National Wildfire Coordinating Group

Hazard Tree - No Work Zones


No work zone (NWZ) graphic showing a large circle shaded with a NWZ clear circle on right side within shaded area indicating the potentially dangerous tree or high-value wildfire area.

Knowing the exact time a given hazard tree (or compromised section) will fail is extremely difficult, and is, in many cases, an unpredictable task. Given this fact, we need to manage firefighters’ exposure to these hazards by creating a safe work area or No Work Zone (NWZ). The size and extent of the NWZ must be determined by onsite conditions, such as terrain, stand structure, and fire impacts on the tree and adjoining trees.

When an identified hazardous tree or trees cannot be felled, then perform an assessment of which areas have too high a risk, and post a lookout to warn the personnel to stay clear of these areas while working in adjacent areas. If hazard still exists before leaving the area, flag the NWZ so that personnel entering the area will be able to recognize the hazard. Use the following failure zone illustrations as examples to help manage firefighter exposure to these identified hazards. Also, remember to include the possibility of the Domino Effect to surrounding trees.

Figure 1 - 1 1/2 X Height of snag    Figure 2 - 1 1/2 X Trunk-to-branch-tip distance      Figure 3 - 1 1/2 X Length of dead top   
Figure 1 - graphic showing the potential failure zone of a dangerous area around a snag tree. Figure 2 - graphic of a tree showing the distance of dead limb hazard area. Figure 3 - graphic showing a pine tree with potential failure zone of the dead top.




Felling Safety
Page Last Modified / Reviewed: 
Mar 2022

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