Fire Retardant Gel

Fire-retardant gels are superabsorbent polymer slurries with a "consistency almost like petroleum jelly." Fire-retardant gels can also be slurries that are composed of a combination of water, starch, and clay. Used as fire retardants, they can be used for structure protection and in direct-attack applications against wildfires. Fire Retardant gels are short-term fire suppressants typically applied with ground equipment. They are also used in the movie industry to protect stunt persons from flames when filming action movie scenes.

History
The practical use of gels was limited until the 1950s as advances in copolymerization techniques led to reproducible, batchwise preparation of swellable resins with uniform cross-linking. This technology was later used in the development of a "substantially continuous, adherent, particulate coating composition of water-swollen, gelled particles of a crosslinked, water-insoluble, water-swellable polymer." The water-absorbent polymers in fire-retardant gels are similar to those used in diapers.

Mechanism
The polymer in gels soaks up hundreds of times its weight in water creating millions of tiny drops of water surrounded by and protected by a polymer shell. The result is a "bubblet" or a drop of water surrounded by a polymer shell in contrast to a bubble which is air surrounded by liquid. As the gel and water are sprayed onto an exposed surface, millions of tiny "bubblets" are stacked one on top of another. The stacking of the water "bubblets" form a thermal protective "blanket" over the surface to which it is applied. In order for the heat of the fire to penetrate the protected surface, it must burn off each layer of the gel "bubblets" coating. Each layer holds the heat away from the next layer of bubblets beneath. The polymer shell of each bubblets and their stacking significantly prevent water evaporation.

Uses
Fire retardant gels create a fire protective gel coating that completely repels flaming embers and is extremely effective in cases of emergency in protecting structures from the flame fronts typical of most wildfires. During a fire in the Black Hills National Forest, "nearly all homes coated with a slimy gel were saved while dozens of houses nearby burned to the ground". Certain supplemental fire protection insurance may include the application of fire-retardant gel to homes during wildfire. Claimed to work "best when applied hours before a fire approaches", gel is applied using specially designed trucks by private firms.