The dominance of plutonium in the smoke is especially worrying since it is hard to detect using Geiger counters owing the very short range of the alpha radiation it emits. Yet even small particles embedded in lung tissue can cause cancer.
The Ukrainian National Guard has been put on high alert due to worsening forest fires around the crippled Chernobyl nuclear power plant, according to Ukraine Interior Minister Arsen Avakov.
"The forest fire situation around the Chernobyl power plant has escalated", a statement on Avakov's Facebook page says.
"The forest fire is heading in the direction of Chernobyl's installations. Treetop flames and strong gusts of wind have created a real danger of the fire spreading to an area within 20 kilometers of the power plant. There are about 400 hectares [988 acres] of forests in the endangered area."
He added that there was "reasonable suspicion of intentional arson" since fires had been ignited on both sides of the river.
Police and National Guard units are on high alert. Ukraine's Prime Minister personally went to the affected area to oversee the firefighting. He says the situation is under control, "but this is the biggest fire since 1992."
However, in comments to Russia's Moscow Speaks radio, a representative of Greenpeace Russia said that the situation is much worse:
"A very large, catastrophic forest fire is taking place in a 30-km zone around the Chernobyl power plant. We estimate the real area of the fire to be 10,000 hectares; this is based on satellite images. This hasn't been officially acknowledged yet."
Serious radiation risk from re-suspended 'hot particles'
The potential danger in this fire comes from the radioactive contaminants the burning plants have absorbed, Christopher Busby, scientific secretary of the European Committee on Radiation Risk, told RT.
"Some of the materials that were contaminating that area would have been incorporated into the woods. In other words, they land on the ground in 1986 and they get absorbed into the trees and all the biosphere.
"And when it burns, they just become re-suspended. It's like Chernobyl all over again. All of that material that fell on the ground will now be burned up into the air and will become available for people to breathe.
"Internal radiation from inhalation is very much more dangerous than the background radiation that comes off the ground", added Dr Busby. "People should stay inside. It's extremely serious. They should not go outside and breathe the air.
"This stuff will remain airborne and there will be radioactive particles that can be inhaled. These particles can travel for great distances - its a serious matter if these particles become volatilised in the intense heat that these fires produce. It is quite a serious health hazard."
Huge accumulation of plutonium in radioactive forest litter
Adding to the ferocity of both the fire and the radiation is the fact that the normal decomposing operation of fungi, bacteria and insects in the forests near Chernobyl has been inhibited by radiation, leading to a large accumulation of flammable and radioactive leaf litter, dead trees and branches and other forest debris.
According to a 2014 study published in Oecologia, decomposers - organisms such as microbes, fungi and some types of insects that drive the process of decay - have also suffered from the contamination. These creatures are responsible for an essential component of any ecosystem: recycling organic matter back into the soil.
"The gist of our results was that the radiation inhibited microbial decomposition of the leaf litter on the top layer of the soil", said Timothy Mousseau, a biologist at the University of South Carolina, Columbia, and lead author of the study.
A further 2006 study in the Journal of Environmental Radioactivity reported the results of small controlled fires, stating that "an increase of several orders of magnitude of the airborne radionuclide concentration was observed in the territory near the fire area ...
"The additional inhalation dose for firemen exposed in the affected area can reach the level of the additional external irradiation in the period of their mission. The plutonium nuclides constitute the dominating contribution to the inhalation dose."
The dominance of plutonium in the smoke is especially worrying since it is hard to detect using normal radiation detection systems such as Geiger counters owing the very short range of the alpha radiation emitted by the main isotope found in used nuclear fuel, 239Pu.
239Pu is especially dangerous when inhaled and even small particles of the isotope embedded in lung tissue can cause cancer. But firemen and others using Geiger counters to assess their safety under exposure to the ash would be lulled into a false sense of security - only to suffer the consequences in years to come.
The answer, my friend, is blowing in the wind
Ecologist Dmitry Shevchenko from the Environmental Watch on North Caucasus says it is difficult to predict where exactly the contaminants will go:
"We don't have a real-time monitoring system for the Chernobyl area. We can hypothesize whether the radionuclides will go here or there, but there is no-one who can reliably predict the situation."
Ukrainian emergency services say 182 people and 34 vehicles have been dispatched to fight the fire. A Mi-8 helicopter and three An-32 water dropping airplanes are also working at the scene. The efforts are being coordinated from a mobile emergency headquarters.
According to the head of the Chernobyl Exclusion Zone management department, radiation levels in the area remain normal. "The area on fire is relatively clean," Vasily Zolotoverkh told the newspaper kp.ua.
He said the fire started at lunchtime, when emergency workers had finished putting out an earlier blaze which started during the night. The emergency services have stated that it could have been caused by a lit cigarette.
Ukraine's acting head of emergency services said earlier the forest fires were not a threat to the sarcophagus sealing off Chernobyl's crippled Reactor 4.
Chernobyl and the surrounding area have been abandoned and remain off-limits following the April 1986 disaster, when an explosion and fire released massive amounts of radioactive material into the atmosphere. Increased radiation levels were detected throughout Europe.
Chernobyl became the worst nuclear disaster in world history in terms of casualties and clean-up costs. Reactor 4, where the blast took place, was sealed off in a giant reinforced concrete sarcophagus to prevent further leaks.
This article is based on an article originally published on RT with additional reporting by The Ecologist.