PLANT SITING AND LAYOUT 59A?7 2001 Edition important structures,equipment, or adjoining property or that could reach waterways: (1) Process areas (2) Vaporization areas (3) Transferareas for LNG, flammable refrigerants, and flammable liquids (4)Areas immediately surrounding flammable refrigerant and flammable liquid storage tanksIf impounding areas also are required in order to complywith 2.1.2, such areas shall be in accordance with 2.2.2and 2.2.3. 2.2.1.3 In certain installations, the provisions of 2.1.2,2.2.1.1, and 2.2.1.2 that apply to adjoining property or waterwaysshall be permitted to be waived or altered at thediscretion of the authority having jurisdiction where the change doesnot constitute a distinct hazard to life or property orconflict with applicable federal, state, and local (national, provincial,and local) regulations. 2.2.1.4 Flammable liquid and flammable refrigerant storagetanks shall not be located within an LNG container impoundingarea. 2.2.2 Impounding Area and Drainage System Design and Capacity.2.2.2.1 Impounding areas serving LNG containers shall have a minimumvolumetric holding capacity, V, including any useful holding capacity ofthe drainage area and with allowance made for the displacementof snow accumulation, other containers, and equipment, in accordance withthe following: (1) For impounding areas serving a singlecontainer, V equals the total volume of liquid in thecontainer, assuming the container is full. (2) For impoundingareas serving more than one container with provision made toprevent low temperature or fire exposure resulting from leakage fromany one container served from causing subsequent leakage from anyother container served, V equals the total volume of liquidin the largest container served, assuming the container is full.(3) For impounding areas serving more than one containerwithout provision made in accordance with 2.2.2.1(b), V equalsthe total volume of liquid in all containers served, assumingall containers are full. 2.2.2.2 Impounding areas, if provided toserve only vaporization, process, or LNG transfer areas, shall havea minimum volumetric capacity equal to the greatest volume ofLNG, flammable refrigerant, or flammable liquid that can be dischargedinto the area during a 10-minute period from anysingle accidental leakage source or during a shorter time periodbased upon demonstrable surveillance and shutdown provisions acceptable to theauthority having jurisdiction. 2.2.2.3 Enclosed drainage channels for LNG shallbe prohibited. Exception: Container downcomers used to rapidly conduct spilledLNG away from critical areas shall be permitted to beenclosed if they are sized for the anticipated liquid flowand vapor formation rates. 2.2.2.4 Dikes, impounding walls, and drainagesystems for LNG and flammable refrigerant containment shall be ofcompacted earth, concrete, metal, or other materials. They shall bepermitted to be independent of the container, or they shallbe permitted to be mounded integral to, or constructed against,the container. They, and any penetrations thereof, shall be designedto withstand the full hydrostatic head of impounded LNG orflammable refrigerant, the effect of rapid cooling to the temperatureof the liquid to be confined, any anticipated fire exposure,and natural forces, such as earthquakes, wind, and rain. Wherethe outer shell of a double-wall tank complies withthese requirements, it shall be permitted to be considered asthe impounding area for purposes of determining the siting areadistances in 2.2.3. Where the containment integrity of such anouter shell can be affected by an inner tank failuremode, an additional impounding area that otherwise satisfies the requirementsof 2.2.1.1 shall be provided. 2.2.2.5 Dikes, impounding walls, anddrainage channels for flammable liquid containment shall conform to NFPA30, Flammable and Combustible Liquids Code. 2.2.2.6 The dike orimpounding wall height and distance from containers operating at 15psi (100 kPa) or less shall be determined inaccordance with Figure 2.2.2.6. FIGURE 2.2.2.6 Dike or impoundment wallproximity to containers. 2.2.2.7 Provision shall be made to clearrain or other water from the impounding area. Automatically controlledsump pumps shall be permitted if equipped with an automaticcutoff device that prevents their operation when exposed to LNGtemperatures. Piping, valves, and fittings whose failure could allow liquidto escape from the impounding area shall be capable ofwithstanding continuous exposure to LNG temperatures. If gravity drainage isemployed for water removal, provision shall be made to preventthe escape of LNG by way of the drainage system.2.2.2.8 Insulation systems used for impounding surfaces shall be, inthe installed condition, noncombustible and suitable for the intended service,considering the anticipated thermal and mechanical stresses and loads. Ifflotation is a problem, mitigating measures shall be provided. 2.2.3Impounding Area Siting. 2.2.3.1 The provisions of 2.2.3 shall notapply to impounding areas serving only transfer areas at thewater? edge of marine terminals. Maximum liquid level Container XX Y Y Dike or impounding wall Notes: ? DimensionX shall equal or exceed the sum of dimension Yplus the equivalent head in LNG of the pressure inthe vapor space above the liquid. Exception: When the heightof the dike or impounding wall is equal to, orgreater than, the maximum liquid level, X may have anyvalue. ? Dimension X is the distance from the innerwall of the container to the closest face of thedike or impounding wall. ? Dimension Y is the distancefrom the maximum liquid level in the container to thetop of the dike or impounding wall.