National Fire Danger Rating System

NFDRS Basics

• Indicator of worst case fire danger

• Five danger classes– Low, moderate, high, very high, extreme

• Describes fire danger for large areas – 10-10,000 acres – 24 hour time period

• Used by fire suppression agencies to:– Plan staffing levels and preparedness– Determine management action (dispatch)– Set public use restrictions (campfires, spark-producing equip.)

NFDRS Calculations

• Local weather + Fuel moisture Regional predictions– 3 indices

• Burning Index (BI)• Occurrence Index (OI)• Fire Load Index (FLI)

– 3 fire behavior components• Spread Component (SC)• Ignition Component (IC)• Energy Release Component (ERC)

• Software– FireFamilyPlus gives SC, ERC for public users– National Computer Center processes fire weather station info – Custom agency programs

NFDRS System

Fuel Model Equivalents

• A = 1, Western annual grassland• C = 2, Open pine with grass• B = 4, Mature brush• H = 8, Short needle closed canopy normal dead• U = 9, Western long needle pine • G = 10, Short needle closed canopy heavy dead

• All 20 NFDRS fuel models can be cross-referenced with the 13 Anderson fuel models

NFDRS System

Spread Component (SC)

• Definition:– forward rate of spread at the head of the fire

• Units = feet/minute– Ex. If SC = 31, forward rate of spread is 31 feet/minute

• SC calculated using:– wind speed– slope– fine fuel moisture (including live herbaceous plants) – live woody fuel moisture (foliage and twigs)

Energy Release Component (ERC)

• Definition:– the potential available energy per square foot of

flaming fire at the head of the fire.

• Similar to “intensity”

• Units = BTUs per square foot.

• Unlike SC, the ERC calculations require moisture inputs for the entire fuel complex. – 1, 10, 100, 1000 hr and live fuel.

NFDRS System

Burning Index (BI)

• Definition:- 10 times the predicted flame length- Refers to the potential amount of effort needed to

contain a single fire.

• Units = feet

• Calculated using a modified version of Byram's flame length equation – based on the Spread Component (SC) and the

available energy (ERC)

Relationship between SC, ERC and BI

NFDRS System

Ignition Component (IC)

Ignition Component (IC)

• Definition:= probability that a spreading fire will result if a firebrand (or other

ignition source) comes into contact with fine fuels.

• IC ranges from 0 (cool, damp conditions) to 100 (dry, windy days). – If IC = 60, approximately 60% of all fire brands that come into

contact with fuels will require suppression action.

• Live fuels reduce the efficiency of ignition, so the IC is adjusted based on the percentage of fine live fuel (herbaceous material).

NFDRS System

Ignition Component (IC) Staffing Level and Adjective Class

Staffing Levels

• Determined using percentiles of a selected NFDRS component or index.– USFS uses the 90th, 97th percentiles of ERC– BLM uses the 80th, 95th percentiles of the BI.

• Percentiles are determined from statistical analysis of historical NFDRS components and indexes using frequency distribution tables and graphs.

Fire Danger Adjective Classes

Low (L), Moderate (M), High (H), Very High (V), Extreme (E)

Staffing Level Fire Danger Adjective

1 L L L M M

2 L M M M H

3 M M H H V

4 M H V V E

5 H V V E EIgnition Component 0-20 21-45 46-65 66-80 81-100

Websites

http://www.seawfo.noaa.gov/fire/olm/nfdrs.htm

http://www.fs.fed.us/land/wfas/nfdr_.html

Other Definitions

• Occurrence Index– Degree to which an area will be exposed to man-caused (MCOI)

and lightning-caused (LCOI) ignition sources.– Scale of 0-100– Ex. OI = 100, expect 10 fires/million acres

• Fire Load Index– number relating the total amount of effort required to contain all

probable fires within the rating area during a specified period of time.

– The difficulty of containing a single fire (Burning Index) multiplied by the probable number of fires projected by the Occurrence Index (OI).

Adjective Class DefinitionsLow (L) = Fuels do not ignite readily from small firebrands although a more

intense heat source, such as lightning, may start fires in duff or punky wood. Fires in open cured grasslands may bum freely a few hours after rain, but woods fires spread slowly by creeping or smoldering, and burn in irregular fingers.

Moderate (M) = Fires can start from most accidental causes, but with the exception of lightning fires in some areas, the number of starts is generally low. Fires in open cured grasslands will burn briskly and spread rapidly on windy days.

High (H) = All fine dead fuels ignite readily and fires start easily from most causes. Unattended brush and campfires are likely to escape.

Very High (VH) = Fires start easily from all causes and, immediately after ignition, spread rapidly and increase quickly in intensity. Spot fires are a constant danger.

Extreme (E) = Fires start quickly, spread furiously, and burn intensely. Direct attack is rarely possible and may be dangerous except immediately after ignition.