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Code for Design of Fire Dikes in Oil Tank Areas SY0075—93 Ministry of Energy of the People’s Republic of China Published on March 27, 1993; Implemented on September 1, 1993 1 General Provisions 1.0.1 This code is formulated to standardize the design requirements for fire dikes in plant, station, and warehouse oil tank areas within the petroleum and natural gas industry, thereby ensuring the safety of such areas. 1.0.2 This specification applies to the design of fire dikes in new construction and expansion projects of above-ground oil storage areas in the petroleum and natural gas industry. Not applicable to the firewall design for liquefied petroleum gas and natural gas condensate tank areas. The design of fire dike renovation projects for oil tank areas may be carried out in accordance with these specifications. 1.0.3 The construction of fire dikes should, while meeting the requirements for flame resistance, sealing, and seismic performance, take into comprehensive consideration factors such as safety, land use, investment, topography, geology, and meteorology. It is also necessary to account for elements like the capacity of the tank cluster and its location, the characteristics of the surrounding environment and the severity of potential accidents, construction and production management, the volume of maintenance work required, as well as the source of materials. The design should be tailored to local conditions to ensure durability and economic Reasonableness. 1.0.4 In the design of fire dikes, in addition to complying with this code, it is also necessary to meet the requirements and provisions of relevant current **standard codes. 2 Terms and Codes 2.1 Terms 2.1.1 Effective volume – the volume enclosed by a fire dike for a group of oil tanks. In the calculations, the volume should be reduced by the volume of the tanks inside it (with the largest tank excluded) below the calculated height of their fire dikes, as well as the volume of all buildings, structures, foundations, piping, and other such elements. 2.1.2 Height of the fire dike – in the overall layout, it is the vertical distance from the ground outside the fire dike to the top surface of the dike. 2.1.3 Fire dike foundation line – refers to the line where the slope of the fire dike meets its inner and outer designed ground levels. 2.2 Codes 2.2.1 Functions and effects PL, PE, Pd – distribution values at various load levels ； PA, PB, PG —— Level distribution values of earth pressure at various points ； Pt, PE, PL, Pd, PtE —— horizontal resultant forces above various load calculation sections ； Mt, ME, ML, Md, MtE —— Bending moments of various loads on the calculated section ； G1 — Standard value of the self-weight load on the embankment per meter of embankment length, calculated based on the cross-section ； G —— Design value of total vertical load ； P —— Design value of total horizontal load ； M —— The design value of the total overturning moment acting on the base. 2.2.2 Resistance and material properties RH – Base frictional resistance ； PP — Passive earth pressure ； Mw——Stability moment ； ——Internal friction angle of soil ； γL — specific gravity of the liquid ； γt——unit weight of the soil ； H1 —— Depth of liquid above the calculation section or height of the dike ； H0 —— Distance from the point of application of the resultant force above the calculation section to the calculation section ； HL — Total liquid depth ； H——Dike height ； α —— Width of the horizontal section of the internal backfill ； β —— Angle between the soil-embanked slope surface and the ground level ； d——foundation burial depth ； B1——Average thickness of the fire dike ； e — horizontal distance from the line of action of the vertical resultant force to the front end of the foundation ； C — Cohesion of soil. 2.2.3 Calculation of coefficients and others αmax – maximum value of the seismic impact coefficient ； α1, α2, α3, α4 —— the corresponding coefficients obtained from X/H ； η1——Coefficient of participation of the first mode ； μ——base friction coefficient ； η —— reduction coefficient for passive earth pressure ； Ka, K′a —— active earth pressure coefficients ； Kp——coefficient of passive earth pressure ； ft——dynamic fluid pressure coefficient. 3 Layout of fire dikes. 3.1 General provisions 3.1.1 The fire dikes installed around oil tank groups must be closed. Dikes and firebreaks must also be closed. 3.1.2 The height of the fire dike for vertical oil tank groups should be 1.0–2.0 m. The design height should be 0.2 m higher than the calculated height. The height of the dike should be 0.2–0.3 m lower than that of the fire dike. The height of the fire dike for horizontal oil tank groups should not be less than 0.5 m. 3.1.3 The ground within the fire dike shall have a slope of not less than 3‰. The drainage of rainwater and the passage of other pipelines shall comply with the following provisions: 3.1.3.1 Collection facilities shall be installed at lower locations within the embankment; the rainwater drainage pipes connected to these facilities shall extend below the ground level, and a device that can be opened and closed shall be provided outside the embankment to connect to them. The opening and closing device shall be equipped with a distinct indicator that shows its open or closed state. 3.1.3.2 Various pipelines and cables entering and leaving the oil tank farm should not pass through the body of the fire dike; instead, they should preferably cross over the top of the dike or pass beneath its foundation. If it is unavoidable to pass through the embankment, sleeves should be pre-installed, and effective sealing measures should be taken. 3.1.4 The floor elevation within the fire dike should not be higher than the elevation of the road surface or ground outside the dike. 3.1.5 When the capacity of a single oil tank within the fire dike is ≥ 20,000 m3, it is advisable to provide a road leading to the tank group. The road leading to the tank group should be single-lane, entering from the top of the fire dike, with a longitudinal slope not exceeding 8%. 3.1.6 When constructing drainage ditches along firebreaks without embankments, the distance between the outer side of the ditch walls and the outer edge of the firebreak foundation should not be less than 0.5 m, and leak-proof measures shall be in place within the ditch. 3.1.7 Each tank group must be equipped with two or more pedestrian steps or ramps on the fire dike, located in different directions. 3.1.8 The distance from the wall of a vertical oil tank to the base line of the fire dike and bulkhead shall not be less than half the height of the tank wall, while the distance from the wall of a horizontal oil tank to the base line of the fire dike shall not be less than 3 m. 3.1.9 A fire fighting clearance with a width of not less than 7 m shall be provided between the outer footlines of the fire dikes of adjacent tank groups. 3.1.10 The distance from the edge of the fire road in the oil tank area to the outer base line of the parallel fire dike shall not be less than 3 m. 3.2 Capacity 3.2.1 The grouping of oil tanks shall comply with the following provisions: 3.2.1.1 The total capacity of oil tanks with fixed roofs shall not exceed 100,000 m3. 3.2.1.2 The total capacity of floating roof oil tanks shall not exceed 200,000 m3. 3.2.1.3 The oil tanks within an oil tank farm should be arranged in no more than two rows, and the total number of tanks should not exceed 12. 3.2.1.4 Tanks with similar fire hazards should be arranged within the tank farm. Boiling and non-boiling oils should not be placed within the same fire dike area. 3.2.2 The effective capacity within the fire dike of the oil tank cluster shall comply with the following provisions: 3.2.2.1 For oil tanks with fixed roofs, it shall not be less than the capacity of the largest oil tank in the cluster. 3.2.2.2 For floating roof oil tanks, it shall be not less than half of the capacity of the largest oil tank in the tank farm. 3.2.2.3 When fixed-roof oil tanks and floating-roof oil tanks are arranged in the same group, the larger value of the two provisions above shall be adopted. 3.2.3 Dikes shall be installed within the oil tank group in accordance with the following requirements: 3.2.3.1 For oil tanks with a capacity of 50,000 m3 or more, there shall be one oil tank within the dike. 3.2.3.2 Oil tanks with a capacity equal to or greater than 10,000 m3 and less than 50,000 m3. There should not be more than 2 such oil tanks within one dike. 3.2.3.3 For oil tanks with a capacity of 3000–5000 m3, no more than 4 such tanks shall be located within an embankment. 3.2.3.4 For oil tanks with a capacity of 2000 m3 or less, there should not be more than 6 such tanks within one dike. 4 Types and Structure of Fire Dams 4.1 Selection 4.1.1 The selection of fire dams shall comply with the following provisions: 4.1.1.1 Earth-filled fire dams should be given priority, provided that the land area available and the soil conditions meet the requirements. 4.1.1.2 Brick fire dikes can generally be used, but reliable protective measures should be taken when applied in low-lying or saline-alkali areas. 4.1.1.3 Reinforced concrete fire dikes, plain concrete fire dikes, and rubble concrete fire dikes can be used in areas with an earthquake resistance intensity of 7 degrees or higher, in regions with complex terrain and a high density of population and industrial facilities, as well as in cases where the capacity of the oil tank farm is 50,000 m3 or more and there are special requirements regarding safety. 4.1.1.4 Grouted rubble fire dikes can be used in all areas except those with an earthquake resistance design intensity greater than 7 degrees or those with complex geological structures that may cause uneven settlement of the foundations. 4.2 Construction 4.2.1 The embedment depth of the foundation for fire dikes (other than earth dikes) should be determined based on factors such as engineering geology, building materials, and the depth of permafrost, and it should not be less than 0.5 m. 4.2.2 Fire dikes (other than earth dikes) shall be provided with expansion joints. The spacing of deformation joints should be determined in accordance with relevant specifications, taking into account the material of the fire dike, as well as climatic and geological conditions ； The seam width should be 30–50 mm, and the seam should be sealed with a flexible material. 4.2.3 Fire dikes (other than earth dikes and partition dikes) shall be protected by filling soil on the inside of the dike or by applying fire-resistant and sealant-coated materials, and shall comply with the following provisions: 4.2.3.1 The height of the soil fill on the inside of the fire dike shall not be less than 2/3 of the dike’s height ； The slope ratio (height to width) of the soil embankment should be 1:1.00–1.25 ； The top width of the soil fill should not be less than 300 mm ； The soil fill should be compacted in layers, and the slope surface should be firmly compressed; the compaction coefficient should not be less than 0.85 ； A surface layer should be applied to the soil mound; this layer must be able to effectively prevent erosion by rainwater, damage by small animals, and the growth of weeds. 4.2.3.2 The compressive strength of the fire-resistant coating layer shall not be less than 1.5 MPa; its adhesion strength to concrete shall be no less than 0.15 MPa. The fire resistance rating shall be at least 2 hours, it shall have frost resistance in the range of -25°C to 20°C, its strength shall remain unchanged after 15 cycles of freezing and thawing, and it shall be able to function in humid environments. 4.2.4 The structure of earth fire dikes shall comply with the following provisions: 4.2.4.1 The width at the top of the dike shall not be less than 500 mm, and the slope of the dike body (height to width ratio) shall be 1:1.2–1.5 ； 4.2.4.2 The embankment material shall be cohesive soil. When the embankment material is highly permeable soil (plastic index Ip ≤ 10), an impermeable layer with a thickness of not less than 300 mm should be installed within the embankment, or materials such as clay should be incorporated to reduce its permeability. 4.2.4.3 The embankment soil shall be compacted in layers, with a compaction coefficient not less than 0.90. 4.2.4.4 Earth fire dikes must be equipped with a surface layer, which should be able to effectively prevent erosion by rainwater, damage by small animals, and the growth of weeds. In humid areas in the south, artificial turf can be used as the surface layer. 4.2.5 The construction of brick fire dikes shall comply with the following provisions: 4.2.5.1 The thickness of the dike wall masonry shall not be less than 370 mm, and it shall be plastered with cement mortar. 4.2.5.2 The strength grade of bricks shall not be lower than MU7.5, and the strength grade of masonry mortar shall not be lower than M5 ； When the foundation is built with rubble masonry, the strength grade of the rubble shall not be lower than MU20. 4.2.5.3 A reinforced concrete cap should be provided at the top of the embankment; the thickness of this cap shall not be less than 100 mm, and the concrete strength grade shall not be lower than C15. Reinforcement shall be arranged in the cap in accordance with structural requirements. 4.2.5.4 Reinforced masonry is advisable in areas with an earthquake resistance intensity of 7 degrees or higher, or in areas with complex geological conditions and significant differences in foundation settlement. 4.2.5.5 When land availability is limited, a brick-built hollow fill fire dike can be used as an alternative to a brick-built fire dike with internal filling; the thickness of the internal filling should be 500 mm. 4.2.6 The construction of reinforced concrete fire dikes shall comply with the following provisions: 4.2.6.1 The thickness of the dike body and the base slab shall not be less than 200 mm. 4.2.6.2 The minimum one-sided reinforcement ratio for the stressed steel bars shall be 0.2%, and the diameter of the steel bars shall not be less than 12 mm ； The minimum reinforcement ratio for all structural rebars along the length of the embankment is 0.2%; the diameter of the rebars shall not be less than 8 mm, and the spacing between the rebars shall not exceed 250 mm ； The cover thickness of the stress-reinforcing bars in the embankment body should be 50 mm. The strength grade of the concrete for the embankment body and foundation should not be lower than C15, while the strength grade of the concrete for the cushion layer should not be lower than C10. 4.2.7 The construction of the rubble-masonry fire dike shall comply with the following provisions: 4.2.7.1 The minimum thickness of the dike body and foundation shall not be less than 500 mm ； Allowable width-to-height ratio for foundation steps: it should be 1:1.25 when the average pressure on the foundation base is not greater than 100 kPa, and 1:1.50 when it is greater than 100 kPa; the width of each step should not exceed 200 mm. 4.2.7.2 The strength grade of the rough stones shall not be lower than MU20, and the strength grade of the mortar shall not be lower than M5. 4.2.7.3 The crest of the embankment shall be provided with a reinforced concrete cap. Follow the same procedure as section 4.2.5.3 ； The embankment body should be jointed with cement mortar. 4.2.8 The construction of fire dikes made of rubble concrete or plain concrete shall comply with the following provisions: 4.2.8.1 The thickness of the dike body shall not be less than 300 mm. 4.2.8.2 The concrete strength grade shall not be lower than C15, and the strength grade of rubble shall not be lower than MU20 ； For rubble concrete, the volume of rubble used in the foundation portion should not exceed 30% of the total volume, while in the embankment portion it should not exceed 25% ； The maximum diameter of the rubble stones should not exceed 1/3 of the thickness of the relevant cross-section. 4.2.8.3 On the side of the embankment at the junction with the foundation, it is advisable to provide structural reinforcement amounting to not less than 0.05% of the cross-sectional area of the embankment; the diameter of such reinforcement should be no less than 10 mm. The anchorage length ls of the reinforcement within the embankment and foundation shall comply with the provisions of Article 6.1.4 of the Code for Design of Concrete Structures. 5 Verification of the strength and stability of the fire dike 5.1 Load combinations and internal force calculations 5.1.1 The design of the fire dike shall employ the basic combination of load effects based on the limit state of bearing capacity. In areas with an earthquake resistance intensity of 7 degrees or lower, combined calculations shall be carried out based on the condition of the dike being filled with liquid ； In areas with temperatures above 7 degrees, combined calculations based on seismic conditions shall still be carried out, and design shall be done according to the most unfavorable combination. The design calculations for fire dikes should include strength calculations and stability calculations. The design value of the load effect combination shall be determined by using equation (5.1.1): ……………………(5.1.1) Where S represents the design value of the load effect combination ； G, 1, L —— are the partial coefficients for self-weight load, static earth pressure, and static hydrostatic pressure load respectively; their values are given in Table 5.1.1. Qi —— is the partial coefficient for the i-th variable load; its value is also provided in Table 5.1.1 ； GK, GtK, QLK represent the standard values of self-weight load, static earth pressure, and static hydrostatic pressure loads, respectively, which are determined in accordance with the provisions of 5.1.2 to 5.1.4 ； QiK —— the standard value of the i-th variable load (including horizontal seismic forces acting on the embankment, dynamic hydrostatic pressure, dynamic earth pressure, etc.), which is determined in accordance with the provisions of 5.1.5 to 5.1.1 ； CG, Ct, CL, CQi —— represent the self-weight load, static earth pressure, static hydrostatic pressure, and the effect coefficient of the i-th variable load, respectively ； ci — the combination value coefficient for the i-th variable load, with values given in Table 5.1.1. 5.1.2 The standard value of the self-weight load is calculated using equation (5.1.2): ……………………(5.1.2) Load effect combinations, partial coefficients, and combination value coefficients Table 5.1.1 Load types: Full liquid condition inside the embankment; Seismic condition Partial coefficient Combination value coefficient Self-weight load 1.0 1.0 – Static earth pressure 1.2 1.2 – Static liquid pressure 1.1 1.1 – Seismic action – 1.3 0.6 Dynamic liquid pressure – Dynamic earth pressure – Note: When checking for overturning and sliding resistance, the partial coefficient for self-weight load is taken as 0.9. In the formula: G1 —— Standard value of the self-weight load of the embankment per meter of embankment length (kN/m) ； H1 — Distance from the cross-section to the top of the dike (m) ； B1 —— Average thickness of the embankment above the cross-section (m) ； ——Material density (kN/m3). 5.1.3 The standard value of the hydrostatic pressure load acting on the inside of the fire dike shall be determined by using equations (5.1.3–1, 2, 3, 4); the calculation diagram is shown in Figure 5.1.3. ……………………(5.1.3—1) ……………………(5.1.3—2) ……………………(5.1.3—3) ……………………(5.1.3—4) Where PL is the horizontal distribution load of the hydrostatic pressure per meter of dike length along the liquid depth (kN/m2); L is the unit weight of the liquid inside the dike, taken as 10 kN/m3 ； Z — Liquid depth (m) ； PL — Standard value of the resultant hydrostatic pressure per meter of embankment length above the calculated section (kN/m) ； H1 —— Distance from the cross-section to the liquid surface (m) ； H0 —— Distance from the position of the resultant hydrostatic pressure per meter of embankment length above the calculation section to the calculation section (m) ； ML – Standard value of the bending moment at the calculation section (kN•m/m), resulting from the resultant hydrostatic pressure per meter of embankment length above the calculation section. 5.1.4 The calculation of the standard value of the static earth pressure load due to the fill soil within the fire dike shall comply with the following provisions; the calculation diagram is shown in Figure 5.1.4. 5.1.4.1 The curve AFD in Figure 5.1.4 represents the soil pressure distribution curve; F is the turning point, and the pressure distribution shall be calculated using equations (5.1.4–1) to (5.1.4–8): ……………………(5.1.4–1) ……………………(5.1.4–2) ……………………(5.1.4–3) ……………………(5.1.4–4) When H1