Above Ground Oil Storage Tanks (PPG2)

Appendix B Calculation of capacity for tanks in open secondary containment systems

We've included this so you can check your existing secondary containment meets the minimum requirements of the OSR.

Calculate the capacity of a tank located within an existing open containment system by making the measurements shown in the table below. If the tank supports, or the primary tank, take up significant space, take this into account in the calculation.

Where the tank is enclosed within a proprietary system, refer to the manufacturer for this information.

Calculation Result s
Maximum capacity of primary tank(s) s s
s s s
If unknown, use tank length x width x depth in metres and multiply by 1,000 to convert to litres. ………………… litres A
Containment capacity = length x width x depth of secondary container in metres. ………………… m3 s
Then multiply by 1,000 to convert to litres ………………… litres B
Volume lost in secondary containment by tank supports (if significant) in cubic metres. ………………… m3 s
Then multiply by 1,000 to convert to litres ………………… litres C
Actual containment capacity = B – C (C = 0 if tank supports don’t occupy a significant volume). ………………… litres D
Minimum containment capacity (110%) = (110/100) x A ………………… litres E

If D is equal or greater than E, then the containment system volume is adequate and will comply with the OSR. We may require additional containment volume in some environmentally sensitive situations.

If D is less than E, then the containment system capacity is insufficient and will not comply with the OSR.

For installations where the tank takes up a significant part of the bund, the capacity available in the event of overfilling may be inadequate. You’ll need to consider delivery procedures and alarm systems to manage this risk.

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