Revised guidance for safety zones is released

Safety Zone Calculation
Safety Zone Calculation, released July, 2014. Bret Butler.

In his continuing efforts to improve the recommended standards for wildland firefighters’ safety zones, researcher Bret Butler has released a revised version based on additional research. Dr. Butler developed the guidelines that had been used for years which were based on the height of the flames, but in May, 2014 released a new recommendation that was based on height of the vegetation, wind speed, slope, fire intensity, and a constant number. This new July, 2014 version replaces the one that was released in May.

A safety zone is an area where wildland firefighters may be forced to take refuge from an approaching wildfire. There, a firefighter should be able to survive without being injured from exposure to the radiant and convective heat from the fire, and would not have to deploy and enter a fire shelter.

The latest version of the guidelines released a few days ago is based on height of the vegetation, wind speed, slope, and the same constant number (8). It removes a factor that could be a little subjective or difficult to quantify accurately in the field, fire intensity.

The new system, like the one unveiled in May, calculates the Safe Separation Distance (SSD) between the fire and the firefighters. To determine the SSD, using the table above multiply the constant number (8) times the number from the table (Slope-Wind Factor) times the height of the vegetation.

Example for 15 mph wind, 24% slope, 6-foot vegetation:

The Safe Separation Distance is   8 x 3 x 6 = 144 feet

Dr. Butlers’ Additional Considerations:

  1. For a 20-person crew, add 10 feet of radius and for a vehicle add another 5 feet of radius.
  2. The area in red requires large natural openings or construction by mechanized equipment.
  3. The proposed rule is to be used for flat ground rather than the existing flame height rule.
  4. Also consider additional lookouts on the ground and in the air to monitor fire activity with early egress to escape routes and safety zones.
  5. At 30% or greater slopes, hot gases tend to stay close to the ground.

Dr. Butler’s disclaimer: This proposed safety zone rule should be considered preliminary because it is based on limited data and analysis and subject to increase or decrease based on additional data. It is presented for release this fire season with the intent of increasing firefighter safety and reducing risk of injury. It is likely that an updated rule will be released in the next year.

For more information see the article in the International Journal of Wildland Fire titled: Wildland Firefighter Safety Zones: A Review of Past Science and Summary of Future Needs

We will let you know if another revised version of the guidelines is released in two months.

(NOTE: if you want a copy of the table above, click on it to open it in a window of its own, then click on Print in your internet browser.

Thanks and a hat tip go out to Ryan.

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Author: Bill Gabbert

After working full time in wildland fire for 33 years, he continues to learn, and strives to be a Student of Fire.