Improper disposal of dry ice for indoor cooling is dangerous.

　　Dry ice is similar to ice in appearance. People who are not familiar with the characteristics of dry ice, especially children, may take it directly, which may lead to frostbite. If dry ice is eaten by children by mistake, the consequences are unimaginable, which can seriously suffocate children.

　　On August 2, many places in China issued high temperature warnings. In the scorching sun, many people have racked their brains to cool down. The reporter noticed on the Internet that in addition to the traditional ways of spending the summer, such as turning on the air conditioner and sleeping on the mat, some people set their eyes on the dry ice that has been well known with the development of cold chain express delivery in recent years.

　　In a short video, a parent put a large piece of dry ice at home to cool his child. She said that dry ice only releases carbon dioxide, which is harmless, and the use of dry ice can cool down at low cost.

　　So, what is the main use of dry ice? Can it cool down? Is it safe to use it for indoor cooling? With these questions, the reporter interviewed relevant experts.

　　Dry ice is not ice, and the cooling effect is remarkable.

　　Although there is "ice" in the name of dry ice, it is not solidified by water.

　　"Dry ice is chemically solid carbon dioxide." Sun Yafei, a special research assistant at the Institute of Natural Science History of the Chinese Academy of Sciences, a Ph.D. student in the Department of Chemistry of Tsinghua University, and a popular science writer, told reporters that "carbon dioxide does not exist in liquid state at standard atmospheric pressure, so when the temperature is below MINUS 78 degrees Celsius, gaseous carbon dioxide will directly condense into solid state; On the contrary, when the temperature is higher than MINUS 78 degrees Celsius, carbon dioxide will sublimate directly from solid to gas. Because the appearance of solid carbon dioxide is like ice cubes, it does not produce liquid substances, so it is called dry ice. "

　　In life, people often use ice cubes to cool drinks, because ice cubes will absorb the heat of drinks during the melting process (from solid to liquid). Using dry ice to cool an object also uses a similar principle. "Dry ice, that is, solid carbon dioxide, changes directly from solid to gas when sublimating. In this process, it will absorb a lot of heat from the surrounding environment and objects. " Sun Yafei explained.

　　Dry ice is a kind of low-cost cooling medium, and it is widely used in production and life. For example, many chemical reactions in the laboratory need to be carried out at extremely low temperature. At this time, scientists often put dry ice into a solvent to create a low-temperature environment in the laboratory through dry ice. In daily life, long-distance cold chain transportation also needs the help of dry ice.

　　"Putting dry ice in the room can really cool down. In addition, when dry ice is placed at room temperature, the low temperature environment around it will condense some water vapor in the air near the dry ice, thus forming a smoky effect, which is also visually beautiful. " Sun Yafei said, "With the development of industry, the price of dry ice is very low now. A kilogram of dry ice costs only a few dollars, and they can theoretically keep a room cool for half a day. "

　　Household needs to be vigilant, or there are many risks.

　　What is the safety of dry ice? Sun Yafei said that the product of sublimation of dry ice is only carbon dioxide, which is not flammable and explosive, and there is no danger in theory.

　　However, Sun Yafei stressed that the temperature of dry ice is too low, and human skin will be frostbitten in a short time after it comes into contact with dry ice. "When researchers use dry ice in the laboratory, they have a complete set of operating procedures, such as not touching it directly by hand and not putting it in the ordinary refrigerator. Dry ice and ice are similar in appearance. If dry ice is placed at home, people who are not familiar with the characteristics of dry ice may operate it directly, and children may play with dry ice as toys, which may lead to frostbite. " Sun Yafei said.

　　In addition, dry ice will sublimate into gas when it is in an environment above MINUS 78 degrees Celsius. "Putting dry ice indoors is tantamount to putting dry ice in' hot oil', and the rapidly evaporating gas will be mixed with dry ice powder. Although the actual damage is not great, it is easy to scare children. " Sun Yafei reminded.

　　In addition, in terms of storage, dry ice cannot be directly put into the refrigerator. Although the temperature in the household refrigerator is low in daily life, it is still high for dry ice.

　　"The temperature of the freezer is generally around MINUS 18 degrees Celsius, and the temperature of the freezer is generally around 4 degrees Celsius, which is much higher than the temperature required for sublimation of dry ice. If dry ice is put directly into the refrigerator as ice, it may lead to more complicated consequences. " Sun Yafei added, for example, dry ice will cool the inside of the refrigerator, especially when the refrigerator is in a closed state, and this cooling effect is obvious. At this time, some foods that cannot be frozen, such as vegetables and fruits, may be frostbitten, and then rot in advance. When the cooling effect of dry ice is too obvious, the temperature in the refrigerator is much lower than the design temperature of the refrigerator, it will also cause some irreversible damage to the refrigerator system and parts.

　　Not only that, some ice was eaten by children by mistake, and the consequences were unimaginable. Sun Yafei said that on the one hand, the ultra-low temperature of dry ice will quickly freeze children's mouths and esophagus; On the other hand, dry ice will vaporize quickly after entering the stomach, producing a lot of carbon dioxide. "If we don't consider the change of air pressure, one unit of dry ice will expand by 700 to 800 times after it is completely converted into carbon dioxide. This will not only make children's stomachs rise rapidly, but also the carbon dioxide flowing back to the mouth and nose will cause children to suffocate. " He said.

　　"In the actual use of dry ice, we should take into account the actual situation of the family environment. Based on the above risk factors, it is not recommended to use this method to cool down at home. " Sun Yafei reminded. (Intern reporter Yan Weiwei)