Design issues of automatic **fire extinguishing systems for warehouse hazard levels

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　Automatic **fire extinguishing systems are the most widely used fixed fire suppression systems. With economic development, the design of warehouse hazard levels will be encountered more and more often. The current code, the \"Code for Design of Automatic **Fire Extinguishing Systems\" (GB50084-2001), contains few provisions regarding the hazard level of warehouses; improper design can directly affect the effectiveness of the system. 1. The boundary between the high-risk and medium-risk categories for warehouses is determined by the fire hazard in that location. Warehouse, Risk, System, Sprinklers. Detailed information: Automatic **fire suppression systems are the most widely used type of fixed fire protection system. With economic development, the design of warehouse hazard levels will be encountered more and more often. The current code, the \"Code for Design of Automatic **Fire Extinguishing Systems\" (GB50084-2001), contains few provisions regarding the hazard level of warehouses; improper design can directly affect the effectiveness of the system. 　　1. The boundary between the high-risk and medium-risk categories for warehouses: The fire risk level of a given location should be determined based on factors such as its purpose, the fire load associated with the items stored there, and the interior space. This is done after analyzing the characteristics of fires and the difficulty of triggering the activation of sprinklers due to heat currents. 　　According to the current regulations in our country, Category I hazardous items in warehouses include food, tobacco, and alcohol ； Non-flammable and slow-burning items packed in wooden or cardboard boxes, shelf areas in warehouse-style shopping malls, etc. Shopping malls with a total construction area of 5,000 m2 or more are classified as medium-risk level II. There are differing views regarding the classification of the hazard level in supermarkets and mall warehouses: some consider it to be of medium hazard level, while others classify it as a warehouse hazard level. Reference 1 classifies the fire hazard levels of warehouses into Grade I, Grade II, Grade III, Grade IV, and Plastic and Rubber categories (A, B, C), based on factors such as the type and size of the stored items, the way they are arranged (degree of density and stacking height), the packaging materials and methods used, and the type of shelving. The appendix lists a large number of categories, making it easy to make appropriate classifications during design. The United States has strict limits on the stacking height in warehouses; generally, when the stacking height is 3.7 m or less, it can be designed using the design parameters for medium or high hazard levels, as detailed in Reference 2. When the specified stacking height is exceeded, the warehouse design parameters should be used. 　　2 Advantages and inappropriate applications of ESFR nozzles for rapid response to early suppression ESFR nozzles were developed in response to the increasing number of automated warehouse systems; warehouse owners need to meet customers’ requests to change the storage space on the shelves within these warehouses, and the structure of those shelves often changes. It turns out that the protection mechanism provided by multiple sprinklers located on different levels within the shelves is not sufficient to meet the requirements. As an insurance company, FM promotes the use of this system in warehouses around the world. Numerous fire suppression tests have shown that, despite the relatively high flow rate of these sprinklers, their rapid response during the early stages of a fire enables them to effectively extinguish severe fires in warehouses, thereby protecting the shelves and the structural elements of the buildings. Fire damage is minimal, smoke damage is minimal, and water damage is minimal. One of the most important features of the ESFR sprinkler system is that it is designed without sprinklers built into the shelves. In the automated logistics warehouse of a tobacco factory, both ESFR sprinklers under the ceiling and sprinklers inside the shelves were installed; such a design is incorrect. ESFR sprinklers should not be used in the following locations: warehouse shelves with solid partitions, and warehouse shelves that contain flammable materials, cartons with open tops, containers, etc. Tyco Group Central Company in the United States recommends a usage height of 7.6m–13.7m. 　　3 Selection of pipe diameter in systems with fast-response early suppression (ESFR) nozzles: For warehouses classified as Category II, the minimum operating pressure for ESFR nozzles is 340 kPa; the K value for these nozzles is 200, and their flow rate is 6.15 liters per second. Therefore, the connection pipe between the nozzle and the branch pipe should have a diameter of at least DN50, with DN80 being preferable. If calculated based on 4 nozzles operating on each of the 3 branch pipes, the flow rate per branch pipe exceeds 25 liters per second; therefore, in an ESFR nozzle system, the diameter of the branch pipes should not be less than DN100, while the diameter of the main pipe can be up to DN200. When the system is large, a ring-shaped piping network is advisable to reduce investment. If designed according to a conventional ordinary control-type sprinkler system, with the maximum diameter of the branch pipes being DN50 and the connection tubes between the sprinklers and these branch pipes having a diameter of DN25, such an ESFR system will definitely not function properly. 　　In addition to controlling the distance between the ESFR sprinkler and the roof of the building, it is also necessary to strictly control the distance between the ESFR sprinkler and obstacles. Only pendant-type ESFR sprinklers are produced domestically; imported ESFR sprinklers are mainly of the pendant type, with the upright type being rarely used. If conventional ordinary control-type nozzles are designed to be upright, the ESFR system is ineffective. 　　4 System selection for fast-response early suppression (ESFR) nozzles ESFR nozzles are suitable only for wet-type fire extinguishing systems; they are not appropriate for dry-type systems or pre-action systems. Using ESFR sprinklers in tobacco warehouses to design a pre-action system will pose safety risks. 　　5. The effect of smoke exhaust on early suppression by ESFR sprinklers. Ventilation openings that expel hot air during a fire can delay the activation of ESFR sprinklers, resulting in increased water consumption; in some cases, this can even lead to the fire growing to such an extent that the ESFR sprinklers are no longer able to control it. 　　Manual operating devices shall be provided for permanent ventilation openings. If local regulations require the installation of automatic control devices, temperature-controlled operating equipment with an operating temperature of 180°C or 141°C can be used to open the ventilation openings. 　　6 Installation of water pump connectors Warehouse hazard level: II. **The maximum water consumption of the fire suppression system is nearly 90 L/s. Based on the water volume, 6 pump connectors are required; operating 6 pumps in parallel will result in a significant decrease in water supply efficiency. ESFR is a fire-extinguishing sprinkler head. According to information from Tyco Group’s Central Company in the United States: “Based on FM fire tests, the number of activations for ESFR sprinklers that successfully extinguished the fire ranged from 1 to 11.” The operation time for the first sprinkler head is 40 seconds to 1 minute, while the operation time for the last sprinkler head is 40 seconds to 7 minutes and 4 seconds. With a water pump coupling, its effectiveness due to the delay in water supply from fire trucks is questionable. Should there be a difference in the installation of water pump connectors for fire-suppression nozzles and fire-control nozzles?