Moisture Values

Moisture is described by 6 parameters. The four of them are known as the dead fuel parameters while the rest of them are the live fuel parameters.

The dead fuel parameters are:
  • Dead1h (< 0.625 cm (0.25 in.) diameter)
    1-hour time lag fuels are the most important for carrying surface fires and their moisture content governs fire behavior. One-hour fuels include fallen needle and leaf litter, grassy fuels, lichens, and small twigs. Within this category, response times vary by fuel type. Lichen, grass, and well-cured needles respond to changes faster than freshly fallen needles and hardwood leaves. Due to their high surface area to volume, low moisture content, and location in the combustion zone, they produce little smoke and have low flame residence time.
  • Dead10h (0.625 - 2.5 cm (0.25 to 1 in.) diameter)
    Common 10-hour fuels include small branches and woody stems. Due to their resistance to drying and greater heat capacity, 10-hour fuels often do not combust in low-intensity surface fires. When moisture is low, however, 10-hour fuels can carry hot fires and help ignite larger (100- and 1000- hour) fuels. Ten-hour fuels are readily consumed when fuel moistures are low.
  • Dead100h (2.5 cm - 7.6 cm (1 - 3 in.) diameter)
    Larger downed woody debris is common 100-hour forest fuels. These fuels take longer to dry, deterring their consumption under most conditions. Likewise, 100-hour fuels are slow to gain moisture, so they can combust after prolonged drought, even with recent precipitation.
  • Dead1000h (> 7.6 cm (3 in.) diameter)
    These fuels, which include large downed branches, logs, and tree stumps, burn only under prolonged dry conditions, or when sufficiently pre-heated by adjacent fuels. Since they do not commonly burn, 1000-hour fuels can act as firebreaks and cause fire shadows.

The live fuel parameters are:
  • Live Herb
  • Live wood
The dead fuel parameters take a value from 0.01 to 0.5 while the live fuel parameters take a value from 0.3 to 3.0.