Storage tanks bunds draining during fire 1

Most bunds are designed to 110 or 125% of the largest tank capacity

I think we should be careful of making general statements as answers to general questions.
We should also make sure we understand the question.

The term "Bund" is used in the question. "Bund" (bnd)
1. An embankment or dike, especially in India.
2. A street running along a harbor or waterway, especially in the Far East.


We can assume that the questioner is referring to deffinition #1 i.e.: Dike, berm, wall or more properly "a product containment barrier around storage tanks." In the U.S. we tend to use the term "Dike"

Product containment does not always mean an earthen dike. Very large (or mega) tanks will normally have an earthen dike. However, small storage tanks may have simple concrete walls.

With the Mega tanks at 200 feet in diameter (223,800 barrels, 9.4 million gallons +/-) it would not be cost effectivs to have 125% or even 110% capacity.

I admit that it has been a few years since I looked at the NFPA Code books but, I remember that we designed storage dikes to contain the contents of the largest tank (+ the displaced volumn of any smaller tank in the same containment ) plus one to one and a half feet of freeboard. The freeboard was to allow for rain co-existing with a fire.
Why did we not allow for firewater? The answer is that oil tank fires are not put put with water. They are put out with FOAM. Foam floats on top of the oil. It does not sink to the bottom and thus does not raise the level of the oil.

As for the drain valves to the containment area.
The containment area for very large tanks should be designed to slope from the center to all four corners. Reason? When there is a fire you do not know which way the wind will be blowing. You will want to get to the up-wind side drain sump outlet valves. These outlet valves should be designed to allow for the draining of pure rain water to the Oily Water Drain System during normal times. There should also be the ability, during a fire, to divert the outlet of the drain sump, to a recovery system and thus pump down the "spilled" oil. By being able to pump out the oil you will reduce the loss of the crude or product and you will also reduce the "burn-off" time of the spilled oil.

Now Carletes:
What size is your tank?
Do you have more than one tank in the same containment area?
What size is the other tank(s)?

Dear Pennpiper,

Thanks a lot for your answer.
Effectively, with bund I wanted to mean the diked area around the tanks used as containment for any spillage.

In my case I have several dikes. For example one of them includes three tanks of 200000 bbl of gasoline (heigth 20 m, diameter 45 m). My concern about fire fighting regards more with the cooling water for exposure protection of the tanks not affected by the fire than the foam used to extinguish the fire itself in the affected tank as it is larger volume.

I see that if the dike valves remain closed during the fire and the affected tank collapses a pool will be created with cooling water at the bottom and oil floating over it which will difficult the extinguishment and will provoke other tanks to be under a higher risk. Moreover the dike capacity could be exceeded as it can only contains the tank volume but not the additional cooling water+foam volume.

Therefore I have proposed to our client to open the drain valves of the dike and divert the effluent (mainly oil+cooling water) towards a retention basin, but it has been considered not necessary.

How are these situations normally managed in other plants?

Best regards and thank you again

"Bunds" are the totally the same as "dikes" pretty much everywhere outside of the US.

All petroleum companies have a specification that clearly states the overage volume that any containment structure must have around their tanks and, as I recall, it has always been at least the largest tank +10%, cost effective or not (after the cost of the tanks, nobody ever concerned themselves with the cost of dirt, but I guess that could all be relative. Usually its just considered very cheap insurance.


BigInch-born in the trenches.

The effective design of the bund(s) is either to contain the 125% volume of the tank or if the tank is too large (1 million bbl per tank in my ex facility) to provide sufficient bund wall height to balance the oil in the tank and bund. The cooling water the application will be low 2lt/m2/s of the exposed surface and should not create a problem of huge water accumulation. As you will be applying foam ,which is already 97% water in most applications, the cooling water application for the other tanks in the same bund area will not create any problem beacuse foam will be flowing into the same bund area.