Fire hazard of sulfuric acid

The explanations in the Code for Fire Protection Design of Non-ferrous Metal Engineering GB50630-2010, as well as the requirements regarding fire protection and corrosion resistance, are quite professional: In terms of process technology, a substance in which SO3 is combined with H2O in any ratio is referred to as sulfuric acid; when the molar ratio of SO3 to H2O is ≤1, it is called sulfuric acid； When the molar ratio > 1, it is called fuming sulfuric acid. Fuming sulfuric acid refers to concentrated sulfuric acid that contains free sulfur trioxide; under normal conditions it continuously releases SO3 into the atmosphere, which reacts directly with reducing substances in the environment, leading to oxidation and exothermic combustion of those substances. Therefore, the fire hazard category for locations where fuming sulfuric acid is stored and used is Class B. In non-ferrous metal engineering, the sulfuric acid produced by flue gas acid production is mainly concentrated sulfuric acid (98% by volume), which is primarily used for export (with a certain amount stored for internal use). In hydrometallurgical processes, dilute sulfuric acid (with a concentration of 60% or less) is commonly used, which is prepared from concentrated sulfuric acid. Sulfuric acid exhibits significant differences in chemical properties depending on its concentration. Concentrated sulfuric acid has strong oxidizing properties; it can react with almost all metals (except gold, platinum, iron, etc.), and it reacts violently when in contact with certain organic substances, releasing heat that can cause fires. On the other hand, dilute sulfuric acid solution exists in ionic form and has the property of undergoing displacement reactions with active metals. Dilute sulfuric acid can react with metals to form salts and release hydrogen gas (it can even react upon contact with unprotected metal containers). One is thick and the other is thin; their properties are very different. The fire hazard associated with sulfuric acid as a medium cannot be ignored. In the long-term practice of non-ferrous metal production, sulfuric acid (both concentrated and dilute) is an important medium (or by-product) in the production process. Due to its excellent chemical properties as a strong acid, it is indispensable in the wet metallurgy of non-ferrous metals. Therefore, engineering design must carefully address the issue of protecting against sulfuric acid corrosion in a targeted manner, so as to make the best use of advantages while minimizing disadvantages. Over the years, in all aspects of its production, storage, transportation, and use, corrosion prevention techniques have played a crucial role in non-ferrous metal engineering projects. Engineering design follows the relevant provisions of the current **standard \"Code for Corrosion Protection Design of Industrial Buildings\" GB50046, by adopting targeted and reliable corrosion protection measures. At the same time, proper construction and installation are carried out, along with timely maintenance and effective management. Decades of practice have shown that in the non-ferrous metals industry, the production and use of sulfuric acid are continuously expanding in terms of scale and volume. The protective measures implemented for various facilities are safe and reliable, with significant results. Although the investigation found that non-ferrous metal enterprises had also experienced related combustion and explosion accidents (for example, in the flue gas acid production of one enterprise, damage to the anti-corrosion layer of the converter led to acid leakage; this acid came into contact with the steel casing, resulting in a reaction that released hydrogen gas, which ignited and caused an explosion, thereby blowing off the top cover of the converter). Meanwhile, similar accidents have also been reported in other industries (for example, at a chemical plant, an explosion occurred while diluting the residual concentrated acid in an existing storage tank for concentrated sulfuric acid and cutting the tank body with an acetylene flame). At their root, they are clearly caused by maintenance errors, poor management, and improper operations, with a high degree of randomness. Through theoretical and practical analysis, it can be determined that in workshops (locations) where sulfuric acid is used in the non-ferrous metal industry, process units, equipment, and pipelines must comply with **the relevant current industry requirements. The factories, structures, and various facilities therein shall comply with the provisions of the current **standard, the ‘Code for Corrosion Prevention Design of Industrial Buildings’ GB50046. When the appropriate anti-corrosion standards are met (including an effective protective coating, a proper structure, prevention of leaks, and the use of dikes around storage tanks), the objective conditions for combustion (explosion) are essentially eliminated; therefore, in the example table above, the production fire hazard category for plants (locations) where sulfuric acid is produced, used, and stored is classified as Class C. At the same time, given that sulfuric acid remains a fire hazard even in environments with inadequate protection, it is essential to establish strict and comprehensive maintenance and management systems for sulfuric acid facilities. Measures such as regular maintenance, routine checks for leaks, the proper construction of fire dikes in areas where sulfuric acid is stored, and strict prohibitions on carrying out welding or other flammable activities are all very necessary.