When homes are densely packed in alignment with the direction of strong fire-season winds, it is nearly almost impossible to cut enough brush to make the homes defensible. Fire burns from house to house, no longer a ‘brush fire’, rather it is referred to as an ‘urban conflagration’ or simply a ‘conflagration’. Wind-driven brush fires cast burning embers long distances, so it can be difficult to define the ‘edge’ of a neighborhood, as spot fires can leap from the wildland far into adjacent neighborhoods, starting many houses on fire at once.
A neighborhood in the path of the Palisades Fire.
Also, a lack of easements to access the back of residential lots makes it nearly impossible to do tree work or other major vegetation management which could lower wildfire hazards.
Small lot sizes and a lack of pre-planning make tree work and other major vegetation management very difficult.
If the primary fuel for wildfires is structures and building materials, the concept of ‘defensible space’ means something different in a dense urban environment than it does in a place with one-acre lots.
The transition from brush to homes is seamless. Fire is free to spread at will, and there are no places from which to launch a coordinated firefighting attack.
A neighborhood is only as strong as the weakest link between the wildland and the built environment. Once a wildfire is into the community and spreading house-to-house, it is almost impossible to stop until the winds die.
This neighborhood was built in ‘alignment’ with the direction that Santa Ana winds usually come from.
From our recent interview with veteran Southern California wildland firefighter Tim Chavez:
Tim Chavez
“When it becomes an urban fire storm, that orientation of the buildings becomes important, because those embers go right from one building to the next building to the next building when it when it starts spreading, building to building like that. You know, the BTU output of a fire like that is so tremendously far above what we experience in brush or even in timber, because of all the modern building materials, plastics, you know, all that stuff.”
Zeke Lunder
“Yes, it’s really important to make that distinguish between an urban conflagration and a wildfire, and that when we talk about wildfire mitigation, things that we think about with wildfire mitigation, like defensible space, they don’t mean anything if your house is 10 feet away from your neighbor’s house and your neighbor’s house is on fire with no firefighters there.”
Tim Chavez
“…and you have palm trees and junipers and Italian Cypress all around your house, and you have landscaping bark on the ground, you know, right up to your to your walls, and you don’t stand a chance. There’s just no there’s no mitigating. There’s nothing that an engine company can do to protect houses at that point, because once the palm trees and pine trees and eucalyptus and ornamental vegetation catches on fire. It’s over. You can’t do anything.”
Zeke Lunder
“So, yeah. So this is one of those neighborhoods that we’re talking about. It’s just, you’ve got the flammable pampas grass and an incredible amount of fuel for the fire!”
Tim Chavez
“Yeah, yeah, that’s a that’s a killer right there. And when you’ve got palms with a lot of dead fronds, each one of those fronds is gonna is going to atomize into a billion embers, and all those embers are gonna go downwind to the next house and to the next house. That pepper tree right there, same thing. All those leaves are gonna, are gonna volatilize, and now that each one of those leaves becomes an ember, it’s just, you know, there’s, there’s nothing we can do (to stop a fire that’s creating a storm of embers on a windy day)”.
