What Is That Red Stuff Falling From The Sky?

Fire Retardants

Planes have been used for water drops since the 1930s, but it wasn't until the mid-'50s that firefighters 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.

Newer retardants use ammonium sulfate or ammonium polyphosphate with attapulgite clay thickener or diammonium phosphate with a guar gum derivative thickener. These are not only less toxic but act as fertilizers to help the regrowth of plants after the fire. Most fire retardant that's dropped from the air is one of the various formulations branded as Phos-Chek, and overall it's deemed safe.

Once mixed, Phos-Chek LC95A contains about 85 per cent water and 15 per cent liquid fertilizer, which is made up of ammonia compounds, plus small amounts of clay, food-grade thickener and iron oxide for a bright red color. 

The thickener makes the retardant splat instead of blowing away. As for the splatter people find on their homes and cars, once dry, it's tough to remove, leaving a faded red stain. But in the face of fire many feel the risk is worth it - “better red than black.”

The first free-flowing water airdrop from an airplane onto a fire was made during the Mendenhall Fire, August 13, 1955, on the Mendocino National Forest when the pilot of a Boeing Stearman 75 Kaydet dropped 6 loads of water in support of ground firefighters. The operation successfully knocked-down the blazing fire.

To increase the effectiveness of fire control operations, in the 1960s, Navy TBM Avengers were converted to handle slurry drops, becoming the first aircraft dedicated to aerial firefighting and capable of dropping 600 gallons of retardant on a single sortie. 

Through the 1960s, the Forest Service explored using a wider variety of military surplus aircraft and discovered that multiengine PBYs, B-24s, DC-6s, and even B-17s could carry up to 2,500 gallons of retardant and were more effective on large fires. 

A wide variety of helicopters are also used for  firefighting. Helicopters may be fitted with tanks (helitankers) or they may carry buckets. Some helitankers, such as the Erickson AirCrane, are also outfitted with a front-mounted foam cannon.

The latest fire-fighting aircraft is the huge Boeing 747 Global Supertanker. It was crucial to suppressing the latest Capell Valley fire and should probably be named the “Official Bird of Lake Berryessa.”

Supertanker Berryessa  edited-2
Smoke and retardant
global-supertanker1



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