Interpretation of OSHA standard about diked area for flammable liquid storage 1

[bottle77]

I have trouble understanding this part of OSHA's code about dikes:

1910.106(b)(2)(vii)(c)(1)
Except as provided in subdivision (2) of this subdivision, the volumetric capacity of the diked area shall not be less than the greatest amount of liquid that can be released from the largest tank within the diked area, assuming a full tank. [highlight #EDD400]The capacity of the diked area enclosing more than one tank shall be calculated by deducting the volume of the tanks other than the largest tank below the height of the dike.[/highlight]

Does this mean that dikes containing more than one tank should be shorter?

 

[BrianPetersen]

It means the volume of the diked area has to account for any volume displaced by the tanks other than the one under consideration (the biggest one).

If a tank other than the one under consideration has its bottom below the top of the dike, the volume of the dike still has to be enough to contain the volume of the biggest tank.

 

[bottle77]

Okay, thanks! that makes a heckuva lot more sense!

 

[IFRs]

NFPA-30 says the same thing, perhaps in a more readable way.
SPCC requires you to account for a rain event in your dike volume.
Accordingly, a "rule of thumb" has been used to have the dike volume 110% of the largest tank volume.
I've seen where local jurisdictions require enough dike volume be available to also contain a 24 hour 100-year rain event, sometimes with an additional cushion.