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AST Compliance Glossary

Plain-language definitions for the terms you'll encounter while sourcing a compliant aboveground storage tank.

Tank sourcing conversations move fast between environmental, fire code, and engineering terminology — often within the same sentence. This glossary covers the terms that come up most often across our state guides and product pages, so you can read a spec sheet or permit application without guessing at acronyms.

AHJ (Authority Having Jurisdiction)
The fire marshal, fire district, or local building/fire official with legal authority to approve tank siting, permits, and inspections for a given site.
AST (Aboveground Storage Tank)
A fuel or oil storage tank installed above grade, as opposed to buried underground (UST). ASTs are regulated primarily under SPCC and NFPA 30/30A rather than UST-specific rules. See our AST vs. UST guide for the full comparison.
SPCC (Spill Prevention, Control, and Countermeasure)
A federal rule (40 CFR Part 112) requiring facilities that store oil aboveground above certain thresholds to prepare a written spill prevention plan and meet secondary containment standards. Generally triggered above 1,320 gallons aggregate aboveground capacity.
NFPA 30
The Flammable and Combustible Liquids Code, published by the National Fire Protection Association. Governs tank construction, siting, spacing, and containment for most AST installations, typically adopted through state or local fire codes. See our SPCC vs. NFPA 30 guide for how it differs from SPCC.
NFPA 30A
A companion standard to NFPA 30 specific to motor fuel dispensing facilities and repair garages — relevant when a tank supplies a fueling operation rather than only backup power or process fuel.
IFC (International Fire Code)
A model fire code published by the International Code Council and adopted (often with local amendments) by most states and municipalities across our territory. The IFC typically references NFPA 30/30A directly for flammable and combustible liquid storage requirements.
UL 142
The Underwriters Laboratories standard for steel aboveground tanks for flammable and combustible liquids. A "UL 142 double-wall" tank has an inner tank and an outer containment shell, both built to this listing. See our UL 142 guide for a full explanation.
Listed / Listing
A tank that has been tested and certified by a recognized testing laboratory (like UL) to meet a specific construction standard. Most AHJs require listed tank construction before evaluating siting and permitting.
Secondary Containment
A barrier — a double-wall tank shell, a berm, or a containment dike — designed to hold the full volume of a tank's contents in the event of a leak or rupture, preventing release to the environment. See our secondary containment guide for sizing details.
Berm / Dike
A site-built earthen or concrete containment structure surrounding a single-wall tank, sized to hold the tank's full capacity plus precipitation freeboard. An alternative to built-in double-wall containment.
Interstitial Monitoring
Detection of a primary tank shell failure via the space between a double-wall tank's inner and outer shells — done visually through a sight gauge, electronically via a leak sensor, or both.
Freeboard
Extra containment volume built into a berm, dike, or containment system above the tank's rated capacity, to account for precipitation accumulation in outdoor, uncovered installations.
Overfill Protection
Equipment or procedures (such as automatic shutoff valves or high-level alarms) designed to prevent a tank from being filled beyond its safe capacity during a fuel delivery.
PE Certification
Review and stamped approval of an SPCC plan or tank installation design by a licensed Professional Engineer, required for many facilities that trigger SPCC.
Tier I / Tier II SPCC Plan
A self-certified SPCC plan template (rather than a full PE-certified plan) available to smaller, lower-risk facilities that meet specific capacity and spill-history criteria under 40 CFR 112.
Setback / Separation Distance
The minimum required distance between a tank and property lines, buildings, or ignition sources, set by NFPA 30/30A and the adopting fire code based on tank capacity and type.
Aggregate Capacity
The combined storage capacity of every regulated container at a facility — not just one tank — used to determine whether SPCC and many state/local thresholds apply. Containers under 55 gallons generally don't count toward this total.
Manifolded (Multi-Tank) System
Two or more tanks connected by piping to function as a single larger storage system — common for large-capacity or high-demand sites rather than a single oversized tank.
SPCC terminology distinguishing a fixed storage facility (like a tank at an industrial site) from tank trucks, rail cars, or other transportation equipment, which fall under separate federal rules.
Fire Code Adoption
The process by which a state or local jurisdiction incorporates a model fire code (often referencing NFPA 30/30A) into its own enforceable regulations, sometimes with local amendments.
Tank Commissioning
The final inspection, testing, and sign-off process confirming a newly installed tank meets its approved design and is ready for service.

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