Fuel Tanks Anchored for Disaster Resistance

    Scope Images
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    A fuel tank should be anchored with ground anchors designed for site conditions to maintain secure connection to its base in a flood or earthquake
    Scope

    In locations prone to earthquakes, floods, hurricanes, and tornadoes, anchor and secure fuel tanks and distribution lines to reduce the risk of fuel leakage, fire, explosions, damage to tanks and surrounding property, and harm to people.

    • Secure tanks to prevent them from becoming detached via flotation, seismic shaking, wind forces, or collision with other unsecured objects during extreme weather events.
    • Prevent forceful damage to the fuel tank supply line.

    See the Compliance Tab for related codes and standards requirements, and criteria to meet national programs such as DOE’s Zero Energy Ready Home programENERGY STAR Single-Family New Homes, and Indoor airPLUS.

    Description

    Homes that use fuel oil or propane for space heating, hot water, cooking, or fireplaces will often have large storage tanks for these fuels located on site. Whether the tank is located above ground or below ground, or indoors or outdoors, it is imperative that the tank be anchored to the ground or a strong structural component to reduce safety risks in case of flooding, earthquakes, or tornadoes (FEMA P-348 2017), to Improve the possibility of continued safe use during or directly following a disaster event, and to reduce repair scope following adverse weather.

    An unanchored liquid propane, natural gas, or fuel oil tank can become a significant physical and environmental hazard during a natural disaster. If left unanchored, a fuel tank located outside of the home can be knocked off of its base by flood waters, hurricane-force winds, or seismic activity, breaking fuel lines and possibly crashing into the home or other buildings (Figure 1) (Home Innovation Research Labs 2012). Similarly, if an unanchored fuel tank located in the basement is moved by flood waters or seismic activity, the supply line can detach. This can contaminate the home with oil or gas and present a fire hazard. These hazards can be reduced by securing the fuel tank, which is often a simple process that can be accomplished using a few straps and anchors (Home Innovation Research Labs 2012).

     

    Improperly installed fuel tanks can break free from attachments under the force of flood waters, risking broken fuel lines which could cause fire or explosion. Here, the tank is tethered only by the gas piping, which is not designed to perform this function.
    Figure 1. Improperly installed fuel tanks can break free from attachments under the force of flood waters, risking broken fuel lines which could cause fire or explosion. Here, the tank is tethered only by the gas piping, which is not designed to perform this function.
    (Source: FEMA P-259 2012)

     

    Floods can present several additional hazards for tanks, especially tanks located on or below ground. The tank or its components can be hit by flood-borne debris; metallic tank or fuel line components can be oxidized by corrosive elements in the floodwaters; sensitive control devices like pressure regulators, solenoids, and meters can be destroyed by flood water; relief valves can allow floodwaters to get into the tank and oil or gas to flow out of the tank; and buried tanks can be exposed by rapid erosion, especially in coastal floods that include wave action (FEMA P-348 2017).

    Flood waters can also lift submerged tanks out of the ground due to buoyant forces. If the flood forces exceed the weight of an above-ground tank and the fuel within, then the tank is at risk of displacement. For underground tanks, if the flood forces exceed the combined weight of the tank, the fuel within, and any soils above the tank, the tank can be displaced. Buoyant forces are proportional to the volume of floodwater displaced. As more of the tank is submerged, the buoyant forces increase. Once a tank is fully submerged, buoyant forces are maximized because greater flood depths do not displace greater amounts of floodwater. The net buoyant forces are less on full tanks than on empty tanks, but full tanks can release their contents when floodwater reaches their fill or vent piping. Refer to Section 5W.13 of FEMA P-259, Engineering Principles and Practices for Retrofitting Flood-Prone Residential Structures, for additional details on how to determine the net buoyant force on a tank and the volume of concrete required to offset buoyancy (FEMA P-348 2017).

    Another possible impact of floodwaters is that submerged tanks can also be crushed by flood forces. For each foot of flood depth, freshwater flooding exerts compressive forces of 62.4 pounds per square foot of tank surface while saltwater exerts compressive forces of 64.0 pounds per square foot. Because compressive forces increase as flood depths increase, tanks exposed to deeper floodwater are much more prone to crushing failure. A fuel tank placed on a basement floor can be exposed to much larger compressive forces than a tank placed in a shallow crawlspace. Similarly, underground tanks can be exposed to greater compressive loads than those placed at grade (FEMA P-348 2017).

    Whether elevated, at grade, or buried, fuel tanks should be anchored to resist the buoyancy effects of flood waters and movement from floods or earthquakes. In coastal areas, tanks should be installed on the landward side of the building; in riverine areas, they should be installed on the downstream side of buildings. Piping and components should be protected from flood loads. Piping can be installed in vertical chases and attached to sturdy parts of the building. In coastal areas, piping should be buried deeper than expected flood and wave scouring (FEMA P-348 2017).

    FEMA has defined Special Flood Hazard Areas (SFHAs) where the National Flood Insurance Program (NFIP)’s floodplain management regulations must be enforced. The various SFHAs, including Zones V, A, and Coastal Zone A, are defined at the bottom of this page.

     

    Tanks Elevated  

    The most effective flood protection technique for fuel storage tanks is elevation of the tank above the Design Flood Elevation (DFE). The DFE is the elevation of the highest flood a protective measure is designed to withstand, usually based on the 100-year flood. In A Zones, tanks can be elevated on platforms, frames, or on structural fill. Methods to elevate tanks are shown in Figures 2 and 3 (FEMA P-348 2017). When the tank is elevated on compacted structural fill, a concrete slab is often placed on top of the fill material for anchorage. Figure 3 shows a tank elevated on fill. In V Zones and Coastal A Zones, however, structural fill is not allowed for new construction or Substantially Improved homes, as defined by the National Flood Insurance Program (FEMA P-348 2017).

    When elevated, the tanks themselves are not likely to be exposed to flood forces during a design flood; however, they still require anchoring and support to resist wind loads and, in seismic areas, earthquake loads. (See definitions at the end of this tab.) The fuel tank should be secured to the platform with straps or anchors to prevent movement caused by high winds or seismic events. In coastal zones, the anchors should be made of non-corrosive material to reduce potential damage from salt spray (FEMA P-348 2017).

    In V Zones and Coastal A Zones, the platform should be supported by posts or columns that are adequately designed for all loads including flood, wind, and earthquake. Bracing may be required to address loads from moving floodwater and structural redundancy may be appropriate to protect against debris impact. The lowest horizontal member of the supporting frame should be above the wave crest. The foundation should be deep enough to resist loads after being undermined by the predicted levels of erosion and scour. A braced pile or post platform may be necessary in riverine locations where moving water and debris pose a risk (FEMA P-348 2017).

     

    Fuel tank is elevated above flood waters and anchored to supporting frame
    Figure 2. Fuel tank is elevated above flood waters and anchored to supporting frame (Source: FEMA P-348 2017).

     

    Fuel tank is elevated above flood waters on a base of structural fill and anchored to the concrete pad
    Figure 3. Fuel tank is elevated above flood waters on a base of structural fill and anchored to the concrete pad (Source: FEMA P-348 2017).

     

    Tanks at or Below Grade

    To meet the national Flood Insurance Requirements, when elevating the tank above the DFE is not feasible, new tanks and tanks for Substantially Improved homes must be designed to resist flood loads and prevent the release of their contents, as described in ASCE 24 (see Compliance tab). Also, ASCE 24 specifies that both above-ground and underground tanks be designed and installed to resist 1.5 times the flood loads acting on an empty tank. Those loads are not just the buoyant forces that tend to dislodge tanks but also the compressive forces that could crush tanks exposed to floodwater (FEMA P-348 2017).

    When fuel tanks cannot be elevated or relocated, dry floodproofing may be an option if the residence is not newly constructed or Substantially Improved. Dry floodproofing is any measure which is designed to physically block flood waters from reaching the tank. For new construction and Substantially Improved residences, dry floodproofing is not allowed by the National Flood Insurance Program (NFIP) for residential occupancy (FEMA P-348 2017).

    Adding weight (dead load) to the foundations supporting the tanks helps resist buoyant forces. Concrete is commonly used to help anchor tanks. Because concrete placed below a flooded tank displaces floodwater and, like the tank, is exposed to buoyant forces, only the submerged weight of the concrete provides resistance to buoyant forces on the tank. Hence, when determining the net buoyant force, the full weight of the concrete can be included in the calculation provided that the volume of the concrete is included as part of the total volume of floodwater displaced. Figure 4 shows a tank installation where concrete is used to resist buoyant forces. Helical earth anchors are occasionally used to resist buoyant forces (see Figure 5). The anchors should be designed to take into account the soil type and any reduction in capacity due to saturated soil conditions. All anchors and connecting hardware should be corrosion resistant (FEMA P-348 2017).

     

    This underground fuel tank is anchored to a concrete base then surrounded with concrete to resist buoyancy forces
    Figure 4. This underground fuel tank is anchored to a concrete base to resist buoyancy forces (Source: FEMA P-348 2017).

     

    This fuel tank sits at grade but is anchored through its concrete base to the ground beneath with helical earth anchors
    Figure 5. This fuel tank sits at grade but is anchored through its concrete base to the ground beneath with helical earth anchors (Source: FEMA P-348 2017).

     

    Definitions

    The FEMA document, Coastal Hazards & Flood Mapping: A Visual Guide, defines Special Flood Hazard Areas (SFHAs), including Zones V and A and Coastal Zone A. Special Flood Hazard Areas are areas where the National Flood Insurance Program (NFIP)’s floodplain management regulations must be enforced. Flood insurance is required in these areas because of the high risk of flooding (FEMA 2021).

    CHHA - Coastal High Hazard Area. A Coastal High Hazard Area (CHHA) is identified as Zone V or Zone VE on FEMA flood maps.

    Zone VE and V – Called “V zones”, these are areas where waves and fast-moving water can cause extensive damage during the base flood event. In V zones, wave heights are larger than 3 feet. The label Zone VE refers to areas for which a detailed study has been done and base flood elevations (BFEs) have been calculated. The label “Zone V” means that a detailed study has not been done for the area, so BFE has not been calculated but wave hazards are still expected. Structures in areas mapped as Zone V and Zone VE are subject to stricter building requirements because of the higher risk of damage from strong waves.

    Zone A – Coastal Zone A areas include areas landward of a V Zone, or landward of an open coast without mapped V Zones. In a Coastal Zone A, the principal source of flooding will be astronomical tides, storm surges, seiches or tsunamis, not riverine flooding.

    Zone AE - Zone AE is used to label parts of the SFHA on flood maps in coastal and non-coastal areas. In coastal areas, AE zones indicate areas that have at least a 1-percent-annual-chance of being flooded and wave heights are less than 3 feet. For Zone AE, detailed analyses have been performed and BFEs have been calculated.

    Zone AO - Zone AO shows areas at risk of flooding during the base flood, where water 1 to 3 feet deep flows over sloping ground. On coastal maps, Zone AO usually marks areas at risk of flooding from wave overtopping, where waves are expected to wash over the crest of a dune or bluff and flow into the area beyond. In AO zones, flood depth is expressed as a height above natural ground. Homes and other buildings in these areas are still vulnerable to flooding from waves, even if they are on higher ground or behind a wall or other structure (FEMA 2021).

    Ensuring Success

    Ensure that tank installation complies with National Flood Insurance Program requirements for the home’s location.

    Climate

    Consult National Flood Insurance Program maps to determine the flood risk of your location. FEMA’s Flood Map Service Center website provides tools home owners and builders can use to determine the flood risk of their specific location.

    Right and Wrong Images
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    An alternative design includes strapping the tank to concrete counterweights on opposite sides of the tank.
    An alternative design includes strapping the tank to concrete counterweights on opposite sides of the tank.
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    Correctly anchoring an outside propane tank can prevent tank displacement if flooding occurs.
    Correctly anchoring an outside propane tank can prevent tank displacement if flooding occurs.
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    Correctly anchoring an outside heating oil tank can prevent tank displacement if flooding occurs.
    Correctly anchoring an outside heating oil tank can prevent tank displacement if flooding occurs.
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    Anchoring a fuel tank to a concrete slab is recommended to avoid displacement if flooding occurs.
    Anchoring a fuel tank to a concrete slab is recommended to avoid displacement if flooding occurs.
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    Install “deadmen” anchors and straps over an underground storage tank to offset the buoyancy of flood waters.
    Install “deadmen” anchors and straps over an underground storage tank to offset the buoyancy of flood waters.
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    An underground fuel tank is anchored onto poured-in-place concrete counterweights.
    An underground fuel tank is anchored onto poured-in-place concrete counterweights.
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    Fuel storage tanks are at risk of displacement during floods and should be securely anchored to the ground or base
    Fuel storage tanks are at risk of displacement during floods and should be securely anchored to the ground or base
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    A fuel tank is strapped onto a concrete slab at the top of compacted fill above the DFE.
    A fuel tank is strapped onto a concrete slab at the top of compacted fill above the DFE.
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    A fuel tank elevated above the design flood elevation on a platform in a high velocity flow area.
    A fuel tank elevated above the design flood elevation on a platform in a high velocity flow area.
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    Install hold-down straps to securely attach the tank to the bottom hold-down pad to offset the buoyancy of flood waters.
    Install hold-down straps to securely attach the tank to the bottom hold-down pad to offset the buoyancy of flood waters.
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    Fuel tank anchored below ground in a flood-prone area anchored to a counterweight to counteract the buoyancy force.
    Fuel tank anchored below ground in a flood-prone area anchored to a counterweight to counteract the buoyancy force.
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    This underground storage tank in Rockaway River, NJ was lifted out of the ground by the buoyant force of flood waters
    This underground storage tank in Rockaway River, NJ was lifted out of the ground by the buoyant force of flood waters
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    This gasoline tank was lifted out of the ground by the buoyant forces of flood waters in the Iowa flood of 2008.
    This gasoline tank was lifted out of the ground by the buoyant forces of flood waters in the Iowa flood of 2008.
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    This underground storage tank was lifted out of the ground by the buoyant force of flood waters
    This underground storage tank was lifted out of the ground by the buoyant force of flood waters

    Compliance

    The Compliance tab contains both program and code information. Code language is excerpted and summarized below. For exact code language, refer to the applicable code, which may require purchase from the publisher. While we continually update our database, links may have changed since posting. Please contact our webmaster if you find broken links.

    2021, 2018, and 2015 IRC

    R322.2.4 Tanks.  Underground tanks shall be anchored to prevent flotation, collapse, and lateral movement under conditions of the base flood. Above-ground tanks shall be installed at or above the elevation required in Section R322.2.1 or shall be anchored to prevent flotation, collapse, and lateral movement under conditions of the base flood.

     

    2021, 2018, 2015, 2012, and 2009 IRC

    R322.2.1 Elevation Requirements.  1. Buildings and structures in flood hazard areas, not including flood hazard areas designated as Coastal A Zones, shall have the lowest floors elevated to or above the base flood elevation plus 1 foot, or the design flood elevation, whichever is higher.

    R322.3 Coastal high-hazard areas (including V Zones and Coastal A Zones, where designated). R322.3.2 Elevation Requirements. 1 Buildings and structures erected withing coastal high-hazard areas and Coastal A Zones shall be elevated so that the bottom of the lowest horizontal structural members supporting the lowest floor, with the exception of piling, pile caps, columns, grade beams, and bracing, is elevated to or above the base flood elevation plus 1 foot, or the design flood elevation, whichever is higher.

     

    ASCE/SEI 24-2014 - Flood Resistant Design and Construction

    Published by the American Society of Civil Engineers (ASCE), Flood Resistant Design and Construction, ASCE 24, is a referenced standard in the International Codes® (I-Codes®). ASCE 24 states the minimum requirements and expected performance for the siting and design and construction of buildings and structures in flood hazard areas that are subject to building code requirements. Types of buildings and structures are described in ASCE 24-14, Table 1-1 (see page 5 of these Highlights), and include commercial, residential, industrial, educational, healthcare, critical facilities, and other occupancy types. Buildings and structures designed according to ASCE 24 are better able to resist flood loads and flood damage. FEMA deems ASCE 24 to meet or exceed the minimum National Flood Insurance Program (NFIP) requirements for buildings and structures. ASCE 24 includes additional specificity, some additional requirements, and some limitations that are not in NFIP regulations. Buildings and structures within the scope of the IBC and proposed to be located in any flood hazard area must be designed in accordance with ASCE 24. The 2015 I-Codes reference ASCE 24-14, while the 2006 through 2012 I-Codes reference ASCE 24-05. The International Residential Code® requires dwellings in floodways to be designed in accordance with ASCE 24, and the 2015 edition of the IRC allows use of ASCE 24 for dwellings in any flood hazard area (the 2012 and 2009 editions allow use of ASCE 24 in Coastal High Hazard Areas).

    Existing Homes

    The measures described for new homes on the Description tab can also be used for existing homes.

    More Info.

    Access to some references may require purchase from the publisher. While we continually update our database, links may have changed since posting. Please contact our webmaster if you find broken links.

    References and Resources*
    Author(s)
    Home Innovation Research Labs
    Organization(s)
    HIRL
    Publication Date
    Description
    A guide on how to anchor fuel tanks to avoid damage from flooding and seismic events to the home by using straps and solid concrete slabs.
    Author(s)
    Federal Emergency Management Agency
    Organization(s)
    FEMA
    Publication Date
    Description
    Fuel systems design guide including installation guidance and formulas for calculating loads and buoyancy forces for specifying number, type and capacity of strapping for hold-downs in flood-prone areas.
    *For non-dated media, such as websites, the date listed is the date accessed.
    Contributors to this Guide

    The following authors and organizations contributed to the content in this Guide.

    The following authors and organizations contributed to the content in this Guide.

    Pacific Northwest National Laboratory

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