In the mid-1970s, fire researcher Carl Wilson identified four common
denominators of fire behavior that caused fatalities and near-misses
on wildland fires. These four common denominators have been cited for
decades in fire safety training, in the “Fireline
Handbook” (PMS No. 410–1), and in the “Incident
Response Pocket Guide” (PMS No. 461).
Based on my analysis of 310 fire fatalities during wildland fire
operations from 1990 to 2006, I believe that it is time to consider
some 21st-century common denominators to help reduce wildland
21st Century Common Denominators for Wildland Firefighter
As the major causes of firefighter fatalities shift, additional factors
need to be considered:
Firefighters are most likely to die in an aircraft accident. Before
every flight, fire managers must ask, “Is this flight
essential?” and “Is everyone onboard essential to the
Firefighters are nearly as likely to die in a vehicle accident as
in an aircraft accident. Driving too fast for the conditions,
failure to wear seat belts, rushing to a fire, and driving home
while exhausted from firefighting kills firefighters.
Firefighters can reduce their risk of dying from heart attacks on
the job by staying fit, maintaining their body weight, and having
regular medical checkups.
Unexpected events such as falling snags, rolling rocks, downed
power lines, and lightning strikes cause more than 8 percent of
fatalities during wildland fire fighting operations. Firefighters
and fire managers can reduce fatalities by learning to expect these
More than 20 percent of fatalities during wildland firefighting
operations continue to occur in burnovers. Carl Wilson’s
original common denominators are just as important in the 21st century
as they were in the 20th.
Carl Wilson’s Common Denominators of Fire Behavior on Tragedy
There are four major common denominators of fire behavior on fatal and
near-fatal fires. Such fires often occur:
Extract from The National Wildfire
Coordinating Group (NWCG)
On relatively small fires or deceptively quiet areas of large
In relatively light fuels, such as grass, herbs, and light brush.
When there is an unexpected shift in wind direction or wind speed.
When fire responds to topographic conditions and runs uphill.
Alignment of topography and wind during the burning period should
always be considered a trigger point to re-evaluate strategy and
- Publication, PMS 841
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Last updated 4 November 2014