【Haichuan Construction Drawing Review】-- Special section on safety design for hazardous chemicals: Accident water tank

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【HaiChuan Building Design Review】Compilation Post–Understand design review requirements and improve standardized design https://bbs.hcbbs.com/forum.php?mod=viewthread&tid=5721370 (Source: HaiChuan Chemical Industry Forum (HuaHaiChuanLiu hcbbs)). Chemical accident tanks (also known as emergency accident tanks or accident buffer tanks) are key environmental protection facilities used by chemical enterprises to collect, store, and treat highly concentrated polluted wastewater generated in case of sudden environmental incidents. Its primary purpose is to prevent accident wastewater (such as leaked materials, fire-fighting cooling water, polluted rainwater, etc.) from being discharged directly into the environment or entering sewage treatment systems, thereby ensuring water quality and ecological stability. Is it a safety facility? It can be said that, basically, there is no controversy; of course, it can also be referred to as environmental protection facilities. The relevant standards all specify specific requirements for implementation. For example, according to the \"Code for Design of Water Supply and Drainage Pipelines in the Chemical Industry GB50873-2013\", \"3.1.8 The accident fire-fighting drainage pipelines in polluted areas such as production units and tank farms can be installed in conjunction with production wastewater pipelines and rainwater pipes (channels), or independently; however, they shall not pass through explosion-proof areas\" ； When crossing is unavoidable, protective measures should be taken. ”Explanation of the provisions: 3.1.8 In an accident scenario, in addition to collecting fire-fighting wastewater and materials that leak during an accident, the accident tank and the collection piping system for accident wastewater must also be capable of capturing rainwater under such conditions. If the entry of rainwater is to be taken into account, special fire emergency drainage pipes with larger diameters and longer lengths must be installed; otherwise they would remain idle during emergency situations, which is not economically reasonable ； For the same reason, the flow rate of wastewater generated is usually low, and the diameter of the drainage pipes is relatively small. When considering the inflow of rainwater in emergency situations, the diameter of the existing wastewater pipes is insufficient to meet the requirements, necessitating an expansion of the pipe diameters – which is not economically viable. Therefore, in design, the production wastewater pipes and stormwater pipe (channel) systems are often used concurrently as collection systems for emergency drainage, which is currently a relatively economical and reasonable choice. Another example is the \"Code for Fire Protection Design of Petrochemical Enterprises GB50160-2008 (2018 Edition)\”, where \"4.2.8A\" states that accident ponds and rainwater monitoring ponds should be located in the lower areas at the edge of the plant site, and can be arranged together with the sewage treatment facilities. The fire protection distance between the accident tank and open flames should be no less than 25 m, and the fire protection distance from elevated flares that may carry flammable liquids should be no less than 60 m. ”Explanation of the provision: 4.2.8A The accident pool is primarily used to collect contaminated fire-fighting water under fire conditions, polluted rainwater, and any combustible liquids that may leak. Accident water and rainwater generally flow by gravity through pipelines to the accident water tank and the rainwater monitoring tank; therefore, these tanks should be located at lower positions on the edge of the plant area. Accident water and rainwater that fails to meet monitoring standards must be treated and rendered compliant before being discharged from the plant. Centralizing them with the sewage treatment plant can reduce pipeline length and contribute to energy conservation and consumption reduction. Since a fire accident may be accompanied by a leak of flammable liquids, fire separation distances have been specified between the accident pool, open flames, and elevated flares that may carry flammable liquids. Since the accident pool remains empty for long periods of time, no fire separation distance is required from other facilities.