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https://www.nist.gov/el/fire-research-division-73300/wildland-urban-interface-fire-73305/hazard-mitigation-methodology-19

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Engineering LaboratoryFire Research Division

## Wildland-Urban Interface Fire Group

-  HAZARD MITIGATION METHODOLOGY (HMM)  Expand or Collapse    -  Why Implement HMM in your Community?  Expand or Collapse      -  Exposures During WUI Fires 
    -  HMM vs Traditional Hazard Mitigation 
    -  WUI Definitions 
    -  Structure Survivability in the WUI 
    -  Community Survivability in the WUI 
    -  Paths forward: Implementing HMM 
    -  Communities already implementing HMM 
  -  How Fire Spreads in the WUI  Expand or Collapse      -  How do Structures Survive WUI Fires? 
    -  Fire Spread Pathways 
    -  Why Exposure Matters, not Parcel Boundary 
    -  Hazard from Fuel Agglomeration 
    -  Community-scale WUI Fire Hazards 
  -  Community-Wide Structure- and Parcel-Level Hardening Actions  Expand or Collapse      -  How Density Impacts Community 
    -  Workflow for HMM Hardening Actions 
    -  Structure Hardening for Embers 
    -  Parcel Hardening for Fire: the Three R’s 
    -  Surrounding Parcel Hazard Mitigation 
    -  Primary Parcel Hazard Mitigation 
    -  Structure Hardening for Fire 
    -  Communities Hardening Actions 
  -  Hardening Actions: Construction Guidance 
  -  Contacts 

# How Density Impacts Community

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The effectiveness of protecting a home from direct flame exposuresis dependent on the density of structures in the community.

The effectiveness of structure hardening is dependent on the potential fire exposure from neighboring structures, wildlands, and other fire sources. Fire hardening can be an effective mitigation method in certain spatial situations where structures are located far enough apart that exposures are moderated and fuel removal or displacement is not possible. Protecting a home from direct flame exposures can be difficult and expensive, and is likely ineffective for the highest exposures, such as from a burning neighboring home.
                  - High-density communities  - must not have any structures ignite as risk of entire community loss is very high due to structure-to-structure fire spread.
                  - Medium-density communities  - greatest impact on structure ignition resistance by hardening for fire exposures from neighboring structures.
                  - Low-density communities  - lower potential losses from individual structure ignitions, low potential for urban conflagration.

The table below outlines the probability of structure survival for potential exposures (fire and ember) for various WUI types. Hover your mouse over each area of the table for specific details.

Click here to view the table as an image.

##### Structure and parcel hardening effectiveness

-  **‹** Community-Wide Structure- and Parcel-Level Hardening Actions 
-  Workflow for HMM Hardening Actions **›** 

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