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Tank containment dike

Enter the tanks, pads and available area to see the volume the dike must hold under the chosen rule, how much the other tanks take up, the wall height with rain and freeboard and whether it stays within the limit.

Pre-sizing and estimating tool: results do not replace design, calculations or reports signed by a licensed professional, nor verification against the applicable codes and standards.

Check
Rule
Largest tank
Other tanks in the same dike
Pads and other volumes
Dike

Changing the rule loads its reference maximum height and freeboard; edit them if the local authority requires others.

—Dike wall height
—

Net capacity versus liquid height

Volume the dike holds at each height, after deducting the other tanks and the pads, compared with the volume the rule requires.

Tap the chart to see the values.

Where the dike volume goes

Gross volume up to the top of the wall, split between the liquid to contain, rain, occupied space and freeboard.

Tap the chart to see the values.

The calculation report gathers this page's inputs, results, equations, assumptions and references, with fields for project, engineer and revision. The full report also includes the charts and interpretations, in color. In the print dialog, choose Save as PDF.

Method, assumptions and references

Equations used

Net capacity at height h: V(h) = A · h − Σ A_pads · min(h, h_p) − Σ A_others · max(h − h_p, 0) − V_other; A = length · width
NFPA 30, NBR 17505-2: V(h) ≥ V_largest; SPCC: V(h) ≥ V_largest + rain · A; APQ-1: V(h) ≥ V_largest (+ rain) and A · h − pads ≥ 10% · Σ V
Wall height = h + freeboard ≤ maximum height; minimum area = (V_largest + displaced(h_a) + V_other) ÷ (h_a − rain), with h_a = maximum height − freeboard

Assumptions and limits

  • Vertical cylindrical tanks on circular pads; flat dike floor (the 1% drainage slope changes volume little); vertical walls. Horizontal tanks, sloped earthen walls and inner channels must be worked out separately.
  • Reference values loaded with each rule: NFPA 30 and SPCC (6 ft average height, no fixed freeboard; 18 in intermediate dikes); NBR 17505-2 with Brazilian fire department rules (0.20 m freeboard, 3 m maximum inside height, 1.5 m tank-to-wall clearance); APQ-1 (1.8 m maximum height, 1 m clearance, 0.15 m inner dikes). Confirm with the code and the authority having jurisdiction.
  • Rain falls on the whole dike area, including tank roofs; firewater and foam are not included.

Standards and technical documents

  • NFPA 30: Flammable and Combustible Liquids Code, chapter 22 (impounding around tanks by open diking)
  • API Standard 2610: Design, Construction, Operation, Maintenance and Inspection of Terminal and Tank Facilities
  • U.S. EPA. SPCC Guidance for Regional Inspectors, chapter 4 (secondary containment) and secondary containment calculation examples
  • ABNT NBR 17505-2: Armazenamento de líquidos inflamáveis e combustíveis — Parte 2: Armazenamento em tanques, em vasos e em recipientes portáteis
  • CIRIA C736: Containment systems for the prevention of pollution, 2014

U.S. regulations

  • EPA 40 CFR Part 112 (SPCC rule), 112.7(c) and 112.8(c)(2): secondary containment for bulk storage containers
  • OSHA 29 CFR 1910.106(b)(2)(vii): drainage, dikes and walls for aboveground tanks
  • NFPA 30, section 22.11: control of spills from aboveground storage tanks (as adopted by the state or local fire code)

Frequently asked questions

What is a containment dike and when is it required?

It is a walled area around aboveground tanks of flammable or combustible liquids that holds the product if a tank leaks or fails. NFPA 30, as adopted by the local fire code, requires diking or remote impounding, and the EPA SPCC rule (40 CFR 112) requires secondary containment for oil storage above its thresholds. It keeps product out of storm drains, waterways and the rest of the site.

How much volume must the dike hold?

NFPA 30 requires at least the full contents of the largest tank, after deducting the volume the other tanks occupy below the dike height. The SPCC rule adds sufficient freeboard for precipitation. In the example, the 250,000 gal tank plus 40,395 gal of rain from a 6 in storm requires 290,395 gal of net capacity.

Is the 110% rule enough for rain?

Not always. Industry often uses 110% of the largest tank as a rule of thumb, but EPA notes it may not cover larger storms and its examples use the 25-year, 24-hour storm. In the example, 110% gives 275,000 gal, less than the 290,395 gal needed with 6 in of rain over the 10,800 ft² dike.

How do I read the calculated height?

In the example the liquid rises to 4.11 ft in a 120 × 90 ft dike, under the 6 ft average interior height allowed by NFPA 30. The other tanks and pads take up 41,782 gal and force the wall about 0.3 ft higher. The page also gives the minimum area to stay within 6 ft: 7,429 ft² here.

What other requirements apply?

Besides volume: the dike floor slopes to drainage, the drain valve stays closed and is opened only after checking the water, the outside base is at least 10 ft from property lines that can be built on, and dikes with two or more tanks are subdivided by channels or intermediate dikes at least 18 in high. SPCC also requires inspection and records.

Does this replace the design?

No. It is a pre-sizing and volume check for vertical tanks with vertical walls. The containment design needs a licensed engineer and approval by the authority having jurisdiction; SPCC plans above the qualified facility thresholds must be certified by a PE.

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