Where there’s smoke: Protecting yourself from air pollution at home

During the 2019-2020 summer, bushfires raged across Australia, destroying homes, forests, farms and lives. Now, as the colder months approach, the fires have stopped burning and the world has moved on to other pressing concerns. But it is important to learn from our experiences. 

Besides the destruction caused by the flames, the fires caused lower level but widespread problems across much of Australia because of smoke. Huge, sprawling smoke clouds spread over hundreds of square kilometres for weeks, causing sustained extreme air pollution even in towns and cities far from the fire fronts. 

Smoke emits various kinds of toxic air pollution. One measure of this is the concentration of particles less than 2.5 micrometres in size, or PM2.5. A level of 50 micrograms per cubic metre (µg/m3) is considered hazardous. In my hometown of Canberra, the city most affected by the bushfire smoke, the PM2.5 level is usually less than 10µg/m3. During the fires it was routinely over 50, often in the hundreds, and hit peaks over one thousand. On days of heavy smoke, the health centres and hospitals experienced influxes of people with respiratory problems. Health experts have noted that the sustained PM2.5 levels were “unprecedented” for a large urban population and will likely have long-term health impacts. Living in Canberra, I experienced this intense, sustained smoke first-hand. 

It was an extraordinary climate event (using climate in the broadest sense), unprecedented in living memory, and hopefully one that we will not experience again any time soon or with regularity. But massive fires could happen again, or some other sustained pollution event could occur. 

Keeping people safe and healthy meant keeping them out of the smoke. With the fires behind us, now is a good time to ask: How did Australian homes perform during the 2019-2020 summer fires? What could we do differently, to help them perform better next time? 

The answer to the first question is ‘poorly’. And not only homes but commercial buildings too. On one particularly smoky day, smoke haze was visible inside Canberra’s shopping malls. Many offices had high concentrations of indoor pollutants but continued to operate anyway. The logic in staying open was that they were not endangering the welfare of employees, because those employees were experiencing just as much particle pollution at home as at work. That may sound callous, but the employers were right: smoke infiltrated all Canberra homes. Even high-performance homes such as those designed by my company Light House Architecture & Science, as well as those built to Passive House guidelines, were not immune to smoke infiltration. 

As Sanctuary readers know, an airtight building is a more energy-efficient building, because it allows in fewer cold draughts in winter and less hot air in summer, stabilising the indoor temperature. It’s important though to allow plenty of opportunities to vent an airtight home with openable windows and possibly mechanical ventilation with heat recovery (MVHR) systems. An airtight home has another benefit: you can close it up and stop outside pollutants coming in, then open up when they have dissipated. This applies not just to bushfire smoke but to pollen, dust and your neighbour’s barbecue smoke. 

That’s the principle that people in the efficient home design business, including me, have worked with. Close up when the air is bad, vent when the air is clear. That system didn’t work last summer with several weeks of extreme bushfire smoke. Highly airtight houses stayed smoke-free for longer than leaky houses, but they eventually caught up. 

The smoke had detrimental effects on air quality in airtight homes in more indirect ways. I mentioned that one of the principles of energy-efficient design is venting. In summer, we close up our airtight, passive solar house during the day, then open it up when the external temperature drops: we describe this as designing for good cross ventilation to cool the house naturally in summer. This was not possible during the fires because ‘venting’ meant that the house would quickly fill with unbearable levels of smoke. The other problem is that if a house is tightly sealed for an extended time, indoor air quality gets worse from the things, residents and activities inside a home. Moisture, carbon dioxide, cooking by-products and other things can build up and compromise our health. 

The reality is that there is no way to keep out sustained pollution with building design alone. It doesn’t matter how airtight your house, unless you like to get around in scuba gear, the air you breathe when you’re inside comes from outside. Airtightness helps, but it is not enough on its own.