Wood smoke is worse than cigarette smoke

Underestimated health hazard from wood smoke

Winter time is known to be fireplace time, especially when it's as cold outside as it is right now. And since the trend is not only towards fireplaces and wood pellet stoves in this country, it is time to point out the underestimated dangers of wood stoves. The smoke from burning wood is far more harmful to health than the exhaust gases from most other fuels.

Humans have been warming themselves in open fires for hundreds of thousands of years, but of course one cannot infer from this that it is safe to breathe the siff. Thanks to its compact structure, wood tends to burn incompletely, especially in open fireplaces, and this creates a lot of unpleasant substances.

In addition to the classic combustion products carbon dioxide and water, which do not bother us any further, large amounts of carbon monoxide (a few ppm in the flue gas), nitrogen oxides (a few ppb in the flue gas) and organic compounds are produced. Alkanes and alkenes mainly appear in the gas phase, while the more dangerous polycyclic aromatic hydrocarbons (which can produce up to several micrograms per kilo of wood) mostly stick to the solid smoke particles. There are also aldehydes, alcohols, carboxylic acids and various types of aromatics, which are distributed among gases and solid particles. The aromatic hydrocarbons come mainly from the lignin, which makes up about a third of the mass of wood, which is why there are so many in it - according to the literature, aromatics are produced in quantities similar to carbon monoxide.

Two million deaths a year

Wood smoke is a major problem in less developed countries, especially in rural areas. In many regions, wood is still the most important source of energy. The technical and social conditions in particular also mean that the health effects of wood smoke are multiplied there. Open wood stoves are less efficient than modern wood pellet heating or the closed fireplaces, which are common in this country, so that more wood has to be burned for the same effect. Sometimes the fuel itself is of poor quality. Fireplaces without a vent, which release wood smoke directly into living spaces, are also a real problem - scientists suspect that around half of all households around the world still cook in this way with solid fuels. Researchers estimate that even today most of the world's particulate matter is due to wood in low-tech fireplaces, and the lion's share of the toxins that are created are inhaled by women who continue to cook in much of the world and their young children that they usually have around when cooking.

Accordingly, more and more studies are linking solid fuels to poor health. According to WHO estimates, around two million people die each year as a result of wood smoke, half of them children under the age of five. There is evidence of a link between wood smoke and respiratory infections in children and chronic bronchitis and lung cancer in adults, especially women. Wood smoke triples their risk of developing chronic bronchitis. According to some studies, wood smoke also promotes tuberculosis - in animal experiments, even low concentrations hinder the transport of pathogenic bacteria from the respiratory tract. Overall, indoor wood smoke causes over three percent of all healthy years of life lost (DALY) worldwide, roughly comparable to a lack of malaria prevention and obesity.

Amazingly, there appears to be only one controlled human exposure study of the effects of wood smoke, and a very small one at that. According to this, smoke gases seem to stimulate inflammation processes even after brief exposure. In animal experiments, researchers found consistent damage to the epithelial cells of the airways and lungs. The damage is probably caused by toxic organic compounds that get into the lungs with smoke particles. Remarkably, low smoke concentrations, at which no acute damage occurs, seem to change the immune response of the epithelial cells permanently, so that even low concentrations of smoke particles could have a negative effect. The whole mixed poke is also potentially carcinogenic - in animal experiments, an extract from wood smoke produces tumors 30 times as effective as cigarette smoke.

Dangerous particles

We westerners cannot feel safe either. We have better stoves and less smoke in the apartments, but wood heating is on the rise again in this country - it is sustainable. The problem, however, is the smoke particles. The most significant fraction of these particles is smaller than a micrometer and penetrates deep into the airways. That these particles are so fine has two additional effects that we should be concerned about. On the one hand, the particles do not settle, but float in the air for a very long time - accordingly, the wood smoke stays for a long time, especially indoors, and of course wafts through the neighborhood after it has left the house through the chimney. Studies show that the fine smoke particles penetrate the interior from the outside without any problems, so that you can get the smoke from the neighbor's chimney into your own room, regardless of whether the windows are closed or not.

The smoke particles have it all. They carry the dangerous substances deep into the lungs and dump them there in a concentrated manner. The particles consist of about one fifth of elemental carbon, the remainder are inorganic ash and the various combustion products that have condensed on the particles. Studies from the 1990s in Canada and the USA indicate a connection between particles from wood smoke and impaired lung function, especially in children - such studies also show a dose-response relationship, i.e. the more smoke, the greater the damage. The effects of open fireplaces, which release smoke particles directly into living spaces, are more pronounced than with stoves. There, four hours of exposure per day increase the likelihood of respiratory problems such as coughing or chest tightness by around 15 to 20 percent.

All of these studies necessarily have methodological problems - in most cases the data on actual exposure are quite sketchy and certainly not standardized, and of course a great number of different factors are brought together, for example different types of fire places. However, there are a number of dose-dependent effects, ranging from slight irritation to serious respiratory damage with hospitalization. We don't know how big the problem is, but we can assume that the dangers of wood smoke are very real.

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  • Tags: asthma, health, heating, wood, fireplace, cancer, medicine, pellets, smoke, technology, apartment