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Hey, Matt:

What is the red stuff the planes drop on the brush fires? How does it work?

-- EED, via e-mail

Works very well, thanks. The red stuff is mostly water. It's mixed with ammonium phosphate or sulfate (fertilizers), with guar gum or clay (thickeners) and iron oxide (color). The Forest Service has used planes for water drops since the 1930s, but it wasn't until the mid-'50s that it began using a heavier slurry of water and additives to keep the water from evaporating in the heat or being blown away from the drop zone before it hit the ground. Thickeners also help avoid runoff. Color marks the area hit by the drop, and the fertilizer encourages regrowth of plants in the burn area. The red stuff is a fire retardant rather than a fire extinguisher, slowing progress to give firefighters time to reach the area. The retardant will stain your house if it lands on it, though it washes off. The fertilizer component is toxic to fish and is harmful to pets and people if they ingest some. So don't stand by a wildfire and look up at the plane with your mouth open in amazement. Besides, the water is moving pretty fast and could knock you on your butt.

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