Before you can design a new secondary containment pad that is custom fit to your needs, you’ll need to determine the expected volume for each containment zone. Checking the total volume of each storage container is just the first step in sizing containment pads. You’ll need to take that information, plus measurements of the widest point of the container, and use a calculation method to choose a total volume for the secondary containment system. You can use this volume to determine the appropriate width, length, and height for the containment pad if you’re designing a custom one.
Why Correct Sizing and Volume Calculation Matters
Both undersized and oversized containment systems pose problems for agricultural and oil-related facilities. Pads that are designed too small will overflow and leak hazardous materials to areas where they can enter drains and escape into the local environment. On the opposite end of the spectrum, oversized containment pads are a waste of space and costly materials. They’re also more work to maintain than what’s strictly necessary without providing much extra protection. Proper sizing takes a little calculation, but it’ll create a perfectly sized custom containment pad for any budget and need.
EPA and OSHA Calculations
Standards for containment volume are fairly standard according to the EPA. Every storage container or collection of them requires a secondary containment pad that can hold either 10% of the total volume of all containers sharing the space or 100% of the largest container’s volume. If you have a set of three 60 gallon (0.23 m³) tanks surrounding a 250-gallon tote, you can either create a containment system that holds 43 gallons (0.16 m³) as 10% of the total or one that can handle the full 250 gallons (0.95 m³) of the largest container. OSHA doesn’t have a specific ratio for their hazardous material rules, but they do stipulate the need for secondary containment capable of holding overflow without spilling it.
State Level Requirements
States impose their own regulations for secondary containment system sizing that are often a bit higher than federal levels. These regulations may apply only to certain industries, such as agriculture, or even to specific chemicals. For example, Massachusetts requires that secondary containment pads for fertilizer storage are sized to contain at least 125% of the total volume of the largest container. If you were a farmer in that state and only sized your containment systems according to the federal regulations, you might end up with fines from the state agricultural department.
Rough Rules of Thumb by Gallon
Once you’ve calculated either the total potential storage volume of an entire group of containers or the volume of the largest single tank, you can use a rule of thumb to get a rough estimate of the size of your containment pad. However, you’ll need to do some further calculations for a more accurate estimate.
The rule of thumb is to take the number of gallons of containment needed, including any displacement from the containers or vehicles, and divide it by 7.48. The number you get is the cubic feet of storage necessary. Take the measurement of the widest part of the pad, based on the tanks or vehicle you need to accommodate, and divide that cubic feet rate by that number as well. This gives you the total length of the pad in feet. The formula is:
Length = Gallons ÷ 7.48 ÷ Width
For more accurate estimations that will help you plan how much liner to order, use BTL Liner’s online calculator.
Extra Space for Ramps and Access Gates
For secondary containment pads designed for loading areas and other vehicle accessible zones, you’ll need to add a little extra space to compensate for the addition of tight sealing access gates or ramps. Vehicles should preferably be able to pull through a containment area with a series of aligned ramps or gates rather than having to back up to exit through the entrance. If only a single ramp or gate can fit into the containment area, consider extra mirrors around the pad to help drivers see their surroundings as they back up large trucks and other vehicles.
Berm Height
The ideal height for the berm or edges of the containment pad is one of the hardest parts of the calculations to complete. The EPA regulation formulas will help you find the right height after measuring displacement based on the size and shape of each tank in the containment pad area. Without proper displacement calculations, it’s all too easy to build a short berm that is flooded over after a serious spill.
With these tools and rules of thumb, you should be able to figure out the dimensions of most contained pad designs on your own. If you’re stumped by a particular design or have an unusual situation to deal with, consider hiring a containment consultant or industrial engineer to help you meet all the relevant federal and state regulations.
