There are many types of chemical substances, a large part of which are hazardous chemicals with varying degrees of hazardous characteristics such as combustion, explosion, corrosion, and radioactivity. In the event of a fire accident involving hazardous chemicals, improper firefighting methods and ineffective measures may lead to the expansion of the fire, and even cause explosions and poisoning accidents, resulting in huge property losses and personal injuries. Therefore, workers and firefighters engaged in chemical production must master the physical and chemical properties of these substances and learn the correct firefighting methods.
1. Firefighting of flammable and combustible liquid fires
Liquid fires, especially flammable liquid fires, develop rapidly and violently, sometimes even leading to explosions. The fire extinguishing methods for such items are mainly determined based on their specific gravity, solubility in water, and other properties.
Generally speaking, compared with flammable and combustible liquids that are light in water (with a specific gravity less than 1) and insoluble in water, such as benzene, toluene, gasoline, kerosene, light diesel oil, etc., fires can be put out with foam or dry powder. When the initial fire occurs, if the burning area is not large or there is not much burning material, carbon dioxide fire extinguishing agent can also be used to extinguish the fire. But it cannot be extinguished with water, because when extinguishing with water, flammable and combustible liquids are lighter than water and will float on the water surface and expand the fire as the water flows. For example, in the coking plant of Meishan Metallurgical Company, due to improper operation by workers, 2t of polybenzene flowed into the Yangtze River from the sewer and spread over a large area on the river surface. Coincidentally, the "Hai Dian No.1" ship with five wooden boats docked by the river to seek shelter from the wind. A crew member threw unburned firewood into the river, which caught fire when exposed to benzene and damaged the ship.
When liquids heavier than water (with a specific gravity greater than 1) and insoluble in water, such as carbon disulfide, naphthalene, anthracene, etc. catch fire, they can be extinguished with water. However, the water layer covering the surface of the liquid must have a certain thickness to suppress the flame. However, the temperature of the liquid trapped under the water is relatively high, and on-site firefighters should be careful not to burn themselves. If a certain factory catches fire and uses water to extinguish it, a large amount of high-temperature tea (with a minimum temperature of 80 ℃ or above) is pressed under the water, and many people are burned by the high-temperature tea under the water during the extinguishing process.
When water soluble liquids, such as alcohols such as methanol and ethanol, esters such as ethyl acetate and butyl acetate, and ketones such as acetone and butanone, fire shall be extinguished by fog water or insoluble foam and dry powder. Carbon dioxide can also be used to extinguish fires in the early stages or when there are few combustibles. If chemical foam is used to extinguish the fire, the strength of foam must be 3~5 times greater than that of extinguishing flammable liquid insoluble in water.
Flammable liquids caught fire in open containers and cannot be extinguished with sand. Because sand not only cannot cover the surface of the liquid, but will instead deposit at the bottom of the container, causing the liquid level to rise and overflow, leading to the spread of fire.
2. Firefighting of flammable solid fires
Flammable solids have a low ignition point and can cause rapid and continuous combustion or explosion when heated, impacted, rubbed, or in contact with oxidants.
In case of fire caused by flammable solids, water, sand, asbestos blanket, foam, carbon dioxide, dry powder and other extinguishing agents can generally be used to put out the fire, but aluminum powder, magnesium powder and other fires cannot be put out with water and foam extinguishing agent. In addition, when powdery solids catch fire, they cannot be directly and strongly impacted with fire extinguishing agents to avoid dust being dispersed and forming explosive mixtures in the air that can cause explosions. When flammable solids such as phosphorus compounds, nitro compounds, and sulfur ignite and burn, toxic and irritating gases are produced. When extinguishing the fire, people should stand upwind to prevent poisoning.
3. Extinguishing fires caused by burning objects in contact with water
The common feature of such items is that they can undergo violent chemical reactions when exposed to water, producing flammable gases and releasing heat, which can cause combustion and explosion. Dry sand, dry powder, etc. shall be used to put out the fire of burning articles in water. Water, acid, alkali extinguishing agent and foam extinguishing agent are strictly prohibited. In the combustion of substances that come into contact with water, such as lithium, sodium, potassium, tough, bright, strontium, etc., due to their highly reactive chemical properties, they can capture oxygen from carbon dioxide and cause chemical reactions, making the combustion more intense. Therefore, carbon dioxide cannot be used to extinguish the fire.
4. Extinguishing fires caused by self igniting materials
This type of item, although not in contact with an open flame, can undergo oxidation and release heat in air at a certain temperature. Due to the accumulation of heat, it reaches its ignition point and causes combustion. Spontaneous combustion can be divided into three types: one is caused by severe oxidation in room temperature air, such as yellow phosphorus; Another type, when heated to the ignition point, releases heat without the need for external oxygen supply, and decomposes into oxygen to continue burning, such as nitrocellulose film, aluminum iron solvent, etc; There is also a type of material that slowly oxidizes in the air and can spontaneously ignite if poorly ventilated and the accumulated heat does not dissipate to the point of self ignition, such as oily paper and other oily materials.
When self igniting materials catch fire, except for triethylaluminum and aluminum iron solvents that cannot be extinguished with water, a large amount of water can generally be used to extinguish the fire. Sand, carbon dioxide, and dry powder fire extinguishing agents can also be used to extinguish the fire. Due to the formation of ethane when triethylaluminum comes into contact with water, the temperature of the aluminum iron solvent during combustion is extremely high, which can cause water to decompose and produce hydrogen gas. So water cannot be used to extinguish the fire. When the material storage tank of a certain chemical plant is used for a long time, due to the high content of sulfides (hydrogen sulfide and organic sulfur) in the material, the contact corrosion between sulfides and equipment forms iron sulfide. After the materials in the storage tank are used up in production, the dried iron sulfide will self heat and burn in room temperature air, causing a fire. Use dry powder to extinguish the fire.
5. Extinguishing oxidant fires
This type of item has a strong oxidizing ability. Although it does not burn itself, it can be oxidized upon contact with combustible materials, and its own reduction can cause combustion and explosion.
Fires caused by oxidants can generally be extinguished with sandy soil, and most fires caused by oxidants can be extinguished with water, preferably with misty water. If pressurized water is used, first cover the burning material with sand and then extinguish it. To prevent water from flowing into other flammable and explosive materials. Peroxides and insoluble liquid organic oxidants should be used to extinguish fires with sand, carbon dioxide, or dry powder fire extinguishing agents. This is because peroxides react with water to release oxygen, accelerating combustion; Liquid organic oxidants that are insoluble in water generally have a specific gravity of less than 1 (lighter than water). When extinguishing fires with water, they will float on top of the water and flow, expanding the fire.
6. Fire extinguishing of toxic and corrosive substances
When toxic substances catch fire, water and other fire extinguishing agents can be used to put out the fire. However, when cyanide, selenide, and phosphide in toxic substances catch fire, acid-base fire extinguishing agents cannot be used, only misty water or carbon dioxide can be used to put out the fire.
When corrosive articles catch fire, they can be put out with atomized water, dry sand, foam, dry powder, etc. Acidic corrosive substances such as sulfuric acid and nitric acid cannot be extinguished with pressurized and dense water flow, as dense water flow can cause the acid solution to heat up or even boil, splashing around and injuring firefighters. When extinguishing fires caused by toxic and corrosive substances, attention should also be paid to conserving water and the direction of water flow. At the same time, efforts should be made to ensure that the extinguished wastewater flows into the sewage pipeline as much as possible. Because toxic or corrosive firefighting wastewater overflowing everywhere can pollute the environment and even water sources.
Personal protective measures should also be taken for extinguishing fires caused by harmful and corrosive substances, such as using gas masks, face shields, etc.
7. Firefighting of flammable gas fires
Flammable gases include hydrogen, coal gas, acetylene, ethylene, methane, ammonia, petroleum gas, etc. These gases pose a risk of combustion and explosion upon impact, heating, or contact with sparks.
In order to facilitate storage and use, many flammable gases are usually compressed and stored in containers using a pressurized method. Due to the different properties of various gases, some are compressed into liquid form, known as liquefied gas, such as liquefied petroleum gas, liquid ammonia, etc., while others remain in gaseous form, known as compressed gas, such as hydrogen gas in hydrogen cylinders, etc. Gas ignition is difficult to extinguish. According to domestic and foreign practices, most gas ignition water can play a role in cooling and extinguishing.
Dry powder and carbon dioxide can also extinguish most gas fires, but they are often powerless against large-scale gas fires.
Therefore, isolating flammable gas sources and using a large amount of water for cooling and temperature reduction are the main means of extinguishing fires.
When extinguishing a combustible gas fire, if the combustible gas continuously sprays out from the container pipeline, the source of the combustible material should be cut off first, and then efforts should be made to successfully extinguish the fire once. Blindly extinguishing fires without cutting off the source of combustible gases is a very dangerous approach. Because once the flame is extinguished, combustible gases continue to spray outward, especially heavier than air combustible gases such as liquefied petroleum gas, which tend to deposit in low-lying areas and are not easy to dissipate quickly. When encountering open flames or hot objects, it can also cause reignition. If the gas concentration reaches the explosive limit, it can also cause an explosion, which can easily lead to the escalation of the accident.
Home