Decryption: Daxinganling fire!

On April 30 , a forest fire broke out at the Yimuhe Forest Farm of the Wuma Forestry Bureau in Daxing'anling, Inner Mongolia.

On May 2nd , a forest fire broke out in the Dahe Forest Farm in Bilahe, Daxinganling, Inner Mongolia Autonomous Region.

Time they occurred almost 30 years ago, 5, 6 fires the same, highlighting the plight of forest fire high fire season. Let's review the Daxinganling fire to see how much we know about the climatic characteristics of major disasters. Every major disaster that exceeds social control capabilities has the contribution of climate change. The Daxing'anling fire 30 years ago was a typical disaster caused by climate change. It has the characteristics of forest fires and the typical fire dynamics. Here I would like to start an analysis and reconsider the fire that happened 30 years ago.

Massive blaze 1987 Nian May 6 to June 2 in Daxing'anling, since the founding of New China, the most serious forest fires. The fire not only caused an 18 million-acre (equivalent to the size of Scotland) area in China to be damaged by fire in various degrees, but also affected 12 million acres of forest in the Soviet Union . In comparison, the Yellowstone Park fire in the United States in the following year was affected. The range is about 1.5 million acres. From a numerical point of view, typical features of the Daxing'anling fire include:

First, the area is large. The total area of ​​fire burned reached 1.33 million hectares, plus 1 county, 4 forestry bureaus, and 5 wood storage yards.

Second, special time. A large area of ​​rainfall in the forest area did not see an open flame, and the follow-up to the fighting ended in the end to prevent a re-ignition.

Third, huge losses. The direct loss of this fire reached 450 million yuan, and indirect losses amounted to more than 8 billion yuan, not including reconstruction costs and loss of forest regeneration resources, as well as forest production reduction after many years, and the cost of resettlement of forest personnel, if the environmental deterioration is counted. The factors, these losses can exceed 20 billion.

Fourth, the death toll is high. That is just a household of people were killed and up to 213 people, burns up to 266 people, 10,000 households, 50,000 people were displaced; that was not a large number of floating population and forest areas of missing persons.

1 . The cause of the fire

According to official sources, the initial cause of the fire was caused by a forest farmer who started the brush cutter and ignited the gasoline on the ground. When the fire was extinguished, only the open flame was extinguished, but no net fire was left over, leaving the fire out of control. On the other hand, the fire in Xilinji (Mohe County) Daxinganling region, and strengthen the country (Figure town), amur (Jin Tao town) and a few tree farms Plata 4 Forest belongs simultaneously. This shows that the climate at that time was conducive to the disaster and was not conducive to fire control. Therefore, it was the ancient so-called "melting wind / burning wind" situation.

On a certain day in 1963 (a specific day was not remembered), fires broke out in several states in the northeastern United States. Eighty percent of firefighting teams were dispatched to fight the wildfire. The next day, all the fires were extinguished, mysteriously occurred, and mysteriously disappeared. It was the special nature of this “melting wind”.

A similar disaster took place on a certain day in 524 BC , "(Calling 18 years, 524BC ) Summer May, the fire began to faint. The child, the wind. At the beginning of the day, its fire was almost seven days away ! " In the afternoon, it was very loud. Song, Wei, Chen, Zheng are all fire. In order to look at the library of the Grand Ascension, he said: "Song, Wei, Chen, Zheng." For several days, they all came to the scene."

Therefore, we should recognize that the special climate at that time was the key to a major disaster. A person’s mistake and someone’s arson were not critical factors in the disaster. The reason why the 5 · 6 fire was out of control was the convenience of the climatic conditions at that time. This was hardly noticeable but it was a key factor that was difficult to control.

Recently, I heard that the Russian forest fire burned into China. I immediately thought that this was the 30 years after the Daxinganling fire , and it was also the peak year of the cold-phased climate. Therefore, the fire can be expected, but disasters will not happen because it is cold. With the climate cycle, without the help of strong winds, the fire is easier to control. The biggest difference between the cold and warm climates is the spread of the fires, with only 6 deaths in the London fire in 1666 and 300 deaths in the Chicago fire after 206 years ( 3.5 cycles) . Climate turbulence is an important driving force that leads to a sudden fire situation, although the logical chain of causation is still not clearly understood.

Fig. 1. 5 · 6 The fire point of the Daxing'anling fire.

In fact, it does not matter where it takes place. The key is that fire control measures have not been taken in a timely manner. This is the key to a fire out of control. In order to fully control the ignition source, it is possible to pay a very high price.

For example, during the Yuan and Yuan Dynasties of the Tang Dynasty, Liu Zongyuan mentioned in “Bibi Fangwen”: “Yongzhou Yuanhe’s seven years ( 812 ) Summer, many fires. Days and nights are sent out in tens of times, but few are still sent out in five or six months. After three months, it is only eight years. Another example is that people are salt-free, they are old and weak, they die in the morning, they don't sleep in the morning, and they don't sleep at night. This rare climate, which occurs in hot, dry seasons, can easily lead to a fire out of control. When Liu Zongyuan wrote "Individual fishing on snow in the cold river", it was in 809 AD that when Bai Juyi wrote "Selling charcoal and cutting down charcoal and burning charcoal in Nanshan" , it was also 809 years. Therefore, the cold-phase climate characteristics at that time were very prominent.

However, although the Daxing'anling fire occurred in the spring, it was a typical warm-phase fire. Its typical characteristics were the fire whistle and the firestorm. They were often related to the instability of the air flow in the fire, and were therefore characterized by the warm-phase climate. Warm-weather fires usually spread rapidly, causing high casualties in the fire field, which can easily cause heavy casualties. The Daxing'anling 1987 fire was very similar to the 1871 Chicago Fire and the Pesticigo fire. The former burned more than 300 people, and the latter burned more than 1,500 people. This is a typical case of a difficult-to-escape situation caused by a warm phase of fire. The Daxing'anling fire occurred after 116 years and was almost a complete two -climate cycle. Therefore, it is inevitable that the casualty result is also possible. Everyone is the result of the El Niño phenomenon, and it is also an inevitable result of the climate pulsation.

Historically, wildfires in the United States have been the first to be caused by railroad trains. Because of incomplete combustion of ash and smoke, forest fires are often caused. However, a more common type of fire cannot be investigated. For example, dewdrops at the tip of the leaves in the morning may converge on light rays like a convex lens, if the convergence spot falls on hot and thin materials (such as fire, fiber, etc.) A fire will occur. In other words, this kind of fire that can be investigated without any clues to fire is derived from the accidental formation of a dewdrop, which is a key factor in the uncontrolled investigation of wildfires. Therefore, the occurrence of a fire may be an accidental accident. The control of a fire is a specialized area that requires professional investment, technology, and manpower. In this regard, China’s general understanding of fire still rests on the simple concept of “controlling people by controlling fire”, which is a very primitive and primitive understanding.

2. The mystery of spread

The premise of fire spread is to heat fresh fuel to flammable temperatures. At this temperature, the solid fuel releases a combustible gas. Only the gas can actually be burned. There are two conditions to promote the spread of fire quickly. Because of the high temperature, the flame is not afraid of high wind speed. A single match can be easily blown off with the mouth, so burning at high speed is not easy. However, after the temperature is raised, the heat release increases, and the ability of the fire site to resist wind speed increases. Because the wind speed is fast, the flame is tilted to one side, resulting in an increase in the preheating power of the flame to fresh fuel. Almost all fuels must be heated, dried, release flammable substances and ignite in several stages, and the intense flame heat transfer (radiation dominated) greatly shortens this process, so that rapid flame transfer is possible. The special wind speed here is caused by the fire flow, which is different from the usual surface wind. The only tool that fire engineers use to judge the speed of the fire is energy balance. The analysis of heat transfer factors is good. The conclusion naturally comes out. Of course, the current level of research is still qualitative, and it is estimated that the results are only of order magnitude. Quantitative prediction requires measuring a large number of parameters, and the parameter measurement is inaccurate (variable in real time), so it is difficult to predict accuracy.

Figure 2. Downwind spread patterns during high winds, favoring flame elongation, warm-up, and spread.

After paper is formed in the paper mill, it needs to be air-dried in the open air, usually hanging vertically. When the paper reaches a certain degree of dryness, it is very dangerous. Once it catches fire, the flame expands rapidly (because the hot gas rises), so the warm-up increases and the flame accelerates from the bottom to the top. There is almost no way to stop it. The fire of the Karamay fire caught on, and similarly, it spread quickly and could not be stopped. Unless the curtain is lowered, put fire on the ground. At that time, some people hoped that this would be unsuccessful and it would be a disaster.

The rapid spread of forest fires, in addition to wind speed, is related to a special kind of spreading phenomenon. In the forest fire, some pieces of wood chips are produced. These burning pieces of wood chips, as the strong plumes rise up and break away from the surface boundary layer, are affected by the environmental wind and land in the distance. This kind of jumping fire spreads. The way is unique to forest fire. At 23:07 on May 1987, Heilongjiang Forest Farm in Marin There is a river, did not stop the spread of fire, those with large Feng Mantian flying pieces of wood, and soon lit Marin forest, after two hours all burned forest farms Finish.

Figure 3. Firefighting in forest fires ( Bureau of the American Bay Area, 1991 )

Figure 4. Debris fuel that has caught fire in the Bay Area fire, up to 5 cm in diameter .

The poet Bai Juyi of the Tang Dynasty wrote in "The Hawthorn", "The old man in the mountains took care of his time, and he lived in the wilderness of Dongxi. The winds of the fire tree turned the flames, and Qiongzhi sun-red yarn. The peaches and plums were all colorless and reflected. Hibiscus is not a flower. The result of the struggle is deep rooted, and no one is moved by others." Although it is described as hawthorn, it can also be understood as the phenomenon of fire in a forest fire: crown fire. For some trees, the leaves are thinner than the trunk and easier to ignite, making it easier to ignite and create a canopy of fire. After the leaves are dried, the ignition process can be rapid, resulting in a rapid ignition combustion phenomenon commonly known as "fire hurricanes."

3. The mystery of the hot

The description of the Daxing'anling fire often refers to a “fire whistle.” The description of the phenomenon in the news and memoirs can be compared with the flashover in a typical indoor fire ( Flashover ). Usually we understand the flame gradually The spread is based on the small scale of the fire, which is caused by surface heat transfer and a small amount of radiation. When the fire source reaches a certain scale, the radiation intensity is greatly increased, so some people say that the flame comes from the air, yellowing, reddish ( The color represents the temperature, which is the Planur's law or the Wien's law in physics. It is a piece of wood in every direction. The leaves of the forest are buzzing, indicating that the radiation intensity is high. When the moisture is baked, the remaining combustibles begin. Warming up and releasing flammable substances, because a forest was roasted, the flammable substances accumulated to a certain degree, they were suddenly ignited, a whistle was heard, and the entire forest was lit. At this time, extinguish forest fires of this size. It is impossible to wait until the fuel burns out and turn off automatically. This phenomenon usually occurs indoors or in the hearth, such as the famous title poem “A bundle of thatch Matted and burnt to the sky, describing the "fire rush" phenomenon, which happened only in the hearth.

Figure 5. In the Daxing'anling blaze, radiation from the smoke layer to the nearby fuel is the key to the “fire scream”.

So why is there a "fire rush"? First, the fuel needs to be dry, which is determined by the local meteorological conditions. Every spring, the cold wind from Siberia is dry, and the flow from the south is warm. Both determine the environmental humidity and fuel dryness. Secondly, as shown in the above figure, a large amount of smoke generates a certain radiation intensity, continues to dry and preheat the nearby fresh wood (fuel), the fuel undergoes a pyrolysis process, and generates a large amount of gaseous fuel; third, once the conditions are met, The fuel gas after preheating is ignited at the same time, causing strong disturbances and loud sounds. It is a "fire whistle."

4 . Fire Whirl Puzzle

The Daxinganling blaze is the largest and most famous forest fire in China's modern history. It can be said that the catastrophe was full of the disaster. However, there are several key fire phenomena that are related to the flow of fire and require special explanations. "May 7, 1987 afternoon, Mohe Gulian tree farm northwest of the fire has burned day and night. The young men of the town are the mountains sparking a 32-year-old Li Guiyun and neighbors together, standing outside the house pointing to the fire Because the forest farms are on fire every year, the locals are commonplace, and after struggling to fight, the fire is getting smaller.The women and children who stay at home have eaten dinner and some have left behind to eat, waiting for the man to go home after the fire. At that time, the wind suddenly changed suddenly, rising steeply from grade 45 to grade 89. In some places, the instantaneous wind reached grade 12. "We can't stand in the woods. “The Guohe Jun, the leader of the Mohe County Fast Fire Fighting Team who was on fire in the mountains at the time, said that the wind rapidly caught the fireball in the forest to the roof of the residents hundreds of meters away. People were caught off guard.” (From Daxinganling Fire, The Beijing News) November 10, 2008)

Afterwards, a very common point is that there is no forecast of strong winds in the fire. The forecast in the record was a 'fire risk' grade, which was about five gales, and it was reported that the winds in the fire reached 14 levels. The former is the natural wind speed, and the latter is the strong wind of the fire, caused by the fire itself. Nature's reaction to energy release is to generate flow. Gale is the result of a fire rather than a cause. As we all know, the gas will expand and decrease in density when heated. (In elementary school textbooks there is this teaching.) In the Earth's gravitational field, gas with a low density will rise and the surrounding gas will be sucked up to form a rising momentum. When the source of fire is small and there is no external disturbance, the desert is solitary. When the fire source has a certain scale , it will cause disturbance to the surrounding air flow, 'wolf smoke rolls'. When the energy reaches a certain scale, it will form a cloud of fireballs and mushrooms. Therefore, the extent of fire disturbance to the surroundings depends on the degree of energy concentration. So, fire May 6, 1987, and will be formed in May 7th day after strong winds, 'fire by the wind, asking for a light wind Viagra', the formation of a major disaster. Its core lies in the accumulation of fuel and the non-linear development of the fire. The so-called non-linearity means that even under a stable flame propagation speed, the burned area is the square of the speed, plus other factors such as wind speed and wind direction, terrain and fuel dryness, the development of the fire field is unpredictable. Therefore, the strong winds of the fire are common sense to fire engineers and there is no special place.

In 1992 , the California Bay Area fire broke out. It is characterized by a large area of ​​fire that creates a strong fire flow. For this reason, Prof. Pagni of the University of California at Berkeley used the theory of fire-induced flow simplification of Baum, an academician of the American Academy of Engineering , and combined observational data from various weather stations to meticulously simulate the situation at that time. Meteorological results can be considered as successful post-event analysis.

Figure 6. The spread of the fire in the Bay Area in the United States in 1991 was affected by the meteorological conditions at that time.

In addition, in the Romance of the Three Kingdoms, Zhuge Liang arranged a fire attack. When the flames began, it began to rain. Theoretically speaking, fire-induced flow interferes with the local climate. If there are cumulonimbus clouds at that time, it is very likely that it will cause rain in advance. The effect is to spread dry ice on the missiles, and the effect of the artificial ice-spraying of ice-splatters is the same. Luo Guanzhong may not understand the truth, and emphasizes that he will be born in heaven. If we don’t understand it, it’s not enough scientific literacy.

However, any forest fire that is out of control always refers to a storm, which leads to an uncontrollable fire. In fact, this kind of storm is caused by the fire itself and is the product of a certain stage of fire development. The flame tornado is also called fire, fire whirlwind and firestorm. It means that when the fire occurs, the temperature of the air and the gradient of heat energy satisfy certain conditions, and the flame forms a vertical whirlpool. The rare phenomenon that the flame is directly inserted into the sky. Rotating flames often occur in bush fires, and the height of the flame ranges from 30 to 200 feet. The duration is limited, usually only a few minutes, but if the wind is strong, it can last longer.

The formation of a flame tornado requires certain conditions:

1. Strong heat generation, resulting in upward plume;

2. The updraft combined with the asymmetry of the supply airflow creates a swirling air vortex together. The formation of a flame tornado must occur after the flame has been heated to cause high convection, and if the wind supply is asymmetric when it rises, the rising air flow will begin to rotate and a so-called flame tornado may form. In appearance, these rotating airflows can be tightened to form a structure similar to a tornado, while rotating, while drawing in, burning, and rising. In general, in the vorticity equation, the suction effect is the biggest factor affecting the change of vorticity. In the fire, the heat of the fire caused the air to rise, and the surrounding air rushed in from all directions to form a sucker. The flame tornado formed.

Figure 7. Flame Tornado

Once the flame is absorbed by the rotating air stream, the unburned gas will reach the inner core of the fire cyclone until it reaches the area with sufficient fresh, heated oxygen to burn these gases. So the flame tornado's core looks very tall and very slim. Common natural fire whirlwind kernel only 0.3 to 0.9 meters wide and 15-30 meters high. However, the conditions under suitable conditions, can form huge fire whirlwind (tens of meters wide and 300 meters high). The flow changes the combustion structure inside the flame tornado and promotes the formation of a hollow combustion state. The hollow combustion state has a central low temperature area. The flame tornado has the longest duration at the lowest temperature in the central low temperature zone. The incoming stream enhances the overall rotation of the flame tornado and exacerbates the spiraling rise of the flame tornado.

Figure 8. Fire whirlwind generation conditions: 1. Flame (energy release); 2. Ascending plume; 3. Unsymmetrical air supply, forming vortex.

We can generate a whirlwind of fire even under small laboratory conditions. The simplest method is to use the lateral supply to directly blow the flame into a whirlwind. If there is no mechanical air supply, the surrounding air supply conditions will be changed. Originally, it is a symmetrical air supply, and now it is changed into a corner air supply. This kind of air supply condition naturally has the effect of a whirlwind (as shown below). Of course, the fire and updraft should not be too small. If the fire is only as large as a candle, natural air supply will not affect the updraft. Because the updraft is weak and the coiling airflow is weak, the joint effect of the two is even weaker.

Figure 9. Man-made fire whirlwind by changing the air supply method under laboratory conditions.

In August 2007, German沃尔夫斯堡斐Orinoco Center for visitors viewing a spectacular fire artificial cyclone is formed by a plurality of air jet vents (FIG. 10). A real-world fire whirlwind will not remain vertical like this, but it will not win any speed record. Only under extreme conditions, such as Japan's earthquake fires and the gale situation in the Bay Area, it is possible to form a rapid and contagious disaster. This is a special disaster caused by climate change. It is usually concentrated and occurs only every 60 years. Possibility of happening.

The most famous natural fire whirlwind is the well-known 1923 Tokyo earthquake. After the earthquake, there was a fire. 38,000 people evacuated in the square . Because of the fire around the building, the fire whirlwind quickly consumed oxygen and died of suffocation. Earthquake, fire, fire whirlwind three together cause more than 100,000 casualties.

Figure 10. The Tokyo earthquake that caused a lot of casualties in the imagination of the artist “Fire tornado”

The most common fire whirlwind is the fire whirlwind in the forest fire. The flame tornado envelops the flames and rotates like a fire dragon. It is ashes everywhere. Its strong winds are enough to uproot a small tree and promote it for more than one hour. The fire caused by it is difficult to extinguish. In the Great Xing’an Mountains in 1987 , more than 200 people died. The most important factor is that the development of fire has come from the wind and surpassed people's ability to escape. Under such meteorological conditions, it is impossible to extinguish fire and escape is inevitable and strategic.

Figure 11. Trend of fire spread and wind direction after the 923 Tokyo earthquake in Japan (research findings of Japanese scholars)

In addition to the famous Tokyo earthquake and fire whirlwind of fire, the fire caused by the historic storm (fire whirl) as well as October 8, 1871, a forest fire swept through the northeastern part of Wisconsin on both sides of the Bay of Green Bay, a total of about 1500 People lost their lives. At the beginning of October of that year , it was a typical late autumn and warm Indian weather: the breeze was blowing and the air was warm and dry. In the past few weeks, there have been a number of small bush and forest fires, most of which were burned by a large number of branches left by the lumberjacks. When the wind is blowing, workers and nearby people can control the fire. However, it is Sunday, October 8, southwest wind increases, many small fire to develop into flames. At the same time the temperature increased significantly, from observations recorded in the vicinity of view, October 7 maximum temperature of 19 ℃, and October 8 rose to 28 ℃, in line with the ancient "Mengqiu of the month row daylight saving time in winter and more fires," Our Ancient observation. By the evening of October 8, two major forest fires from advancing slowly towards the northeast near the city of Green Bay, although residents put out the fire, trying to stop the spread of the fire, but the fire ruthless, through the Department destroyed a large number of The dwellings, East to Franken, all villages in the west to Pestigo were all destroyed.

Figure 12. The climatic conditions during the Chicago fire, in line with our ancient "Lu Shi Chun Qiu" and "Huainan Zi Shi Xuan" on the "(Meng Qiu) line of summer, it is more fire, cold and heat, malaria and more people." Empirical observations are worth studying in depth.

May 6,