Forest fires have occurred many times in Liangshan, endangering the safety of firefighters. Why are forest fires always difficult to put out?

Every year, a fire breaks out in Liangshan, Sichuan, endangering the safety of firefighters. Why are forest fires always difficult to put out?

The altitude of Xichang is above1500m. The terrain is mainly Zhongshan, accounting for 78.9% of the city's total area, with high mountains and low mountains accounting for 1. 1% and 3.4% respectively. The flat dam area of the valley 16.4% is the second largest valley plain in Sichuan Province. There are many kinds of wild plants growing in the forest, which are rich in resources, with a total of more than 2000 species belonging to 532 genera and 233 families.

At present, Xichang's forestry land area is 159926 hectares, accounting for 60.22% of the total area, and the forest area is 129427 hectares, with a forest coverage rate of 48.74% and a vast forest area.

Liangshan, where Xichang is located, belongs to the subtropical monsoon climate zone, with distinct dry and wet conditions, sufficient sunshine in winter, less rain and dry and warm; It is cloudy and rainy in summer, and the climate is cool. Except the Niger River has four distinct seasons, other places divide the seasons by the average temperature, and the four seasons are not obvious. There is no summer in high altitude areas in the south and no winter in low altitude areas. Although the four seasons are not obvious, the dry and wet seasons are significant. Approximately 1 1? April is a dry season, 5? October is the rainy season. The characteristics of dry season and rainy season are obviously different. The climate in dry season is characterized by scarce precipitation, small temperature difference, abundant sunshine and warm climate. The rainy season is characterized by warm, cool, humid and rainy weather. The obvious feature of rainy season is rainy, so it is customary to call rainy season rainy season.

This is why Liangshan is always prone to fire in March and April.

Ever since the forest appeared on the earth, forest fires have accompanied it. There are more than 200,000 forest fires in the world every year, and the burned forest area accounts for about 1 of the total forest area in the world. Above. At present, there are about 1000 forest fires every year in China, which burn hundreds of thousands to millions of hectares, accounting for about 5 ~ 8 of the national forest area? .

Fire not only brings ecological losses, but also poses a serious threat to the life safety of towns and people around forest areas. But the biggest problem of forest fires is that they are difficult to put out.

Take the fire in Australia as an example. The fire in Australia burned for nearly five months, burning 2,500 houses, and the burned forest area in Australia was about11.2000 hectares. The Amazon rainforest fire that shocked the world last year only destroyed about 6.5438+0.8 million hectares of forest. In addition, the coastline of 1.400 kilometers is burning, which is equivalent to going from the northeast to Jiangsu, Zhejiang and Shanghai. According to statistics, about 1 100 million wild animals died directly or indirectly in this forest fire.

There are four main difficulties: there are many fires and long fire lines; The mountainous area is small and the climate is complex; The mountain is not high, but the forest is dense and the road is difficult to walk; The temperature will continue to rise and the wind direction will always change. Moreover, the altitude of Xichang area is above 1500m, and the high altitude hypoxia is also a severe test for rescuers, and the rescue is extremely difficult.

One of the most dangerous situations in the process of forest fire fighting is the explosion, which will form huge fireballs, mushroom clouds and other phenomena in a short time, and the temperature generated during the explosion is extremely high. Forest fire can be said to be the biggest demon that threatens the life safety of firefighters.

A major cause of deflagration is the simultaneous combustion of various combustible materials in steep slopes, ridges, Caotanggou and other special dangerous terrain.

Forest deflagration fire is instantaneous, powerful, sudden and accidental. According to foreign literature, when the fire develops extremely violently, the deflagration fire temperature can reach more than 1000℃ and the flame can reach more than 30 meters. When this happens, if there are fire fighters on the ground, they will be scorched by high temperature and smoke. Coupled with shock waves, it is difficult for fire fighters to get away and have no time to react, so they may often cause heavy casualties. 20 19 forest fire in Liangshan, Sichuan, firefighters suddenly exploded and 30 people died.

In addition, there will be flashover in the forest. There are two main reasons for flashover. One is the long-term accumulation and decay of combustible materials in the forest, which produces combustible gas mainly methane, and suddenly meets fire, which is caused by the action of small combustible materials.

Another reason is that forest fires burn to narrow ridges, single-mouth valleys, steep slopes, saddles, thatched cottages, rock protrusions and other special terrain, so that combustible materials are preheated at the same time and burned together, instantly forming huge fireballs and mushroom clouds, and the maximum spread range can reach 30 mu.

For example, the narrow ridge line is affected by thermal radiation and thermal convection, and the temperature is extremely high; Moreover, it is easy to form erratic airflow, and the direction of mountain fire is difficult to predict.

It can be said that in forest fires, terrain and wind direction are the biggest problems that hinder fire fighting. Because the important factors closely related to the spread speed of forest fire are wind and terrain. Under the same conditions of wind, combustible and oxygen, the fire on the hillside will spread faster than that on the flat ground.

This is because when the fire burns from the mountain to the foot of the mountain, the terrain blocks the wind, which will form an updraft and accelerate the spread of forest fire to the hillside. Therefore, after a forest fire breaks out, the fire will spread rapidly and get bigger and bigger.

If you encounter forest fires in turbulent areas, such as narrow ditches, ridge lines, sunny depressions, rocky cliff vegetation junctions, places where trees, shrubs and grasses are lush and mixed, and places where young trees and shrubs are dense, especially where the density is above 0.8, young coniferous forests and shrubs are connected, and the microenvironment wind of the fire site is inconsistent with the main wind direction of the fire site, the fire will erupt instantly, seriously endangering the safety of firefighters.

In windy weather, when a special fire behavior occurs, the fire scene expands rapidly and the fire turns into a crown fire. Firefighters and helicopters can't get close to the scene of the fire, and large-scale fire-fighting equipment can't enter the mountainous area to participate in the fire fighting. This situation is extremely dangerous, manpower is basically beyond the reach, and it is very difficult to put out the fire. We can only take measures such as opening up isolation belts from the periphery, fighting fire with fire, or waiting for weather conditions to change (relying on natural forces instead of manpower) to put out the fire.

At present, firefighters mainly use remote water supply systems, large water tanks and foam fire truck, and carry enough materials, such as hand-held electric pumps and fire hoses, as well as wind extinguishers. Because this will not be limited by the problem of water source, the wind fire extinguisher uses high-speed airflow to impact the flame, so that the ambient temperature around the burning combustible material drops sharply below the ignition point, and the flame is blown away from the combustible material, thus achieving the purpose of blocking combustion. The instantaneous wind speed of the wind extinguisher can be as high as 90 meters per second, while the typhoon wind speed of 12 is only about 32 meters per second.

In case of forest fire, avoid the dangerous fire environment. It is not suitable to approach the fire line directly, or when there are major safety hazards in the approach route, you should take the initiative to avoid dangerous terrain, dangerous time and dangerous vegetation types, and choose a safe area to rest or a safe approach route.

When forest fires threaten personal safety, rivers, streams, areas with no vegetation or sparse vegetation and low-lying areas should be chosen. You can cover your head with water, cover your nose and mouth, or pull open the raw soil layer and lie down with your hands on your chest to avoid danger. When lying down, try to stay away from flammable items such as oilers, igniters and oil drums, or throw flammable items out.

In addition, you can also ignite the oncoming fire with an igniter on the relatively open flat ground, relying on rivers, streams and roads, so that the new fire head can spread against the wind in the direction of the fire head and prevent the fire front from cleaning up.

If conditions do not allow, you can also take the following four ways to save yourself:

Ignition gap? In the absence of rivers, streams and roads to rely on, when time permits, light a downwind fire, follow the fire into the burned area to avoid the fire, dig out the wet soil underground by hand, breathe near the wet soil or cover your nose and mouth with a wet towel to prevent carbon monoxide poisoning.

Forcing the wind to cross the line of fire? Avoid running downwind when ignition or other conditions are not available. Choose an area that has been burned or has sparse weeds and flat terrain, cover your head with clothes, cross the fire line quickly against the wind, and enter the burned area to escape safely.

Lie down and avoid fireworks? When it is too late to clear the fire, and there are rivers (ditches), windward flat areas with no vegetation or sparse vegetation nearby, cover your head with clothes soaked in water, put your hands on your chest, and lie down to avoid fireworks. When lying down to avoid the fireworks, in order to prevent the smoke from choking, cover your nose and mouth with a wet towel, dig a hole, and breathe close to the wet soil to avoid the smoke injury.

Fast transfer? When the fire is found and the manpower is out of control, as long as time permits, it should be quickly moved to a safe place to avoid casualties.

Anyway, I hope there are no casualties in this Xichang fire and all the fire fighters can return safely.