Bushfire smoke and your body: a Perth guide
Perth doesn't need a fire on its doorstep to get smoky air. This guide covers what smoke does inside the body, who feels it most, why Perth gets more of it than people expect, and what to do on a bad air day.
What's actually in smoke
Bushfire smoke is a mix of gases, including carbon monoxide, nitrogen oxides and a long list of organic compounds, and particles. The particles do most of the damage. Health agencies track two sizes: PM10, particles up to 10 micrometres across, and PM2.5, those up to 2.5 micrometres. A micrometre is a thousandth of a millimetre.
Most of the particle load in smoke falls in the PM2.5 range. That's why smoke is much harder on the body than a dusty day, and why a HEPA filter, which is built to trap particles this small, is the right tool indoors.
What it does to your body
Size decides where a particle ends up. Larger ones mostly get caught in the nose and throat, which is why dust tends to make you sneeze and cough. PM2.5 travels further, into the small airways and air sacs deep in the lungs, and the very smallest particles can pass from the lungs into the bloodstream.
Once there, they drive inflammation through the body. That's the reason smoke is linked to heart attacks and strokes as well as asthma, and why the heart-related hospital figures below are so high.
Within hours or days
- Stinging eyes, runny nose and a scratchy throat
- Coughing, wheezing and chest tightness
- Asthma attacks and flare-ups of COPD
- More heart-related emergencies in people with heart disease
Over years of exposure
- Higher rates of heart disease and stroke
- Reduced lung function and chronic lung disease
- Lung cancer: the WHO's cancer agency classes outdoor particle pollution as a known cause
- Poorer pregnancy outcomes, such as lower birth weight
There's no known level of PM2.5 below which harm stops. The aim is to cut your exposure, not to stay under a magic number.
Who needs to take most care
WA Health singles out the following groups as most likely to be affected:
- People with asthma, COPD or other lung conditions. Keep your asthma action plan current and your reliever with you.
- People with heart disease or diabetes.
- Older people.
- Pregnant women.
- Babies and children, who breathe more air for their body size and whose lungs are still developing.
Outdoor workers and anyone exercising hard outside are also exposed more, simply because they're breathing faster and deeper.
Why Perth gets smoky without a fire nearby
Summer bushfires are only part of Perth's smoke story. A study of WA's air monitoring from 2002 to 2017 found particle pollution broke the national standard on 271 days. Landscape fires caused 197 of them, and prescribed burns accounted for 138 days, more than twice the 59 caused by bushfires.
Summer bushfires
The Perth Hills and the south-west forests burn most summers. Summer mornings often bring easterly winds off the Hills, which can carry smoke across the suburbs until the afternoon sea breeze pushes in. The February 2021 Wooroloo fire, in the Shire of Mundaring, was a reminder of how close to the suburbs these fires can start.
Prescribed burns
The Department of Biodiversity, Conservation and Attractions (DBCA) runs planned burns across the south-west, mostly in autumn and spring, when cooler and more stable weather keeps fires controllable. The trade-off is that the same still conditions can trap smoke near the ground, especially overnight and into the morning. DBCA lists each day's burns online and issues smoke alerts through Emergency WA.
Winter wood heaters
WA's air monitoring shows particle haze in Perth is usually worst in the colder months, when home wood heaters are running. Across Australia, wood-heater smoke has been estimated to cause between 558 and 1,555 deaths a year. It doesn't stay outside, either: smoke from your own heater and your neighbours' finds its way back indoors.
Stubble and backyard burning
Burning on farms and private land adds to the mix, particularly on the city's rural fringe.
The toll in numbers
The 2019–20 figures come from a season Perth largely escaped. They show what a severe smoke season does to a population; they aren't a forecast for WA. Air pollution of all kinds was estimated to cause 2,566 deaths in Australia in 2015.
How much is too much
Australia's national standard for PM2.5 is 25 micrograms per cubic metre, averaged over 24 hours. The World Health Organization's 2021 guideline is tighter, at 15. On a heavy smoke day, readings can run to several times either figure.
| Measure | Australian standard | WHO guideline (2021) |
|---|---|---|
| PM2.5, 24-hour average | 25 µg/m³ | 15 µg/m³ |
| PM2.5, yearly average | 8 µg/m³ | 5 µg/m³ |
| PM10, 24-hour average | 50 µg/m³ | 45 µg/m³ |
The live reading on our home page uses the US EPA index that the World Air Quality Index project reports, where 0 to 50 is good and anything over 100 is a problem for sensitive groups. DWER's site publishes the raw hourly concentrations if you want exact figures.
Your smoke-day plan
Print it. This page prints cleanly without the menus, so you can stick the plan on the fridge before summer.
Before the season (September)
- Fit a fresh filter. Winter wood smoke will have loaded up the old one.
- Pick your clean room. Usually the main bedroom: few windows, a door that shuts, somewhere you can sleep. That's where the purifier lives on smoke days.
- Buy P2 masks now. A box in the cupboard before summer, not a search after the shelves empty.
- Update action plans. If anyone at home has asthma or a heart condition, check their plan with the GP.
- Know where to look. Emergency WA for alerts, DBCA's today's burns, and our live reading.
On the day
- Close up. Windows, doors, and the pet door too.
- Turn off the evaporative cooler. It pulls outside air through the whole house, so on a smoky day it fills the house with smoke. If fire is close, follow DFES advice on keeping the pads wet.
- Recirculate. Reverse-cycle air conditioning is fine on recirculate. Avoid any setting that draws in outside air.
- Run the purifier on high in the clean room, with the door shut.
- Don't add to it. No candles, incense, frying, gas heaters or wood fire. Put off vacuuming unless your vacuum has a HEPA filter.
- Take it easy. Skip the run or the training session. Exercise indoors, if at all.
- Check on people nearby who are older, live alone or have heart or lung conditions.
- If your home can't be kept clear, air-conditioned public buildings such as libraries and shopping centres are a reasonable place to spend the day.
When it clears
- Air the house once the reading is back to good. Check first: smoke often lingers into the next morning.
- Check the filter after a long smoky stretch. It may need replacing sooner than the maker says.
Masks: what works
Surgical and cloth masks don't stop fine smoke particles. They don't seal against the face and the material isn't designed for it. A P2 mask, the Australian equivalent of an N95, can, provided it fits properly.
- Fit matters more than brand. It should seal around the nose and under the chin with no gaps. Facial hair breaks the seal.
- They aren't designed for children and won't fit small faces properly.
- They make breathing harder work. If you have a heart or lung condition, ask your doctor before relying on one.
- They're for short trips outside, not a reason to stay out longer.
WA Health has a factsheet on masks and bushfire smoke.
A DIY filter in a pinch
If you're caught without a purifier, a fan with good filters taped to it moves a surprising amount of clean air. The best-known design, the Corsi–Rosenthal box, uses four or five filters taped into a cube with a square box fan on top, blowing out.
- Filters: US guides call for MERV 13. In Australia, look for panel filters rated F7 or better, or ePM1 50% or higher under ISO 16890. Air-conditioning and HVAC suppliers stock them.
- Fan: square box fans are less common here than in the US. A pedestal fan with a filter held firmly across the back works, though not as well.
- Limits: it's louder than a purifier and does nothing for smoke smell, because there's no carbon. Don't leave it running while you're out, and keep the fan's motor vents clear.
Treat it as a stopgap, not a plan.
When to get help
- Call 000 for chest pain, severe breathlessness, blue lips, or if someone collapses.
- Follow your asthma action plan at the first sign of symptoms. If the reliever isn't helping, treat it as an emergency.
- Call healthdirect on 1800 022 222 for advice, day or night.
- See your GP if a cough or wheeze hangs around after the smoke has cleared.
Sources
- Borchers Arriagada N. et al. (2020). Unprecedented smoke-related health burden associated with the 2019–20 bushfires in eastern Australia. Medical Journal of Australia.
- Borchers Arriagada N. et al. (2020). Exceedances of national air quality standards for particulate matter in Western Australia: sources and health-related impacts. Medical Journal of Australia.
- The mortality burden attributable to wood heater smoke particulate matter (PM2.5) in Australia (2024). Science of the Total Environment.
- Australia State of the Environment 2021: Air quality, outlook and impacts, including AIHW mortality data and the $1.95 billion cost estimate for the 2019–20 smoke.
- HealthyWA: Smoke hazards from bushfires and the masks and bushfire smoke factsheet.
- DFES: Evaporative air conditioners bushfire factsheet (hosted by the City of South Perth).
- DBCA: Smoke from prescribed burns and today's burns.
- DWER: Air quality data.
- World Health Organization (2021). WHO global air quality guidelines.
- National Environment Protection (Ambient Air Quality) Measure, for the Australian standards.
- International Agency for Research on Cancer (2013), classification of outdoor air pollution and particulate matter as carcinogenic to humans (Group 1).
This guide is general information, not medical advice. If you're unsure how smoke affects a condition you have, ask your GP.