Most burn plans map fuel, weather windows, control lines, water points and escape routes. Fewer map the trees that can kill a crew member standing on a completed control line. Hazard tree exclusion zones belong in the plan and on the ground, and the geometry is not intuitive.
The rule: two tree lengths
Operational doctrine sets the exclusion zone around a hazardous tree at a minimum of two tree lengths. For a 30-metre flooded gum that is a 60-metre radius — a footprint of well over a hectare around a single stem.
Where terrain or a recognisable lean makes the fall direction predictable, the zone can be applied as 180 degrees in the applicable direction rather than a full circle. That is the concession that makes the rule workable on a real block.
A tree does not land as a point. It lands as a line, and material bounces, rolls and slides beyond the tip on impact — further on a slope. One tree length is the reach. Two is the reach plus what happens on arrival.
The planning problem this creates
Apply a 60-metre buffer around every hazardous stem on a forested block and you can quickly discover that your control line, your anchor point and your safety zone are all inside an exclusion zone. That is the point of doing it on a map, in the office, rather than discovering it at 0700 on the burn day.
Three practical consequences follow:
- Control lines get moved. Existing tracks were cut for access, not safety, and they characteristically run beneath the largest and oldest trees on the block.
- Some trees get removed before the burn. Cheaper and safer than planning around them, and it can be scheduled rather than improvised.
- Some burns get re-scoped. Occasionally the honest answer is that a unit cannot be burnt safely until hazard trees are dealt with.
Getting it onto the ground
A zone on a map that is not visible in the field does nothing. Marking convention is a yellow circle-and-cross symbol, roughly 30 cm across, at about 1.5 m above ground level, applied to two sides of the stem where it is safe to do so.
Mark the tree, not the zone — the zone is too large to flag — and brief the radius so crews can apply it from the marked stem.
What goes in the plan document
- Hazard tree register — GPS location, species, height, defect, quantified risk of harm, and the exclusion radius derived from height.
- Map overlay showing exclusion zones against control lines, anchor points, safety zones, access tracks and water points.
- Conflict list — every place a planned line, node or route intersects a zone, with the resolution recorded.
- Removal schedule for trees being dealt with pre-burn.
- Crew briefing extract — one page, plain language, showing marked trees and the radius rule.
Dynamic assessment still applies
Pre-planning does not replace the shift-by-shift obligation. Work areas are inspected before each shift and reassessed as conditions change, because fire creates new hazard trees in real time: a sound tree at 0600 can be a pipe by 1400. Suspected hazardous trees are identified from a distance and escalated to the incident controller and safety adviser rather than approached.
Doctrine also discourages felling after dark other than in exceptional circumstances with full illumination — which is worth knowing at the planning stage, because it constrains what mop-up can safely achieve on a late-finishing burn.