🚒Phases of fires

🚒Phases of fires

Phases of a Wildfire

Understanding fire progression helps predict behavior and plan suppression strategies.


Visual Overview



The Five Phases

1. Ignition

What happens:Initial spark or heat source ignites fuel. Fire begins at a single point and requires heat, fuel, and oxygen to sustain.
Key characteristics:
  • Single ignition point
  • Small, localized fire
  • Critical window for early suppression
  • Fuel moisture and weather determine if fire will grow
Weather factors matter most:
  • Temperature
  • Relative humidity
  • Wind speed at ground level


2. Growth (Active Phase)

What happens:Fire spreads rapidly, consuming available fuel. Heat increases, flames grow taller, and fire behavior intensifies.
Key characteristics:
  • Exponential spread rate
  • Fire behavior driven by wind, topography, fuel type
  • Pre-heating of adjacent fuels
  • Ember spotting may begin
  • Most critical phase for resource deployment
What drives growth:
  • Wind: Pushes flames forward, pre-heats fuel ahead
  • Slope: Fire moves faster uphill (doubles speed every 10° of slope)
  • Fuel continuity: Connected vegetation allows rapid spread
Suppression priority:Establish control lines, protect structures, prevent spot fires.


3. Fully Developed

What happens:Peak fire intensity. Maximum heat release and flame height. All available fuel in the area is burning.
Key characteristics:
  • Highest flame lengths
  • Maximum rate of spread
  • Crown fires in forested areas
  • Fire creates its own weather (convection columns, fire whirls)
  • Most dangerous for suppression crews
Fire behavior:
  • Temperatures: 800–1200°C at flame front
  • Radiant heat extends 50+ meters
  • Ember transport 1–5 km ahead of fire front
  • Oxygen consumption creates low-pressure zones
Suppression strategy:Often indirect attack only. Wait for fire intensity to decrease before engaging.


4. Decay (Controlled Phase)

What happens:Fuel consumption decreases, fire intensity drops. Flames lower as available fuel is exhausted. Control lines may be holding.
Key characteristics:
  • Reduced flame height
  • Slower spread rate
  • Transition from flaming to smoldering
  • Contained within perimeter (if control lines successful)
  • Hot spots remain
Why fires reach this phase:
  • Available fuel exhausted
  • Weather conditions improve (humidity up, wind down, rain)
  • Natural barriers (rivers, roads, bare ground)
  • Effective suppression efforts
Operations focus:Strengthen control lines, mop up hot spots, patrol perimeter.


5. Extinguished

What happens:No active flames or heat. All fuel consumed or cooled below ignition temperature. Mop-up operations complete.
Key characteristics:
  • No visible smoke or flames
  • Ground temperature below ignition point (<60°C)
  • All hot spots eliminated
  • Perimeter secured
Verification:
  • Hand checks for heat
  • Thermal imaging for hidden hot spots
  • Moisture content checks
  • Multiple patrol cycles
Important: Area monitored for potential rekindling, especially:
  • In duff layers and roots (can smolder for days)
  • When weather conditions deteriorate
  • Around stumps and logs


Critical Reminder

"Controlled" ≠ "Extinguished"
A fire in the decay phase is controlled but not out. Risk remains until full extinguishment:
  • Weather changes can reignite growth
  • Hidden smoldering areas can flare up
  • Wind can carry embers beyond control lines
  • Fuel moisture can decrease overnight
Always maintain vigilance until confirmed extinguishment.


Fire Triangle Reminder

All phases require three elements:
    Heat - Ignition source and sustained temperature
    Fuel - Combustible material (vegetation, structures)
    Oxygen - Typically 21% in atmosphere, fire needs ~16% minimum
Remove any one element → fire cannot sustain.


Factors That Influence Phase Transitions

Accelerating transitions (Ignition → Fully Developed):

  • Low fuel moisture (<10%)
  • High temperatures (>30°C)
  • Low relative humidity (<30%)
  • Strong winds (>25 km/h)
  • Steep slopes (>30%)
  • Dense, continuous fuels

Slowing transitions (Growth → Decay):

  • High fuel moisture (>20%)
  • Cool temperatures (<15°C)
  • High relative humidity (>70%)
  • Calm winds (<10 km/h)
  • Natural barriers
  • Effective suppression


Questions?

Understanding fire phases helps predict behavior and allocate resources effectively.
For real-time fire behavior assessment, use Wildflyer's integrated weather and fire danger forecasts.

Wildflyer: where wildfire intelligence connects.
Last updated: February 2026