Distance from the fire does not equal safety
Smoke from bushfires can travel hundreds of kilometres from the fire front. A clear sky at your trailhead means nothing if smoke is drifting in from a fire in another region. Wind shifts can bring hazardous air quality to areas that looked fine at departure.
The most common mistake hikers make is treating smoke as a visibility problem. If you can see clearly, you assume you are safe. But the particles most dangerous to health — PM2.5 — are invisible. You cannot see them, smell them at dangerous concentrations, or feel them until exposure has already occurred.
Distance from the fire, wind direction, and smoke forecasts matter far more than what you can observe at the trailhead.
What PM2.5 is and why it matters for hikers
PM2.5 refers to fine particulate matter smaller than 2.5 micrometres in diameter. These particles are produced in large quantities by bushfires and penetrate deep into the lungs. Unlike larger particles that the nose and throat filter out, PM2.5 bypasses the body’s natural defences.
During sustained aerobic exercise — which hiking involves — breathing rate increases significantly. This means hikers inhale more air per minute than someone at rest, increasing total PM2.5 intake. The harder the terrain and the longer the hike, the greater the exposure.
Physical exertion in smoke-affected air is not the same as resting in the same conditions. A level of air quality that is tolerable at rest can be genuinely harmful during several hours of uphill hiking.
How smoke affects visibility and navigation
Smoke does more than affect breathing. It reduces visibility, flattens terrain contrast, and changes how the landscape looks. Features that are normally distinct — ridgelines, saddles, distant peaks — can become indistinct or disappear entirely.
This increases navigation error risk in ways that are easy to underestimate. In clear conditions, visual cues constantly confirm your position. In smoke, those cues are reduced or absent. The effect is similar to fog or low cloud but without the obvious warning that those conditions provide. Smoke can look thin and hazy from a distance but significantly impair sightlines in the field.
If your route involves complex navigation, off-track travel, or relies on distant landmarks, smoke is a navigation risk as much as a health risk. See the Navigation in Poor Visibility guide for relevant techniques.
Reading air quality before you leave
The Air Quality Index (AQI) is the standard measure used in Australia to communicate daily air quality conditions. State environment agencies publish AQI data by region, and forecasts are increasingly available alongside weather forecasts during fire season.
For hiking decisions, use these bands as a starting point:
| AQI Range | Category | Hiking Decision |
|---|---|---|
| 0–33 | Very Good | Proceed normally |
| 34–66 | Good | Proceed. Monitor conditions. |
| 67–99 | Fair | Modify. Reduce intensity and duration. Avoid remote terrain. |
| 100–149 | Poor | Reconsider. High-exertion hiking not recommended. Sensitive groups should cancel. |
| 150–200 | Very Poor | Cancel. Outdoor physical activity not appropriate. |
| 200+ | Hazardous | Cancel. Do not go outdoors for sustained activity. |
These thresholds assume healthy adults. If you have asthma, cardiovascular conditions, or respiratory illness, apply more conservative thresholds and consider cancelling at Fair or above.
Check AQI through your state environment agency before departure. AQI can change rapidly during fire season as wind direction and fire behaviour shift.
Who is most at risk
Smoke affects everyone, but some hikers face greater risk:
- People with asthma or respiratory conditions — smoke is a known trigger and can cause rapid deterioration
- People with cardiovascular conditions — PM2.5 increases cardiovascular stress
- Children and older adults — lungs are more vulnerable at both ends of the age spectrum
- Anyone undertaking high-intensity or long-duration hiking — increased breathing rate amplifies exposure
Healthy adults without underlying conditions can tolerate moderate smoke exposure better, but sustained high-exertion activity in poor air quality still carries real risk.
Making the go, modify, or cancel decision
Smoke conditions can develop quickly and change during a hike. Apply the same discipline to smoke that you would apply to fire danger ratings or severe weather forecasts — treat it as a decision trigger, not background information.
Go when AQI is Good or Very Good, smoke forecasts are stable, and your route does not involve high exertion in exposed terrain.
Modify when AQI is Fair, or conditions are Good but deteriorating. Choose shorter, lower-intensity routes. Stay closer to exit points. Avoid remote terrain where bail-out options are limited. Carry your medication if you have respiratory conditions.
Cancel when AQI is Poor or above, smoke is visibly thick at the trailhead, conditions are forecast to worsen, or any member of your group has respiratory or cardiovascular conditions.
If conditions deteriorate on trail — increasing smoke density, worsening visibility, respiratory symptoms developing — move to exit. Do not wait for conditions to become severe before making that decision.
What to do if caught in deteriorating smoke on trail
If air quality worsens while you are out:
- Reduce exertion immediately — slow your pace, reduce the load on your lungs
- Move toward your exit, not deeper into the route
- Use any medication you carry — if you have a Ventolin inhaler or similar, use it as directed
- Monitor your group for symptoms — coughing, shortness of breath, chest tightness, or headache are signals to act
- A P2 or N95 mask provides partial protection from PM2.5, but does not make it safe to continue strenuous activity in hazardous air
Smoke conditions affecting navigation — reduced visibility, flattened terrain contrast — should be treated with the same discipline as fog or low cloud. Slow down, confirm position more frequently, and do not push on if orientation becomes uncertain.
Key points to remember
- Distance from a fire does not mean clean air — smoke travels hundreds of kilometres
- PM2.5 is invisible and the primary health concern, not visible smoke density
- Hiking increases PM2.5 intake significantly compared to rest
- Smoke reduces visibility and increases navigation risk
- Check AQI before departure and treat it as a decision trigger
- Cancel or modify early — do not wait until conditions are obviously hazardous
