The LP-Gas Code is clear about anchoring requirements.

“Where necessary to prevent flotation due to possible high flood waters around aboveground or mounded containers, or high water table for those underground and partially underground, containers shall be securely anchored.”  (NFPA 58, section 6.8.1.6)

The code is less clear about how to meet those requirements. We have seen a variety of methods employed. A few types seem to be the most effective. Others are questionable. The bottom line is any low-level sites with propane tanks or sites where tanks are located in a flood plain run the risk of flooding.

The most popular anchors for propane containers are helix anchors, also known as mobile home anchors. These are rods with helical discs attached that you literally screw into the ground.  They vary in length, disc diameter and number of discs. They should be used with soil charts or test probe charts, which will show which size anchors can be expected to hold in the soil at the tank site. The cable or straps that connect the anchors to the tank are a key part of the anchoring system. These, too, must be properly sized to ensure they do not fail.

The best anchors are those with some engineering behind them. There are a number of resources online, such as Minute Man Anchors in East Flat Rock, N.C. They have drawings, load tables, soil charts and other good information. Tie Down Engineering also has information online including a worksheet for propane tank anchorage. 

In North Carolina, anything below the 100-year flood level must be anchored; this is also a FEMA requirement. For many of the barrier islands, that includes the whole island.  Most counties have flood maps showing the 100-year flood level. If you place tanks, it is your responsibility to know where this level is and to anchor where appropriate. That said, in the last couple of years FEMA, through the National Flood Insurance Program (NFIP) has taken the position that elevation of tanks, rather than anchoring is required, for new installations. This is up to each county to adopt this guidance, in return for better flood insurance rates for their citizens, so we would encourage you to contact your county manager of commissioner. Remember, this applies to all areas of the state, as all counties are subject to occasional flooding.

Anchoring also means that the tank will not turn bottom side up. If it does so, the propane line will most assuredly break, causing a potentially hazardous gas leak. Be sure to run a cable through the legs or foot ring instead of the lifting lugs. Or, you can run a strap or two over the tank and snug it down on the anchors. Another choice is to weigh the tank down by fastening it to a concrete slab heavy enough to hold it. Keep in mind the likely action of wind, waves and current when you do this. Also, consider adding an insulator between the strap and tank, as these are usually dissimilar metals and you can set up galvanic action, which will corrode the tank and/or the strap.

In summary:
• Tanks in flood-prone areas or in high-water-table areas must be securely anchored.
• We recognize that even well-secured tanks can be dislodged by strong storms.
• Owners of tanks must secure tanks in threatened areas using anchors or anchoring systems that have some engineered basis for being able to resist the forces of wind, wave, and current in the type of soil present at the tank location.
• The tanks must be secured against being dislodged and against turning bottom up.
• Tanks located in the 100-year flood zone must be secured.

You should be aware that three municipalities have adopted at least enough of NFPA 58 so they can enforce the anchoring requirements. The municipalities are New Hanover County, Wrightsville Beach and Leland.  Other coastal municipalities are considering it.