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LP Gas Concerns > Anchoring Tanks For Flood Areas

In response to some requests for information about anchoring LP-Gas containers to resist the effects of flooding, the following articles that appeared in the North Carolina Propane Gas Association magazine are posted here. Some of the information is old and you can see the progression of information and requirements with time. If you have questions, please contact Richard Fredenburg.

Article 1, September 1996 - ANCHORING OF PROPANE TANKS IN AREAS SUBJECT TO FLOODING

As Hurricane Bertha was heading north after making landfall in North Carolina, it became evident that many propane tanks near the coast were no longer where they were supposed to be. We received many calls about how to properly anchor propane tanks when there is reason to believe they may float away.

National Fire Protection Association Standard 58 (NFPA 58) makes the following statement concerning flooding and propane tanks. "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 under-ground, containers shall be securely anchored." [NFPA 58 Section 3-2.2.7(h)] Admittedly, this is a statement that leaves a lot of room for interpretation.

In an effort to resolve questions relating to the problem of propane tanks floating away or causing damage due to floods, the following guidelines were worked out in a meeting in 1994 with several propane companies and Dare County emergency personnel for tanks subject to high flood waters:

  1. For tanks installed adjacent to a structure (upright DOT or ASME tanks), the tanks would be secured to that structure by means of cable, chain, or heavy rope.
  2. Horizontal containers would be secured by using two mobile home type anchors and 1/4 inch stainless steel cable. The anchors are to be located at each end of the tank. The cable must be run through the tank legs and not over the tank or through the tank lifting lugs. (If a cable is looped over the tank, where the tank and cable come in contact there is great potential for corrosion. Running the cable through lifting lugs or over the tank does not prevent the tank from rolling and breaking fittings and/or tubing.)
  3. New installations in areas subject to high flood waters will incorporate the anchoring requirement.
  4. Existing installations will be brought into compliance at a rate of around 25% per year.
Even with these guidelines, there is little that can be done to prevent tanks from breaking loose in a severe storm. However, this anchoring should keep tanks in place during most storms.

Keep in mind that the coast is not the only place to be concerned about flooding. Many rivers and streams flow out of their banks during sudden storms or after sustained rains. Consider the entire flood plain of a river or stream. One inspector found tanks floating in a residential area in Fayetteville. Tanks have also been found floating in mountain lakes.

The typical mobile home anchors are not sufficient in some areas. They are not large enough for some soils or strong enough for some storm conditions. We have received some recommendations for sizes of helical anchors to secure propane tanks of various sizes. The calculations accompanying the presentation have not been verified, but the numbers seem appropriate. The following chart is a summary of their presentation. The values given are for clay or sandy soils. Other soils may require an anchor with more or less holding strength. You are encouraged to work with this company or another anchoring supplier to determine how to best keep your tanks in place.

Tank Size Recommended Anchor Diameter at Each End
120 gal. 8 inch
250 gal. 8 inch
330 gal. 8 inch
500 gal. 10 inch
1000 gal. 14 inch

The company providing the above information is Brent & Associates, represented by Randy Brent. You may contact him at 919-498-7405 or P. O. Box 221, Harbinger, NC 27941. This is not an endorsement of the company or their product, only a summary of their findings. This contact information is provided here in fairness to this company for their efforts at developing appropriate tank anchors. Please note that we are not requiring use of these or similar anchors and this table is not part of any state law or regulation. This is not to be interpreted as anything except a presentation of information made available to this office.

Where do you need to be concerned about providing anchors? There is no clear, statewide answer to this question. A guideline is to provide anchors anywhere the tank is below the ten-year flood level. What is the ten-year flood level? Another good question difficult to answer. We have been working with state officials to determine this level. So far all we have is the 100-year level for some counties. (Recent conversations with FEMA personnel may force us to rethink the ten-year flood level idea.) Until we get good information, work with the county emergency management people. Some counties have a level, such as, nine feet above mean sea level (coast) or five feet above flood stage of a river (inland), below which they consider a tank to be at risk. Tanks in these areas are to be anchored.

Obviously, a loose tank in a flooded neighborhood can be about as dangerous as a loose cannon on a ship in stormy seas. Please use care in securing tanks in areas subject to flooding.

Article 2, November 1996 - CONTAINER ANCHORING - REVISITED

This subject was covered in the September [1996] issue of the North Carolina Propane Gas Association News. That article created some enforcement ideas that were not intended and a lot of interest. (I appreciate the interest!)

The table showing the size of anchors suggested for various size tanks was based on information supplied by a company selling anchoring systems. The information looks reasonable and calculations were provided to support the information. Those calculations have not been verified. Please note, we are not requiring use of those or similar anchors and the table is not part of any state law or regulation. The table is not to be interpreted as anything except a presentation of information made available to this office.

However, the requirement to anchor tanks in flood-prone areas remains. Anchors you want to use should be evaluated to determine if they will do the job you intend them to do. If you cannot find information about the strain an anchor can resist, you should reconsider using that anchor. The definition of flood-prone areas is also being reconsidered, based on some FEMA information recently made known to us. Obviously, there is no system that will protect under all conditions. If you anchor a tank with a seven-foot anchor on a ten-foot dune that disappears during a hurricane, the tank will disappear, too. Similarly, a river bank supporting a tank with mobile home tie-downs that normally hold in that soil can be undercut by a flooding river, causing the tank and attached anchors to float downstream.

NFPA 58 is vague on providing information for flood-prone areas. That vagueness is intentional. The authors realize they cannot predict all problems or foresee all conditions for the entire country. By being vague, they allow creative problem solving. Be creative, using sound reasoning and available technical information, when you decide how to anchor a tank.

There is another action you can promote to improve safety when a flood is expected. Insist that your customers close the service valve(s) on their tank(s) when they are evacuating because of a flood or storm. Encourage them to close the valve(s) when they will not be using a vacation house for a long time. Many of the tanks found after the Hurricane Fran had an open service valve and were empty of propane. It must have been a combination of wind, rain, and luck that kept us from having fires and/or explosions when these tanks came loose. Let's not press luck any more than we have to.

Article 3, January 1997 - CONTAINER ANCHORING - RE-REVISITED

Hardware and methods for anchoring tanks continue to be of major interest. Some county inspection departments are actively encouraging or demanding a plan be developed by the propane companies in their area before they begin replacement of tanks removed or lost during hurricane Fran. As this article goes to the printers, I will be meeting with county officials at the coast in an attempt to clearly define some anchoring requirements.

The information presented here is an attempt to get information to the gas companies looking for information on anchoring tanks. It is not an endorsement of or recommendation for this company or their products. If you know of other companies providing these products or services, please share them with us.

The company is Minute Man Anchors, 305 W. King Street, East Flat Rock, North Carolina, 28726. Their telephone is (704) 692-0256 or 800-438-7277. The contact people are Boyce Cockman, Frank Cockman, and Albert Moreno. [These people are no longer with Minute Man Anchors. The new contact is George Wachter.]

Minute Man claims their systems to keep tanks in place using four mobile-home-type anchors and some strapping designed for propane tanks will cost under $50 for materials. They have installation crews around the state or might be able to train your employees to do the anchor installation. Minute Man has been building tie-down systems for mobile homes for years and has recently been working with California to secure tanks in earthquake and mud slide areas, so they have experience in many aspects of securing things people don't want to move. I saw them install one anchoring system. With what we know now, we would not reject a tank being held by this system.

Article 4, October 1998 - Container Anchoring - Again

Another hurricane season is winding down, we hope, and container anchoring is back in the news. Literally. We have a copy of an article that appeared in a newspaper from Nags Head concerning propane containers that came loose during Hurricane Bonnie's trip up the coast. We also received calls from Belhaven and some other low-lying towns that had problems with floating tanks.

This is not an everything-is-bad report. We can report significant success in anchoring tanks in the Wrightsville Beach area. I had previously visited the area and found all tanks I viewed to be well anchored. After Hurricane Bonnie, we checked with the fire department in Wrightsville Beach and they reported that, as far as they knew, no tanks floated or came loose. This success is the result of inspections by state, county, and town officials and because of an ordinance the town enacted requiring securing of containers.

However, more must be done in other places. As previously mentioned, Nags Head, Belhaven, and some other places still have problems with containers during high water. Some of this problem is because the gas companies have not secured tanks, even after an inspector informs them of potential problem installations. Some of the problems come from the type of soil at the locations. Other problems result from demands of customers.

There is no excuse for a tank to float away because the gas company failed to attempt to secure it. The requirement is clear in NFPA 58, the Liquefied Petroleum Gas Code. "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." Our talks with FEMA and state emergency management officials make it clear we are concerned with 100-year flood levels. LP-Gas inspectors will continue to write up containers in flood-prone areas, instructing the gas companies to secure these tanks. Failure to properly secure tanks after a violation is written could subject the gas company to more liability if injury or property damage results, could result in civil penalties, and could ultimately affect the status of their LP-Gas Dealer license.

Soil type continues to hamper efforts to properly secure containers. We have reports and photographs of anchored containers that did not stay anchored. In some cases the containers were not properly anchored. Maybe they were anchored only by the lifting rings and turned bottom up because the footring or legs were not secured. Once a tank turns bottom up, wind and wave action will almost certainly pull the anchors out of the soil. However, sometimes the soil cannot withstand the pull of an otherwise properly secured container. In these cases, larger anchors or alternate methods will have to be used. There are tests that can be performed on the soil to determine what type and size anchors will resist what forces. If a large enough auger-type anchor is not available, attachment to concrete slabs or weights may be required.

Sometimes the homeowner does not want their siding messed up by attaching a container to the wall. This usually happens with 100-pound cylinders. The geometry of these cylinders presents special challenges to designing effective securing methods. Straps around the collar going to anchors in the ground will usually not properly restrain these cylinders. A method to restrain the foot of the tank is required, but often there are no slots in the footrings. If you have a method for securing 100-pound cylinders when no posts or walls are available, please share it with us.

As a starting point to design a way to secure 100-pound cylinders, allow me to describe a possibility. The flotation force on an empty 100-pound cylinder is approximately 165 pounds (239 pounds water capacity minus about 74 pounds tare weight). If a concrete slab of about 200 pounds was built with pegs to keep the foot of the cylinder from moving and rings or loops for attaching a cable to keep the cylinder snug on the slab, this could be a free-standing 100-pound cylinder installation. Even if the cylinder is broken loose from the piping because of exceptionally strong wind and waves, it shouldn't go far since it would be attached to a substantial weight. The slab would meet the requirement to place the cylinder off the ground and could be built with convex top to promote drainage from around the footring. Some drawbacks to this idea would be the need to use a hoist to place the slab and the extra effort required if this cylinder is exchanged rather than filled on site. As I said, this idea will hopefully generate other ideas that may be more practical. Also, please bear in mind that fire departments prefer cables instead of thin straps in case they need to remove a container from beside a burning structure. Their bolt cutters often won't cut straps.

As you can see, securing containers in flood-prone areas is still a problem. Some of the problem is inaction from the gas company. Sometimes there are technological challenges to meet. And sometimes there are aesthetic concerns. These challenges can be met. Inspectors will continue to demand anchoring in problem areas. Proven existing methods and innovative new methods will help meet the challenge. For safety's sake, we must meet the challenge.

Article 5, October 2004 - Hit By Floods Again

August and September have not been nice to North Carolina and the Southeast this year. Hurricanes Bonnie, Charley, Frances, and Ivan have drenched various parts of the state and some serious flooding happened in the western part of the state. That is somewhat of a switch for what usually happens to us when tropical storms hit the state. As I write this, other storms in the Atlantic are threatening, with the real possibility that we can get a lot more rain while the soil is saturated.

So far, we have not had many reports of propane tanks relocated by flooding. Some other tanks have been moved, though. It's a real problem when a large fuel oil tank gets moved and breaks apart.

Some areas that are not traditional flood-prone areas have had flooding this year. And some propane tanks have floated away. Granted, it looks like the flooding may have been more like a 500-year flood after Frances. You cannot protect against all floods. But, we expect tanks in areas affected by 100-year flood levels to be secured.

Nearly all of the counties in North Carolina have maps showing flood-prone areas and the level of the 100-year flood. You can view and, possibly, purchase these maps at each county's map repository office. Call your county government office to locate the repository. If you are unsuccessful, call 877-FEMA-MAP (toll free) to get details on the location of your county repository. Or you can purchase maps online at www.fema.gov/maps.shtm and click on the FEMA Flood Map Store symbol.

Maybe it is time for you to review your tank locations to see if they are in the 100-year flood zone. These tanks must be secured to prevent them from floating away and causing more problems during the recovery period after a storm.

Article 6, November 2011 - Anchoring Tanks – More to Learn

The 2011 Atlantic hurricane season comes to an end Nov. 30, but that does not prevent hurricane-like storms outside of the season. We have seen some nasty storms pop up in the spring, too.  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.

Although we don’t know the true extent of the losses yet, Hurricane Irene caused hundreds of tanks to float away or turn bottom up.  We do realize that not all tanks can be secured against the forces of hurricanes or other acts of nature, but judging from preliminary reports, it is fair to say that anchoring requirements of the LP-Gas Code were not followed at several locations.

Hurricanes can cause sand and soil to wash away, sometimes resulting in breaches where land disappears. If a dune disappears, a tank on top of it is gone, too. No reasonable amount of anchoring in that situation will keep the tank there.

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 6.6.1.6)

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 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.

I found some information on earth anchors, another effective anchor, which uses triangular wedges with an attached cable that you drive into the ground with a hammer. Once the wedge reaches the desired depth, you pull on the cable and the anchor pivots to the most pull-resistive configuration. Again, proper sizing and depth are dictated by use of appropriate charts.

We have seen and heard stories of imaginative uses of various devices to anchor tanks.  I must warn you against most of these, as they have no engineering basis to determine if they will do as expected.  One person told me he digs a hole, runs a cable through the hole of an old harrow disc, buries the disc, and attaches the cable to the tank.  There are a couple of problems with this.  Since the soil is disturbed by digging, he does not know what its strength is unless he follows some specific soil compaction steps as he puts the soil back.  Also, what is the appropriate depth for the disc?  That will depend on the soil characteristics and disk diameter.  If the conclusion when you finish installing the anchor is, “Well, that oughta hold,” then you probably did not use the right type of anchor.  You should think, “That’s gonna keep it there, and I’ve got documentation to support it.”

The best anchors are those with some engineering behind them. There are a number of resources online. The manufacturer I am most familiar with is Minute Man Anchors in East Flat Rock, N.C. You can access information at minutemananchors.com/propane-tank-anchors-and-supplies. They have drawings, load tables, soil charts and other good information. Tie Down Engineering also has information online at www.tiedown.com.  I suggest you look at a couple of tables they have at www.tiedown.com/pdf/d909.pdf and www.tiedown.com/pdf/d215.pdf.  FEMA also has online information at www.scemd.org/library/DisasterMitigation/Flood/ProtectPropFloodPropaneTank.pdf. 

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. 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.

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.

This is a quick rundown on anchoring. It probably raises almost as many questions as answers.  I’ll post this information and other stuff as I can on our website.  I encourage you to ask questions. There will be a section for frequently asked questions about anchoring in the LP-Gas Concerns section, along with all of the articles about anchoring written over the last several years.

 

Last updated December 1, 2011

Contact: Richard.Fredenburg@ncagr.gov

 

 

NCDA&CS Standards Division, Stephen Benjamin, Director
Mailing Address:1050 Mail Service Center Raleigh, NC 27699-1050
Physical Address: 2 West Edenton Street, Raleigh, NC 27601
Phone: (919) 707-3225; FAX: (919) 715-0524