Discontinuous Treatment for Flame-Spread Control

The effectiveness of discrete islands of highly concentrated fire-retardant salts was evaluated as a means of flame spread control in wood products. Materials tested were especially prepared laboratory plywood, commercially manufactured 5/8 inch Douglas-fir plywood, and 3/4 inch particleboard. Fire retardants used included diammonium phosphate, dicyan-diamide-phosphoric acid, “Non Coma” “Pyresote,” and “Minalith.” Discontinuous treatment was achieved by injecting 20 to 40 percent solutions of fire retardants into the wood as pulsed, high-velocity jets, 0.006 inches in diameter, 1,200 ft./sec. velocity. Typical placement in plywood was 1 to 2 inches along and 1/4 to 3/4 inch across the grain of the face ply. Salt loading was 3 to 4 lb./ft.3. Treated laboratory panels were evaluated in a 2-foot tunnel on a comparative basis and showed flame spread control equal to uniform treatment. Commercial panels were tested in a 25-foot tunnel (ASTM E-84-60). Typical results for 5/8 inch Douglas-fir were flame spreads of 15 feet at 10 minutes and 20 feet at 30 minutes. This is equivalent to Underwriters Class 1 noncombustible. Jet-treated particleboard had a 10-minute flame spread of 18 feet with fuel contribution of 15 at salt loading equal to half that of similar board integrally treated.

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