High Pressure Storage Tanks and Spheres | Safety Considerations for Plant Layout Levels
Site Location and Spacing
Location of spheres shall be downgrade and downwind from ignition sources, with the maximum possible separation from other facilities and neighboring properties.
a. A minimum of 75 m shall be required between spheres and the property line, normally occupied buildings, or any continuous source of ignition such as a process furnace or fired boiler. The distance from the base of a flare shall be at least 90 m.
b. A minimum of 30 m shall be required between pressure storage spheres and atmospheric storage tanks containing flammable products.
c. Spacing between spheres shall be a least one and one-half diameters of the larger sphere.
Spheres and cylindrical pressure storage vessels should be spaced a minimum of 60 m from process unit equipment. Locate these tanks downgrade and downwind from ignition sources. Horizontal cylindrical vessels should not be oriented so that their longitudinal axis is pointed toward offices, shops, or process units that are located closer than 450 m to the vessels. Onsite pressure storage required for processing, such as solvent propane, should have the same spacing as specified for accumulators.
Grading and Drainage
There should be no possibility of flammable liquids from other sources flowing into the area beneath the sphere. The surface beneath the sphere shall be stabilized, raised, and sloped away from the sphere to prevent accumulation of flammable vapors or liquids. It is preferred that a diversion dike system be
provided. It should consist of open channels draining to a retention area in a safe location. The retention area may be of simple earthen construction, with a capacity equal to 50 percent of the volume of the largest sphere draining into it. When climatic conditions result in prolonged periods during which storage
temperatures may be below the boiling point at atmospheric pressure, it is advisable to size the retention area up to 100 percent of the largest vessel capacity.
If the terrain does not permit a diversion dike system, dike enclosures shall be provided. The capacity shall be the same as required for retention areas, as stated above. Sealed and valved drains shall be provided to drain the diked enclosure. Dike walls shall be low and far enough away from the vessel to provide good natural ventilation.