What's All The Fuss About?
Most of us are aware of the obvious problems associated with woodsmoke - irritation of the nose, sinuses, and throat, coughs, hair and clothes smelling of smoke, being unable to open windows because of a neighbour's smoking chimney, finding it difficult to exercise outdoors in the evenings. But is it just an irritating annoyance, or can woodsmoke actually be harmful?
The fact that woodsmoke poses a real risk to health arises from two sources
1. Health Risk from Fine Particles
In Sydney, Dr Geoff Morgan of NSW Health analysed the relationship between particulate air pollution and death rates. After adjusting for temperature, weather and seasonal variation, a robust relationship was found between particle pollution and death rates. It is estimated that 400 people die prematurely each year in Sydney from particulate air pollution. Particle levels (and deaths) were generally found to be higher in the colder months, when two thirds of these particles originate from the 13% of households which burn wood. In Armidale, about 55% of households use solid fuel and 40-50% of these (ie 25% of households), use the heater 24 hours a day. This explains why Armidale has very much higher levels of particle pollution than Sydney. (See comparison with Sydney, above).
This graph shows annual mortality vs annual PM2.5 air pollution (from Dockery et al., New Engl J Med, Dec 1993). Note the 6 US cities were chosen to be representative of the range of air pollution in the US. The value for Armidale isn't strictly comparable. It applies to winter only. Outside the wood heating season, Armidale air pollution is virtually zero.
Numerous other health studies around the world have confirmed
the association between fine particulate air pollution and
adverse respiratory and cardiac health effects. A recent World
Health Organisation report concluded that there was no safe level
of particulate air pollution.
Researchers at Harvard University have recently conducted an experiment, involving two groups of rats with bronchitis, one group were exposed to air with particulate concentrations similar to those measured in parts of Armidale ( graph ), and the other group exposed to filtered air only. 37% of the rats exposed to the particles died within 3 days, while none of those in the second group died. This result demonstrates a direct cause and effect relationship between fine particles and premature death.
More information can be obtained from:
EPA fact sheet: Health And Environmental Effects of Particulate
Matter A very good summary of the health effects.
Readable article in the Philadelphia Enquirer
Harvard Uni Summary
Research idea for Armidale
Premature mortality due to particulate pollution in 239 American Cities
Summary of studies of respiratory effects of exposure to wood smoke.
Research report showing woodsmoke inhalation compromises important pulmonary immune defence mechanisms leading to increased incidence of respiratory infection.
Recent report on relationship between PM10 air pollution and causes of infant deaths in the U.S.:-
Overview of report and access to copy to download
Authors' abstract of report
2. Health Risk from Carcinogens
We may think of air pollution in the US as predominantly from cars, but 42% of cases of failure to meet air quality standards were due at least in part to residential wood burning (RWB). In addition, more than 30% of all mutagenic (cancer-causing) material emitted to the atmosphere in the US each year comes from wood combustion. The proportion in areas with cold winters and significant numbers of wood heaters would obviously be much higher.
A US EPA study (Lewtas et al., 1991) has concluded that the lifetime cancer risk from woodstove emissions may be 12 times greater than exposure to an equal amount of cigarette smoke.
A recent research study has found a direct link between a specific carcinogen found in woodsmoke and cigarette smoke, and mutations in the gene associated with human lung cancer. Benzo(alpha)pyrene is one of several carcinogenic chemicals which have been measured in woodsmoke. In fact, over 100 chemicals found in cigarette smoke have also been identified in woodsmoke. In Launceston, Tasmania, which experiences similar levels of woodsmoke to Armidale, but with a larger population exposure, "disturbingly high levels of carcinogens such as benzo(a)pyrene" were measured in 1991 and 1992, which were 2 - 3 times higher than levels measured in London over a similar period. (Report on an investigation by an expert Working Party into Air Pollution, Environmental Health & Respiratory Diseases, Launceston and Upper Tamar Valley, Tasmania, 1991-94.)
prepared by Doug Johnson, at the Ministry of Environment, British
Columbia, contains a good overview of the byproducts of woodsmoke
combustion, and their associated health effects. This is well
worth reading before you light the fire tonight. British Columbia
has serious problems with several areas impacted by woodsmoke
pollution from residential woodburning, burn-off of land clearing
residue, and burning of saw-mill residue. This document describes
how harmful byproducts are formed from the hydrocarbons and
organic compounds in wood, if the combustion process is starved
of oxygen or if the wood has a high moisture content. "Many
of the pollutants contained in wood smoke are strongly associated
with chronic respiratory impacts such as increased airway
resistance and decreased vital capacity. Most researchers believe
that these impacts far outweigh all other possible human health
"Common pollutants produced by incomplete combustion of wood (PIC), and their potential human health impacts, are :-
For detailed chemical analysis of woodsmoke see also the paper by J A Cooper and analysis by US EPA.
How does wood heating compare with other heating methods.