Research Letter #9
WHERE THERE’S SMOKE ...
... THERE’S A HEALTH ISSUE
Most of the concern about the smoke from fires is about health
effects. We hear heaps about the smoke from tobacco but much less
about the health effects of other sources. In building fires the main
smoke problems seem to be caused by: lack of visibility; carbon
monoxide; and, arguably, toxic gases from the breakdown of synthetic
materials (Terrill et al
. 1978; Drysdale 1985). Particulates in
tobacco smoke may be highly toxic too (U.S. Surgeon General 1979).
What about smoke from natural fuels?
Recently, Schwela (1998), of the World Health Organization (WHO),
wrote about the health effects of smoke from natural fuels. The
following points are from his article.
"Specific studies of exposure to biomass smoke or
‘haze’ indicate a consistent relationship between
exposure and increased respiratory symptoms, increased risk of
respiratory illness and decreased lung function."
"Numerous epidemiological studies have also indicated that
levels of suspended particulate matter currently monitored in
many areas of the world are associated with increased daily
mortality, increased outpatient emergency room visits and
hospital admissions, and exacerbation and increase in number of
Studies of firefighters "indicate an association between
exposure and acute effects on the respiratory system." "Symptoms
observed included .. decreased lung function . [and] high
prevalence of headaches, light headedness, cough, wheeze and
shortness of breath." [It is unclear here whether or not he was
referring to rural fire fighters.]
"The association between an increase of daily mortality and
particulate matter concentrations existed primarily in the
elderly and in individuals with pre-existing respiratory and/or
cardiovascular illness. A linear model was found to well
represent the data" [as it did with] "hospital admissions and
various respiratory symptoms". There was no threshold for an
effect. [That is, any increased level of particulate matter
created an increased response.]
"Fire fighters are a particularly fit and healthy group and
cannot be considered representative of the general population."
An expert task force, charged to update the WHO air-quality
guidelines for Europe, did not succeed in doing so.
Choosing a maximum value for the concentration of smoke
particulates less than 10 micron in diameter (PM-10), or less
than 2.5 micron in diameter (PM-2.5), as an acceptable threshold
seems impossible given the relationship declared in the last
point, above. [Remember that most smoke particles from biomass
fires have diameters much less than 10, or 2.5, micron.]
Particulate concentrations, PM-10, vary widely according to
circumstance. Inside houses in some countries values were
850-1400 micrograms per cubic metre over 24 hours (because of
indoor fires for cooking presumably). [For simplicity
let’s call micrograms per cubic metre over 24 hours
"units".] In urban areas values "approximately range from
50-200" units. The PM-3.5 value at a forest fire in Brazil was
190 units – but over a 12-hour period. [PM-3.5 refers to
particles less than 3.5 micron in diameter.] "In a study of 221
fire fighters at 39 prescribed fires, mean .. PM-3.5
concentration [was] .. 0.63mg/cubic metre." [This is 630
microgram per cubic metre. "Prescribed fires" in some countries
mean logging-slash fires.]
By way of contrast the values of PM-10 for Canberra in 1997
averaged about 20 units (ACT Government Analytical Laboratory).
Note that this is about half the minimum of the range of
values recorded for urban areas by Schwela (1998), above. In the
ACT, measurements are made at Civic, Woden and Gowrie every 6 days.
Maximum values in Canberra in 1997 reached 56 units (Gowrie).
Values for the ACT are published every 3 months.
Any raised level of particulate matter in the air can cause a health
problem for someone, especially if they have a history of respiratory
disease or are elderly. Setting a logical standard for air quality,
therefore, is very difficult. Setting realistic standards in relation
to fires could be based on background levels in the area and
documented medical effects of any increased values associated with
bushfire smoke. Thus a "standard" may be set at different levels in
different places. An alternate approach is to set guidelines for the
smoke management of prescribed fires in which the aim is to disperse
the smoke away from urban areas.
ACT Government Analytical Laboratory. ACT Air and Recreational
Water Quality Data (published every 6 months).
Drysdale, D. (1985). An Introduction to Fire Dynamics.
Schwela, D. (1998). Forest fires and their public health impacts:
global aspects. In: D.X. Viegas (ed.) Third International
Conference on Forest Fire Research and 14th Conference
on Fire and Forest Meteorology Proceedings I, 23-37.
Terrill, J.B., Montgomery, R.R. and Reinhardt (1978). Toxic gases
from fires. Science 200 (4348), 1343-1347.
U.S. Surgeon General (1979). Smoking and Health. U.S.
Department of Health, Education and Welfare Publication No.
18 February 1999