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Irvine Co. erected a 6-foot wall around an enclave on the north part of the neighborhood — where a Santa Ana wind-driven fire would most likely hit first — to protect the most vulnerable properties from radiant heat and keep low-flying embers out of the development.

Orchard Hills homes are constructed with two factors in mind: radiant heat and ember intrusion.

Radiant heat is the heat projected by fire; if a home’s exterior is made of flammable materials, the house can heat up to the point of igniting.

“Window panes will burst readily under radiant heat and that’s a very common source of entry for embers,” said Syphard, who recommends double-pane windows, along with fine-mesh screens on vents.

And what we’ve seen with the science is once you get over 30 feet of separation between structures, you have much less concern about radiant heat as a factor in causing urban conflagrations.