GB50121-92 Code for Design of Low-Expansion Foam Fire Extinguishing Systems

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Chapter 1 General Provisions Article 1.0.1 These specifications are formulated in order to reasonably design low-expansion air foam fire suppression systems (hereinafter referred to as foam fire suppression systems), reduce fire losses, and protect human life and property. Article 1.0.2 The design of foam fire extinguishing systems must comply with the relevant guidelines and policies, ensuring safety and reliability, advanced technology, economic Rationality, and ease of management. Article 1.0.3 These specifications apply to the design of foam fire extinguishing systems in facilities where Class A (excluding liquefied hydrocarbons), Class B, and Class C liquids are processed, stored, loaded, unloaded, or used. These specifications do not apply to the design of foam fire suppression systems installed on ships, offshore oil platforms, and similar facilities. Article 1.0.4 The design of foam fire extinguishing systems shall, in addition to complying with the provisions of these specifications, also meet the requirements of **current relevant standards and specifications. 【Note】According to China’s regulatory framework, building codes specify the locations where low-expansion foam fire suppression systems should be installed, while this code addresses the selection and detailed design of such systems. To make this clearer, this modification is made. Chapter 2 Selection of Foam Fluids and System Types Section 1 Selection, Storage, and Preparation of Foam Fluids Article 2.1.1 For storage tanks containing water-insoluble Class A, B, and C liquids, when using surface-foam fire extinguishing systems, protein, fluoroprotein, aqueous film-forming, or film-forming fluoroprotein foam fluids can be used ； When using submersed foam fire extinguishing, fluoroprotein, aqueous film-forming, or film-forming fluoroprotein foam agents should be selected. 【Note】The provisions of this standard are similar to those of **relevant standards in the United States, the United Kingdom, etc.** In the early 1980s, the British company Angus developed Film-Forming Fluoroprotein Foam (FFFP) by using hydrolyzed proteins as a base and adding appropriate fluorocarbon surfactants. China developed this type of foam in the 1990s. This foam agent not only possesses the characteristics of fluoroprotein foam agents but also those of aqueous film-forming foam agents, making it one of the commonly used types of foam agents today. From a fire extinguishing perspective, water-resistant fluoroprotein foam, water-resistant aqueous film-forming foam, and water-resistant film-forming fluoroprotein foam are also suitable for underwater foam fire suppression; however, they are expensive. For storage tanks containing non-water-soluble flammable liquids of types A, B, and C, the use of such water-resistant foams is not recommended according to these standards. Article 2.1.1A Foam spray systems, foam guns, and foam cannon systems for protecting water-insoluble Class A, B, and C liquids; when suction-type foam generating devices such as foam nozzles, foam guns, and foam cannons are used, protein, fluoroprotein, aqueous film-forming, or film-forming fluoroprotein foam liquids can be selected ； When using non-suction spraying devices such as water nozzles, water guns, and water cannons, film-forming or film-forming fluoroprotein foam should be selected. 【Note】When a water-based film-forming, fluoroprotein foam mixture is applied to the surface of a water-insoluble liquid fuel, it forms a protective film. Its fire-extinguishing capacity is not only related to the properties of the foam, but more importantly depends on its film-forming ability as well as the toughness and strength of the protective film it forms. Therefore, water film-forming and film-forming fluoroprotein foam liquids are also suitable for non-suction-type spraying devices such as water nozzles, water guns, and water cannons. Article 2.1.2 For water-soluble Class A, B, and C liquids, lead-free gasoline with an oxygen-containing additive content exceeding 10% by volume, and systems using a single foam extinguishing system to protect both water-soluble and water-insoluble Class A, B, and C liquids, alcohol-resistant foam must be used. 【Note】The oxygen-containing additives in gasoline are mainly water-soluble liquids such as ethers and alcohols, which have a strong destructive effect on ordinary foam. When the volume percentage of oxygen-containing additives in lead-free gasoline exceeds 10%, it is difficult to extinguish the fire using ordinary foam agents; therefore, water-resistant foam agents must also be used. To this end, corresponding requirements are added with reference to NFPA 11-1998, the Standard for Low-Expansion Foam Fire Extinguishing Systems. When the additive is a multi-component mixture, only the net content of those components containing oxygen elements is calculated. Some tank areas contain both water-soluble and non-water-soluble liquid tanks, and some barrel storage facilities hold both types of liquids. To reduce construction costs, it is feasible to design a foam fire extinguishing system, but it is necessary to use a solvent-resistant foam. When using anti-soluble foam to extinguish water-insoluble Class A, B, and C liquids, its design requirements are the same as those for ordinary foam. Article 2.1.3 The storage temperature for the foam solution should be between 0 and 40°C, and it is advisable to store it in a well-ventilated and dry room or shed. Article 2.1.4 The water source used for preparing the foam mixture shall meet the following requirements: 1. The water source for preparing the foam mixture should be equipped in accordance with the appropriate water quality requirements for the foam solution ； II. The water temperature for preparing the foam mixture should be between 4°C and 35°C℃ ； 【Note】Fresh water is the best source for preparing various foam mixtures. Certain foam agents are also suitable for preparing mixtures with seawater. Whether a foam solution is suitable for preparing a mixture with seawater depends on its resistance to seawater (or hard water). Therefore, when selecting a water source, it is necessary to consider whether its quality is suitable for the requirements of the foam solution chosen. To this end, paragraphs 1, 2, and 3 of the original specification have been merged into the current paragraph, while paragraph 4 has been changed to two paragraphs. Section 2 Selection of System Types Article 2.2.1 When selecting between fixed, semi-fixed, or mobile foam fire extinguishing system types, the provisions of relevant codes shall be complied with. 【Note】The current **standards, namely the Code for Fire Protection Design of Petrochemical Enterprises, the Code for Design of Oil Depots, and the Code for Fire Protection Design of Crude Oil and Natural Gas Engineering, specify the locations in their respective industries where fixed, semi-fixed, and mobile foam fire extinguishing systems should be used. The Code for Fire Protection Design of Buildings, which is under comprehensive revision, aims to address those locations where foam fire extinguishing systems are used but are not covered by the aforementioned three codes; therefore, the type of foam fire extinguishing system to be selected during design should be determined in accordance with these codes. Therefore, the original text of this section shall be deleted and rewritten. Article 2.2.2 The selection of the foam fire extinguishing system for tank areas shall meet the following requirements: 1. For fixed-roof tanks storing water-insoluble liquids of categories A, B, and C, a foam fire extinguishing system with above-surface spraying, below-surface spraying, or semi-below-surface spraying can be used ； II. For fixed-roof storage tanks holding water-soluble Class A, B, and C liquids, a foam fire extinguishing system that sprays foam from above the liquid level or a semi-submerged foam fire extinguishing system should be used ； III. For floating roof and internal floating roof storage tanks holding Class A, B, and C liquids, a foam fire extinguishing system installed above the liquid level should be used ； IV. For storage tanks with external floating roofs or internal floating roofs used for water-insoluble liquids, fixed-roof storage tanks with a diameter greater than 18 meters, and vertical storage tanks used for water-soluble liquids, foam nozzles should not be used as the primary fire extinguishing facility. V. For fixed-roof storage tanks with a height greater than 7 m and a diameter greater than 9 m, foam guns should not be used as the primary fire extinguishing equipment. 【Instructions】1. The above-surface foam fire extinguishing system is suitable for three types of storage tanks: fixed-roof, external floating-roof, and internal floating-roof tanks ； II. Submerged foam fire suppression systems are not suitable for storage tanks with external or internal floating roofs, as the floating roof hinders the proper distribution of foam. When protection is provided only at the annular seal of such tanks, it is not possible to deliver foam to that area. When foam is injected into a water-soluble liquid by submersion spraying, its structure is destroyed due to the polarity of the molecules in the water-soluble liquid and the dehydration effect, preventing it from rising to the surface to extinguish the fire. Therefore, the submersed foam fire extinguishing system is not suitable for extinguishing fires in fixed-roof storage tanks containing water-soluble Class A, B, and C liquids. III. Semi-submerged injection is one of the application forms of foam fire suppression systems, and it has been used in some developed countries for many years. IV. For external floating roof storage tanks, the protected area is the annular sealing zone, and it is difficult for foam nozzles to apply foam to this area. For similar reasons, foam guns are also not suitable for internal floating roof storage tanks. Foam guns are used to spray foam forcefully; however, since the foam penetrates into water-soluble liquids, causing it to dehydrate and become damaged, they are not suitable for fixed-roof storage tanks containing such liquids. In the event of a fire in a fixed-roof storage tank with a diameter greater than 18 meters, only one opening usually forms in the roof; cases where the entire roof is lifted off are rare. It is difficult for foam guns to deliver foam inside the tank. Relevant standards in the US, UK, and other countries also contain similar or comparable provisions. V. It is difficult for firefighters using foam guns to extinguish fires in storage tanks that are taller and have a larger diameter. Similar provisions are also set out in the relevant standards of the US, UK, and other countries. Article 2.2.3 The following areas are suitable for the use of foam spray systems: I. Indoor areas where water-insoluble flammable liquids of categories A, B, and C may leak ； II. Indoor areas where water-soluble Class A, B, and C liquids with a leakage thickness of no more than 25 mm may leak ； III. Indoor areas where water-soluble Class A, B, and C liquids, with a leakage thickness exceeding 25 mm but equipped with cushioning, may leak. 【Note】This clause is formulated based on years of experimental research, practical experience in engineering applications, and reference to the standards of developed ** countries; it also retains the content of the original \"specifications\". The buffer mentioned can be a specially designed buffering device, or it can be fixed equipment, metal objects, or other solid non-flammable materials that are not specifically designed for this purpose. According to tests conducted by the Tianjin Fire Science Research Institute of the Ministry of Public Security, fire extinguishment is feasible for thicknesses over 25 mm when there are buffers such as metal plates or metal tanks. Article 2.2.4 For the loading and unloading platforms for Classes A, B, and C liquids in road tankers or rail tank cars, a foam spray system or a foam cannon system may be employed. 【Note】This clause is formulated with reference to NFPA 11-1998, the Standard for Low-Expansion Foam Extinguishing Systems. When selecting a foam fire extinguishing system for a storage platform, factors such as the overall dimensions of the platform, the types of liquids stored there, other nearby hazardous and exposed areas, drainage facilities, prevailing wind directions, ambient temperature, and the available staffing should all be taken into consideration. Article 2.2.5 For outdoor spill fire areas involving Class A, B, and C liquids that are enclosed by dikes, a foam spray system, foam cannon system, or foam gun system shall be selected based on the specific conditions of the area to be protected. 【Note】The cofferdam referred to in this clause is a retaining dike constructed from soil or other non-combustible structural materials, capable of containing fuel at depths greater than 25 mm. This clause is based on Article 2.2.6: For outdoor flow fires involving Class A, B, and C liquids without cofferdams, mobile foam cannon or foam gun systems are recommended. 【Note】The outdoor spill fire areas for Class A, B, and C liquids without cofferdams referred to in this clause are those where spills of such liquids occur in areas not restricted by structures such as curbs, embankments, or building walls. The flow thickness of Class A, B, and C liquids in this area is limited to 25 mm. This clause is formulated with reference to NFPA 11-1998 \"Standard for Low-Expansion Foam Extinguishing Systems\", BS5306, Part \"Standard for Low-Expansion Foam Extinguishing Systems\". Chapter 3 System Design Section 1 General Provisions Article 3.1.1 The design amount of foam mixture required for use in foam fire extinguishing systems shall meet the following requirements: 1. The design amount of foam mixture needed to extinguish a single fire in a storage tank area shall be calculated using Equation 3.1.1-1. It shall be determined based on the maximum value of the sum of the amount required inside the tank, the amount required for the auxiliary foam nozzles associated with that tank, and the remaining amount in the pipelines: M1 = A1·R1·T1 + n·Qf·t + V (3.1.1-1) Where: M1 – Design amount of foam mixture required to extinguish a single fire (L) ； A1—Protection area per single storage tank (m2) ； R1—Foam mixture supply rate (L/min·m2) ； T1—Continuous supply time of foam mixture (min) ； n—Calculate the number of auxiliary foam guns for the storage tank ； Qf—Foam mixture flow rate per auxiliary foam gun (L/min) ； t—Continuous supply time of the mixture from the foam gun (min) ； V—Remaining amount of foam mixture in the system pipes (L). II. The designed amount of foam mixture required by the foam spray system to extinguish a single fire should be calculated using Equation 3.1.1-2: M2 = A2 · R2 · T2 (3.1.1-2) Where: M2 — the designed amount of foam mixture required by the foam spray system to extinguish a single fire (L) ； A2—Maximum protected area of the foam spray system (m2) ； R2—Foam mixture supply rate of the foam spray system (L/min) ； T2—Continuous supply time of the foam mixture in the foam spray system (min). III. The designed amount of foam mixture required by the foam cannon and foam gun systems to extinguish a single fire should be calculated using Equation 3.1.1-3: M3 = 1.2A3·R3·T3 (3.1.1-3) Where: M3 is the designed amount of foam mixture (in L) required by the foam cannon and foam gun systems to extinguish a single fire ； A3—Maximum protected area (m2) per fire extinguished by foam cannon and foam gun systems ； R3—Foam cannon, foam gun system foam mixture supply rate (L/min·m2) ； T3—Continuous supply time of foam mixture for foam cannon and foam gun systems (min). 【Note】The first part of this clause is a consolidation and revision of Articles 3.1.1 and 3.1.2 of the original standard. As stipulated in clause 3.1.1 of the original specifications, \"For the design of the foam fire extinguishing system in tank areas, the amount of foam mixture required should meet the sum of the maximum amount needed to extinguish a fire in a single tank and the amount required by the auxiliary foam nozzles for extinguishing fires that spread from such tanks.\" This requirement may lead to incorrect designs in tank areas where multiple types of tanks are present and/or where water-soluble and water-insoluble flammable liquids of categories A, B, and C coexist, and moreover, the wording of this clause is unclear. The revised provisions stipulate that for extinguishing a single fire in a tank farm using a foam fire suppression system, the designed amount of foam mixture is determined based on the maximum of three values: the amount required inside the tank, the amount needed for the auxiliary nozzles attached to that tank, and the remaining amount in the pipelines. This approach avoids the aforementioned problems. When using a foam cannon or foam gun to extinguish a fire, the foam emitted can suffer some loss due to environmental factors such as wind. The stronger the wind, the greater the range, and the greater the losses. Therefore, when determining the flow rate of foam cannons and foam guns, their losses should be taken into account. For safety reasons, a parameter of 1.2 times was determined. Article 3.1.2 The protection area of storage tanks shall be determined in accordance with the following provisions: 1. For fixed-roof storage tanks, shallow-dish type storage tanks, and internal floating-roof storage tanks made of fusible materials, it shall be the cross-sectional area of the tank ； II. For external floating roof storage tanks, as well as single- and double-disc internal floating roof storage tanks, it refers to the annular area between the tank wall and the foam weir plate. 1. Paragraph 1 of this article is part of Article 3.2.1 of the original regulations; this provision also applies to submersed and semi-submersed foam fire extinguishing systems, therefore it has been moved to this section as a general provision. II. Paragraph 2 of this article is compiled from parts of Articles 3.2.2 and 3.2.3 of the original regulations. Since the early 1980s, for the foam nozzles (including foam generators) of foam fire suppression systems in developed **external floating roof storage tanks, there have been two installation methods: on the tank wall and on the floating roof. In recent years, some areas in our country have adopted the floating roof design; this specification provides for the determination of the protected area using a floating roof system that includes foam nozzles (including foam generators) for injecting foam from above the floating roof seal and beneath the metal rain shield. III. This specification uses the tank names specified in the current \"Code for Design of Oil Storage Tanks.\" However, the current industry standard \"Code for Design of Vertical Circular Steel Welded Storage Tanks in Petrochemical Industries\" SH3046-92 classifies internal floating roof tanks into four types: single-disc, compartmentalized single-disc, double-disc, and metal roof on top of the floating disk; hence the names used in the two standards are not identical. The term \"shallow tray\" as used in these specifications refers to the \"single tray\" mentioned in the latter documents; the terms \"single tray\" and \"double tray\" as used in these specifications correspond to the \"compartmentalized single tray\" and \"double tray\" mentioned in the latter documents. If the “Code for Design of Oil Depots” changes its name, this code will also be modified accordingly. Article 3.1.3 When a fixed foam fire extinguishing system is used, in addition to installing fixed foam fire extinguishing equipment, mobile foam fire extinguishing equipment such as foam hoses, foam nozzles, and foam fire trucks shall also be provided. Article 3.1.4 In tank areas equipped with fixed foam fire extinguishing systems, auxiliary foam nozzles for extinguishing fires caused by the spread of liquids shall be installed outside their fire dikes. The number of such nozzles, together with the continuous supply time of the foam mixture, shall not be less than those specified in Table 3.1.4. The foam mixture flow rate for each auxiliary foam gun should not be less than 240 L/min. Number of foam guns and continuous supply time schedule: 3.1.4 Tank diameter (m), Number of foam guns installed, Continuous supply time (min): ≤10, >10 and ≤20, >20 and ≤30, >30 and ≤40, >40. 1, 12, 22, 3; 10, 20, 20, 30, 30. This clause has three meanings: first, it stipulates that for tank areas equipped with fixed foam fire suppression systems, auxiliary foam guns should be installed outside the fire dike to combat fires caused by the spread of liquids, which is a more explicit requirement than in the original standards ； Secondly, it proposes the requirement that the quantity to be used and the continuous supply time of the foam mixture be determined based on the diameter of the tank to be protected, in line with Article 3.1.1 of this section ； Third is the requirement of the original specification. The original specification specified models of auxiliary foam guns, whose flow rate per unit was more than twice as high as that required by BS5306 Part 6 and NFPA11; therefore, it was modified. Article 3.1.5: When the flow rate of the foam mixture in the fixed foam fire extinguishing system installed in the tank area is 100 L/s or greater, the pumps, proportioning devices, and control valves on the pipelines as well as the main pipe control valves of the system should have remote control capabilities. When the selected equipment is installed in an environment with explosion and fire hazards, it must comply with the provisions of the Code for Design of Electrical Installations in Explosive and Fire Hazardous Environments. The degree of risk in storage areas for liquids of categories A, B, and C, as well as the losses resulting from fires there, are generally higher than those in other civilian facilities. However, the design requirements for the control functions of foam fire extinguishing systems used in such facilities are usually lower than those for other types of fire extinguishing systems. This requirement is put forward in order to appropriately enhance the protective capabilities of foam fire extinguishing systems. Article 3.1.6 A location for installing foam mixture flow measurement instruments shall be provided on the main foam mixture pipeline of fixed foam fire extinguishing systems ； Test and inspection ports should be provided on the foam mixture pipeline. To verify whether the installed foam fire extinguishing system meets the regulatory requirements, the installed system must be tested in accordance with the relevant standards; therefore, the design should facilitate the installation of testing equipment and the taking of samples. Article 3.1.7 When a fixed foam fire extinguishing system in the tank farm shares a single set of fire water supply pumps with the fire cooling system, measures shall be in place to ensure that the supply rate of the foam mixture meets the design requirements; such requirements shall not be met through temporary adjustments during a fire. To reduce construction costs, some designs share the fire pump of the foam fire suppression system in the tank area with that of the fire cooling water system. However, due to the different operating conditions of the two systems, as well as the varying specifications of the storage tanks in most tank areas – with some differences being quite significant – it becomes difficult to use certain systems. This requirement is put forward for this purpose to impose constraints on such designs. Article 3.1.8 In tank areas equipped with fixed foam fire suppression systems, foam fire hydrants shall be evenly installed along the outside of the fire dike. The spacing between foam fire hydrants should not exceed 60 m, and the number of such hydrants should be no less than 4. The foam fire hydrants specified in this provision are designed to be connected to foam guns for extinguishing fires that break out within the fire dike of storage tank areas. There are roughly two ways in which foam fire hydrants can be installed; one is by attaching them to the foam mixture pipelines of a fixed system ； Another type consists of a water fire hydrant, a separate foam liquid storage tank (barrel), and a foam proportioning mixer. Regardless of the form, it is necessary to ensure a certain quantity and spacing. The current **standard, the Code for Fire Protection Design of Petrochemical Enterprises, specifies that the spacing between water fire hydrants should not exceed 60 m; this parameter is adopted in this clause to ensure an organized layout of fire protection facilities in the tank storage area. Article 3.1.9 The fixed foam fire extinguishing system in the tank farm should preferably have the functions of a semi-fixed system. In the event of a fire in Class A, B, or C liquid storage tanks, rescue efforts typically involve foam fire trucks and other such equipment. According to statistics from relevant organizations on ground-mounted metal fixed-roof storage tank fires that have occurred in our country, in tanks with a volume of over 2000 m3 (diameter of 16 m), fires usually start when a gap forms at the weak welds between the tank roof and the tank walls; it is less likely for the entire roof to be lifted off. Moreover, the larger the diameter of the tank, the lower the likelihood of the roof being lifted off. Foam fire trucks are unable to deliver firefighting foam effectively directly into the burning tank through such local openings ； The foam fire suppression system for floating roof storage tanks is designed primarily to deal with fires in their sealed areas. Foam fire trucks are unable to deliver foam effectively directly to these sealed areas, and the floating roof itself is not taken into account with regard to the impact forces generated; its use therefore poses a risk of sinking the floating roof ； Foam fire trucks should also not be used to supply foam directly to storage tanks containing water-soluble Class A, B, or C liquids, as most of the foam will sink into the liquid and dissipate, failing to extinguish the fire. Therefore, it is recommended that fixed foam fire suppression systems in storage tank areas have the functions of semi-fixed systems, which provides an additional layer of protection. When the foam mixture pipelines are arranged in a circular pattern outside the fire dike, the function of a semi-fixed system can be achieved by using foam fire hydrants installed on these circular pipelines; however, it is more convenient to use pipe thread connections equipped with control valves on the branch pipes leading to the foam generators. How to implement this function is determined through negotiation between the designer and the client. Section 2 Design of Above-Surface Foam Extinguishing Systems in Tank Areas Article 3.2.1 For fixed-roof tanks, the foam mixture supply rate and continuous supply time for fixed and semi-fixed above-surface foam extinguishing systems shall comply with the following provisions: 1. For water-insoluble liquids of Classes A, B, and C, these values shall not be lower than those specified in Table 3.2.1-1. Foam mixture supply rate and continuous supply time Table 3.2.1-1 Types of foam liquids, supply rate (L/min), continuous supply time (min): Class A and B liquids, Class C liquids; Protein: 6.0, 40, 30; Fluoroprotein, water-based film-forming agents, film-forming fluoroprotein: 5.0, 45, 30. Note 1: If a higher supply rate for the mixture is used than that specified in the table above, the continuous supply time can be reduced proportionally, but it must not be less than 80% of the time specified in the table. Note 2: For lead-free gasoline with an oxygen-containing additive content by volume of more than 10%, the supply rate of the antisolvent foam mixture should be no less than 6 L/min·m2, and the continuous supply time should be no less than 40 minutes. II. For water-soluble liquids of categories A, B, and C, the value shall not be lower than that specified in Table 3.3.1-2. Foam mixture supply rate and continuous supply time Table 3.2.1-2 Liquid type Supply rate (L/min·m2) Continuous supply time (min) Propanol, butanol 1230 Methanol, ethanol, propanol, acrylonitrile, ethyl acetate 1225 Note: For water-soluble liquids not listed in this table, their foam mixture supply rate and continuous supply time are determined through testing. The content regarding the determination of the combustion area for fixed-roof storage tanks in the original text was removed, and Table 3.2.1-1 was revised with reference to NFPA 11-1998 \"Standard for Low-Expansion Foam Extinguishing Systems\", BS5306, Part \"Standard for Low-Expansion Foam Extinguishing Systems\", and other standards. Article 3.2.2 The design of the foam fire extinguishing system for external floating roof storage tanks shall comply with the following provisions: 1. The supply rate of the foam mixture shall not be less than 12.5 L/min·m2, and the continuous supply time shall not be less than 30 minutes. The maximum protection perimeter for a single foam generator shall meet the requirements specified in Table 3.2.2: Maximum Protection Perimeter for a Single Foam Generator Table 3.2.2 Location of Foam Nozzles Height of Weir Plate (m) Protection Perimeter (m) Top of tank wall, above sealing or rain shield Soft seal ≥0.92 4 Mechanical seal 25 to ≤30 3 >30 to ≤35 4 Note: For storage tanks with a diameter greater than 35 m, at least one additional foam generator shall be added for every 300 m2 increase in cross-sectional area. II. For the foam generators of external floating roof storage tanks and single- and double-disc internal floating roof storage tanks, their models and quantities shall be determined in accordance with the requirements of Article 3.2.2 of these specifications. III. When more than one foam generator is required for a storage tank, foam generators of the same specification should be selected and arranged evenly around the perimeter of the tank. IV. Fixed-roof storage tanks containing water-soluble Class A, B, and C liquids shall be equipped with foam cushioning devices. V. When the foam nozzles are installed at the top of the tank wall of an external floating roof storage tank, foam deflector shields should be provided ； When the foam nozzles are installed on the floating roof, they should be of T-type design, with both straight sections connecting to the nozzles having a length of not less than 5 times their diameter; moreover, the horizontal section of the T-piece must remain level ； The foam nozzles located above the seal or weatherboard should be inclined downward at 30-60° after extending into the foam baffle. Table 3.2.4 of the original specifications specified an excessive number of foam generators based on the diameter of the storage tank; for example, for a tank with a diameter of 22.5 m and a capacity of 5000 m3, the minimum number of foam generators required according to the original specifications was 1, which is a significant discrepancy. Table 3.2.4 has been modified to ensure that the parameters specified in these standards are both safe and reliable, as well as cost-effective. The provisions of the original third paragraph of the “Specifications” have been deleted. To ensure a balanced operating pressure and flow rate among the foam generators for effective fire suppression, it is recommended to use foam generators of the same model and to arrange them evenly. For fixed-roof storage tanks holding water-soluble Class A, B, and C liquids, it is difficult to extinguish fires in the absence of a buffering device; the design parameters specified in these codes are based on the use of such a buffering device. The original specifications outlined the installation requirements in their explanatory notes; these are now clarified. This requirement is aimed at reducing foam loss and facilitating foam distribution; installing foam guides and foam nozzles on the floating roof, with T-shaped tubes, is an effective measure. Article 3.2.5 The installation of foam mixture pipes on storage tanks shall comply with the following provisions: For fixed-roof storage tanks, shallow-dish type storage tanks, and internal floating-roof storage tanks made of fusible materials, each foam generator shall be connected to a separate mixture pipe leading outside the fire dike ； II. For external floating roof storage tanks with foam nozzles installed at the top of the tank wall, as well as single and double disk type internal floating roof storage tanks, the foam generators can be connected in pairs, using one common pipeline leading from the bottom of the foam mixture riser to outside the fire dike. When three or more foam generators are connected through a single pipe at the lower end of the foam mixture riser and led outside the fire dike, it is advisable to install a control valve on each foam mixture riser. In semi-fixed foam fire suppression systems, the flow rate of foam mixture required for each foam mixture pipeline extending outside the fire dike should not exceed the supply capacity of one fire truck ； III. The foam mixture riser connecting to the foam generator should be fixed to the tank wall using pipe clamps, with a spacing of no more than 3 m between them. A rust and debris removal outlet should be provided at the lower end of the foam mixture riser. Regarding the installation location of the foam nozzles on the floating roof of external floating-roof storage tanks, when the foam mixture passes through the tank, pressure-resistant hoses with a repetitive twisting motion trajectory should be used; such hoses must not collide with the supports of the floating roof, and they should be at a distance of more than 0.5 meters from the heat-exchange pipes located at the bottom of the tank ； IV. On the ladder platform of the external floating roof storage tank, pipe threaded connections with caps are provided; these connections are connected by pipes along the tank wall to a point 0.7 m above the ground outside the fire dike, and corresponding pipe threaded connections should also be installed there. Due to the introduction of the floating roof installation method with foam nozzles, this second clause has been supplemented with that descriptor. The three specifications add requirements regarding pressure-resistant hoses and pipe connections in the installation method of foam nozzles on floating roofs, and move the requirement that metal hoses should be used for connections to horizontal pipes to clause 3.2.6, paragraph 1. Article 3.2.6 The installation of foam mixture pipes within the fire dike shall comply with the following provisions: 1. Horizontal foam mixture pipes above ground level shall be laid on pipe supports or pipe racks, but shall not be fixed to them. A flexible metal hose is recommended to be used for connecting it to the foam mixture riser on the tank wall. II. The depth of buried pipes below the ground surface should be greater than 0.3 m, and they should be connected to the foam mixture vertical pipes on the tank wall using metal hoses or metal elbows ； III. The pipes for the foam mixture should have a slope of 3‰ leading toward the fire dike. 1. This paragraph is a combination of the provisions of the first paragraph of the original standard and certain provisions of Paragraph 3.2.5, Subparagraph 3. II. Burying the pipeline underground has the significant advantage of keeping the area within the fire dike tidy, which facilitates daily operations there. However, there are also disadvantages; one is that the valve for controlling the foam generator must be installed underground, which makes operation difficult ； Secondly, buried pipelines have limited movement and are sensitive to uneven settlement of the foundation as well as the upward force exerted on the tank body in the event of an explosion or fire in the tank ； Third, it is not conducive to the maintenance and replacement of pipelines. To this end, the code intends to imply a non-recommendation against burying pipes underground; however, since this practice is used both domestically and internationally and it is not practical for the code to impose restrictions, this clause has been added. The purpose of this clause is to protect the pipeline from damage. The metal steering joint can be made of cast steel, ductile iron, or malleable iron. The three paragraphs of this article are the second paragraph of the original specification. Article 3.2.7 The installation of foam mixture pipes outside the fire dike shall comply with the following provisions: 1. A pressure gauge interface for detecting the operating pressure of the foam generator shall be provided on the horizontal pipe near the outer side of the fire dike. II. The pipes for the foam mixture shall have a slope of 2‰ leading toward the drain valve. The control valves on these pipes shall be located outside the fire dike and shall be clearly marked ； III. An exhaust valve should be installed at a high position on the foam mixture pipeline. The original first paragraph was not precise enough; its content has now been incorporated into section 3.1.8. After the foam system is installed, it must be tested to determine whether its design and installation meet the relevant specification requirements; the additional provisions are intended for such system testing. Article 3.2.8 is deleted. The content related to design calculations has been rewritten; see Section 6 of this chapter. Section 3 Design of Submersed Foam Fire Extinguishing Systems in Tank Farm Sections 3.3.1: This section has been deleted; its content has been incorporated into Section 2 of Chapter 2. Article 3.3.2 For fixed-roof storage tanks on the ground containing water-insoluble Class A, B, and C liquids, when a submersed foam fire extinguishing system is used, the following requirements shall be met: 1. The supply rate of the foam mixture shall not be less than 5.0 L/min·m2 ； For liquids with a storage temperature above 50°C or a viscosity greater than 40 mm2/s, as well as lead-free gasoline with an oxygen-containing additive content by volume of more than 10%, the foam mixture supply rate shall be determined through testing ； II. The continuous supply time of the foam mixture should not be less than 40 minutes ； III. Speed at which foam enters water-insoluble liquids: For Category A and Category B liquids, it should not exceed 3 m/s ； For Class C liquids, it should not be greater than 6 m/s ； IV. The foam nozzle should have an upwardly inclined shape, with an inclination angle of 45°; the length of the foam injection tube must be at least 20 times the diameter of the tube. When there is a nozzle, it should be located at the center of the storage tank ； When there is more than one nozzle, they should be arranged evenly around the tank, and the flow rate of each nozzle should be approximately equal ； V. The foam nozzles should be installed 0.3 m above the water level in the storage tank, and the number of such nozzles shall not be less than that specified in Table 3.3.2. Number of foam nozzles: Table 3.3.2 shows that for tank diameters of ≤23 m, the number of nozzles is 1; for diameters >23 m and ≤33 m, it is 2; and for diameters >33 m and ≤40 m, it is 3. Referencing NFPA11 \"Standard for Low-Expansion Foam Extinguishing Systems\" and BS5306 Part \"Standard for Low-Expansion Foam Extinguishing Systems\", adjustments have been made to the supply rate of the foam mixture as well as the continuous supply time. The speed at which foam enters non-water-soluble liquids is specified separately for Class A, Class B, and Class C substances. Most designers in China understand foam pipes to be foam nozzles; as a result, many systems are designed with pipes of the same diameter running from the outlet of the high-backpressure foam generator to the foam nozzles inside the storage tank, which causes inconvenience in some projects. To provide design flexibility while also taking into account the determination of hydrodynamic parameters, length requirements for the foam injection tube are proposed. Article 3.3.3 The installation of high-backpressure foam generators in submersible foam fire extinguishing systems shall comply with the following provisions: 1. The number of generators to be installed shall be determined based on the flow rate of the foam mixture calculated in Article 3.3.2 of these specifications ； II. It should be located outside the fire dike ； III. When the number of high backpressure generators required for a storage tank is more than 1, it is advisable to use them in parallel ； IV. A pressure gauge interface for monitoring should be installed on the inlet side of the high-backpressure foam generator, while a pressure gauge, a backpressure control valve, and a foam sampling port should be provided on its outlet side. The amended provisions of the original second and third paragraphs of this article are respectively summarized in Section 6 of this chapter and Section 4 of Chapter 4. Based on the problems identified during the project and the needs of project inspection, the requirements of the second, third, and fourth paragraphs have been proposed. Article 3.3.4 The installation of foam pipelines in submersible foam fire extinguishing systems shall comply with the following provisions: 1. The foam pipelines within the fire dike shall be determined in accordance with Article 3.2.6 of these specifications ； II. Foam pipelines outside the fire dike should be equipped with vent valves, and it is advisable to have a slope of 2‰ leading toward the vent valves ； Fire hydrants and exhaust valves should not be installed. III. A branch pipe equipped with a removable blind plate for system testing should be installed on the foam pipeline near the storage tank ； IV. The foam pipes of semi-fixed systems shall be led outside the fire dike, and corresponding quick-install interfaces for high-backpressure foam generators shall be provided. The addition of a third item is due to the needs of engineering inspection and testing ； Paragraph 4 is a supplement to the original “specifications”. Article 3.3.5 is deleted. The original content of section 3.3.5 has been incorporated into Section 6 of this chapter. Article 3.3.6 The installation of the foam mixture pipeline for the submersed foam injection system shall be determined in accordance with Article 3.2.7 of these specifications. The requirements for hydraulic calculations are summarized in Section 6 of this chapter. Article 3.3.7: The foam pipes of the submersed foam fire extinguishing system shall be equipped with steel control valves and check valves, as well as oil leakage prevention devices that do not interfere with the normal operation of the foam system. A prominent problem with current submersed foam injection systems is the poor sealing of the check valves on the foam injection pipes. In some systems, in addition to closing the gate valve at the base of the storage tank, another gate valve that is also in the closed position is installed outside the fire dike, which renders the system partially dysfunctional; even so, oil leakage still occurs ； Some systems even arrange the foam injection pipe in an Ω shape with its top above the liquid level, which not only makes installation difficult but also increases the resistance of the foam pipeline and affects its appearance. Currently, measures such as blast membranes and shuttle check valves are being used, so relevant requirements have been added. Section 4: Foam Sprinkler Systems, Article 3.4.1: The protection area of a foam sprinkler system shall be determined based on the horizontal surface area or the projected horizontal surface area of the area to be protected. Article 3.4.2 When a foam spray system is used to protect water-insoluble Class A, B, and C liquids, the supply rate of the foam mixture and the continuous supply time shall not be less than those specified in Table 3.4.2. When a foam spray system is used to protect water-soluble Class A, B, and C liquids, the supply intensity of the foam mixture and the continuous supply time should be determined through testing. Supply intensity of foam mixture and continuous supply time Table 3.4.2 Types of foam agents, nozzle installation height (m), supply intensity of foam mixture L/min·m2, supply time (min): Protein, fluoroprotein ≤10; 8; 10 >10; 10. Water-based film-forming agents, film-forming fluoroprotein ≤10; 6.5 >10; 8. This provision is formulated on the basis of original clause 3.4.3, with reference to NFPA16-1995 \"Code for Installation of Foam-Water Deluge Systems and Foam-Water Sprinkler Systems\", BS5306 Part6 \"Standard for Low-Expansion Foam Fire Extinguishing Systems\", ISO7076 \"Standard for Foam Fire Extinguishing Systems\" 등, taking into account China’s national conditions. Article 3.4.3 When a foam spray system is used to protect water-insoluble Class A, B, and C liquids, suction-type nozzles or open-type non-suction nozzles equipped with splash plates are recommended ； When protecting water-soluble Class A, B, and C liquids, suction-type sprinklers should be selected. To protect water-insoluble Class A, B, and C liquids, when using non-film-forming foam agents such as protein or fluoroprotein-based foams, traditional suction-type foam nozzles should be employed ； When choosing film-forming foams such as aqueous film-forming foams and fluoroprotein-based film-forming foams, either suction-type nozzles or open-type non-suction nozzles can be used. To reduce the impact of foam on the protective liquid, when using film-forming foams such as aqueous film-forming foams or fluoroprotein-based film-forming foams along with open-type non-suction nozzles, it is advisable to choose open-type non-suction nozzles equipped with a splash plate. When protecting water-soluble Class A, B, and C liquids, no antisolvent foam will form a film regardless of the type chosen; therefore, absorbent foam nozzles should be used. Article 3.4.4 The layout of foam nozzles shall meet the following requirements: 1. The layout of foam nozzles shall be determined based on the designed supply rate of the foam mixture, the protected area, and the characteristics of the nozzles ； II. Directly spray the foam onto the object to be protected ； III. The layout of the foam nozzles shall ensure a uniform supply intensity of the foam mixture across the entire protected area; the average supply intensity of the foam mixture within the quadrilateral area formed by any four adjacent nozzles shall not be less than the designed intensity ； IV. There should be no obstacles around the foam nozzles that could interfere with the spraying of foam ； V. The protection area and spacing of foam nozzles shall comply with the provisions in Table 3.4.5-5: Protection Area and Spacing of Foam Nozzles. Table 3.4.4-5 shows the nozzle installation height (in meters), the maximum protection area per nozzle (in m2), and the maximum horizontal distance between nozzles. For heights ≤10, the values are 12.5 and 3.6; for heights >10, the values are 10 and 3.2. This provision was formulated with reference to standards and codes such as NFPA13 “Standard for the Installation of Water Sprinkler Systems”, NFPA16 “Standard for Foam-Water Sprinkler Systems”, the “Design Code for Automatic Fire Extinguishing Systems” GBJ84-85, and the “Design Code for Water Spray Fire Extinguishing Systems” GB 50219-95, taking into account the characteristics of foam sprinkler systems. Article 3.4.5 Foam spray systems should be equipped with deluge valves and hydraulic alarms, and pressure switches should be installed on the outlet pipelines of each deluge valve; however, single-zone foam spray systems with fewer than 10 nozzles may not require deluge valves or pressure switches. A foam spray system is a fire extinguishing system that activates automatically to put out initial fires involving flammable liquids of categories A, B, and C. To ensure a fast response time, to notify relevant personnel promptly once the system is activated, and to enable monitoring via the system control panel, deluge valves, hydraulic alarms, and pressure switches must be installed. It should be noted that, as proven by practice, the probability of failure for solenoid valves currently in use is quite high. Using electric butterfly valves also results in a higher probability of failure compared to deluge valves, as well as longer response times. In areas protected by single-zone small-system protection, the fire load is low and the pipelines are short, making it easy to ensure a timely response; therefore, deluge valves and pressure switches may not be necessary in order to save on costs. Article 3.4.6 The foam spray system shall have automatic, manual, and emergency mechanical start functions. In automatic control mode, the system’s response time should not exceed 60 seconds. Automatic start-up, along with manual and emergency mechanical start functions, is a general requirement for automatic systems. The response time is determined with reference to the \"Code for Design of Water Sprinkler Systems\" (GB 50219-95), taking into account the characteristics of foam spray systems. Article 3.4.7 The fire detection and alarm system for foam spray systems shall comply with the relevant provisions of the **standard \"Code for Design of Automatic Fire Alarm Systems\". When a transmission pipe equipped with closed-nozzle sprinklers is used to transmit fire signals, the length of the transmission pipe should not exceed 300 m; its nominal diameter should be between 15 mm and 25 mm. The spacing between the closed-nozzle sprinklers installed on the transmission pipe should not be greater than 2.5 m. The fire detection and alarm functions of the system shall comply with the relevant provisions of the **standard \"Code for Design of Automatic Fire Alarm Systems\" as a general guideline. Since certain locations are suitable for using transmission pipes with closed-nozzle sprinklers to transmit fire signals, many projects do indeed adopt this approach; these regulations were established to ensure their reliability. Article 3.4.8 The foam-water spray system installed in aircraft hangars shall be constructed in accordance with the **Standard ‘Code for Fire Protection Design of Aircraft Hangars’**. Section 5: Foam Pump Stations Article 3.5.1 Foam pump stations should be constructed together with fire pump rooms, and the fire resistance rating of their buildings shall not be lower than grade II. The distance between the foam pump station and the protected area should not be less than 30 m, and it should be ensured that, after the foam fire pump is started, it takes no more than 5 minutes to deliver the foam mixture or foam to the farthest protected area. Article 3.5.2 Foam fire pumps should preferably be started by self-priming. A set of foam fire pumps should have no fewer than two suction pipes; in the event that one of them is damaged, the remaining suction pipes should be able to handle the total water demand. Article 3.5.3 Fire hydrants should be installed on the foam mixture pipelines inside or near the foam fire pump station ； Foam guns should be installed inside the foam pumping station. Article 3.5.4: Foam fire pumps shall be equipped with a standby pump, the capacity of which shall not be less than that of the largest pump. A standby pump may not be required when one of the following conditions is met: 1. The total storage capacity for water-insoluble liquids of categories A, B, and C is less than 2500 m3, and the capacity of any single tank is less than 500 m3 ； II. The total storage capacity of water-soluble Class A, B, and C liquids is less than 1,000 m3, with the capacity of each individual tank being less than 100 m3. Article 3.5.5 The power source for foam pumping stations shall meet one of the following requirements: 1. A power source for first-class electrical load ； II. Power sources for secondary electrical loads, along with diesel engines designated as backup power ； III. All diesel engines are used ； IV. Foam pumping stations that do not have a backup pump do not need to be equipped with a backup power source. Setting up a diesel engine is more economical than setting up a diesel generator, and it is safer than setting up a gasoline engine; hence this regulation is in place. For the load classification and corresponding requirements of power supply systems, please refer to the \"Code for Design of Power Supply and Distribution Systems\" (GB 50052-95). Article 3.5.6: A water level indicator device shall be installed in the foam pump station. Foam pumping stations should be equipped with communication devices that allow direct contact with the unit’s fire station or fire protection department. Article 3.5.7 It is strictly prohibited to install standalone foam stations within fire dikes, cofferdams, or within the coverage area of foam spray systems. The distance between the separate foam station located outside the fire dike and the tank wall should be greater than 20 m, and it should have remote control functionality. It is a basic requirement to have separate foam stations located outside the system protection area, that is, outside the fire area. Some tank farms are large and contain many tank groups; if the foam supply is centralized at a pump station, it will not be possible to deliver the foam mixture or foam to the farthest protected areas within 5 minutes, resulting in delays in extinguishing the fire. Therefore, in such cases, the foam station and the pump room can be built separately. Some projects even have two or more foam stations to meet the requirements regarding delivery time. These regulations have been established for safety reasons. Section 6: Foam Cannon and Foam Gun Systems, Article 3.6.1: When foam cannon and foam gun systems are used as the primary fire extinguishing equipment for fixed-roof storage tanks containing water-insoluble Class A, B, and C liquids, the supply rate of the foam mixture and the continuous supply time must be no less than those specified in Table 3.6.1. Minimum supply rate of foam mixture and continuous supply time Table 3.6.1 Types of foam agents Supply rate of mixture L/(min·m2) Continuous supply time (min) Class A and B liquids Class C liquids Protein, fluoroprotein 8.0 60 45 Water-based film-forming agents, film-forming fluoroproteins 6.5 60 45 This provision is derived from Paragraph 1 of Article 3.2.1 of the original regulations for mobile systems, and has been modified with reference to BS standards. Article 3.6.2 When a foam cannon system is used to protect loading and unloading platforms for tank cars carrying Class A, B, and C liquids, the following requirements shall be met: 1. It shall be capable of protecting the platform’s roof, pumps, measuring instruments, vehicles, and various other devices related to the loading and unloading of the products ； II. The protection area of the system: for automobile tank trucks and loading docks, it should be determined based on the total surface area of the dock floor ； The surface area of the train tank car loading platform shall be determined based on sections divided by lengths of no less than 5 tank cars ； III. The supply intensity of the foam mixture and the continuous supply time shall not be less than those specified in Table 3.6.2. Foam mixture supply rate and continuous supply time Table 3.6.2 Types of foam agents, supply rate (L/min·m2), supply time (min): Types of liquids to be handled – Proteins, fluoroproteins: 6.5, 20; Water-insoluble liquids, water-based film-forming agents, film-forming fluoroproteins: 5.0, 20; Alcohol-resistant foam: 12, 30; Water-soluble liquids. This clause is new and has been formulated with reference to standards such as NFPA11-1998 \"Standard for Low-Expansion Foam Extinguishing Systems\". Article 3.6.3 When foam cannon or foam gun systems are used to protect areas where non-water-soluble Class A, B, and C liquids are flowing in fire situations, the protected area shall be calculated as the difference between the area of the ground enclosed by the dike and the area occupied by non-combustible structures. The supply rate of the foam mixture and the continuous supply time must not be less than those specified in Table 3.6.3. Minimum supply rate of foam mixture and continuous supply time 3.6.3 Types of foam liquids, supply rate of mixture L/(min·m2), continuous supply time (min): Class A and B liquids, Class C liquids, protein-based and fluoroprotein-based foams – 6.5/40/30; water-based film-forming foams and film-forming fluoroprotein foams – 6.5/30/20. This provision is new; due to the constraints imposed by cofferdams, liquids accumulate to a certain depth. Therefore, the supply rate of the foam mixture and the continuous supply time are determined with reference to the provisions in Clause 3.2.1, Paragraph 1 of this standard, as well as standards from abroad such as NFPA 11-1998 \"Standard for Low-Expansion Foam Fire Extinguishing Systems\" and BS 5306 Part 6 \"Standard for Low-Expansion Foam Fire Extinguishing Systems\". Article 3.6.4 When foam cannon or foam gun systems are used to protect areas affected by outdoor spreading fires caused by leaks of Class A, B, or C liquids, the maximum spreading area shall be determined based on the specific conditions of the area to be protected. The supply intensity of the foam mixture and the continuous supply time shall not be less than those specified in Table 3.6.4. Foam mixture supply rate and continuous supply time Table 3.6.2 Types of foam agents, supply rate (L/min·m2), and supply time (min): Types of liquids to be handled: Proteins, fluoroproteins – 6.5/15; Water-insoluble liquids, water-based film-forming agents, film-forming fluoroproteins – 5.0/15; Alcohol-resistant foams – 12/15; Water-soluble liquids. This clause is new and has been formulated with reference to NFPA11-1998 \"Standard for Low-Expansion Foam Fire Extinguishing Systems\" and BS5306 Part6 \"Standard for Low-Expansion Foam Fire Extinguishing Systems\", among others. Due to the absence of restrictions such as cofferdams, the thickness of the flowing liquid is shallower, resulting in a lower difficulty level in extinguishing the fire per unit area compared to cases where cofferdams are present. Article 3.6.5 In addition to complying with the provisions of these specifications, fixed foam gun systems shall also meet the requirements of the Code for Design of Fixed Fire Pump Systems. Section 7: Hydraulic Calculations Article 3.7.1: The foam mixture flow rate for foam generating devices such as foam generators, high-backpressure foam generators, and foam nozzles should be calculated using Equation 3.7.1; it can also be determined based on the pressure-flow characteristic curve provided by the manufacturer. (3.7.1) In the formula: q — flow rate of the foam mixture (L/s) ； k—flow characteristic coefficient of the foam generation device ； P—Inlet pressure of the foam generation unit (MPa). This section is newly added. Paragraphs 3 of Article 3.2.4 and paragraph 3 of Article 3.3.3 of the original \"Specifications\" provided separate \"pressure–flow\" calculation formulas; these formulas are more suitable for the foam nozzles in foam spray systems, so they have been combined into one formula. This formula applies to different foam-generating devices in the “specifications”. The above calculation formula is given in accordance with the principles of the compilation specifications. However, aside from foam nozzles, most manufacturers currently do not provide the k coefficients for foam generators and high-backpressure foam generators; therefore, the flow rate of the foam mixture can also be determined using the pressure-flow curve. Article 3.7.2 The design flow rate of the foam mixture for foam fire extinguishing systems shall be calculated according to Equation 3.7.2 ； Q = k1Qj (3.7.2) Where: Q is the designed flow rate of the foam mixture in the system (L/s) ； k1—margin coefficient (k1≥1.05) ； Qj—calculated flow rate of the foam mixture in the system (L/s). The requirement of this clause is a general guideline aimed at ensuring that the actual flow rate is not lower than the calculated flow rate. Article 3.7.3 The flow velocity of the foam mixture in the pipes of the foam fire extinguishing system in the tank farm should not exceed 3 m/s ； The flow rate of the foam mixture in the pipes of the foam spray system should not exceed 5 m/s ； The foam flow rate in the foam pipeline prior to the foam nozzle of the submersible foam fire extinguishing system should be between 3 m/s and 9 m/s. This clause summarizes Articles 3.2.8 and 3.3.8 of the Far \"Specifications\", and with reference to BS5306 Part 6, specifies the flow rate of the foam mixture and the foam flow rate within the pipes of foam fire extinguishing systems. The foam in the pipes of submersible spray fire extinguishing systems is a fluid with highly unstable physical properties; its 25% liquid separation time is around 2 to 3 minutes. If the flow rate of this foam within the pipes is too low and its residence time is too long, it will inevitably lead to some liquid separating out, thereby affecting the fire extinguishing efficiency of the foam. Therefore, in the design of submersible spray fire extinguishing systems, the foam flow rate in the foam pipes should be increased as much as possible, provided that pressure losses are acceptable. A higher foam flow rate facilitates the stirring and mixing of the foam during flow, reducing liquid separation in the foam flow. Article 3.7.4 The pressure loss per unit length of the foam mixture pipeline shall be calculated using Equation 3.7.4: Where: i — pressure loss per meter of length of the foam mixture pipeline (MPa/m) ； V—Average flow velocity of the foam mixture in the pipe (m/s) ； D—Inner diameter of the pipe (m). This formula is the one specified in the \"Code for Design of Interior Water Supply, Drainage and Hot Water Supply\" for flow rates greater than 1.2 m/s; it is also adopted in the \"Code for Design of Automatic Fire Extinguishing Systems\" (GBJ84-85) and the \"Code for Design of Water Sprinkler Fire Extinguishing Systems\" (GB50219-95), and therefore it is adopted in this code as well. Article 3.7.5 The pressure loss of the foam ratio mixer shall be determined according to the parameters provided by the manufacturer. This clause summarizes the provisions of Paragraph 2 of the original Article 4.2.4, clarifying the principles for determining the pressure loss of foam proportioning mixers. Article 3.7.6 The pressure loss of the deluge valve should be calculated using Equation 3.7.6: (3.7.6) Where: hr — Pressure loss of the deluge valve (MPa) ； BR—Specific resistance value of the rain shower valve ； Qy—Foam mixture flow rate of the deluge valve (L/s). The provisions of the \"Code for Design of Water Sprinkler Systems\" (GB50219-95) have been adopted. This formula is used for foam systems equipped with deluge valves. Article 3.7.7 The local pressure loss in foam mixture pipelines can be calculated using the equivalent length method, or it can be estimated as 20%~30% of the total pressure loss along the system pipelines. The equivalent length of valves and fittings on the foam mixture pipeline can be taken as that of the valves and fittings on the water pipeline. Article 7.2.2 of the \"Code for Design of Water Sprinkler Fire Extinguishing Systems\" (GB50219-95) stipulates that the local head loss in pipes should be calculated using the equivalent length method, or as 20% to 30% of the total head loss along the pipe. Article 2.6.1 of the Code for Design of Building Water Supply and Drainage stipulates that when the water supply networks for domestic use, production, and fire protection are shared, the local head loss shall be 20% ； When it is the fire supply network for a fire hydrant system, the local head loss is 10% ； When a water supply network is shared for production and fire protection, the local head loss is 15%. Given that low-expansion foam fire suppression systems include tank farm foam systems and foam spray systems, a coefficient of 20% to 30% has been adopted. The foam system in the tank farm can use a lower limit, while foam spray systems equipped with deluge valves and filters should use an upper limit. Article 3.7.8 The hydraulic calculation of the foam pipes in a submersed foam fire extinguishing system shall comply with the following provisions: 1. The pressure loss in the foam pipes can be calculated using Equation 3.7.8 ； (3.7.8) Where: h—is the pressure loss per 10m of foam pipeline (Pa/10m) ； C pipe pressure loss coefficient ； Qp—foam flow rate (L/s). II. The foaming ratio of foam should be calculated on a hidden basis ； III. The pressure loss coefficient can be taken from Table 3.7.8-1 ； IV. The equivalent lengths of the valves and certain pipe fittings on foam pipes can be determined according to Table 3.7.8-2. Table 3.7.8-1: Coefficient of pressure loss for pipes – Pipe diameter (m), Coefficient c1: 100 → 12.9; 200 → 20.1; 500 → 21.4; 1000 → 0.555; 2500 → 0.210; 3000 → 0.111; 3500 → 0.071. Table 3.7.8-2: Equivalent length of valves and certain pipe fittings on foam pipes – Nominal diameter (mm), Type of fitting: 150, 200, 250, 300; Gate valve: 1.25, 1.50, 1.75, 2.00; 90-degree elbow: 4.25, 5.00, 6.75, 8.00; Swing check valve: 12.00, 15.25, 20.50, 24.50. This information is derived from parts of clauses 3.3.5 and 3.3.2(1) of the original specifications. Article 3.7.9 The head of the water supply pump for foam fire extinguishing systems, or the water supply pressure in the water supply pipes, shall be calculated using Equation 3.7.9: H=∑h+h0+hz (3.7.9) Where: H is the head of the foam fire pump or the water supply pressure in the water supply pipes (MPa) ； ∑h—The sum of the frictional pressure loss and the local pressure loss in the system pipes (MPa) ； h0—Operating pressure of the foam generation device at the most unfavorable point (MPa) ； hz—The static pressure difference (MPa) between the foam generation device at the most unfavorable point and the lowest water level of the fire tank or the centerline of the supply pipeline inlet. Chapter 4 System Components Section 1 General Provisions Article 4.1.1 System components such as foam fire pumps, foam proportioning mixers, foam liquid pressure storage tanks, foam generators, valves, and pipelines must be products that have passed the inspection by the **-level Fire Product Quality Supervision and Inspection Center. Article 4.1.2 The coloring of the main components of the system shall meet the following requirements: 1. The foam liquid pump, foam mixture pipelines, foam liquid storage tanks, foam proportioning mixers, and foam generators shall be painted red ； II. Paint foam fire pumps and water supply pipes green. Note: When there are many pipes and coloring conflicts with the process piping, corresponding color strips or rings can also be applied. Section 2: Foam Fire Pumps and Foam Proportioning Mixers Article 4.2.1: For foam fire pumps, centrifugal pumps with a gentle characteristic curve are preferred; when a ring-type proportioning mixer is used, the rated flow rate of the pump should be 1.1 times the system’s designed flow rate ； When a hydraulically driven balanced pressure proportional mixer is used, its flow rate consumption should be included in the pump’s rated flow rate. The hydraulically driven balanced pressure proportioning mixer is powered by the pressure water of the system itself; its water consumption is related to the type of foam concentrate used (3% or 6%). When selecting a pump, it is necessary to take into account the water flow rate required by the proportioning mixer based on the specific design. Article 4.2.2 A vacuum pressure gauge or vacuum gauge shall be installed on the inlet pipe of the foam fire pump. A pressure gauge, a check valve, and a return pipe with a control valve should be installed on the outlet pipe of the foam fire pump. Article 4.2.2A: The foam proportion mixer selected shall ensure that the mixing ratio of the foam mixture within the designed flow rate range is not less than its rated value, nor more than 30% of its rated value; furthermore, the difference between the actual mixing ratio and the rated mixing ratio shall not exceed 1 percentage point. At present, the lack of requirements regarding the mixing ratio of the foam mixture in some foam systems results in too low a mixing ratio, which reduces the reliability of those systems ； In some systems, the mixing ratio of the foam mixture is too high, which results in waste of foam solution and is detrimental to submersible spraying systems. To this end, this clause is formulated with reference to NFPA 11-1998, the Standard for Low-Expansion Foam Extinguishing Systems. The meaning is that, when the rated mixing ratio is 3%, the actual mixing ratio should be between 6% and 7%. Section 4.2.2 B: The inlet operating pressure of the foam ratio mixer shall be within the specified operating pressure range. The operating pressure range at the inlet of the foam ratio mixer is provided by the manufacturer and is usually indicated in the product manual. Article 4.2.3 When a ring-pump type foam proportioning mixer is used, the following requirements shall be met: 1. The outlet back pressure should be zero or negative; when the inlet pressure is 0.7–0.9 MPa, the outlet back pressure can be 0.02–0.03 MPa ； II. The liquid suction port shall not be 1 m above the lowest liquid level of the foam liquid storage tank ； III. When the back pressure at the outlet of the proportional mixer is greater than zero, measures should be in place on its liquid intake pipe to prevent water from flowing back into the foam liquid storage tank ； IV. The installation of proportional mixers should be equipped with at least one spare unit. Article 4.2.4 When a pressure proportional mixer is used, the following requirements shall be met: 1. The volume of a single tank in the pressure proportional mixer should not exceed 10 m3 ； II. For non-cyst-type pressure proportional mixers, when the volume of a single tank is greater than 5 m3 and there are no partitioning devices within the tank, it is advisable to install a pressure proportional mixer with a smaller volume; this mixer should have a volume of more than 0.5 m3 and be capable of supplying foam mixture at the maximum designed flow rate for 3 minutes continuously. I. In engineering practice, there have been instances where, in pressure proportional mixers, problems such as water inlet issues, control valves that are difficult to open due to their large diameter, and bladder leakage or even rupture have occurred. To reduce costs, some projects use pressure proportioning mixers with very large capacities, some exceeding 25 m3; should such mixers fail, the foam system in place will become non-functional. These restrictive provisions were formulated based on the principles of economy, safety and reliability, as well as ease of use. II. Facilitates engineering inspection and routine testing. Article 4.2.5 When a balanced-pressure foam proportioning mixer is used, the following requirements shall be met: 1. The pressure at the foam inlet of the proportioning mixer shall be higher than the pressure at the water inlet, but the pressure difference shall not exceed 0.2 MPa ； II. A check valve should be installed on the foam liquid inlet pipe of the proportional mixer. III. When a hydraulically driven foam liquid pump is used, a backup pump is not required ； When using a foam liquid pump powered by another power source, a backup pump should be installed, and the power source must meet the requirements of Article 3.5.5 ； IV. Flushing and venting pipes should be provided on the foam liquid pipeline. The first two paragraphs of this article set out the principle-based requirements for such a proportional mixer; the third paragraph was formulated taking into account the reliability of hydraulically driven foam liquid pumps compared to electric pumps; the fourth paragraph ensures that the system is rinsed thoroughly with water after use or testing, so that no residual liquids remain. Article 4.2.6 When a pipeline-type foam proportioning mixer is used, it shall be connected in series to the fire hose, and its outlet pressure shall meet the requirements of the inlet pressure of the foam equipment. Section 3: Foam Liquid Storage Tanks Article 4.3.1 When a ring pump or balanced-pressure foam proportioning system is used, foam liquid storage tanks should be atmospheric pressure tanks ； When a pressure-type foam proportioning system is used, a pressure tank should be selected for the foam liquid storage tank. Article 4.3.2 Foam liquid storage tanks should be made of corrosion-resistant materials ； When steel tanks are used, their inner walls must be treated to prevent corrosion; the inner walls that come into direct contact with the foam solution, or the anti-corrosion coating on those walls, should not have an adverse effect on the properties of the foam solution. I. Protein-based foams contain inorganic salts, small amounts of hydrocarbon and fluorocarbon surfactants, as well as other additives; during storage, they primarily have a corrosive effect on metals. Aqueous film-forming foams contain a high proportion of hydrocarbon surfactants, fluorocarbon surfactants, and organic solvents. Over time, these hydrocarbon surfactants and organic solvents not only cause corrosion to metals but also have a strong effect of dissolving, swelling, and penetrating many non-metallic materials. If the material used for the inner walls of the foam storage tank does not meet the required standards, it will **reduce the service life of the tank. II. Certain materials or anti-corrosion coatings have an adverse effect on the performance of foam agents, with carbon steel having the greatest impact on the performance of water-based film-forming foams. When aqueous film-forming foam is in prolonged contact with carbon steel, the iron ions present can degrade the fluorocarbon surfactants; therefore, the foam should not come into direct contact with carbon steel storage tanks. Many non-metallic material molecules or ions dissolved in hydrocarbon surfactants and organic solvents that enter the foam also affect its properties. Therefore, when selecting the material for the inner wall of the foam liquid storage tank or the anti-corrosion coating, special attention should be paid to ensuring that it is suitable for the type of foam liquid being used; otherwise, it will **shorten the effective storage period of the foam liquid and significantly reduce its fire-fighting effectiveness. Article 4.3.3 At normal pressure, storage tanks should preferably be horizontal or vertical cylindrical tanks, and they should be equipped with a level gauge, slag discharge ports, feed ports, manholes, sampling ports, a vent valve, or a vent pipe with a control valve. The pressure storage tank should be equipped with a safety valve, slag discharge hole, feed hole, manhole, and sampling hole. Section 4: Foam Generators Article 4.4.1 Foam generators shall meet the following requirements: 1. The operating pressure at the inlet of the foam generator shall be its rated value ±0.1 MPa. II. Foam generators and outdoor foam nozzles shall be equipped with metal screens to prevent foreign objects from entering ； III. There should be a straight pipe section of at least 1m in front of the foam generator inlet ； IV. Foam generators on external floating roof storage tanks shall not be equipped with sealed glass. 1. This clause is derived from parts of Paragraph 3 of Article 3.2.4 of the original “Specifications,” and it was formulated to ensure that the foam generator operates under reasonable pressure. II. Prevent blockage of the foam generator or foam nozzle. III. It facilitates the proper operation of the foam generator; otherwise, it will cause scattering of the foam mixture. IV. External floating roof storage tanks do not have any space containing explosive gases; therefore, the sealed glass installed on foam generators is not only useless but may also interfere with foam emission. Article 4.4.2 High-backpressure foam generators shall meet the following requirements: 1. The inlet operating pressure shall be within the specified operating pressure range ； II. The pressure required for export should be greater than the sum of the resistance of the foam pipeline and the hydrostatic pressure of the liquid in the tank ； III. The foaming ratio of the foam should not be less than 2 times, nor greater than 4 times. One version is derived from Amendment 3 of Clause 3.3.3 of the original standards; the operating pressure range at the inlet of the foam generator is provided by the manufacturer and is usually indicated in the product manual. The other two versions correspond to Amendment 2 of Clause 3.3.3 of the original standards, while the third version was formulated based on testing experience and foreign engineering standards. Article 4.4.3 The operating pressure of foam nozzles shall be within the specified operating pressure range, and shall not be less than 0.8 times their rated pressure. Too low pressure reduces the foam ratio. Section 5: Valves and Pipes, Article 4.5.1: When the diameter of the outlet pipe of the foam fire pump is greater than 300 mm, electric, pneumatic, or hydraulic valves should be used. The valve should have clear opening and closing indicators. Article 4.5.2 Pipes for foam and foam mixtures shall be made of steel pipes. The outer wall of the pipeline should be treated for corrosion prevention, and asbestos rubber gaskets should be used at its flange connections. Appendix I: Glossary of Terms

**Low-expansion foam**: A fire-fighting foam with an expansion ratio of no more than 20.
**Surface-foam injection system**: A fire-fighting system in which foam is injected into the tank from the surface of the liquid.
**Subsurface-foam injection system**: A fire-fighting system in which foam is injected into the tank from below the liquid surface.
**Foam mixture**: An aqueous solution formed by mixing foam concentrate and water in a certain proportion.
**Fixed foam fire extinguishing system**: A fire-fighting system consisting of a fixed foam pump, a foam proportioning mixer, a foam generator, and pipes.
**Semi-fixed foam fire extinguishing system**: A fire-fighting system composed of a fixed foam generator, a foam truck or mobile pump, connected by hoses.
**Mobile foam fire extinguishing system**: A fire-fighting system made up of a fire truck or mobile pump, a foam proportioning mixer, a mobile foam generator, all connected by hoses.
**Fixed-roof tank**: A vertical cylindrical tank with a fixed roof.
**External floating roof tank**: A tank whose roof floats on the surface of the liquid and can move up and down with the liquid level.
**Internal floating roof tank**: A tank that has a fixed roof as well as an internal floating roof.
**Dual-disc floating roof**: A floating roof that consists of multiple compartments separated by partitions.
**Single-disc floating roof**: A floating roof that has only some compartments.
**Shallow-disc floating roof**: A floating roof that is disc-shaped without any compartments.
**Foam spray system**: A fixed fire-fighting system that uses nozzles to spray foam.
**High-backpressure foam generator (i.e., subsurface-foam generator)**: A device through which air can be drawn into the foam mixture, resulting in low-expansion foam; its outlet has a certain pressure (gauge pressure).
**Mixing ratio**: The volume percentage of foam concentrate in the foam mixture.
**Semi-subsurface-foam injection system**: A foam fire-fighting system in which foam is injected from the bottom of the tank and rises to the surface of the liquid fuel via hoses.
**Balanced-pressure proportioning device**: A proportioning device in which a separate foam concentrate pump injects foam concentrate into the pressurized water stream according to a set pressure difference; it automatically controls the mixing ratio over a wide range of water flow pressures or volumes, using balance valves, orifice plates, or Venturi tubes (or a combination of these). Appendix II Explanation of Terms Used in This Specification I. To facilitate differentiated treatment when implementing the provisions of this specification, the terms with varying degrees of strictness are explained as follows: 1. Terms indicating a very high level of strictness, where action is mandatory: The positive term used is “must”” ； The opposite term is “strictly prohibited”. 2. Words indicating strictness, meaning that this should be done under normal circumstances: the positive term is “should”” ； The negative form uses “should not” or “must not”. 3. Words indicating that slight choice is allowed, and that this should be done first when conditions permit: positive terms are “should” or “may”” ； The antonym is “not suitable”. II. When the provisions state that compliance with other relevant standards or specifications is required, it should be expressed as “shall be carried out in accordance with…”) or “shall meet the requirements of…”. This post was last edited by hw197358 on 2009-3-4 13:34.]