Five common denominators of fire behavior on fatal and near-fatal fires have been identified through studies of tragedy fires. It is important for firefighters to readily recognize them to prevent future disasters.
Such fires often occur:
- On relatively small fires or deceptively quiet areas of large fires.
- In relatively light fuels, such as grass, herbs, and light brush.
- When there is an unexpected shift in wind direction or in wind speed.
- When fire responds to topographic conditions and runs uphill.
- Critical burn period between 1400 and 1700.
Alignment of topography and wind during the critical burning period should be considered a trigger point to reevaluate tactics.
Blowup to burnover conditions generally occur in less than 60 minutes and can be as little as 5 minutes.
On October 9, 2019 a document was published that summarized the work of four researchers who sought to find commonalities that led to the entrapments of firefighters on wildland fires. The paper is titled, “A Classification of US Wildland Firefighter Entrapments Based on Coincident Fuels, Weather, and Topography.” Apparently they were hoping to confirm, fine tune, revise, or update the “Common Denominators of Fire Behavior on Tragedy Fires” defined by Carl C. Wilson after the 1976 Battlement Creek Fire where three firefighters were killed near Parachute, Colorado.
The researchers conducted an analysis of the environmental conditions at the times and locations of 166 firefighter entrapments involving 1,202 people and 117 fatalities that occurred between 1981 and 2017 in the conterminous United States. They identified one characteristic that was common for 91 percent of the entrapments — high fire danger — specifically, when the Energy Release Component and Burning Index are both above their historical 80th percentile.
They also generated an update of the time of day the entrapments occurred as seen in the figure at the top of this article. This has been done before, but it’s worthwhile to get an update. And, this version includes the month.
You can read the entire open access article here. If you’re thinking of quickly skimming it, the 7,000 words and the dozens of abbreviations and acronyms make that a challenge. There is no appendix which lists and defines the abbreviations and acronyms.
The authors of the paper are Wesley G. Page, Patrick H. Freeborn, Bret W. Butler, and W. Matt Jolly.
Below are excerpts from their research:
…Given the findings of this study and previously published firefighter safety guidelines, we have identified a few key practical implications for wildland firefighters:
- The fire environment conditions or subsequent fire behavior, particularly rate of spread, at the time of the entrapment does not need to be extreme or unusual for an entrapment to occur; it only needs to be unexpected in the sense that the firefighters involved did not anticipate or could not adapt to the observed fire behavior in enough time to reach an adequate safety zone;
- The site and regional-specific environmental conditions at the time and location of the entrapment are important; in other words, the set of environmental conditions common to firefighter entrapments in one region do not necessarily translate to other locations;
- As noted by several authors, human factors or human behavior are a critical component of firefighter entrapments, so much so that while an analysis of the common environmental conditions associated with entrapments will yield a better understanding of the conditions that increase the likelihood of an entrapment, it will not produce models or define characteristics that predict where and when entrapments are likely to occur.
The factor that was common for the majority of entrapments (~91%) was high fire danger. As a general guideline, regardless of location, the data suggest that entrapment potential is highest when the fire danger indices (Energy Release Component and Burning Index) are both above their historical 80th percentile.
More information about this research.
Recent burnovers in the United States that resulted in fatalities; with time and date:
- El Dorado Fire around 7 p.m. September 17, 2020.
- Corn field fire 2:30 p.m. October 26,2021.
- August Complex, 2:15 p.m. August 31, 2020.
- Twisp River Fire, around 3 p.m., August 19, 2015.
- Spring Coulee Fire, 4:26 p.m., September 1, 2019.
One thing that will be interesting to watch is if the historical three-hour window from 1 to 4 p.m. when many of the fatalities have occurred is going to be stretched as the earth warms and extreme fire behavior becomes more frequent.