Bushfire, like cigarette and wood-heater smoke, consists of tiny particles less than 2.5 millionth of a metre - called PM2.5. They are so small they behave like gases. Like the air we breathe, PM2.5 enter our homes even when all doors and windows are shut.

Their small size allows them to penetrate the deepest recesses of our lungs. They cause inflammation, and can cross into the bloodstream to transport toxins (e.g. nicotine, or cancer-causing chemicals) to every organ of the body, including our brains.

PM2.5 pollution increases the risk of high blood pressure, heart attacks, strokes, dementia, lung diseases, cancers, and many other ailments, including those affecting the health of young and unborn children.

A pollution reading of over 200 is considered hazardous. On Sunday from 5 to 6 pm, ours was 1599!

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The good news is that our health can be protected by using HEPA (High Efficiency Particulate Air) filters; they trap 99.97% of the PM2.5 inside our homes and cost as little as $100.

Most have multi-speed fans and operate quietly overnight. Cheaper models often filter a small area - great if you don't need the whole house. Costlier models can make use of particle sensors to increase the fan speed when high levels of indoor pollution are detected.

A study compared blood markers of healthy volunteers in a small Canadian town with average outdoor PM2.5 of 10 ug/m3 from wood-heater-smoke. To avoid possible biases, the volunteers didn't know whether the HEPAs were in filter or sham mode. Blood inflammatory markers (and indoor PM2.5) were significantly lower when the units really were filtering the air in their homes.

Many other studies show similar results, confirming that HEPA filters protect us. Staying inside without filtration or avoiding outdoor exercise doesn't have the same benefits.

Armidale residents can use a Purple Air system to warn us when smoke levels are high, so we can use filters before hazardous PM2.5 levels build up inside our homes.

Armidale Regional Council recently declared a Climate Emergency. This year's unprecedented drought and bushfires is a foretaste of why we need to take urgent action to reduce emissions and allow our region to enjoy cheaper, reliable, renewable energy.

But we'll also need to adapt to a warmer climate, perhaps building more energy-efficient airtight homes that resist bushfires, and equipping them with HEPA filters to protect our heath.