BISMARCK, ND (KXNET) — If you've paid a visit to any of North Dakota's grassy areas, there's a strong chance you're aware of the Fire Danger Index... but what exactly do these ratings mean, and how are they determined? The National Fire Danger Rating System (NFDRS) allows fire managers to estimate the current and upcoming fire danger for a given area. These managers then impose restrictions or closures to public lands, plan to combat blazes, and decide whether or not to activate burn restrictions. While the system received minor updates during the 2016 and 2018 fire seasons, it has remained mostly static for almost 40 years. Fire Danger indexes are generally calculated by analyzing multiple factors in an area — including the temperature, humidity, cloud cover, wind speed, and vegetative conditions. Wildfires can damage your water systems. Here’s how Once these factors are weighed, the risk is categorized into one of five main 'Adjective Ratings': short descriptions of the current fire danger situation in a general area. They are generally posted on either 'Smokey Bear signs' or at agency offices, and are usually denoted by different color-coded levels. As a general rule, the higher the level, the more likely a fire is to occur, and some outdoor activities are prohibited when the index is particularly dire. The five Fire Danger Ratings, as well as what exactly they entail, are listed below: Low (L, Dark Green): In an area with a low rating, fuels do not ignite readily from small heat sources — although more intense sources such as lightning may stoke flames in decayed or thin wood. Outside of fires in open, dry grasslands, most wood fires that break out will spread slowly, and controlling them is generally easy. Moderate (M, Light Green or Blue): Fires in moderate areas can start by accident, but these incidents are generally uncommon outside of lightning strikes. Fires in open grasslands spread rapidly on windy days, and timber fires grow slowly to moderately fast. The average fire is moderately strong, but unlikely to become serious, and is controlled easily. High (H, Yellow): Fine dead fuels ignite easily in a high-risk area, and fires start easily from most causes. Unattended brush and campfires are very likely to escape. High-intensity burnings may develop on slopes or in concentrations of fine fuels. Fires in these areas spread rapidly, and may quickly become serious and difficult to contain unless extinguished while small. Very High (VH, Orange): In very high fire risk areas, fires start easily from all causes, and immediately increase in both size and intensity. Fires burning in lighter fuels may quickly become high-intensity burns, and even become fire whirlwinds when they spread to heavy fuels. Extreme (E, Red): In extreme conditions, fires of any size are dangerous, as they start quickly, spread furiously, and burn intensely. Development from smaller to larger fires is much faster, and those that develop in dense vegetation may be entirely unmanageable while conditions last. Direct attacks on these fires are rarely possible. Under these conditions, the only safe and effective control method is remaining on the flanks of the blaze until a change in weather or the fuel supply decreases. For more information on how the Fire Danger Index is put to use in North Dakota, and to view the ratings currently present across the state, visit this page on the ND Game and Fish Department's website. Close Thanks for signing up! Watch for us in your inbox. Subscribe Now Today's Top Stories SIGN UP NOW