Changes in fire behavior have always been present in cases of shelter deployment. Firefighters maintain a heightened awareness of daily fluctuations in live and dead fuel moistures, along with current and predicted weather conditions. Other inputs like fuel type and topography add to the picture. Firefighters must cultivate a healthy respect for these factors. When fuel moistures, fuel type, weather conditions, and topography align, extreme fire behavior is likely. As fire behavior moves from mild to moderate to extreme, it is critical to recognize the changing situation and act appropriately.

Discuss the following factors that can contribute to extreme fire behavior:

• Relative humidity less than 15%
• 1-hour fuel moisture less than 5%
• Transition from surface to crown fire
• Light flashy fuels
• Smoldering fires that exist in the early part of the day are beginning to burn very actively as the day progresses
• Approaching thunderheads with dark clouds beneath
• Presence of dust devils indicating atmospheric instability
• Increased spotting
• Sudden calm
• Volatile fuel types
• High clouds moving fast in a direction that is different from surface wind
• Predicted high mixing height as an indicator of atmospheric instability and the potential for vertical column development
• Fire whirls
• Topography
   

Discussion Questions: 

• What combination of conditions and local factors (weather, fuel type, fuel moisture, topography) on your home unit contribute to extreme fire behavior?
• How might you adjust your tactical approach or objectives when those conditions are present? How do you balance this with Fire Order #10?
• What actions can you take to keep calm, think clearly, and act decisively before and during sudden changes in fire behavior impacting your work area?
• How do you communicate changes in fire behavior which could impact your crew? How are those messages passed to convey any necessary changes to operational tempo or urgency?
• What terms are needed to paint a common operating picture of the fire behavior and rates of spread you’re seeing? (Work to get on the same page about what specific terms mean. Is the fire “pulsing” or “making a sustained run”? Are the spots “catchable” or “forming a new head fire”? Do you need to “adjust tactics”, or “adopt a new strategy”?)

References:

Fire Whirls video produced by Rocky Mountain Research Station 
Extreme Fire Behavior – II, 6MFS Topic
NWCG Incident Response Pocket Guide (IRPG), PMS 461, Common Denominators of Fire Behavior on Tragedy Fires, Operational Engagement (green)