bell on the outside wall of the office. There were flash marks on the building near the bell, which was 8 feet above the ground, giving some indication of the vapor cloud depth. The bell has since been removed.