Timelag
Fuels can be placed into more specific categories based on the size of the materials and a factor called timelag. Timelag is the time it takes for a fuel to gain or lose moisture due to changes in its environment. The following table shows size classes of fuels and the approximate time for fuel moisture to change in response to its environment.
| Grasses, litter and duff | <¼ inch in diameter | 1-hour timelag |
| Twigs and small stems | ¼ to 1 inch in diameter | 10-hour timelag |
| Branches | 1 to 3 inches in diameter | 100-hour timelag |
| Large stems and branches | >3 inches in diameter | 1000-hour timelag |
The concept is more important here than the calculation. Small fuels dry quicker than large ones. It is possible to have rain at 10 a.m. and still have an intense grass fire at 2 p.m. if conditions are right.
Courtesy of MDC