Abstract: The present invention is directed to an above-ground, explosion-retardant containment vessel for the storage of a flammable liquid. The containment vessel preferably comprises a primary storage tank capable of storing the flammable liquid and a containment dike surrounding the primary storage tank. The containment dike contains any leakage from the primary storage tank within the interstitial space existing between the exterior of the primary storage tank and the interior of the containment dike. An inert gas is preferably located within the interstitial space, and the interstitial space is further substantially free of oxygen. The inert environment retards the explosion of any flammable fluids which may leak into or otherwise be contained within the interstitial space. The containment vessel preferably further comprises a system capable of maintaining the pressure of the inert gas within the interstitial space to at least a predetermined pressure despite temperature variations.