Select tank type → then protection. Live results on the right.
Liquid grouping
Select which NFPA 30 (22.4.1) method applies:
Stable Class I/II/IIIA: FP < 200°F (93°C)
Stable Class IIIB: FP ≥ 200°F (93°C)
Boil-over: ignitible liquids with boil-over behavior
This tool does not classify liquids; use your project’s classification basis.
Liquid class (stable)
Used to enable the optional half-distance permission for certain Class IIIA weak-seam tanks (NFPA 30 22.4.1.2).
Class I/II: FP < 140°F (60°C)
Class IIIA: 140°F ≤ FP < 200°F (93°C)
IIIB dike/drainage condition
For Class IIIB tanks, NFPA 30 uses the Class IIIB table unless the IIIB tank is within the same diked area
or drainage path of a Class I/II tank. In that case, location distances follow the more stringent 22.4.1.1 method.
Tank type
For stable liquids, this list includes 4 options limited to ≤2.5 psig (22.4.1.1) plus
Any type — permitted to exceed 2.5 psig (22.4.1.3). For boil-over, tank type follows the boil-over table.
For Class IIIB (no Class I/II influence), tank type does not change the result (capacity table governs).
Protection / system
Options change based on tank type, matching NFPA 30 rows (e.g., “protection for exposures” or “approved foam/inerting”).
This tool does not verify system qualification — it uses your selection.
Results update instantly. If a required value is missing, the Results panel will show what’s needed.
Tank diameter
Required when the applicable NFPA row is diameter-based (floating roof, weak-seam, boil-over).
Typical range: 5–350 ft (1.5–105 m). Must be > 0.
ft
Tank capacity
Required when the applicable NFPA row is capacity-based (reference distances).
Typical range: 100–5,000,000 gal (0.4–19,000 m³). Must be > 0.
gal
Half-distance allowance (22.4.1.2)
Applies only when ALL are true:
Stable Class IIIA liquid
Vertical tank with weak roof-to-shell seam
Not within the same diked area as, and not in the drainage path of, a Class I/II tank
If selected, this tool applies a 0.5 multiplier and still enforces the 5 ft minimum.
Live: waiting for inputs…
Output includes two minima: (1) to a buildable property line / opposite side of public way, and (2) to a public way edge or important building on the same property. Apply the relevant one for each exposure direction.
Inputs — Tank-to-tank spacing (22.4.2)
Shell-to-shell spacing between adjacent tanks.
Roof/type basis
Select which Table 22.4.2.1 column applies:
Fixed roof or horizontal tanks
Floating roof tanks
This affects the spacing factor for large tanks (>150 ft).
Liquid class for spacing
For fixed roof/horizontal tanks, Table 22.4.2.1 uses different factors for Class I/II vs Class IIIA (large tanks).
For Class IIIB-only tanks, a special rule can cap spacing at 3 ft under certain conditions.
IIIB spacing — dike/drainage
If a IIIB tank is within the same diked area as, or within the drainage path of, a Class I/II tank, spacing follows the Class IIIA requirements.
Otherwise, IIIB-only tanks are not required to be separated by more than 3 ft.
Containment basis for >150 ft tanks
When any adjacent tank exceeds 150 ft diameter, Table 22.4.2.1 uses different factors depending on containment approach
(remote impounding vs open diking). Select the approach used for the tank group.
Tank A diameter
Enter the nominal diameter used for spacing calculations. Must be > 0.
Table 22.4.2.1 uses the sum of adjacent tank diameters.
ft
Tank B diameter
Enter the nominal diameter used for spacing calculations. Must be > 0.
If any tank exceeds 150 ft, the large-tank branch is applied.
ft
Special case (22.4.2.1.1)
If the specific crude-oil production facility conditions are met (including capacity threshold and isolated location),
NFPA 30 allows that tanks are not required to be separated by more than 3 ft.
Live: results update as you type.
Spacing results are minimum code requirements. Engineering evaluation (e.g., thermal radiation escalation) can require larger separations or mitigation.
Assumptions & Applicability
Read before use
This tool implements minimum distance logic for aboveground storage tanks under NFPA 30 Section 22.4 (2024 excerpt provided by the user).
Location distances: outputs two minima (to buildable property line/opposite side of public way, and to public way/important building on the same property). Apply to each exposure direction as applicable.
Tank-to-tank spacing: computes shell-to-shell spacing between adjacent tanks. For compacted three-row/irregular patterns, additional access/spacing can be required by the AHJ.
This calculator does not determine whether a protection system qualifies as “protection for exposures” or an “approved” foam/inerting system — it uses your selection.
Unit conversions use exact factors; printed SI equivalents in standards may be rounded.
