Fire danger rating in the United States: an evolution since 1916

Fire scientists in the United States began exploring the relationships of fire danger and hazard with weather, fuel moisture, and ignition probabilities as early as 1916. Many of the relationships identified then persist today in the form of our National Fire Danger Rating System. This paper traces the evolution of fire danger rating in the United States, including discussions of significant development milestones, innovative instrumentation, and a succession of analog fire danger meters, or calculators. We present this evolution within the context of three periods of development: first, the pioneering efforts initiated at the Priest River Experiment Station in northern Idaho; second, the proliferation of local and regional variants; and third, the implementation of a national, standardized fire danger rating system.

Devastating forest fires in the Western U.S. during the first fifteen years of the fledgling US Forest Service forced foresters to realize that a formal fire research program was needed. This led to Harry T. Gisborne becoming the Nation's first person to tackle this enormous task on a full time basis. A major goal was to incorporate common knowledge along with measurable components of fire behavior, such as relative humidity, fuel moisture, and wind velocity into a common language that all users could understand. One product was the sets of 1/2" sticks for fuel moisture predictions; they are still used today. Further recognition of the need for a common language came in the form of the Model One Fire Danger Meter developed and adopted for use in 1931. This made intelligent fire control planning possible and also contributed to a unification of the language.

The Thirties were pretty well involved into putting into practice what was learned before. A number of test fire-danger stations were set up by 1934. Use of Model One at Pete King Ranger Station, on the Selway National Forest, proved its value in a negative manner. The extremely high readings indicated blow-up conditions that did not exist elsewhere. These were therefore ignored by key decision-makers. The ensuing lack of a few extra available men caused the fire to roar to a final size of one quarter million acres! That incident became a national imperative for fire-danger rating research and development.

With the establishment of fire research laboratories in the late fifties and early sixties at Macon, Georgia,, Missoula, Montana, and Riverside, California, these basic concepts from pioneering research performed three quarters of a century ago continue to be refined and greatly extended. A national system was first introduced in 1964. The current system used throughout the U.S., called the National Fire Danger rating System, was implemented in 1978, with optional revisions added in 1988. Now, the system is hosted within the Wildland Fire Assessment System (WFAS), an internet-based information system. The current implementation provides a national view of weather and fire potential, including national fire danger and weather maps and satellite-derived "Greenness" maps. New research and development continues to focus on creating new knowledge and products related to the National Fire Danger rating System.