Why cannot water be used directly to extinguish fires involving alcoholic liquids?

Substances that are lighter than water and insoluble in it, if extinguished with water, will cause the water to sink to the bottom of the liquid. When heated, this can lead to boiling over, resulting in splashing and leakage of the flammable liquid and thus exacerbating the fire.

It is a water-soluble flammable liquid; in theory, it can be extinguished by dilution with water, but for this method to work and eliminate the liquid’s flash point, water must constitute a large proportion of the solution. This not only requires a large amount of water but also makes it easy for the liquid to spill over, while ordinary foam can be damaged by water-soluble liquids; therefore, it is best to use water-resistant foam for extinguishing such fires ； For flammable liquids that are lighter than water and insoluble in water, using water to extinguish the fire can cause these liquids to float on the surface of the water and flow around with the current, thereby leading to an expansion of the fire

Basic measures for controlling flammable liquids: Flammable liquids are usually stored in containers or transported through pipelines. Unlike gases, liquid containers can be either sealed or open; they are generally at atmospheric pressure, with only the pressure of liquids in reaction vessels (kettles, reactors) and delivery pipelines being relatively high. Whether on fire or not, if a liquid leaks or spills, it will flow along the ground (or water surface). Moreover, flammable liquids have properties such as specific gravity and water solubility, which affect whether they can be extinguished using water or ordinary foam; in addition, there are serious risks of boiling over and splashing. Therefore, fighting fires involving flammable liquids is often a challenging task. In the event of a fire involving flammable liquids, the following basic measures should generally be taken. ① First, the pathways for the spread of the fire must be blocked, pressure vessels and sealed containers as well as flammable materials under threat from the fire must be cooled and evacuated, the scope of the fire must be controlled, and efforts must be made to rescue those who are injured or trapped. If liquid is flowing, dikes should be built (or oil barriers used) to contain the spreading flammable liquid, or ditches should be dug to direct its flow. ② It is necessary to promptly understand and keep track of the name, specific gravity, water solubility of the burning liquid, as well as whether it poses hazards such as toxicity, corrosiveness, boiling over, or splashing, so that appropriate fire extinguishing and protective measures can be taken. ③ For larger storage tanks or flowing fires, it is necessary to accurately determine the area affected by the fire. Small-scale liquid fires (usually within 50 m2) can generally be extinguished using mist water. Using foam, dry powder, carbon dioxide, or halogenated hydrocarbons (1211, 1301) is generally more effective for extinguishing fires. For large-scale liquid fires, the appropriate extinguishing agent must be selected based on their relative density (specific gravity), water solubility, and the size of the burning area. Liquids that are lighter than water and insoluble in water (such as gasoline, benzene, etc.) often cannot be extinguished using straight water jets or misted water. It can be extinguished using ordinary protein foam or light water foam. When using dry powder or halogenated hydrocarbons to extinguish a fire, the effectiveness depends on the size of the burning area and the burning conditions; it is best to cool the tank walls with water. Liquids that are heavier than water and insoluble in water (such as carbon dioxide) can be extinguished using water, as water can cover the surface of the liquid and put out the fire. Using foam also works. Using dry powder or halogenated hydrocarbons for fire suppression, the effectiveness of extinguishing the fire depends on the size of the burning area and the conditions of the fire. It is best to cool the tank walls with water. Water-soluble liquids (such as alcohols and the like), although theoretically they can be diluted with water for extinguishing purposes, require a large proportion of water in the solution in order to eliminate the liquid’s flash point when this method is used. This not only requires a large amount of water but also makes it easy for the liquid to spill over. Moreover, ordinary foam can be damaged by water-soluble liquids (although increasing the strength of ordinary foam can help reduce the intensity of the fire). Therefore, it is best to use flame-retardant foam for extinguishing the fire. When using dry powder or halons, the effectiveness of fire suppression depends on the size of the burning area and the conditions of the fire; it is also necessary to use water to cool the tank walls. ④ When fighting fires involving flammable liquids that are toxic, corrosive, or produce toxic combustion products, firefighters must wear protective masks and take appropriate safety measures. ⑤ Extinguishing liquid fires involving crude oil and heavy oil, which pose risks of boiling over and splashing. If possible, measures such as adding or removing water and stirring can be employed to prevent boiling over and splashing. While extinguishing the fire, it is essential to calculate the time when boiling over or splashing may occur and to watch for any signs of such phenomena. When the commander detects signs of danger, he must make an accurate judgment promptly and issue orders to withdraw in a timely manner, in order to avoid casualties and losses of equipment. Upon seeing or hearing the unified evacuation signal, the rescue personnel should immediately retreat to a safe area. ⑥ In the event of a fire caused by a leak in pipes or storage tanks containing flammable liquids, while preventing the fire from spreading and containing it within a certain area, efforts should be made to locate and close the inlet and outlet valves of the pipelines. If the pipeline valves are damaged or there is a leak in the storage tank, sealing materials should be prepared promptly. First, the flowing flames on the ground should be extinguished using foam, dry powder, carbon dioxide, or water mist, thereby clearing the way for sealing the leak; afterwards, the flames at the source of the leak should be put out, and sealing measures should be taken immediately. Unlike gas leaks, if a liquid leak is sealed unsuccessfully on the first attempt, it can be tried several more times; by covering the ground with foam, preventing the liquid from flowing, and controlling any nearby sources of fire, it is not necessary to ignite the liquid at the leak site.

The methods of fighting fires can generally be divided into cooling, smothering, suppression, and isolation. Using water for extinguishing provides both cooling and smothering effects. However, water cannot be used to extinguish alcoholic liquids with water-soluble properties. Alcoholic liquids are lighter than water; using water to extinguish them can easily cause the liquid to spill out of the container, allowing the fire to spread. It is best to use foam extinguishers.

Alcohols are lighter than water, so they float on the surface, making it difficult to extinguish the fire.