F921® aboveground storage tanks are manufactured with a double‐wall steel design. Standard features include built‐in, testable, interstitial monitoring capability and impermeable secondary containment. The F921® delivers uncompromising performance, reliability, service and economy.

F921 ® features:

Compatible With a Wide Range of Fuels and Chemicals, Including Biodiesel and Ethanol

  • Meets UL 142, Standard for Steel Aboveground Tanks for
    Flammable and Combustible Liquids
  • Double‐wall design offers integral, impermeable secondary
    containment to meet EPA SPCC requirements
  • Primary and secondary tank can be tightness tested on site
    with standard testing procedures, or manufacturer may
    ship with vacuum in the interstice to prove integrity of
    both walls during installation
  • Interstitial space can be monitored for leak detection
  • Primary storage tank and secondary containment
    compatible with a wide range of fuels and chemicals

Additional features:

  • Support designs available for all seismic requirements
  • Choose from many integral support types, including
    saddles and skids
  • Vertical tanks supported on legs, and skirted
    available, with Listing label
  • Capacities range up to 75,000 gallons

F921 ® Benefits:

  • Steel construction allows for recycling
  • Low cost compartments and customization
  • Built to nationally‐recognized STI standards with
    strict third‐party quality control inspection program

Economical Double-Wall Design

Available Designs:

  • Horizontal
  • Vertical
  • Rectangular

F921® is available from a large network of STI Licensed Manufacturers • www.steeltank.com

F921® Double-Wall Aboveground Steel Storage Tanks

  • Steel Tank Institute F921® and Listing Labeled
  • 300o or 360o outer wall for secondary containment
  • Variety of Listed supports available
  • Compatible with a wide range of fuels and chemicals
  • Capacities range up to 75,000 gallons
  • Easily relocated

F921® Guideline Specification

A) General

1. Provide F921® double‐wall steel aboveground storage tanks.


B) Labeling

1. Tanks shall bear the Steel Tank Institute F921® Double‐Wall Aboveground Storage Tank identification label.


C) Product Description

1. Tanks shall be manufactured in accordance with Steel Tank Institute F921®
, Standard for Double‐Wall Aboveground
Storage Tanks.

2. Aboveground tank primary and secondary containment (inner and outer walls) shall be manufactured in accor‐
dance and listed with Underwriters Laboratories UL 142, Standard for Steel Aboveground Tanks for Flammable and
Combustible Liquids.

3. Tanks shall be double‐wall with a steel inner wall for primary containment and provide integral secondary
containment by an impervious steel outer wall.

4. Integral secondary containment shall be testable and provide access for interstitial leak detection monitoring.

5. Listed supports shall be used for all horizontal, rectangular and vertical double‐wall tanks. Supports are designed
for seismic loading, if necessary.


D) Manufacturer

1. Manufacturer shall be a licensed member company of the Steel Tank Institute and subject to Steel Tank Institute’s
Quality Assurance program.

F921® is available from an extensive group of Steel Tank Institute fabricators who participate in the STI Quality Assurance Program.
Under the program, independent quality control inspectors make unannounced visits to STI members, ensuring fabrication to the highest possible standards.