Woodburners triple the level of harmful pollutant particles inside homes and must be sold with a health warning, the scientists warned, advising people not to use them near the elderly or children.
The tiny particles “flood” the room when the burner doors are opened to refuel, their study showed. Furthermore, people who load firewood two or more times during the night experience pollution peaks two to four times higher than those who refuel only once or never.
The tiny particles can pass through the lungs and enter the body and have been linked to a wide range of health damages, especially in children and the elderly. For these groups, the use of wood burners should be avoided, the researchers said, particularly since Covid-19 restrictions mean that people spend more time indoors. Dirty air has also been linked to an increase in coronavirus infections and deaths.
The investigation was carried out over a month in 19 homes in Sheffield in early 2020. The wood burners used were all government-certified “smoke-free appliances”, meaning they produce less smoke. But this and the new EcoDesign standard, which will be mandatory in 2022, only assess outdoor pollution.
The government is phasing out the sale of wet wood, which produces more smoke, but the people in the study only used dry, cured wood. It is estimated that the burning of wood and charcoal in homes causes nearly 40% of minute particle pollution outdoorsBut the new research is among the first to look at indoor pollution in real-life settings. Almost 16% of people use firewood in the south east of England and 18% in Northern Ireland, according to 2016 government data, and around 175,000 wood burners are sold each year.
“Our findings are cause for concern,” said Rohit Chakraborty of the University of Sheffield, who led the study. “It is recommended that people living with people particularly susceptible to air pollution, such as children, the elderly or the vulnerable, avoid the use of wood stoves. If people want to use them, we recommend minimizing the time the stove is open during lighting or refueling. “
Wood burners cause less indoor pollution than open fires. “But every time you open the door, you turn the stove down to an open fire and particulate matter floods the house,” he said. Spikes take an hour or two to dissipate. “But when the time comes, someone opens the door again to refuel and you get pick after pick,” Chakraborty said. Some burners have filters, but these only reduce pollution that is vented to the outside.
Some people without central heating rely on wood burners for heat, and Chakraborty did not ask for a ban. “We should let people decide, but they should at least know what’s going on and of course not use it if they don’t have to.”
The study, published in Atmosphere magazine, analyzed data collected every few minutes from household pollution monitors and in total evaluated 260 uses of wood burners. The results showed that the burners generally lit for about four hours at a time and during this period the level of harmful particles in homes was three times higher than when no stoves were used.
During those four hours, average particulate levels rose between 27 and 195 micrograms per cubic meter of air. The World Health Organization limit is 25 μg / m3 for 24 hours. “Epidemiologists increasingly recognize that exposure to high intensities of [small particles] over much shorter periods of time, hours rather than days, is linked to a variety of health problems, ”the researchers wrote.
They concluded: “It is recommended that new residential stoves be accompanied by a health warning at the point of sale in order to indicate the risks to the health of users.” Government approval schemes should also assess indoor pollution, the scientists said.
Increased outdoor air pollution and kitchen fumes were ruled out as causes of indoor peaks. Particulates are the most harmful pollutants in wood smoke, but also contains carcinogenic chemicals including benzene and formaldehyde.
“Rather than being seen as a harmless appliance, wood stoves should be recognized as potentially harmful,” said James Heydon of the University of Nottingham and part of the study team. “Most of our participants were not aware of this and more needs to be done to raise awareness of the risks.”
Three of the households in the study stopped using their burners after seeing the results, and another 12 took action, such as refueling faster or less frequently, or making sure the firewood was really dry.
“There is no reason to believe that particulates from wood burning stoves are less toxic than those from other sources, such as the burning of fossil fuels,” said Professor Jonathan Grigg, from Queen Mary University of London, who led a recent report on the health effects of indoor air pollution on children for the Royal College of Physicians and the Royal College of Paediatrics and Child Health.
“This study confirms that indoor wood burners contribute significantly to indoor air pollution,” he said. “It also suggests that even government-certified solid fuel stoves harm local outdoor air quality. Therefore, it is difficult to justify its use in any urban area ”.
A Defra spokeswoman said: “Air pollution has dropped significantly in recent years, and fine particulate matter emissions fell 9% in the last decade. But we know that there is more to do and domestic burning is an important factor ”. The next environmental bill will facilitate local authorities to enforce existing restrictions within smoke control areas, he said. But the ministers do not plan to ban the wood burners.
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