BURNING BEHAVIOR IN A POOR-VENTILATION COMPARTMENT FIRE - GHOSTING FIRE

We investigated compartment fire behavior under poor-ventilation conditions using a methyl alcohol pool fire as the source with a diameter of 30 cm set in a tight box of 2 m (W) x 3 m(L) x 0.6 m(H). The temperatures in the box and the fuel, gas concentrations of CO, CO2, and O2, and the fuel consumption rate were measured simultaneously. The burning fuel surface level was kept constant during the test by means of an automatic fuel supply system. It was found that the flame begun to detach from the fuel surface as the oxygen concentration decreased to about 16%, and the color changed to pale blue. The flame detached completely from the fuel and a "ghosting flame" was observed just under the ceiling which showed a thin pale blue flame and looked line an aurora. The oxygen concentration measured in the ghosting period under the ceiling was 9-10 vol%, and CO2 was 4.5 vol% so that the oxygen of such concentration acted as in inert gas. CO2 gas concentration looked almost a single-layer with gradient in the upper half part in ghosting period. Temperatures in the same layer decreased after ghosting occurred with gradient. For poor-ventilated fires, air exchange rate as 1.6-2.4 times/hr was estimated in the test; the burning rate decreased finally to about 1/6 of the fuel controlled fire. It has been tacitly assumed that the flame (reaction zone) and pyrolyzing material area (fuel) exit in almost the same zone, but ghosting fire is not necessarily the case. Therefore, extinguishment of ghosting fire which may occur in an enclosure with fuel and energy rich but poor-ventilation such as a power plant will be extremely difficult.