Burning Indexes Explanation
| Chandler Burning Index The Chandler Burning Index (CBI) uses air temperature and relative humidity to create a numerical index of fire danger. That number is then equated to an Adjective Fire Danger. It is based solely on weather conditions, with no adjustment for wind speed, fuel load or moisture content. |
| Low (L) (Green) |
Numeric equivalent: < 50. 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) |
Numeric equivalent: 50 - 75. 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) |
Numeric equivalent: 75 - 90. 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) |
Numeric equivalent: 90 - 97.5. 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) |
Numeric equivalent: > 97.5. 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 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. |
| Haines Index The National Weather Service uses the Lower Atmospheric Severity Index (LASI) to quantify the potential for forest fire growth. This index was developed in 1988 by a USDA Forest Service research meteorologist named Don Haines. Commonly called the Haines Index, this index is a measure of how readily atmospheric conditions, roughly 1 to 3 km (0.5 to 2 miles) above the ground, would support the development of a large or erratic plume dominated wildfire. The Haines Index combines two atmospheric factors that are known to have an effect on wildfires: Stability and Dryness. * Stability: Stability is a term used to describe the tendency for vertical air motion in an air mass. A stable atmosphere tends to discourage any vertical air motion while an unstable atmosphere promotes it. A wildfire stands a much better chance of growing large in an unstable air mass because vertical motion encourages the growth of the smoke column. This would increase the chance of spotting and crowning and a very strong smoke column can eventually create its own wind. i.e. become a plume dominated fire. * Dryness: The drier the air mass, the drier the fuels are likely to be. Thus, more combustive energy is released and fire spread is enhanced. |
