Single Wall vs. Double Wall Fuel Tanks

Seat belts and air bags. Your ATM card and the PIN. Wearing a bib and having a napkin at the ready. More often than not, in ways we might not think about, we put ourselves behind two layers of protection. We shouldn’t be surprised, then, that fuel storage works the same way. Whether you opt for a single-wall or double-wall tank, you’ll ultimately have two physical barriers between the fuel and the environment.

what's the difference?

If you have a single-wall tank, it has to be located within an enclosure typically with a volume 110% the capacity of the tank, per NFPA 30 (National Fire Protection Association).  Or you can have a double-wall tank, which does not have the additional requirement but does have the additional wall. Either way, two layers of protection.

Deciding between the two options involves weighing the relative risks of a few different safety and security aspects. Ultimately, the big question is: What do you need to protect your fuel tank from?

where will your fuel tank be located?

First, consider the weather. Double-wall tanks are extremely strong, but if you’re someplace susceptible to high winds and lots of debris flying the air – think tornadoes or hurricanes, or just a Thursday afternoon in a place like Oklahoma – then you may want an enclosure just for the brute physical protection from projectiles. Better, an epoxy-sealed wall absorbs that buffeting better than the outer wall of your tank. 

A related consideration is the proximal environment of your tank. Will it be directly exposed to the wind, or does your property have a lot of wind breaks like buildings, stockade fences or large stacks of inventory? Conversely, do you have a lot of low- to mid-weight items laying out in the open, ready for one angry gust to send them airborne? If your winds tend to come from one direction, can you place your tank on the “lee” side of a building?

One more thought about the weather is precipitation. If your area is prone to hurricanes or torrential downpours, or, heading further north, snowfall, you’ll need to factor those into your decision for what kind of enclosure you would need for a single-wall tank. Especially during blizzards, simply accessing the tank in the enclosure may become as much of a concern as the structural integrity of the tank and enclosure.

security concerns

On the security side, is there anything we should be worried about? <checks price of diesel> Yes, yes there is. 

Theft is always going to be the major concern, and with the price of all forms of fuel not coming down any time soon, the incentives for the bad guys will keep going up, too. An enclosure will give you more security than a double-wall tank, especially if the enclosure can be locked. 

The other security issues are vandalism or sabotage. We don’t want to rely on the bad guys being not-particularly-smart guys, but let’s face it, smart people don’t go around messing with fuel storage tanks. Someone with ill intent may not even recognize a fuel tank enclosure for what it is, so they may be stymied before they can even get started and your tank stays safe by default. Alternatively, someone looking to puncture your tank for (malicious) fun or (ill gotten) profit may not realize that your tank has two walls. If they drill a hole through the outer wall and nothing comes out, they may give up and move on, with your fuel safely behind the inner wall.

how do double wall tanks help detect a leak?

That points to one other feature of double-wall tanks. A vacuum exists between the two walls, and the tanks have a gauge that reports the pressure in the inter-wall space. Anything that’s not 0 psi is a problem. This makes it pretty easy to monitor the integrity of the tank’s walls. Whereas with a single-wall tank the only indication of wall integrity is the level indicator, which will alert you to a problem only after it’s a bit too late.

Either type of tank can work in a variety of contexts. On top of these operational or logistical concerns is the price. Double-wall tanks are more expensive than single-wall tanks for a given capacity. But enclosures don’t build themselves. Adding the price of the right enclosure to the price of a single-wall tank may end up being more than a double-wall tank. Or, as you weigh all the factors that go into the decision, you may need the more expensive option.

Whatever it takes to get the two layers of protection you always want to have.

Whatley Oil can help you work through these decision points, as well as go over the pros and cons of different tanks available for sale. Let us know how we can help you select the right fuel tank and, of course, what we can do to keep it full.