fire rescue: do you want wet or dry clothes?

As many people are debating now, if the equipment on firefighters is wet, will it have better heat resistance than dry? This problem has been discussed for a long time not only in China, but also abroad, because firefighters often wet their clothes, such as shooting water, sweating and so on. 1n order to understand the mystery, the author found two similar articles in the United States, and then translated them for your reference

in the issue of moisture for Fire clothing, some fire clothing manufacturers will also mark the information about moisture and heat resistance in the instruction manual. Some are correct, while others are misleading. The reason is that there is no definite answer to the effect of moisture on heat resistance. Sometimes when the humidity reaches a certain saturation, it will increase the heat resistance effect of the fire jacket; Sometimes humidity can be dangerous. Perhaps the only definite conclusion that can be written down is that “the heat resistance of a dry fire jacket is better than that of a wet one”. The same characteristics can be applied to gloves, fire shoes and headgear

experiment of headgear

the article on the website mentioned that a few years ago, there was a large team in the United States, in which the team members were just familiar with the use of headgear, and the way to use it was to wet the headgear. After the spread of this practice in other units, it was unanimously considered that it was unsafe to use this method. After that, most of the firefighters chose not to wear headgear rather than wet headgear. 1n order to verify which method is right, they gathered experts and scholars to carry out experiments, and divided the hoods into three situations: “dry”, “wet” and “saturated wet”, and began to carry out heat resistance experiments from low radiation heat flow to extreme flash heat flow

in this experiment, an interesting finding is that under the condition of the lowest thermal radiation, the dry headgear is better than the wet headgear, but the saturated wet headgear is also better than the wet headgear; 1n the case of moderate thermal radiation, the protective effects of dry, wet and saturated wet are equivalent; Under the extreme flash heat flux, the saturated wet hood is slightly better than the wet hood, while the dry hood is the worst. On the whole, with the increase of thermal radiation, the thermal resistance of the three kinds of materials is also lower. Finally, the test results of the human body model show that the face, neck and ears that are not protected by the headgear are burned under the high radiant heat test

according to the above experimental results, the most clear conclusion is that wearing headgear without headgear must be worse than wearing headgear, and the heat resistance of protective equipment will be different under different degrees of moisture< 1n general, the composition of the fire jacket is composed of three layers: outer layer, water-proof (or completely waterproof) layer and heat-resistant layer. According to a 30-year study, the heat resistance of fire-fighting clothing will change under three conditions: the outer layer, the inner layer or both layers are wet. The experiment also mentioned that when the inner layer is wet but the outer layer is dry, the fastest heat conduction warning can be given before firefighters are burned; The interior decoration made of completely waterproof material has more water storage and more warning than the waterproof material in recent years, there are more studies to verify the thermal energy storage and conduction of clothing under relatively long-term low radiation heat exposure. 1n these experiments, it is found that when the water resisting layer is completely waterproof material, at a certain humidity, it will lead to the worst heat resistance result readers can quickly find that there are some contradictions in the above conclusions. 1n fact, these experiments can not give any clear conclusion. The purpose of this paper is to tell readers that it is quite difficult to write down the influence of moisture on fire clothes from one or two set conditions. Why is it so complicated? You need to understand how water exerts its characteristics and influence in the fire jacket Where does water come from firefighters will have many opportunities to get wet. For example, when shooting water at the fire point, some water mist will fly back and sprinkle on the firefighters; Some of the water attached to the ceiling drips down and then adheres to the sighting hand; Even when firefighters feel the radiant heat is overheating, they sprinkle water on themselves. The outer layer of the new fire jacket will be treated with waterproof treatment, but this kind of waterproof treatment will be washed away quickly when water is attached to the firefighters, the equipment will become bulky and the anti-skid device of gloves will be passivated. Then water will pass through the outer layer to the fiber on the surface of the anti flooding layer. At this time, the surface will absorb some water, and then the water will be blocked by the anti flooding layer, and it will continue to flow to the inner layer only through the collar, cuff, lapel and other openings however, when firemen come into contact with wet places, a new pipe of water will enter the inner layer. For example, when the knee is squatting or crawling forward, even if the knee is waterproof, when it comes into contact with the wet place, the water will flow along the knee to the non waterproof place at the bottom of the trousers, and then the fiber at the bottom of the trousers will absorb the water to the inner layer; When the fire shoes step into the ponding place, even if the sole is waterproof, the water will be led to the inner layer of the fire clothes through the joint between the shoes and the trousers finally, we should mention that firefighters must have sweat anyway. Sweat is constantly generated. Even if readers are reading like sitting on a chair now, the reason why they don’t see sweat is that compared with clothes, the air between clothes and skin is drier, so sweat will evaporate; Then, when the air humidity between the clothes and the skin reaches saturation, evaporation decreases and sweat droplets form. 1n the same concept, when firefighters wear a fire jacket, the inner heat-resistant layer is in contact with the skin. At this time, the sweat of firefighters will face two situations. 1f the waterproof layer is a material that is easy to absorb water, the sweat of firefighters will be absorbed by the heat-resistant layer, and then spread in the heat dissipation layer; 1f the material is not easy to absorb water, the sweat will flow into the shoes according to the gravity characteristics, which is why some firefighters complain that they feel the sweat flowing into their shoes the media function of water as mentioned above, the fire clothes are easy to get wet under various conditions. However, once the fire jacket is wet, its heat resistance will be affected. Why? Because the water in the fire jacket becomes an important medium. When water becomes a medium, there are two remarkable characteristics. The first is the high heat capacity of water. Because of its high specific heat and latent heat of gasification, water can store and absorb more heat energy. Therefore, wet clothes can store more heat than dry clothes one notable feature is the conductivity of water, which is easier to conduct heat than air. One of the reasons why the heat resistant layer can resist heat is that there are gaps between the fibers of the heat resistant layer. The air between the gaps makes it difficult for heat to conduct into the skin layer. When water fills the gaps, it will make the heat resistant layer form a new heat conduction path the high heat absorption capacity and high thermal conductivity of water are very important concepts. When wearing a wet fire jacket in a fire, water becomes an additional heat absorbing material. However, when the water absorbs heat continuously but does not make the heat disappear in other ways, the heat may reach the scald temperature. The water attached to the clothing surface is closest to the heat source, so the temperature rises very fast. At this time, there are two paths for the water, one is evaporation from the surface, and the other is moving to the inner layer through the path that can penetrate into the inner layer. At this time, it may touch the skin and cause damage of course, water is definitely not the only factor that can affect the protection of Fire clothing, but the variability of water in Fire clothing can not be ignored. How to effectively manage the moisture of fire clothes is a matter that can not be ignored practical application from the above description, we can clearly understand that water adhering to the fire clothes may cause different changes in the heat resistance of the fire clothes when the water inside the fire jacket can absorb heat continuously and remove the heat in various ways, the water may become the addition protection of the fire jacket; 1n contrast, when the high heat absorption capacity of water can not be effectively removed, its high heat conduction characteristics will quickly transfer heat to the human skin, increasing the possibility of scalding of course, the previous experiment also mentioned that when water is left in the fire jacket, because of its high conductivity, when there is high temperature at the scene, the firefighters will feel the heat faster than the dry fire jacket it was mentioned at the beginning of the article that the heat resistance of dry fire clothes is higher than that of wet ones. Because wet fire clothes may have many kinds of changes according to different humidity, thermal radiation and clothing materials, which may make the fire safety unpredictable. 1n practice, there are also actual cases of accidental burns and scalds caused by the damp of fire clothes about the author: head of Disaster Rescue Department, Yunlin County, Taiwan

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