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Wind-driven versus plume-dominated fire
A wind-driven fire generally spreads with the wind and is more predictable. A plume-dominated fire, in the language PNW-GTR-891 records, has a smoke column standing almost vertically and little visible influence of horizontal wind. Direction of spread can change unexpectedly. That chapter does not give a hours-versus-minutes clock. This is not R327 and not a FHSZ overlay.
You are watching the column. If it lies down with the wind, the head is more likely that way. If it stands up, do not assume the fire will wait. That is the distinction. It is not a permit.
No g3-passed exhibit matches this object. Do not reuse SIT-100 as a plume. The scene is the column.
Why it matters
People hear “plume-driven” and pack for a slow afternoon, or they hear “wind-driven” and think spotting cannot happen. The Forest Service synthesis is for fire-behavior specialists and NWS incident meteorologists. Home ignition is still the house and about 40 meters. See home ignitability. A vertical column can still loft embers. A wind-driven run can still arrive as flame.
How the documents split
| Object | What GTR-891 Chapter 6 says | What it is not |
|---|---|---|
| Wind-driven | Generally more predictable. Spreads with the wind. | A guarantee of hours |
| Plume-dominated | Nearly vertical column. Little visible horizontal-wind influence. Behavior may change rapidly. Spread direction can change unexpectedly. | A safer fire |
| Convection number Nc | Ratio of power of the fire to power of the wind | A homeowner formula on this page |
| Home ignitability | House + ~40 m | This classification |
| National WUI | Census housing + vegetation | Plume vs wind |
The paths
1. Watch the column, not a clock. The chapter does not assign minutes. This page does not invent them.
2. Wind-driven is alignment. Fire and wind in the same direction. More predictable does not mean slow. Foehn and critical fire-weather patterns are other chapters in that volume.
3. Plume-dominated is a standing column. Common usage, the authors say, implies rapid change. Do not treat a vertical smoke column as “the fire is just venting.”
4. Spotting is a sibling chapter. Volume 2 Chapter 7 is spot fires. Embers can originate far from the house. They still need a landing pad. Mesh and Zone 0 are that pad.
5. Construction is a different book. R327, CWUIC, and IBHS do not choose this classification. Spec the adopted covering. Do not write “plume-dominated, therefore Class A” on a drawing.
What people mix up
- A hours-versus-minutes table that this source does not print.
- Plume-dominated as safer.
- Wind-driven as no spotting.
- This classification as a FHSZ or WUI census layer.
- A convection-number calculation as a homeowner checklist.
How to check
- Open Treesearch 50530, Chapter 6. Find “wind-driven.” Find “plume-dominated.”
- Confirm there is no hours table in that section.
- Walk 40 meters from the walls. That is Cohen, not Byram.
- If an official or a newscast uses these words, ask which document. This synthesis is 2016.
- Do not spec a vent from a smoke column.
Limits
This page does not forecast a fire. It does not replace an incident meteorologist. It does not reprint Byram’s or Nelson’s equations. FireApproved is not the Forest Service and not NWS. Evacuation orders come from the sheriff and the fire district, not this page.
Related records
Questions
Does plume-dominated mean I have hours to pack?
PNW-GTR-891 Chapter 6 does not assign hours or minutes to either class. Wind-driven fires are generally more predictable because they spread with the wind. Plume-dominated, in common usage, means the column stands nearly vertical and direction of spread can change unexpectedly. Do not take a clock from this page.
Is a vertical smoke column safer?
Not as a rule. The same chapter says the implication of the plume-dominated label is that behavior may change rapidly. Spotting from a strong column is a different chapter in that volume. Distant firebrands still need a landing pad at the house. See home ignitability.
Can I read this on an Oregon R327 drawing?
No. R327 is adopted construction. This is fire-behavior language for specialists and meteorologists. It does not choose a vent model.
Is this the same as the national WUI map?
No. Radeloff maps houses and vegetation. This page is how a fire’s plume and the wind interact. See how the WUI is mapped.