Fire Protection from Polymer Gel

Introduction

Precision Lift's Fire-Fighting Module can be used to apply a coating of superabsorbent polymer gel to houses threatened by forest fire. Gel is different from foam. Foam consists of air bubbles in water (and a small amount of surfactant). When the bubbles burst, the foam collapses. Water in gel is held by a three-dimensional network of cross-linked polymers. When the water evaporates, the gel collapses. It takes longer for water to evaporate, than for air bubbles to burst. Thus, gel provides protection that lasts longer than foam.

Under the most severe conditions with relative humidity less than 10%, a hot wind, and temperatures in the 90's or higher, a thin coating of gel on a dark surface in direct sunlight remains effective for less than an hour. However, if the fire is coming over the ridge, this protection can be the difference between saving a house and having it burn to the ground. Applying a fine mist of water droplets renews the effectiveness of the gel.

Gel, when properly applied as a protective blanket, provides superior fire protection for structures. It adheres to walls and to the underside of overhanging eves. [Care needs to be taken to cover air vents under the eves so that burning embers are not sucked into the attic.]

Polymer Gel Chemistry

Polymer gels used for protection of structures from fire are superabsorbents. They use cross-linked polymers to absorb many times their weight of water. The superabsorbent material in Pampers^® brand disposable diapers is sodium polyacrylate. At the present time only three superabsorbent gels are used commercially. These are potassium polyacrylate (Chemical Abstracts Services or CAS Registry No. 25608-12-2), sodium polyacrylate (CAS No. 9003-04-7), and polyacrylamide (CAS No. 9003-05-8). All three have been used to protect structures from fire. The superabsorbent gel commonly used to absorb chemical spills is potassium polyacrylate. Polyacrylamide gel is widely used in horticulture to retain moisture around root systems of seedlings.

The structural formula of potassium polyacrylate is:

[ -CH₂-CH(COOK)- ]_n

The structural formula of sodium polyacrylate is:

[ -CH₂-CH(COONa)- ]_n

The structural formula of polyacrylamide:

[ -CH₂-CH(CONH₂)- ]_n

(In the formulas above, C is the symbol for carbon, H stands for hydrogen, N for nitrogen, O for oxygen, K for potassium, and Na for sodium.)

Application and Dosage for Gel Supplied as a Liquid Concentrate

Several vendors supply gel as a liquid concentrate (eg. Thermo-Gel^®, AFG Firewall^®, and Barricade^®). Phos-Chek^® AquaGel-K is supplied as a dry powder which is mixed with water to make a concentrate. The liquid containing the polyer gel is applied at concentrations ranging from 1% to 6% by volume using an eductor at the end of the fire hose. Using 1" fire hose and a pump that can generate 100 psi at the nozzle, the gel is sprayed on at a rate of about 15 gallons per minute. Covering a house takes typically 10 minutes, but can take twice as long for a larger house. A thick layer is applied to doors, windows, flammable roof, under the eves, wooden deck, and firewood under the deck. Using the thickest gel (or highest concentration) provides the longest lasting protection and the best response to rejuvenation by mist. Vertical walls do not catch fire as easily and can receive a thinner coating. A typical house can be covered by 5 gallons of concentrate, costing less than $250. (Barricade lists a Homeowner's Kit for $320.) As discussed below, removal after the fire danger is over may be a problem.

Hazardous Properties

The gels are very slippery. Extra caution is required, especially when working on roofs, on ladders, and on sloping ground.

Thermo-Gel and AFG Wildfire contain mineral oil as an additive. Barricade contains canola oil. However, these additives are not rated as hazardous to workers.

Removal

The gel blanket should be hosed off of the house as soon as the fire danger is over. If the gel blanket is left to bake in the sun for days or baked by the fire, a water mist should be used to soften the gel before hosing it off. Otherwise a pressure washer may be needed to remove the gel from the house. Wildfire(Tyco) has a product--AFG Gel-Buster^™--to aid in removing gel which has dried on the exterior of a house. Check with the vendor/manufacturer for removal instructions.

Environmental Impact

The gels are biodegradable, especially in sunlight; however, this takes time.

Compared with foams, the gels are environmentally friendly. All of the gel productes listed below meet the U.S. Forest Service requirement to be non-toxic to rainbow trout minnows. The impact of nonylphenol ethoxylates on aquatic life is currently being investigated.

Useful Links to Other Sites

Commercially Available Polymer Gels for Fire Protection

Phos-Chek AquaGel-K. This product consists of a superabsorbent polymer--potassium polyacrylate--and a colorant. It is supplied as a dry powder. It contains no polyacrylamide, nonnylphenol ethoxylates, oils or solvents. This product has been approved by the US Forest Service.

Thermo-Gel. This product consists of superabsorbent polymers--polyacrylamide and sodium polyacrylate--, mineral oil, and surfactants, and is supplied as a liquid concentrate which is mixed in an eductor. This product has been approved by the US Forest Service.

AFG Firewall from Wildfire--a Tyco Company. The superabsorbent polymer is polyacrylamide. It contains a surfactant, mineral oil, and other additives. It is supplied as a concentrate which is mixed in an eductor at the end of the fire hose. This product has been approved by the US Forest Service.

Barricade Fire-Blocking Gel. The superabsorbent polymer is potassium polyacrylate. It also contains canola oil and other additives; but does not contain any nonnylphenol ethoxylates. It is supplied as a concentrate which is mixed in an eductor at the end of the fire hose. This product has been approved by the US Forest Service.

Hardware for Coating Houses with Gel

Gel Application Kits for the Fire Hose and Garden Hose from Scotty Firefighter

Kitchen Sink Experiments with Gel

Experiment with sodium polyacrylate as found in diapers from the American Chemical Society website. Demonstrates increase in volume as gel absorbs water. Demonstrates decrease in absorbency with salinity using sodium chloride. The experiment can be repeated with calcium chloride instead of sodium chloride to show the large effect of divalent cations compared with monovalent cations on the gel.

A similar experiment from Steve Spangler.

Potassium polyacrylate can be ordered from Loose in the Lab.

BASF (Badische Analin und Soda Fabrik) makes potassium polyacrylate. The U.S. plant is located in Aberdeen, MS.

Stockhausen GmbH makes polyacrylamide and sodium polyacrylate.

Home Site Map Products Fire-Fighting Module Structure Protection Chemicals Foams Contact Us Orders