03.02 When should double wall versus single wall tanks be used?

All fire, building, and environmental codes will require secondary containment of aboveground storage tanks. Double wall tanks are commonly used to provide this containment. Double wall tanks have the benefit of excluding rainwater from the containment when they are installed outside.

Diked tanks are single wall tanks with integral steel containment provided by an open top dike. Most double wall tanks will have a secondary containment volume of 5-20% of the primary tanks. In some places the codes may require a secondary containment of 125% or 150% of the primary tank and diked tanks can fulfill this requirement. Diked tanks should be shielded or covered outside to prevent rainwater accumulation.

Single wall tanks are commonly used, either inside or outside of a building, where concrete structures provide the required secondary containment. Typically the concrete is coated with an epoxy or other material to make it impervious to fuel.