Meyer, CP; Cope, M; Lee, S
The potential health impacts from smoke are well known. Protracted exposure of rural and urban populations, particularly the more susceptible groups including the elderly, people with impaired cardiovascular function and allergies, extends the risk from bushfires to the entire population and, in some cases, due to the number of people exposed, may constitute the greatest risk to health. The cost of these impacts can be substantial. Consequently smoke management is now a major issue for fire agencies. The exposure risks vary widely with the class and location of the fire events, and range from extensive fumigation of SE Australian populations from fires that persist for weeks to localised impacts from small fires. The fire decision tools project of the Bushfire Cooperative Research Centre has been developing techniques for assessing the risks and impacts through a series of case studies. The key issue to emerge is not the total emission of smoke, but the extent to which the emissions mix back into the surface layer, and the persistence of the smoke in the air shed.
This study analyses the smoke dispersion and regional health impact on population of three fire events of the last decade: the 2006 alpine fire, the Kilmore East fire of Black Saturday (8th February 2009), and a high intensity prescribed burning event in the Huon Valley, Tasmania in April 2010. Relative health impact was assessed by combining the mean daily surface PM2.5 concentration from smoke during the duration of each event, with population density and the mortality risk factor of 1% increase in mortality per 10 mu g m(-3) increase in PM2.5 concentration. The greatest health impact was from the 2006 alpine fire, which burned 1.1 Mha over a period of 60 days. Smoke from the fire significantly impacted all of Victoria, including the Melbourne air shed, and producing a risk equivalent to an increase in mortality of 84. This was largely due to the long duration of the event which led to widespread smoke dispersion that reflected seasonal climatology. In contrast, the impacts from the Kilmore East fire and the Huon Valley prescribed burning events were minor, primarily because smoke did not impact regions of high population density and the events were of short duration and therefore determined by the weather of the day. All events emitted large amounts carbon to the atmosphere; however the size of the emission was not a reliable indicator of risk to health.
Prescribed burning is extensive, it averages approximately 70% of the annual fire area in Victoria, and is confined to a relatively short season. While individual fires are small and short lived, collectively they are a large distributed source and may function similarly to a single large protracted wildfire event. The policy to increase the current rate by 250% to 400 kha per year therefore will pose significant challenges for regional managers if PM2.5 impacts on population health are to be avoided.