Revisiting the home ignition zone: the intermediate 5-30 feet

The home ignition zone (HIZ) is the foundation NFPA has built its wildfire preparedness programs and resources on.  A concept coined by retired USFS researcher Dr. Jack Cohen, the basic premise of the HIZ is that the condition of the home (what it is made of and its state of repair) and the vegetation surrounding it, out to 100 feet, have the biggest influence on whether or not a home will ignite from a wildfire.  It is broken down into three areas of concern, the immediate, intermediate, and extended.  Previously we learned about the immediate 0-5 feet, today we'll cover the 5-30 foot zone.

The Intermediate Zone is 5-30 feet from the furthest exterior point of the home.  While the 0-5 foot focuses on eliminating combustible material, this area is all about spacing and maintenance, making sure there isn't continuous vegetation all around the home.  It uses landscaping and breaks (areas of non-combustible materials such as dirt, cement, or rock) to help influence and decrease fire behavior. 

When looking at a home or group of homes, here are items to consider:      

  • Are there fuel breaks such as driveways, walkways/paths, patios, and decks?
  • Are lawns and native grasses maintained? General recommendation is a height of 4 inches.
  • Is vegetation in this area spread out? It is recommended that trees and shrubs should be limited to small clusters of a few each to break up continuity; trees should be spaced to a minimum of 18 feet between crowns.
  • Have ladder fuels (vegetation under trees) been removed so a surface fire cannot reach the crowns?  Have trees been pruned? General recommendations are up to 6 to 10 feet from the ground; for shorter trees, do not exceed 1/3 of the overall tree height.

TreeSpacingGraphic_2020

  •  Are plants, trees, and lawns watered to keep them from becoming dry?
  •  There is potential for a lot of work needed in this area, but don't get overwhelmed.  Take stock of what you have, prioritize tasks - maybe put some easy wins first, and keep chipping away.  Our preparing homes for wildfire page has excellent tips to help you on your way.

This intermediate zone presents an opportunity for overlap with adjacent properties.  As you work on projects, consider reaching out to your neighbors to collaborate and leverage resources. 

Sign up for NFPA Network to stay up to date with the latest news and information on key wildfire issues. You can also follow me on twitter @meganfitz34 more wildfire-related topics.  

As we navigate the evolving situation with COVID-19, NFPA remains committed to supporting you with the resources you need to minimize risk and help prevent loss, injuries, and death from fire, electrical, and other hazards. For information on NFPA's response to the coronavirus, pleasevisit our webpage.

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Megan Fitzgerald-McGowan
Program Specialist, Megan manages Firewise USA® and holds a deep belief that collaboration is the best way to reduce risk and loss from wildfire.

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