Deadlier than flames: The devastating impacts of bushfire smoke

2023 has made headlines as the hottest year in recorded history, and Australia is gearing up for a serious bushfire season. In today’s post, VicHealth Postdoctoral Research Fellow Rongbin Xu (@RongbinXu) of Monash University (@MonashUni) shares his research into how bushfire smoke is an increasingly hazardous public health threat and needs a more focused policy response.

Bushfire smoke is deadly

Policy responses to bushfires have not focused enough on the health dangers of smoke, which impacts more people and are often deadlier than the fires themselves. Photo credit CazzJj on Wikimedia Commons.

Bushfires, also often called wildfires, refer to uncontrolled and unplanned fires burned at vegetation lands. Climate change is making bushfires increasingly severe and frequent through inducing hotter, drier and windier weather.  Bushfires have been recognized as one of the major threats to the public health, as highlighted in the Lancet and MJA-Lancet countdown reports on climate change and health.

For Australians, the most devastating bushfire event in recent years was the 2019-2020 Black Summer Bushfires, which killed 34 people, destroyed more than 5,900 houses, burned over 24 million hectares of land, and killed or displaced 3 billion animals.. In addition to the devastating effects of bushfire flames, which are restricted to fire-prone areas, the health impacts of bushfire smoke are often both overlooked and underestimated.

Bushfire smoke can often travel hundreds and sometimes even thousands of kilometers. The smoke from the Australian Black Summer bushfires travelled to South America, showing up in satellite images. In July of this year, the wildfire smoke from the record-breaking bushfires in western Canada traveled to eastern US, and making many US cities (including New York) covered by heavy smoke and very poor air quality.

The ability of smoke to travel vast distances makes the population affected by bushfire smoke much larger than those affected by bushfire flames. As the planet warms, smoke from bushfires is increasingly a public health concern.

Our exposure is increasing

I recently led a study that documented an increasing trend of global air pollution caused by landscape fire smoke from 2000 to 2019.  Here, the landscape fires include both bushfires and fires induced by human activity (e.g., prescribed or agricultural burns). This is because currently most researchers rely on satellite images or satellite-based products to identify fire events, but the satellite cannot tell the difference between bushfires and non-bushfires.  Given that human induced fires only account for a small proportion, all landscape fires detected by satellites are treated as an acceptable surrogate measure of bushfires.

The study assessed global daily landscape fire sourced PM2.5 and ozone, both are major pollutants in fire smoke that can travel far and affect large swathes of the general population. PM2.5 refers to particles with a diameter of 2.5 micrometres or less, which is less than 1/20 of the diameter of human hair. With this small size, these particles dive deep into human lungs and the bloodstream, causing various health impacts, such as cardiorespiratory diseases (e.g., asthma, respiratory infection, heart attack and/or stoke), lung cancer, and even death. While the ozone in the high atmosphere layer (15 to 35 kilometres above Earth's surface) protects humans from harmful ultraviolet radiation, it becomes harmful to human health when it is at the earth’s surface where humans inhale it. Ozone is a powerful oxidant that can irritate human airways significantly, which can also cause or exacerbate various health risks like those caused by PM2.5.

 Our analyses estimated that 2.18 billion people were exposed to at least one day of substantial fire-sourced air pollution (SFAP) per year, with each person in the world having on average 9.9 days of exposure per year. A day of SFAP was defined as daily PM2.5 or ozone levels exceeding the WHO guideline values (representing a value that will induce notable acute health impacts), and at least 50% of the PM2.5 or O3 were contributed by landscape fire emissions.

Here at home, almost all Australians has exposure to at least one day of SFAP in 2019, and on average each Australian was exposed to 31 days of SFAP.

Many studies, both Australian and global, have found that exposure to high levels of fire-sourced PM2.5 can induce increased mortality, hospital admissions, and emergency department visits within a few days following the exposure. The team led by Prof Fay Johnston from the University of Tasmania has estimated that population exposure to bushfire-sourced PM2.5 during the “Black Summer” was responsible for 417 excess deaths, 1,124 cardiovascular and 2,027 respiratory hospital admissions, and 1,305  asthma-related emergency department presentations in Australia.6 This is much more than the 34 direct deaths caused by the “Black Summer”.

Policy gaps in Australia’s current bushfire response

Despite the health impacts of bushfire smoke, Australia’s current  strategies focus more on the bushfire flames in the application of disaster and emergency management frameworks. For example, in September 2022, the National Emergency Management Agency was formed to provide national strategic oversight and coordination during major bushfire disasters.

However, response to bushfire smoke is an underdeveloped aspect of government adaptation policy. My colleagues and I have stated: “Policy attention is needed to identify groups most vulnerable to smoke, including understanding regional and local scale human smoke vulnerability to plan targeted warnings and other prevention responses. Local governments should consistently include smoke health risks in municipal bushfire planning. Both state and local governments should work more closely to assess smoke vulnerability at regional and local scales.”

In order to successfully adapt to bushfire smoke risks in a warming climate, further policy development is required, including but limited to：

• nationally consistent real-time air quality monitoring, early warnings targeted at at-risk groups (e.g., elderly people, children, pregnant women, people with pre-existing illness, outdoor workers)

• mask access and messaging, health education

• outdoor worker safety

• building ventilation designs, safe air shelters

• secure access to health services and supply of medicines

• cross-jurisdictional smoke management.

The management of bushfires and bushfire smoke are not mutually exclusive, but often crosses different government agencies. Generally, bushfire warnings and smoke hazard alerts are governed by fire and emergency management agencies, while detailed smoke health warnings come from public health or environmental agencies. Co-operation and cross-jurisdictional collaboration are critical to promoting consistent responses, increasing community confidence and reducing conflict or duplication in responses across Australia.

Dr Rongbin Xu currently holds a VicHealth Postdoctoral Research Fellowship. His research will map the effects of extreme heat and bushfire smoke across Victoria, calculate the health impacts, and generate appropriate policy responses. His views may not reflect the position of VicHealth.

Posted by @SusanMaury