Fire Danger Period Announcements
Vic Emergency Incident MapFire Weather Index Definitions
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FFMC (Fine Fuel Moisture Code) This is a numerical rating of the moisture content of surface litter and other cured fine fuels. It shows the relative ease of ignition and flammability of fine fuels. The moisture content of fine fuels is very sensitive to the weather. Even a day of rain, or of fine and windy weather, will significantly affect the FFMC rating. The system uses a time lag of two-thirds of a day to accurately measure the moisture content in fine fuels. The FFMC rating is on a scale of 0 to 99. Any figure above 70 is high, and above 90 is extreme. DMC (Duff Moisture Code) DMC is a numerical rating of the average moisture content of loosely compacted organic layers of moderate depth. The code indicates the depth that fire will burn in moderate duff layers and medium size woody material. Duff layers take longer than surface fuels to dry out but weather conditions over the past couple of weeks will significantly affect the DMC. The system applies a time lag of 12 days to calculate the DMC. A DMC rating of more than 30 is dry, and above 40 indicates that intensive burning will occur in the duff and medium fuels. Burning off operations should not be carried out when the DMC rating is above 40. DC (Drought Code) The DC is a numerical rating of the moisture content of deep, compact, organic layers. It is a useful indicator of seasonal drought and shows the likelihood of fire involving the deep duff layers and large logs. A long period of dry weather (the system uses 52 days) is needed to dry out these fuels and affect the Drought Code. A DC rating of 200 is high, and 300 or more is extreme indicating that fire will involve deep sub-surface and heavy fuels. Burning off should not be permitted when the DC rating is above 300. ISI (Initial Spread Index) This indicates the rate fire will spread in its early stages. It is calculated from the FFMC rating and the wind factor. The open-ended ISI scale starts at zero and a rating of 10 indicates high rate of spread shortly after ignition. A rating of 16 or more indicates extremely rapid rate of spread. BUI (Build Up Index) The BUI index shows the amount of fuel available for combustion, indicating how the fire will develop after initial spread. It is calculated from the Duff Moisture Code and the Drought Code. The BUI scale starts at zero and is open-ended. A rating above 40 is high, above 60 is extreme. FWI (Fire Weather Index)
Information from the ISI and BUI is combined to provide a numerical rating of fire intensity - the Fire Weather Index.
The FWI indicates the likely intensity of a fire.
FDI (Fire Danger Index) The Australian Bureau of Meteorology uses a variant of FWI to define fire danger. FFDC (Forest Fire Danger Code) Based on predicted generated "fire intensity (kw/m²)" in forest type vegetation. This code denotes how difficult it would be to control a fire in this vegetation type should one start. (Values: Low, Moderate, High, Very High, Extreme) SFDC (Scrub Fire Danger Code) Based on predicted generated "fire intensity (kw/m²)" in scrub type vegetation. This code denotes how difficult it would be to control a fire in this vegetation type should one start. (Values: Low, Moderate, High, Very High, Extreme) GFDC (Grass Fire Danger Code) Based on predicted generated "fire intensity (kw/m²)" in grass type vegetation. This code denotes how difficult it would be to control a fire in this vegetation type should one start. (Values: Low, Moderate, High, Very High, Extreme) CBI (Chandler Burning Index) The Chandler Burning Index (CBI) uses the air temperature and relative humidity to calculate a numerical index of fire danger. It is based solely on weather conditions, with no adjustment for fuel moisture. That number is then equated to an «Objective Fire Danger Severity» of either low (less than 50), moderate (between 50 and 75), high (between 75 and 90), very high (between 90 and 97.5), or extreme (above 97.5). This station uses data averaged over 30 days for its calculations.
Daily CBI ratings are calculated using this formula:
Averaged 30 day CBI rating is calculated using this formula:
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| LOW < 50 |
MODERATE 50 - 75 |
HIGH 75 - 90 |
VERY HIGH 90 - 97.5 |
EXTREME 97.5 > |
| Fire Danger Rating and Color Code |
Description |
| Low (L) (Light Blue or Green) |
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 burn freely a few hours after rain, but woods fires spread slowly by creeping or smoldering, and burn in irregular fingers. There is little danger of spotting. |
| Moderate (M) (Blue) |
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. Timber fires spread slowly to moderately fast. The average fire is of moderate intensity, although heavy concentrations of fuel, especially draped fuel, may burn hot. Short-distance spotting may occur, but is not persistent. Fires are not likely to become serious and control is relatively easy. |
| High (H) (Yellow) |
All fine dead fuels ignite readily and fires start easily from most causes. Unattended brush and campfires are likely to escape. Fires spread rapidly and short-distance spotting is common. High-intensity burning may develop on slopes or in concentrations of fine fuels. Fires may become serious and their control difficult unless they are attacked successfully while small. |
| Very High (VH) (Orange) |
Fires start easily from all causes and, immediately after ignition, spread rapidly and increase quickly in intensity. Spot fires are a constant danger. Fires burning in light fuels may quickly develop high intensity characteristics such as long-distance spotting and fire whirlwinds when they burn into heavier fuels. |
| Extreme (E) (Red) |
Fires start quickly, spread furiously, and burn intensely. All fires are potentially serious. Development into high intensity burning will usually be faster and occur from smaller fires than in the very high fire danger class. Direct attack is rarely possible and may be dangerous except immediately after ignition. Fires that develop headway in heavy slash or in conifer stands may be unmanageable while the extreme burning condition lasts. Under these conditions the only effective and safe control action is on the flanks until the weather changes or the fuel supply lessens. |
The data provided here is offered without any warranties expressed or implied, and is intended to only supplement official forecasts and information. No claims are made as to the accuracy or reliability of this data.