How to extinguish fires involving hazardous chemicals? Varies by nature

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A fire broke out at a fluorosilicon materials company in Quzhou, Zhejiang. The material burning at the scene was silicon powder in powder form. When water was used to extinguish the fire, the rapid cooling of the surface led to the formation of a protective layer on it, which affected the effectiveness of the fire suppression efforts. As a result, the combustible material continued to burn slowly inside. Additionally, given the long duration of the fire in the warehouse and the high risk of collapse, it was difficult and dangerous to extinguish the fire in a short time. For safety reasons, experts recommended adopting a strategy of controlling the spread of the fire instead. This accident shows that when hazardous chemicals catch fire, using water to extinguish the fire may exacerbate the situation; therefore, it is necessary to employ appropriate methods for extinguishing such fires based on the properties of the hazardous chemicals. Next, Weiwei will share with you the characteristics of fires involving chemical hazards as well as some basic knowledge on how to combat them within the framework of fire safety management. 1. Flammable solids are substances that exist in a solid state at normal temperatures, have a low ignition point, and can catch fire when exposed to heat, impact, friction, or in contact with oxidizing agents. Such as red phosphorus, sulfur, rosin, camphor, magnesium powder, etc. Among them, the lower the ignition point and the greater the degree of dispersion, the greater the danger of flammable solids; in particular, powdered flammable materials, when mixed with oxygen in the air in a certain proportion, can explode upon exposure to an open flame. Flammable solids burn rapidly and are difficult to extinguish; therefore, when storing them it is important to do so in appropriate quantities – there should not be too much stock in one warehouse. A certain safety distance must also be maintained from adjacent warehouses, and in particular, warehouses storing acidic substances must not hold flammable solids together with them. In case of a fire, it can be extinguished using fogged water, sand, carbon dioxide, or dry powder extinguishants. http://p1.itc.cn/images01/20201118/9a4e6e1acea044d2b1e9d9caf1b57eeb.png II. Flammable liquids are those that exist in a liquid state at room temperature, with a flash point of 60°C or lower. There are a wide variety of flammable liquids, including chemical raw materials, fuels, organic solvents, additives, adhesives, and more. Flammable liquids generally have a low density, low boiling point, are flammable, volatile, and prone to flowing and spreading. The vapor emitted by flammable liquids, when mixed with oxygen in the air in a certain proportion, can explode upon contact with an open flame. Fires involving flammable liquids spread rapidly, often accompanied by explosions, and are difficult to extinguish. There are certain rules for fighting fires involving flammable liquids: For fires involving hydrocarbon compounds that are lighter than water and insoluble in water, such as fuel oils, ethers, benzene, and its derivatives, dry powder can be used. Carbon dioxide can be employed to extinguish the fire at its initial stage, but water should not be used, as it will only exacerbate the fire. For substances that are insoluble in water and have a density greater than that of water, such as carbon disulfide, water can be used to extinguish the fire, as it can cover these substances and put out the fire. Flammable substances that are soluble in water, such as methanol and propanol, can be extinguished during a fire using fogged water, chemical foam, or dry powder; halogenated hydrocarbon extinguishers such as 1301 and 1211 can also be used for this purpose. III. Spontaneously combustible materials are those that, due to physical, chemical, or biological changes, generate heat sufficient to reach their own ignition point and thus catch fire on their own without the need for an external flame. Spontaneously combustible materials have reactive chemical properties, a low ignition point, and are prone to oxidation. During oxidative decomposition, they release large amounts of heat; when this heat reaches their own ignition point, the materials ignite on their own. For example, the ignition point of white phosphorus is 34°C, and it can catch fire spontaneously in air; the ignition point of nitrocellulose is between 120°C and 160°C, and it may also ignite spontaneously under conditions of long-term storage, poor ventilation, or large quantities being stored together. This is the reason why spontaneous combustion of table tennis balls has occurred repeatedly in commercial warehouses. When self-igniting materials catch fire, with the exception of triethylaluminum, which cannot be extinguished with water, the rest can be put out using large amounts of water, as well as sand, carbon dioxide, and dry powder fire extinguishers. http://p6.itc.cn/images01/20201118/bd23766a0fc344cdab7db0fe65f01a73.png IV. Water-reactive substances: Those items that can rapidly decompose when they absorb water vapor from the air or come into contact with moisture, generating high temperatures and releasing flammable gases that trigger combustion, are known as water-reactive substances. Based on their properties, they can be classified into the following categories: 1. Reactive metals such as lithium, sodium, potassium, etc., undergo a chemical reaction when in contact with water, producing flammable hydrogen gas. 2. Metal hydrides such as lithium hydride, sodium hydride, and calcium oxide also produce hydrogen when in contact with water. 3. Metal carbides such as calcium carbide produce flammable acetylene gas when in contact with water. 4. Sodium dithionite (safe powder) produces flammable hydrogen, hydrogen sulfide, and sulfur dioxide when it comes into contact with water. Use sand or a dry powder fire extinguisher to put out the fire. V. Oxidizing agents: Chemical hazardous materials referred to as oxidizing agents are those with strong oxidizing capacity ； Substances that undergo decomposition reactions under certain conditions, resulting in combustion or explosion. Such as chlorates, perchlorates, nitrates, etc. The main characteristics of oxidizers are their strong oxidizing power and instability; they react immediately upon contact with reducers, acids, or organic substances, causing combustion. The reason why the match head, which we see in our daily lives, catches fire immediately when rubbed against the outside of the match box is that the main component of the match head is red phosphorus, while the outside of the match box is coated with an oxidizing agent called potassium chlorate; through friction, potassium chlorate oxidizes the red phosphorus, causing it to burn. Many oxidizers are highly unstable; they decompose when subjected to friction, vibration, or impact, releasing large amounts of oxygen and heat. If they come into contact with flammable materials, they can catch fire or explode. http://p1.itc.cn/images01/20201118/d6e4f978bdc34aff9cfed02db3fefa54.jpeg Water, foam, and carbon dioxide are prohibited from being used to extinguish such fires; instead, dry sand, dry soil, or dry powder can be used to put out the fire. VI. In production, compressed gas and liquefied gas involve storing the required gases under pressure in gas cylinders. Some gases, when pressurized, also have their temperature reduced to very low levels, causing them to liquefy; these are known as liquefied gases. All compressed and liquefied gases must be contained in specially designed pressure-resistant cylinders. The operating pressure of ordinary gas cylinders is usually above 150 kg/cm2; therefore, in the event of a fire, the gas expands due to heat and the pressure increases. If this gas pressure exceeds the capacity of the cylinder to withstand it, an explosion may occur. The explosive power of an ordinary oxygen tank is equivalent to that of 5 tons of T*T**, and an explosion would have extremely serious consequences. In the event of a fire involving compressed gas or liquefied gas, it must be extinguished promptly; if this is not possible, the unaffected gas cylinders should be moved to a safe location as soon as possible. When it is impossible to move, mist water can be sprayed on the gas cylinder to cool it down, preventing the gas from heating up and expanding, which could lead to an explosion; carbon dioxide and other extinguishing agents can also be used. Firefighters also need to be careful about exposure to toxins when fighting such fires, as the gases in many high-pressure cylinders are toxic. A fire involving hazardous chemicals can have severe consequences; it not only endangers the lives of employees and causes property damage to the factory, but it also pollutes the environment and affects nearby residents. Chemical plants must pay close attention to safe production in order to prevent accidents. In the event of a fire, appropriate extinguishing measures must be taken promptly to minimize the potential harm. This article is reproduced from the Hazardous Chemicals Logistics Network.