Regulators in Missouri are cautioning aboveground storage tank (AST) owners and managers everywhere to beware of icy weather conditions that could affect the safe operation of vents. Investigators are examining whether two frozen vents could have led to a bulk-plant fire in Marshall, Mo. about 80 miles (129 kilometers) east of Kansas City as a driver was unloading fuel from his truck into a standing 12,000-gallon (45,425-liter) AST.
The source of ignition may have been the idling tank truck, but that question is still under investigation. The Jan. 7 incident, which led to the death of the truck driver, occurred during a period in which rain, mist and freezing temperatures could have caused the lockup of both the emergency vent and the primary
pressure-vacuum vent of the AST.
Investigators believe the frozen vents led to over-pressurization. Without adequate venting, stored hydrocarbons will vaporize during a fire and strain the limits of an atmospheric-rated tank. After the initial explosion, firefighters spent more than a day extinguishing a pool fire, which at times featured non-insulated tanks with burning product and vent-flame surges of 60 to 100 feet (18.3 to 30.5 meters) in the air, said John Albert, an investigator and trainer with the Missouri Department of Agriculture’s Division of Weights and Measures. An elevated water cannon was used to extinguish the flames inside any tank containing ignited fuel.
In the bulk plant’s yard, firefighters sprayed tanks with water and foam on the trucks to prevent additional explosions. The tower truck and three other unstaffed devices were used to spray water on tanks to keep vapor spaces cool. Investigators discovered a nine-inch split in the bottom of an AST that exploded initially, then again about 18 hours after the start of the blaze.
They are trying to determine the impact of the split on the overall blaze, which ultimately affected seven other nearby tanks – some storing various grades of gasoline and others diesel fuel. Of the eight non-insulated atmospheric tanks exposed to a pool fire for about 32 hours, only one showed distortion.
Fortunately for all involved, two 30,000-gallon (113,562-liter) propane tanks at the bulk-fuel facility were located far enough from the fire to remain unaffected.
About 50,000 gallons (189,271 liters) of gasoline and diesel – including about 8,000 gallons (30,283 liters) in the truck and the rest in the eight standing tanks – caught fire. As vent fires eventually developed, emergency vents on all of the other nearby ASTs operated as designed. Witnesses said the explosions could be heard several miles away. During January, the Division of Weights and Measures received reports of several other tanks in Missouri
that experienced frozen vents. However, the Marshall incident was the most dramatic.
Source: Steel Tank Institute-Steel Plate Fabricators Association