(119b) Hazards of Performing Hot Work in Gasoline Storage Tanks

This paper presents a recent investigation into explosion that occurred in an unleaded gasoline storage tank during hot work operations.  The storage tank had a floating roof design that was covered by a geodesic dome.  The floating roof was subdivided into many isolated pontoons.  Sometime after 12:00 pm, an explosion occurred during hot work operations in the tank that was cleaned and cleared for confined space entry.  The explosion blew the geodesic dome roof off of the tank where it fractured into multiple sections, split the top plate of the floating roof from the bottom and propelled it up and out of the tank, deformed the bottom section of the floating roof towards the floor and northern section of the tank, deformed/collapsed the sidewalls of the tank, and killed three welding employees, who were on the floating roof at the time of the explosion and were blown out of the tank.

GexCon performed an advanced CFD explosion analysis into the cause of the accident, which could reconcile the observed evidence in the case.  The studied concluded that residual gasoline vapors were present within an exterior pontoon in the floating roof, which subsequently ignited when the welders began cutting into the floating roof.  In addition, inspection revealed that this particular pontoon had a small hole on its sidewall near the liquid level of the tank.  This hole allowed gasoline to seep within the pontoon resulting in residual vapors on the day of the incident.  This study will present the lessons learned regarding isolation of the tank, cleaning the tank for hot work operations, confined space entry and continual atmosphere monitoring.