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Hazardous chemicals are prone to fires and explosions. Moreover, the methods of extinguishing fires involving different chemicals under various conditions vary significantly. If not handled properly, these methods may fail to put out the fire; instead, they could exacerbate the situation. Furthermore, since chemicals themselves and their combustion products are largely highly toxic and corrosive, they can easily cause poisoning, burns, and other injuries to people. Therefore, extinguishing fires involving hazardous chemicals is a extremely important yet very dangerous task. In actual work, personnel involved in the production, use, storage, and transportation of chemicals should be familiar with and understand the main hazardous properties of these chemicals. In the event of a fire, every worker must clearly know their roles and responsibilities. It is essential to have a thorough command of the appropriate firefighting measures to be taken when a fire occurs. Generally speaking, when fighting chemical fires, the following points should be noted first: firefighters should not act alone ； The entrances and exits at the accident scene should always be kept clean and unobstructed ； It is necessary to select the correct fire extinguishing agent and appropriate fire-fighting equipment ； The safety of personnel must always be considered when fighting fires. One must never act blindly when fighting fires involving hazardous chemicals. For each type of chemical, the correct extinguishing agent and appropriate firefighting equipment should be selected to safely control the fire. The extinguishing of chemical fires must be carried out by professional fire brigades. Other personnel should not act rashly; they should wait for the professional fire brigade to arrive and assist in the firefighting. I. General requirements for fighting fires involving hazardous chemicals: Personnel involved in the production, operation, storage, transportation, loading/unloading, packaging, and use of hazardous chemicals, as well as those responsible for disposing of such waste, along with firefighters and rescue workers, should be familiar with and understand the main hazardous properties of these substances and the corresponding methods for extinguishing fires. Only by knowing oneself and the enemy, and taking preventive measures, can one succeed in extinguishing fires involving various hazardous chemicals. The general principle for extinguishing fires involving hazardous chemicals is: control first, then extinguish. In light of the characteristics of hazardous chemical fires, such as rapid spread of the fire and large burning areas, firefighting tactics that involve unified command, acting swiftly to contain the fire and prevent its spread, making focused efforts to eliminate threats, encircling the fire source, and resolving the situation quickly are employed. Firefighters should take positions upwind or crosswind to avoid exposure to toxic and harmful gases. When conducting fire reconnaissance, fighting fires, and evacuating people from fire scenes, appropriate self-protection measures should be taken, such as wearing protective masks and special protective clothing. It is necessary to promptly determine the extent of the fire, the names and main hazardous characteristics of the burning materials and those in their vicinity, as well as the main pathways of fire spread. Correctly select the most suitable extinguishing agent and method. When a fire is large in scale, it is necessary to first contain its spread and limit the area of combustion, and then gradually extinguish it. In situations involving particular dangers such as explosions, ruptures, or splashes that require an immediate evacuation, evacuation must be carried out promptly using unified evacuation signals and methods (the evacuation signals should be highly visible so that all people on site can see or hear them, and regular drills should be conducted in advance). After the fire is extinguished, the unit where the fire occurred shall protect the scene, cooperate with the investigation, assist the public security fire supervision department and the work safety supervision department in determining the cause of the fire, assessing the losses incurred, and identifying those responsible. Without the consent of the public security supervision department and the work safety supervision department, no one may tamper with or clean up the fire scene. II. Basic measures for extinguishing fires involving compressed or liquefied gases. Liquefied gases are generally stored in various containers or transported through pipelines. In the event of a fire, the following basic measures should be taken: When fighting gas fires, it is crucial not to attempt to extinguish them blindly; without taking measures to seal leaks, it is necessary to allow the fire to burn steadily. Otherwise, flammable gases may leak out and mix with air; upon encountering a source of ignition, an explosion could occur, with unimaginable consequences. First, the large fires in the surrounding areas that have been ignited by the source of fire must be extinguished, so as to cut off the pathways for the fire to spread, control the extent of the combustion, and immediately rescue those who are injured or trapped. If there are pressure vessels in the fire, or pressure vessels at risk of being exposed to radiant heat from the flames, they should be evacuated to a safe area, if possible, under the protection of water streams. In the event of a leak and fire in a gas pipeline, efforts should be made to locate the gas source valve. Once it is confirmed that the valve is intact, closing the valve will cause the flame to extinguish automatically. When the valves for stopping leaks in storage tanks or pipelines are ineffective, it is necessary to assess the gas pressure as well as the size and location of the leak based on the intensity of the fire, and to prepare appropriate materials for sealing the leak (such as cork plugs, rubber plugs, airbag plugs, adhesives, pipe-bending tools, etc.). Once leak-sealing preparations are complete, effective measures can be taken to extinguish the fire. After the fire is put out, leak-sealing materials should be used immediately to seal the leak, while misted water should be applied to dilute and disperse any leaked gases. If the leak is large enough to be impossible to seal, measures can be taken to cool the container on fire as well as the surrounding containers and flammable materials, thereby controlling the scope of the fire until the gas is exhausted, at which point the flame will extinguish itself. The on-site commander should pay close attention to various signs of danger; once the situation deteriorates, the commander must make an accurate judgment and issue an order to retreat promptly. III. Basic strategies for extinguishing fires involving flammable liquids Flammable liquids are usually stored in various containers or transported through pipelines. Unlike gases, liquid containers can be either sealed or open. It is usually at atmospheric pressure, with only the liquid pressure inside the reaction vessels (reactors, kettles) and delivery pipes being higher. Flammable liquids have properties such as specific gravity and water solubility, which relate to the question of whether they can be extinguished using water and ordinary foam, as well as the serious risks of boiling over and splashing. Therefore, fighting fires involving flammable liquids is a very difficult battle. The following basic measures are generally taken: First, cut off the pathways for the fire to spread, cool down and evacuate pressure vessels, sealed containers, and flammable materials that are at risk from the fire, in order to control the scope of the combustion. In case of any liquid leakage, dikes should be built (or oil booms used) to contain it, or trenches should be dug to divert it. It is necessary to promptly understand and determine the name, specific gravity, solubility of the burning liquid, as well as any hazards such as toxicity, corrosiveness, boiling over, or splashing, so as to take appropriate fire-fighting and protective measures. For larger storage tanks or flowing fires, the area on fire should be accurately determined. For small-scale liquid fires (typically within 50 square meters), fog-type water spray can generally be used to extinguish them. Using foam, dry chemical, carbon dioxide, or halon (1211, 1301) to extinguish fires is generally more effective. For large-scale liquid fires, the appropriate extinguishing agent must be selected based on the liquid’s relative density (specific gravity), water solubility, and size of the burning area. Liquids with low specific gravity and insoluble in water (such as gasoline, benzene, etc.) are often impossible to extinguish using straight water or water mist. Ordinary protein foam or light water foam is generally used to extinguish fires. Water can be used to extinguish fires involving liquids that are heavier than water and insoluble in it; foam can also be used. The use of dry powder or halogenated alkane extinguishers depends on the size of the burning area and the burning conditions. Water-soluble liquids (such as alcohols and the like) can, in theory, be extinguished by dilution with water. However, for this method to effectively eliminate the liquid’s flash point, water must constitute a significant proportion of the solution. Therefore, water-resistant foam is generally used for extinguishing. When fighting fires involving flammable liquids that are toxic, corrosive, or have highly toxic combustion products, firefighters must wear protective masks and take other protective measures. When fighting fires involving liquids such as crude oil and heavy oil that pose a risk of boiling over and splashing, measures such as using water to stir and cool the mixture can be employed, if possible, to prevent boiling over and splashing. In the event of a fire caused by a leak in a pipeline or storage tank containing flammable liquids, while preventing the spread of the fire and confining it to a certain area, efforts should be made to locate and close the inlet and outlet valves of the pipeline. If the inlet and outlet valves of the pipeline are damaged or the storage tank is leaking, sealing materials should be prepared promptly to effectively extinguish the flames spreading on the ground and clear the way for sealing; afterwards, the flames at the leak site should be put out as well, and sealing measures should be taken immediately. IV. Basic measures for extinguishing fires involving explosives. Fires involving explosives can be extinguished using water, air foam (high-expansion foam is preferable), carbon dioxide, dry powder, and other extinguishing agents; water is the best extinguishing agent. Water can penetrate into the interior of explosives, forming a pliable, soft film on the surface of the crystals; this film surrounds the crystals and renders them less sensitive. In the event of a fire involving explosives, the primary measure is to cool them using large amounts of water. It is prohibited to cover them with sand; steam and acid-base foam extinguishers must also not be used to put out the fire. In case of a fire inside a room, carriage, or cabin, promptly open all doors, windows, carriage doors, and hatch covers, then spray water inward to cool the area. Under no circumstances should doors, windows, carriage doors, or hatch covers be closed to smother the fire. Be sure to make use of cover. In a fire, walls, low-lying areas, tree trunks, etc., can be utilized for protection to prevent injuries. Since some explosives are not only toxic in themselves, but their combustion products are also toxic, precautions must be taken to prevent poisoning during fire-fighting efforts: when fires involving toxic explosives occur, isolative oxygen or air respirators should be worn to prevent poisoning. **Products generally have dedicated or temporary storage warehouses. Due to the presence of explosive elements in their internal structure, such items are highly prone to explosion when exposed to external factors such as friction, impact, vibration, or high temperatures; they become even more dangerous in the presence of an open flame. In the event of a **material fire**, the following basic measures are generally taken: promptly assess and determine the likelihood and risks of a secondary explosion; seize the favorable opportunity that exists after the initial explosion but before any subsequent explosion occurs; and take all possible measures to prevent such a secondary explosion from happening. Never cover it with sand or soil, as this may increase the explosive power of the **item. If evacuation is possible and personal safety can be reliably ensured, efforts should be made promptly to evacuate the items surrounding the area where the fire is occurring, thereby creating a buffer zone around it. When extinguishing a fire involving stacks of ** products, water should be sprayed from above to prevent the forceful stream from directly hitting the stacks; this helps avoid collapse of the stacks, which could lead to a secondary explosion. Firefighters should make use of any cover available at the scene or shoot water from a low position such as lying down, while paying attention to taking self-protection measures. When firefighters detect a risk of another explosion, they should immediately report it to the on-site commander; once confirmed by the commander, an order to evacuate should be given right away. V. Basic measures for fighting fires involving oxidizers and organic peroxides. From a fire-fighting perspective, oxidizers and organic peroxides constitute a miscellaneous category; they can be solids, liquids, or gases. Some oxides themselves are non-flammable, but can ignite or explode when exposed to combustible materials or acids and bases. Some peroxides (such as benzoyl peroxide, etc.) can ignite and explode on their own, posing a particularly high risk. Pay attention to personal protection when carrying out firefighting. Some different oxidizers and organic peroxides can be extinguished with water or foam, while others cannot ； Some cannot be extinguished using carbon dioxide, while almost none can be dealt with using acid-base fire extinguishing agents. In the event of a fire involving oxidizers and organic peroxides, the following basic measures should be taken: promptly determine the name, quantity, hazard level, combustion range, pathways for fire spread of the oxidizers, organic peroxides, and other combustible materials involved in the fire or reaction, as well as whether water or foam can be used to extinguish it. When it is possible to use water or foam to extinguish the fire, every effort should be made to control the spread of the flames, isolate the area affected by the fire, and limit the scope of the combustion. When water, foam, or carbon dioxide cannot be used to extinguish the fire, dry powder, cement, or dry sand should be used for covering. 1 Leakage handling: In the event of a leak of oxidizers or organic peroxides during transportation, they should be carefully collected or absorbed using inert materials. The residues should then be rinsed away with plenty of water at a location as far away as possible. The use of combustible materials such as sawdust and waste cotton yarn as absorbent materials is strictly prohibited to prevent fires caused by oxidation reactions. The collected leaks must not be reloaded into their original packaging or into intact packages, so as to prevent impurities from mixing in and causing hazards. Depending on their characteristics, they should be dealt with using safe and feasible methods or considered for burial underground. 2. Fire suppression: When an oxidizer catches fire or is involved in a fire, it releases oxygen that exacerbates the flames. Even in an inert gas environment, the fire will continue to burn. Sealing the cargo hold, containers, or storage areas, or using steam, carbon dioxide, and other inert gases to extinguish the fire is ineffective; using a small amount of water to put out the fire is also ineffective, as it can cause violent reactions of peroxides present in the materials. Therefore, a large amount of water or flooding with water should be used to extinguish the fire; this is the most effective method for controlling fires involving oxidizers. When organic peroxides catch fire or are involved in a fire, they can cause an explosion. Therefore, these packages should be promptly removed from the fire scene. Personnel should stay as far away from the fire as possible, and large amounts of water should be used to extinguish the fire at a protected location. Any packages containing organic peroxides that have been involved in a fire or exposed to high temperatures may undergo violent decomposition at any time, even after the fire has been extinguished, as long as the packages have not cooled down completely. If possible, these packages should be handled under the technical guidance of professionals; if such possibility does not exist, in cases of emergency during water transport, consideration should be given to dumping them into the water. VI. Basic measures for fighting fires involving toxic and corrosive substances. Toxic and corrosive substances are harmful to the human body to varying degrees. Poisons mainly cause poisoning in the human body through ingestion, inhalation of vapors, or skin contact. Corrosives cause chemical burns to the human body through skin contact. Toxic and corrosive substances: some of them can ignite on their own, while others do not ignite by themselves but can catch fire when in contact with other flammable materials. In case of a fire involving such items, the following basic measures should generally be taken: Firefighters must wear protective clothing and protective masks. For fires involving special materials, professional protective clothing should be used. When fighting fires involving toxic substances, it is advisable to use isolated oxygen or gas masks as much as possible. First, limit the scope of combustion. Fires involving toxic or corrosive substances can easily result in casualties. After taking protective measures, firefighters must immediately proceed to rescue the injured and trapped individuals, so as to minimize harm to people. During firefighting, use low-pressure water streams or foggy water whenever possible to prevent toxic or corrosive substances from splashing out. In case of acid or alkali corrosives, it is advisable to prepare a corresponding neutralizer to dilute and neutralize them. In the event of a leak from containers containing toxic or corrosive substances, sealing measures should be taken immediately after extinguishing the fire. Corrosive substances require anti-corrosion materials to seal leaks. Concentrated sulfuric acid and nitric acid release a large amount of heat when they come into contact with water, which can cause boiling and splashing; therefore, special precautions are necessary. 1. Emergency measures in case of fire involving toxic substances: Since the vast majority of organic toxic substances are flammable and produce large amounts of toxic or highly toxic gases when burned, it is very important to have appropriate emergency firefighting measures in such situations. Under normal circumstances, in the case of liquid toxic substances, anti-solvent foam, mechanical foam, or chemical foam can be used for extinguishing the fire, depending on the properties of the liquid (such as its water solubility and relative density), or measures such as sand, dry powder, or stone dust can be employed. For fires involving solid toxic substances, water, misted water, or sand, dry powder, and stone dust can be used to put out the fire, again depending on the properties of those solids. 2 Emergency measures in case of a fire involving corrosive substances: When a fire breaks out involving corrosive substances, it can generally be extinguished using misted water, dry sand, foam, or dry powder. High-pressure water should not be used to prevent the acid from splashing and injuring those trying to put out the fire. For substances such as sulfuric acid, halides, and strong bases that generate heat or decompose when exposed to water, or that produce acidic fumes when wet, water must not be used for extinguishing the fire; instead, dry sand, foam, or dry powder can be used. Firefighters must take precautions against corrosion and toxic gases; they should wear gas masks, protective goggles or face shields, rubber raincoats and long rubber boots, as well as corrosion-resistant gloves. When putting out a fire, one should stand upwind. If someone is found to be poisoned, they should be taken to the hospital immediately for treatment, and the name of the poisonous substance should be provided so that doctors can provide appropriate care. VII. Basic strategies for fighting fires involving radioactive materials. Radioactive materials are a type of special substance that emits alpha, beta, gamma rays and neutrons, which are invisible to the human eye but can cause severe damage to human life and health. To extinguish fires involving such items, special measures to protect against radiation exposure must be taken. First, send skilled personnel equipped with radiation testing instruments to measure the level and range of radiation. Testers must take protective measures. In areas where the radiation dose exceeds 0.0387 C/KG, warning signs stating “Life-threatening – No entry” should be installed. In areas with a radiation dose of less than 0.0387 C/KG, warning signs stating “Life-threatening – Do not enter” should be installed. For radioactive materials at the combustion site whose packaging is undamaged, it is possible to evacuate them by wearing protective gear under the cover of water guns. When evacuation is not possible, local cooling measures should be taken to prevent further damage and an increase in radiation exposure. Never move or wash the damaged container with water in order to prevent the spread of radioactive contamination. VIII. Basic strategies for extinguishing fires involving flammable solids and self-igniting materials. Some flammable solids and self-igniting materials are not only flammable in the presence of air, water, or acids, but they are also toxic; their combustion products are generally highly poisonous as well. Metals such as red phosphorus, yellow phosphorus, and calcium phosphide possess strong toxicity, and their combustion products, including phosphorus pentoxide and the flammable gas phosphine produced when they come into contact with moisture, are also highly poisonous. Phosphine has a smell similar to that of garlic, and inhalation of even 0.01 mg/L of this gas can cause poisoning. Therefore, when fighting fires involving flammable solids, self-igniting materials, and materials that become flammable when exposed to moisture, special attention must be paid to protection against poison and corrosion; appropriate protective equipment must be worn to ensure personal safety. 1 Flammable solids: In most cases, fires involving flammable solids can be extinguished using water. In particular, wet explosives, solids that may catch fire or contribute to the initiation of a fire through friction, as well as Class C flammable solids, can all be extinguished with water. As a backup, foam extinguishers, carbon dioxide extinguishers, dry powder extinguishers, and similar devices can also be used in emergency situations. For natural reactive substances such as aliphatic azo compounds, aromatic thioacylhydrazide compounds, nitroso compounds, and diazonium salts (e.g., azobisisobutyronitrile, benzene sulfonylhydrazide, etc.), since their combustion does not require oxygen from the external air, the smothering method cannot be used to extinguish them; it is best to cool them down with a large amount of water. In cases of fires involving powders of metal elements such as magnesium powder, aluminum powder, titanium powder, and zirconium powder, it is not possible to use water or carbon dioxide for extinguishing the fire. Because when such substances catch fire, they can generate extremely high temperatures; these high temperatures can cause water molecules or carbon dioxide molecules to decompose, thereby leading to explosions or intensifying the combustion. For example, when metallic magnesium burns, it can reach a temperature of 2500°C. When a burning magnesium strip is placed in carbon dioxide gas, magnesium reacts with the oxygen in the carbon dioxide to form magnesium oxide, while amorphous carbon is also produced. Therefore, when metal elements catch fire, water and carbon dioxide should not be used to extinguish them. Since phosphides such as tetraphosphorus trisulfide and diphosphorus pentasulfide decompose when exposed to water or humid air, producing flammable and toxic hydrogen sulfide gas, they cannot be extinguished using water either. 2 Self-igniting materials: Yellow phosphorus can be extinguished using water, and it is best to submerge it in water. Materials such as wet cotton, oilpaper, oilcloth, oil-treated fabric, and celluloid fragments, which pose a risk of self-ignition due to accumulated heat, can generally be put out with water when on fire. IX. Basic methods for extinguishing fires involving moisture-sensitive flammable materials. In the event of a fire involving such materials, it is absolutely forbidden to use water or water-based extinguishing agents; likewise, water-free extinguishing agents such as carbon dioxide, nitrogen, and halogenated hydrocarbons cannot be used either. Since the vast majority of moisture-sensitive flammable materials are alkali metals, alkaline earth metals, and their compounds, they are not only flammable when exposed to water but also generate very high temperatures during combustion. At such high temperatures, most of these substances can react with carbon dioxide and halogenated hydrocarbons; therefore, they cannot be used to extinguish fires involving moisture-sensitive flammable materials. For example, when carbon tetrachloride is brought into contact with burning sodium, a cloud of carbon vapor is immediately generated, causing the fire to burn more intensely. Nitrogen is non-flammable, non-toxic, and free of moisture, so it can be used to extinguish fires involving materials that are flammable when exposed to moisture. However, nitrogen can react directly with lithium metal to form lithium nitride, and it can also form calcium nitride with calcium metal at 500°C; therefore, it cannot be used for such purposes. Based on current research, the best extinguishing agent for fires involving moisture-sensitive materials is trimethyl borate. Dry sand, loam, dry powder, and stone dust can also be used. For fires involving potassium and sodium metals, dry table salt, graphite, iron powder, and similar substances are also very effective. But note that when metallic lithium catches fire, if dry sand containing SiO2 is used to extinguish it, the combustion product Li2O can react with SiO2; if sodium carbonate or table salt is used for extinguishing, the high temperature generated by the combustion can cause sodium carbonate and sodium chloride to decompose, releasing sodium, which is even more dangerous than lithium. Therefore, when metallic lithium catches fire, it cannot be extinguished using sand, sodium carbonate powder, or table salt. Furthermore, since metallic cesium can react with graphite to form cesium carbide, graphite cannot be used to extinguish a fire involving metallic cesium.