Oxidative thermal degradation of PVC-derived, fiberglass, cotton, and jute brattices, and other mine materials. A comparison of toxic gas and liquid concentrations and smoke-particle characterization.
The Bureau of Mines performed experiments to determine concentrations of toxic gases and liquids, and smoke-particle diameters and diameter-concentrations evolved during degradation of PVC-derived brattice with and without nylon-woven fabrics, fiberglass, cotton, and jute brattices, and other mine materials. The samples were exposed in a 20-l chamber at temperatures of 150 degrees to 450 degrees c, with a chamber airflow of 10 l/min; 27.3 Cm3/s of which was directed into a submicrometer-particle detector- analyzer. During the degradation of pvc-derived brattice, large concentrations of hydrogen chloride (tlv, 5 ppm; stel, 100 ppm) evolved at a temperature as low as 200 degrees c. The minimum toxic load of 3.1 Mg or 40 ppm in 50 l of dilution air, with 0.1-G weight loss, may be reached at a mine face with 314,000 l of dilution air, at the 5th min, during which less the 1 kg of brattice undergoes combustion. Fiberglass, cotton, and jute brattices, pine wood dust, and coal dust showed small concentrations of carbon monoxide evolving during early stages of combustion. Hydrogen cyanide gas evolved from the pvc-derived, nylon-reinforced brattice; at a later stage of combustion, large concentrations of carbon monoxide and dense smoke evolved from all pvc-derived brattices. Experiments to characterize smoke particles showed that marked differences exist in particle diameter-concentrations among the materials.