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Petroleum Tank Concrete Enclosure

Petroleum Tank Concrete Enclosure

Petroleum Tank Concrete Enclosure

(OP)
I have another unique question that came up last week and I have been noodling on ways to resolve the issue.

A local company has (2) large petroleum tanks above ground. The tanks were put in approximately 20 years ago, but the tanks were designed to be "in-ground" tanks. The fire marshal is just now bringing this up as an issue. There is about a 2ft tall concrete wall around the tanks to contain spills.

Question: The only way I see possibly to make these tanks be "under-ground" is to build tall concrete walls around them and fill it with sand so that the tanks have "positive" pressure to push against, like they would if they were actually buried.

I'm not even sure if I will attempt this project because of liability reasons, but was curious what your thoughts are!

RE: Petroleum Tank Concrete Enclosure

CBSE:
Why not do it? You need containment, in terms of volume, but otherwise the tank has been there for 20 years without being confined in sand, so why now? In many cases, the bigger problem is the empty tank compressed by the external fill, so is that really needed? If you fill it completely with sand you need an even larger containment depth/width for the lack of void volume. Is the liability really significantly greater here than on a building which could fall on people and hurt them? They need your help, and they may be thinking the wrong way, and so may I.

RE: Petroleum Tank Concrete Enclosure

Is there a tag or nameplate or anything else on it that will tell you what standard it was built to?

You might be fine from a tank standpoint. Then it's a question of ensuring the support is adequate and making sure you're up to local above ground tank standards for containment and fire code issues (refer to local codes, EPA and probably NFPA 30)

RE: Petroleum Tank Concrete Enclosure

If the Fire Marshall is involved the issue is fire safety. Storing flammable liquids underground is much safer than above ground. Fire Marshall's prefer underground storage of flammable liquids. In California, many underground tanks have had to be dug-up because of leakage and ground water contamination. Pretty much all underground tanks now have to be double walled with leak detection systems.

RE: Petroleum Tank Concrete Enclosure

One problem is that the codes involved don't always tell you WHY they require what they require.

For example, one advantage of the tank being underground is that that it will absorb less heat if it's surrounded by a fire. And if it explodes, it'd be more contained. It's not entirely clear to what extent a proposed burying scheme per your sketch would fix that, and would be more than just a structural issue. Maybe they don't have proper saddles and support, in which case, adding fill may make the problem worse rather than better.

One solution would be to go ahead and bury the tanks in the ground like they were intended. Before doing so, make sure they are in good shape, make sure the codes and laws relating to them haven't changed in the meantime. There have been a awful lot of tanks dug up through the years, and you don't want to be burying them one year and digging them up the next.

Don't be too surprised if it's cheaper to install new tanks than to bury the old, especially if the tanks aren't double-walled but need to be.
There are more crash-resistant tanks available for above-ground use that might also be alternates if that would work.

It'd be worthwhile to find out exactly what the issue is with them being above ground as well. Maybe it's just a paper shuffle, the drawings show them buried so they ought to be buried. Maybe it's property set-back issues, but if they're not near a building or property lines, that may not matter. Anyway, if the reason is something pretty minor, see if they can get a variance for the installation.

RE: Petroleum Tank Concrete Enclosure

Not necessarily. The fire authorities get involved with lots of tank related things depending on the jurisdiction because they're the the most applicable enforcement group, even if it's not perfect.

Either way, unless there are additional issues, or things like zoning or land use concerns, above ground tanks can be dealt with from a fire perspective.

I'd suggest reviewing at least chapters 21 through 23 of NFPA 30, and any local fire code you have.

RE: Petroleum Tank Concrete Enclosure

Sorry, the 'not necessarily' was directed at Compositepro's message about the fire authorities. I left my reply window open too long!

RE: Petroleum Tank Concrete Enclosure

(OP)
In speaking with the fire marshal, his major concern is the tank rupturing...not fire. I need to dig further with him because if he is only concerned about the tank rupturing and fuel spraying outside the spill containment area, then a quick fix would be to just build taller concrete walls around the tanks.

Thanks for all of the input!!!

RE: Petroleum Tank Concrete Enclosure

If it's tank rupture, then it's just ensuring that:

(a) the tank is appropriately rated from the pressure/service and can do that when unburied
(b) ensuring you've provided the secondary containment required by the governing fire and environmental codes (this generally includes a setback requirement between the containment structure and the tank itself so that things like spray are okay.

RE: Petroleum Tank Concrete Enclosure

Larger above-ground tanks normally require either emergency venting or a frangible roof so they don't overpressure in fire exposure situations. I'm not sure what the rules are on underground tanks or small above-ground tanks- but that could be what they are concerned with. Effects of fire exposure on a vertical tank are seen here: https://www.youtube.com/watch?v=6qcrwNM74sg

Vehicle impact may be another concern.

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