The National Fire Danger Rating System
The National Fire Danger Rating System (NFDRS) is a set of calculated indices used by fire management agencies across the United States to assess daily fire danger conditions. The system converts weather observations — temperature, relative humidity, wind speed, precipitation, and fuel moisture measurements — into standardized danger levels that communicate how difficult a fire would be to suppress if it started.
The five fire danger classes are: Low, Moderate, High, Very High, and Extreme. Each state forestry agency uses these classes (or their own color-coded equivalents) to govern permit issuance and restrictions.
| Level | Color | What It Means | Typical Permit Impact |
|---|---|---|---|
| Low | ■ Green | Fires unlikely to start. If started, easily contained. | Permits issued normally |
| Moderate | ■ Blue/Teal | Some risk. Fires can start but spread slowly with normal suppression. | Permits issued normally |
| High | ■ Yellow | Fires start easily, spread at moderate rate. Extra caution needed. | Permits usually issued with caution |
| Very High | ■ Orange | Fires start very easily, spread rapidly. Suppression difficult. | Most states deny permits |
| Extreme | ■ Red | Fires start almost instantly, spread explosively. Suppression dangerous. | No permits issued anywhere |
How Fire Danger Ratings Are Calculated
NFDRS integrates multiple inputs into composite indices:
- Fine Dead Fuel Moisture (FDFM): The moisture content of small dead fuels (grass, leaves, small sticks under ¼ inch diameter). This is the fuel that ignites first and carries fire. At 5% moisture, grass ignites from a spark. At 15%+, ignition is difficult.
- Live Fuel Moisture: Moisture content of living vegetation. Green grasses and shrubs resist fire; dormant or drought-stressed plants become as flammable as dead fuel.
- Wind Speed: Wind drives fire spread and affects drying. The Spread Component (SC) increases exponentially with wind speed — doubling wind speed more than doubles fire spread rate.
- Energy Release Component (ERC): A measure of the potential heat per unit area in the flaming front of a fire. High ERC indicates fires that are more difficult to suppress.
- Ignition Component (IC): The probability that a glowing ember will initiate a fire that persists long enough to be reported.
Where to Check Fire Danger for Your Location
- Your state forestry commission website — most post current fire danger levels by county or district
- National Interagency Fire Center (NIFC): nifc.gov — national-level fire danger outlooks
- Wildland Fire Assessment System (WFAS): wfas.net — maps current fire danger by county nationwide
- InciWeb: inciweb.nwcg.gov — active fire and restriction information
- State-specific burn ban maps: cofirebans.us (Colorado), tfsweb.tamu.edu (Texas), wildfire.ok.gov (Oklahoma)
- National Weather Service: weather.gov — Red Flag Warnings and Fire Weather Watches which indicate extreme fire conditions
What Each Level Means for Your Burn Decision
Low and Moderate — Generally Safe to Proceed
At Low and Moderate danger levels, fire behavior is predictable and manageable. Fires started accidentally are unlikely to escape control quickly. Permits are issued in essentially all states at these levels. If conditions are Low or Moderate and you have a valid permit, your burn can proceed — but you still need to follow all safety requirements.
High — Proceed With Extra Caution
High fire danger is when experienced burn practitioners become more careful and inexperienced burners should seriously consider postponing. Fires start easily, spread at a moderate-to-fast rate, and can become difficult to control in changing conditions. Most states still issue permits at High, but the margin for error shrinks significantly. If conditions are High and wind picks up mid-burn, you need to be able to suppress quickly.
Very High — Most States Deny Permits
Very High is the threshold where most state forestry agencies automatically deny burn permits. Georgia's GFC system, for example, checks fire danger before issuing any permit — Very High means no permit, period. At Very High danger, a small fire can become a large fire faster than suppression resources can respond. The risk-to-benefit ratio for residential debris burning becomes untenable.
Extreme — Absolute Prohibition
At Extreme fire danger, no permits are issued by any agency anywhere. Extreme conditions produce fire behavior that can outrun firefighters, generate long-range spotting from embers, and produce fire whirls (fire tornadoes) that throw embers hundreds of yards. Major catastrophic wildfires — the 2018 Camp Fire, the 2020 Creek Fire, Washington's 2020 season — all burned under Extreme fire conditions.
Red Flag Warnings and Fire Weather Watches
The National Weather Service issues fire weather products that work alongside fire danger ratings:
- Fire Weather Watch: Conditions favorable for extreme fire behavior are possible in the next 48–72 hours. Consider postponing any planned burns.
- Red Flag Warning: Critical fire weather conditions are occurring or imminent — typically relative humidity below 15%, wind speeds above 25 mph, or both. Do not burn during a Red Flag Warning under any circumstances. Most state agencies will not issue permits, and responsible burn practitioners will extinguish or postpone any planned burns immediately.
Frequently Asked Questions
Most professional guidance treats High fire danger as the threshold for extra caution, and Very High as the practical prohibition for residential burning. Most state forestry permit systems automatically deny permits at Very High or Extreme. Even at High, experienced burn practitioners often postpone if conditions are trending worse. Check wfas.net or your state forestry commission for current conditions.
Check your state forestry commission's website — most post current fire danger by county or district. The Wildland Fire Assessment System at wfas.net shows a national map updated daily. Your state's burn permit portal (e.g., GaTrees.org for Georgia) typically checks fire danger automatically when you apply.
Yes. Fire danger typically peaks in the early-to-mid afternoon when temperatures are highest and relative humidity is lowest. Morning conditions are usually more favorable for burning — this is why some states specify morning burn windows. If conditions deteriorate after you start burning, you are legally required to extinguish, even if you had a permit when you started.
Technically yes, if your state issued you a permit at High danger — but High is when caution is most warranted. Evaluate the specific conditions: is wind speed increasing? Is humidity dropping further? Is the afternoon weather forecast showing any change? High fire danger with stable or improving conditions is manageable; High with deteriorating conditions means postponing is the smart call.
If a Red Flag Warning is issued after you've obtained a permit but before you've started burning, treat it as an effective prohibition. Most state agencies explicitly advise permit holders not to burn during Red Flag conditions. If you've started burning and a Red Flag Warning is issued mid-burn, extinguish immediately and monitor the area through the warning period.