Maximum height of dike

[PAN]

In my experience, the maximum height of dike surrounding the crude oil tank could be 1.8 m.

However, there is an assignment to design and construct the dike with 6 m height.
- I understand that the height of 6 m will be confined space. I can install the stairway at the dike. But I'm not sure about other safty precautions especially the ventilation in dike area. Should we construct as above requirement? Anyone who have experience for the case, plese advise me.
- Are there any international standards (API, NPFA or etc.) for the subject? Please comment.

 

[JoeTank]

I do not have a copy of NFPA-30 available to me, but if memory serves me correctly there is a requirement that if the dike exceeds 6 feet in height then a walkway from the top of the dike to the tank shell is required. In addition, I think a remote means of operating the valves is also required. This same requirement shows up in the OSHA regs also. I suggest that you get copies of each in order verify my recollections as correct.

Steve Braune
Tank Industry Consultants

http://www.tankindustry.com

 

[Guidoo]

NFPA 30 section 4.3.2.3.2 states that "the walls of the diked area shall be restricted to an average interior height of 1.8 m (6 ft) above interior grade." but then continues with "dikes shall be permitted to exceed this height where provisions are made for normal access, necessary emergency access to tanks, valves, and other equipment, and safe egress from the diked enclosure" and gives 3 further requirements that need to be met. Please read this section of NFPA 30 yourself for all the details.

 

[Montemayor]

Pan:

You haven't stated or identified the obvious: What kind of dike are you talking about or what is it made up of?

I presume it is a conventional EARTHEN dike - as opposed to concrete dike walls. I've had both built for me, and I don't believe you're going to be allowed to erect a concrete wall that tall. Even a 6 meter-high earthen dike is a formidable construction. Depending on where it is located, I forsee maintenance problems already. I can't rationalize a continuous maintenance program on weed and, eventually trees inside the dike area. You're going to have to coat or top-layer a low-maintenance cover of some sort, I think, because you don't want to send personnel inside such a high confined enclosure for ground maintenance. Keeping it drained in order to protect the ground and its bearing property is going to require a pumping station and all equipment will have to be remote.

I think Guidoo's reference is a positive place to start.

 

[PAN]

Thanks for all comments. I will study NPFA 30 as your suggestion.

The dike will be the combination of earthen dike (lower part) and concrete (upper part).

I believe that the dike height of 6 meteres will not pass the authority approval. There is an idea to connect between adjacent dike areas with underground pipe. The height of dike will be decreased.

 

[quark]

I don't think connecting two dike areas via an underground pipeline is a good idea. What happens if the pipe gets chocked(I didn't mean choked) by debris or something?

Further, the available static head for a leakage from tank(say, from tank discharge nozzle) is higher than that causes flow from one dike area to the other.

Regards,

 

[quark]

On a second thought, you can play with pipe sizes but still I am not comfortable with the idea.

Regards,

 

[PAN]

quark,

Thanks for the comment. You are right. I can play with pipe size...may be 30 inches or more.

In my case, there is road crossing between two dike areas. Therefore, I propose an idea to have underground pipe.

The debris should be prevented. Both ends will be installed in horizontal position with 45 degree inclined cutting. The elevation of both ends will be ~300 mm above grade. They will sit on concrete support.

The insect screen or bird screen will be installed for both ends. That is an idea.

 

[JOM]

PAN,

With the underground connecting pipe, would you need a sump pump to deal with rainwater?

How would you stop the pump from pumping out oil in the case of spillage?

I'm curious about the regulations or guidelines that lead to the specification of a six metre dyke. What is the rule connecting the tank capacity to the dyke height?

John

J.

 

[JoeTank]

JOM,
These tall dikes often occur when steel dikes are installed around steel tanks. Real estate is lacking, so the dike capacity is obtained with a tall dike. In these cases, the dike is at least ten feet largeer in diameter than the tank. Rain water collection is often a problem, so some dikes are cover. This creates a confined space entry problem too.

Steve Braune
Tank Industry Consultants

http://www.tankindustry.com

 

[JStephen]

You have a confined entry space whether the top is covered or not with high dike or steel containment tank.

 

[PAN]

The end of pipe will be as shown belows.

---------
/
/ End of pipe
/
-----/
| Concrete support
---___ (Above Grade)

From NFPA 30 (1996 Edition), elevated walkway to tank roof and remote-operated valves are required.

 

[Hookem]

Be sure that in case the tank is empty and the area around the tank is full of liquid that the tank will not float. One does this by bolting the tank down to a foundation (ring wall, slab, piles, etc.).

 

[hianbotech]

One of the important issues it is the safety. Where will be located the monitors for firefighting, which with a high height of dike can diminish his efficiency and scope. Since they must be installed these out of the area of the dike.

Regards, Angel

 

[athomas236]

Hookem

Under what practical circumstances do you see the tank being empty and the area around the tank full. In the event of a leak surely the level of the liquid will be the same in the tank and the surrounding area.

athomas236

 

[PAN]

athomas236,

Hookem may comment for "group of tanks". The leakage from one tank can affect other tanks in the dike area.

 

[athomas236]

Silly me, never thought of that