From Spain to France and Portugal, from California to Siberia.
The wave of devastating forest fires and flames does not stop.
But there are other fires less known that can be equally destructive: those of latent combustion.
These fires without flames are so difficult to fight that one of them, in Australia, has been burning for at least six thousand years, Spanish engineer Guillermo Rein, professor of Fire Sciences in the Department of Mechanical Engineering at Imperial College, told BBC Mundo. in London.
And among the latent combustion fires, there is a particularly complex and surprising type: the so-called “zombie fires”.
Guillermo Rein explained to the BBC World what kinds of fires there are, why when escaping we should never run up a slope and how fires that “seem to come back from the dead” come about.
What types of fires have you Y?
There are different types of fires depending on where the combustion is seen, pointed out the expert from Imperial College.
“If the combustion occurs in the treetops, the flames they are very tall. These fires are tremendously dangerous and ferocious”.
“Something more normal and intermediate in ferocity is what happens when what is burning is the surface fuel, the bushes, the grass, the small trees, the fuel that we see at our height”.
The third type is latent combustion, the fire that has no flame and in which what burns is the soil.
“Not all soils are combustible, but when they are flammable, as in the case of peat, the soil burns without flame”.
What is peat and how does it ignite?
“If the humidity is very, very high, that is, if it is basically flooded, or it is very cold, like near the poles, the forest vegetation that falls to the ground does not degrade. There are no germs, no bacteria that eat it, so it accumulates and compacts,” Rein explained.
What results from this process is peat, a carbon-rich material that can be thousands of years old.
“Basically, when we pick up peat with our hands the deeper we go, we are talking about forests that may be older than humans coming out of Africa”.
The peat must be either very wet or very cold. But if it is dry and hot it becomes a flammable material, explained engineer Rein.
“Typically what can happen is a forest fire with a flame, for example by lightning or by human action. The flame that ignites the peat is extinguished but the peat continues to burn for weeks, months or years”.
Although all smoke is toxic, in the case of smoldering combustion fires “smoke is the most toxic known”.
“It is the smoke that has been registered, for example, in peat fires in Indonesia. As there is no flame, the smoke is not very hot and does not rise by buoyancy, it stays on the ground where people are”, said Rein.
Although they can be devastating, the absence of flames makes that it is difficult to convey in the media “the immensity or horror of smoldering combustion fires”.
What are zombie fires?
Zombie fire is a type of smoldering peat combustion.
“The zombie name has been a fantastic success. It is an informal name, but it works very well to communicate”, Rein pointed out.
The term was first used by scientists in Alaska to describe fires that occur in summer.
“There are flame fires that occur in summer. Then the flame is typically extinguished for natural reasons, because it reaches a river or it rains and everyone is very happy”.
“But they haven’t realized that the mob it has caught fire and is starting to burn downwards”.
When the snow arrives it covers the ground completely.
“But the fire continues below. The insulating layer of snow protects the smoldering combustion underground and when spring comes and the snow melts, the smoldering combustion rises to the surface and is even capable of igniting flames“.
“The fire that was extinguished last summer then returns to the same place, but people cannot find out what the possible ignition process is.”
“They are fires zombie in the sense that they thought they were dead but they were alive like zombies and then they scared us again”.
Can there be zombie fires in places where there is no snow?
The term is usually reserved for fires in areas where it is very cold, such as Alaska or Siberia.
Rein pointed out that there are also fires well-known smoldering combustion in sites without snow. But it is not known if they could be properly called “zombie fires” because it is unknown if there were flames at first that were extinguished or if they started directly as smoldering combustion, in what is called selfheating or self-heating.
The oldest fire known to mankind is in Australia and is Burning Mountain or Burning Mountain, as Mount Wigan is popularly called, about 220 km north of Sydney.
“It is a case of latent combustion, but not peat , but the peat after several million years became coal, it is the fossilized forest of antiquity”, explained the expert from Imperial College.
“It has been burning for at least six thousand years under the mountain following the coal seam”.
Another famous case of latent combustion is that of Centralia, a town in Pennsylvania, United States United States.
“In the years 63 Centralia er to a very tiny mining town”.
“There was a mine where people worked and extracted coal,” said Rein.
“And one day on a holiday they lit a fire and the fire ended at the entrance to the mine and set the mine on fire. The flames ended but since 220 have not been able to extinguish the latent combustion“ .
“The fire has moved into the galleries of the mine that are below the town of Centralia, creating sinkholes. And smoke comes out everywhere with sulfur, with toxic smoke. That is why the United States government had to close the town.”
How do you fight zombie fires?
“It is really very difficult. In fact, the vast majority of the time they cannot be turned off, only the smallest ones”, Rein pointed out.
“But the ones that concern us the most, in Siberia for example, start to go very deep and continue to consume fuel. The density of the peat is very high and they produce a lot of smoke. In fact, smoldering fires produce more smoke than flaming fires.”
The most effective way to put out a zombie fire is to flood the ground, said the Imperial College expert.
“Peat occurs on sites that flood naturally. So, basically, if the water has disappeared, it has to be brought back.”
“In the United States, smoldering combustion fires have been extinguished by flooding the land, but with a gigantic human effort. We are talking about hundreds of water pumps, or 87, 138 firefighters working for a month and moving a lot of water . Or to temporarily divert the course of a river”.
“Another response is not to turn it off but to reduce its impact, for example, by compacting the soil with tractors. That prevents oxygen from reaching the smoldering combustion. It doesn’t turn it off, but it makes it weaker”.
What is the most effective way to fight flame fires?
“The most effective way to put them out is with firefighters on the ground who create trenches in which they remove fuel, vegetation . They create a firewall in real time”.
The role of helicopters or planes is to drop water with chemical retardant products to slow down the fire and give more time to firefighters. (Photo: GETTY IMAGES)
“They cut down trees, remove bushes, remove weeds. Imagine that the physical effort is brutal”, said Rein.
The emphasis on audiovisual is always in images of airplanes and helicopters, “but really the action, the merit, is in the people on the ground”.
The function of helicopters or airplanes is to drop water with chemical products retardants to slow down the fire.
“The water wets the vegetation, which slows down the flame, and gives the firefighters on the ground more time to build firebreaks”.
What determines how fast a fire spreads? And why when escaping you should never run up a slope?
There are three elements that define speed of the flame, explained Rein.
“Number one is the fuel. There are pine trees, for example, which are less combustible”.
“Another factor is the weather, that is, the wind and the humidity. Fire spreads much faster in the direction of the wind than against it, and wet fuel is not the same as dry fuel”.
The third is the topography.
“Due to gravity, the flame always goes upwards. It is because if a gas is hot it expands, and as the weight per unit of volume expands, the density decreases”.
“And the surrounding air, which is cold, weighs more, lowers and pushes the lighter air up”.
“Then , if there is a sloping ground, the heat has to travel less space upwards than downwards”.
The flame always heats the fuel that is above it more, so it spreads faster in that direction, Rein explained.
“The fire always goes much faster uphill than downhill. And so if we see a fire and there is a slope, we should not go up. We have to go down”.
What are the fires so powerful that they create their own weather?
They are the fires that in English are called megafires or megafires.
“No can be turned off, it is absolutely impossible. The firefighters can only wait for it to fade somewhat and turn into a normal fire,” said Rein.
“These fires produce giant flames and drafts. The flames consume oxygen and create winds”.
“ And the smoke that rises up into the atmosphere carries a lot of water vapor. Because the combustion process generates water vapour, it is one of the combustion products in engines”.
“These fires take a lot of water into the atmosphere, which creates clouds, and these clouds are charged with particles and then they create electrical charge, lightning, rain”.
“So what you have is an absolutely gigantic fire that creates a mini-meteorological system with its clouds, with its rains, with its lightning and its winds”.
Is the number of fires increasing globally?
Studies with satellites have determined that globally the number of fires is neither increasing nor decreasing, said Rein.
“But the number of fires is not the problem. The problem is the damage they cause”.
“The damage can be measured by the size of the fire, how much area has been burned, or by the danger it has created for human beings”.
“And when we measure that, the size or the danger they have generated, what we see is that year after year the impact of forest fires is increasing“.
What is the most worrying thing currently in relation to fires?
“I am concerned that unfortunately it is still not understood at a global level what to do with forest fires”.
Rein pointed out that for millions of years there have been fires with beneficial effects on ecosystems, since they create clearings in the forests for new vegetation, or favor the cones of some tree species to open and release their seeds.
“Not all fires are bad and if all the fires are put out, the problem could be even more serious“, explained Rein.
“This is what has happened, for example, in the United States, with what is known as the ‘exclusion of fire ‘”.
“The United States has been putting out forest fires for a hundred years. They have excluded fire from many forests and many ecosystems, so the forests have been accumulating fuel, dead matter. And this means that now when there is a fire it will be much bigger”.
“It must be shown that burning every twenty years with a low-intensity fire, in spring, when the vegetation has more moisture and is not very hot and the subsoil is moist, basically cleans the undergrowth”.
Rein is also concerned about the uncertainty about the future impact of climate change.
“Global climate change is warming the planet”.
When vegetation heats up, it loses water and that increases the flammability of the vegetation, the expert pointed out.
“So what climate change is doing is that globally, not in all places, but in most of the sites, is increasing the flammability of the vegetation, which means that it can light more easily and that when it lights the fire it will be faster and with higher flames”.
What can Latin American countries do to better prepare for forest fires?
“The idea is to prepare, but preparing is not just having firefighters with large trucks full of water or having planes and helicopters.”
“That is very important, but it is the last thing. Basically after that we have nothing”.
“There are many things that can be done beforehand. For example, create knowledge at the community level to clean the forest“.
“The communities that live inside the forest can also be prepared so that when the fire comes it does not destroy everything”.
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“That is done a lot in the United States. Communities have to take a look at their immediate environment and take into account how flammable it is“.
“They can, for example, cut off the continuity of fuels, the line of bushes to the house, or change the trees for trees that are more protected from the fire, or put roofs that are not made of wood but of ceramic tiles”.
“Obviously they are going to have a scare, they are going to have best to evacuate. But that town is much more resistant to fire.”
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