As a lad, I learned that fires need three ingredients: fuel, air, and heat. Heat was the tricky one to get, but that’s what you take away when you throw water on a fire. The fuel and air supply are unchanged, after all.
2 big wildfires merge in S. California – Yahoo! News:
YUCCA VALLEY, Calif. – Thousands of firefighters aided by aircraft worked Friday in fierce heat to keep two big wildfires from gaining a foothold in the heavily populated San Bernardino Mountains, where millions of trees killed by drought and bark beetles could provide explosive fuel.
The lightning-caused fires, covering more than 95 square miles combined, merged Friday afternoon. Wildfires can grow more unpredictable after merging, but the two blazes were moving slowly Friday and U.S. Forest Service officials said it appeared that their combination was unlikely to seriously increase fire activity.
I look at that photo and without knowing anything about the retardants they use, I wonder if dropping CO2 — dry ice — would have any effect. Consider: it would cool the fire (at -109°F), if enough of it were used (and I assume it would be dropped in the heart of the hottest part) and when it sublimated to a gas, it would deprive the fire of oxygen.
Maybe not something you could use on a really large fire, but perhaps it could be used to protect homes or knock a small fire before it gets too large?