Storage tanks in the chemical process industries (CPI) can be most broadly divided into those buried underground, and those constructed aboveground. The following is an outline of considerations associated with each category and positive and negative aspects of each....
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There is a third option, overlooked by most and that is to place the tank in a vault. The result is that the tank is regulated as an above ground tank, with all of the advantages of an underground tank. Their next comment is, but no one told me.
Yes, the initial cost is a little more, but the savings over the long run are considerable.
For installations that store flammable or combustible liquids, the vault is governed by Chapter 25 of the 2008 edition of NFPA 30, Flammable and Combustible Liquids Code. (Chapters 21 and 22 of this code apply to the tank itself.)
Chapter 25 establishes construction requirements for the vault, including a requirement for anchoring the vault, so that it cannot “float” due to high ground water levels. The chapter also includes requirements for the following: means to admit a fire suppressing agent; possible need for hazardous (classified) electrical utilization equipment and wiring; containment and drainage of spills; ventilation systems; vapor and liquid detection and alarm systems; etc.
While NFPA 30 applies only to flammable and combustible liquids, some of the provisions of Chapter 25 would likely be considered appropriate for storage of liquids with other hazards. Of course, the designer must factor in the cost of all these features, as well as the cost of proper inspection and maintenance.
NFPA 30 is adopted in the laws of 30-plus states.
Robert P. Benedetti, CSP, PE
Principal Flammable Liquids Engineer
National Fire Protection Association