Fire and smoke behavior over time
In the builder, a scene is static: what you place is what you see. In a drill, the exercise clock runs and fire advances on its own. This page describes exactly what happens, so you can set growth rates that produce the drill you intend.
Fire growth#
Each fire has a stage (0 through 4) and a growth rate per minute. Once the drill starts, the fire advances from its starting stage at that rate:
stage now = starting stage + (growth per minute × minutes elapsed), capped at Flashover
Growth is computed from the clock, not from a timer, so it is the same on every member's screen and identical when the drill is replayed later.
| Growth per minute | Effect |
|---|---|
| 0.00 | Static. The fire holds until an instructor, a level, or an inject changes it. |
| 0.10 | Slow. About one stage every ten minutes. |
| 0.30 | Moderate. About one stage every three minutes. |
| 1.00 and up | Fast. Reaches flashover within a few minutes. |
For a drill about a specific decision, use 0.00 and stage the changes yourself with levels and injects. That way the escalation happens when the training calls for it, not on the clock. For a drill about recognizing deterioration, give it a real growth rate and let it run.
Knockdown#
When water goes on the fire, its intensity decays toward zero at about two stages per minute, then stays out.
During a drill the instructor triggers this with the Knockdown button. With an element selected it applies to that fire; with nothing selected it applies to every fire on the scene. Knockdown also changes the smoke that fire produces to a lighter, steam-like appearance, and once every fire on a view is knocked down, the smoke you placed on that view converts too: dark smoke turns to white steam over about twenty seconds, swelling briefly, then thins to nothing over the next three minutes, trailing the fire's own decay. Flashover clears the knockdown and the placed smoke returns to exactly what you authored.
Flashover#
The instructor's Flashover button jumps fire to its maximum stage immediately, again for the selected element or for all fires. Use it when crews have made a decision that would have produced that result, and you want them to live with it.
Smoke#
Smoke you place does not grow on its own. Its density and darkness are what you set until something changes them, which keeps smoke under your control rather than compounding with fire growth. The one thing that moves it without you is a knockdown of every fire on its view (steam conversion, described above), and even then you keep the last word: a situation level or a hand edit fired after the knockdown shows exactly as you set it, so a surprise re-ignition or a sudden change in conditions still lands the way you authored it.
What a fire's own smoke says#
Fire produces its own smoke on top of any you place, and that smoke is not the same at every stage. It gets darker, heavier and faster as the fire develops, because that is what real smoke does:
| Stage | Its smoke |
|---|---|
| Smouldering | Light grey, thin, barely moving. No flame yet: at this stage a fire is almost entirely smoke. |
| Incipient | Light grey, a little more of it, starting to lift. |
| Growth | Grey and darkening, more volume, rising properly. |
| Fully developed | Thick, dark grey, pushing. |
| Flashover | Near black, dense, pushing hard. |
This matters because it is a size-up read. Crews are taught to judge a fire by its smoke before they can see any fire at all, and a scene that showed the same grey plume at every stage would train them out of the habit. A fire left to grow darkens its own smoke as it advances, with nothing for you to set.
A smouldering fire is worth placing deliberately. It shows light smoke and no flame, which is exactly the condition a crew has to recognise and report rather than dismiss.
Smoke pushes in slugs#
Smoke does not leave a building at a constant rate. It streams, and every so often a slug rolls out of the opening, billows across the front and briefly hides the fire before it lifts. That happens on its own, on every exterior view, and each fire on a scene breathes to its own rhythm rather than in time with the others.
It is there because pulsing smoke is itself a fireground indicator, and because a fire that is never obscured is easier to read than a real one.
On a phone or tablet the scene is drawn a cheaper way and the plume stays steady. The colours are the same; the slugs are a desktop detail.
On the aerial#
An aerial or terrain view looks straight down, so fire and smoke behave as they would on a map rather than in an elevation. Nothing rises up the screen, because from above a rise is straight at the camera:
- fire spreads across the ground, running out ahead of itself downwind and creeping at the heel, which is the head/flanks/heel shape of a real fire,
- smoke leaves the seat along the wind and widens as it goes, and with no wind it spreads evenly around the fire, which is what a column looks like from directly overhead,
- brands blow downwind ahead of the head, which is the spotting a crew watches for.
The wind comes from the scenario's weather (Setup tab), read the way the fire service reads it: the direction it blows from. Overhead imagery is north-up, so wind from the west lays the plume out to the east.
Interior smoke#
On an interior view, smoke behaves differently. Instead of a rising plume, each smoke element becomes a rolling bank that churns in place, and the room loses visibility from the ceiling down. How far that reaches comes from the combined density of the smoke on that view (plus a contribution from any free-burning fire in the room), and the color comes from the darkness setting.
Consequences worth knowing when you build:
- Turning density up thickens the banks and pushes the loss of visibility further down the room.
- At high density and darkness the room approaches blackout. That is the intended condition for search and CAN-report training.
- A victim low in the room stays visible until the layer reaches them.
- After a knockdown, the banks whiten to steam and then thin out as the placed smoke converts; the fire's own steam does not add to the layer.
Changing conditions mid-drill#
Three tools change the scene while crews are working:
- Direct edits. The instructor can select any element during a drill and change its settings, exactly as in the builder.
- Situation levels. A saved arrangement of the whole scene, applied in one click.
- Injects. A named event, optionally announced by the dispatcher, optionally linked to a level, fired manually or on a schedule.
Every one of these is recorded, so the after-action review shows exactly when conditions changed and what they changed to.