Fire spread mechanisms along steel cylinders in high pressure oxygen

Abstract

Fire spread along steel cylinders in high pressure oxygen has been studied. Upward and downward fire spread experiments were conducted in a cylindrical, high pressure oxygen chamber of about 2.5 × 10 7 mm 3 capacity. The fire spread phenomena were recorded photographically and by television and analyzed. Based on the experimental results, the mechanisms of fire spread are discussed. Fire spread was found to depend on the test piece diameter, oxygen pressure, and spread direction. Upward fire spread was rather steady, although periodic detachment of molten iron oxide mass and cyclic variation in spread rate occurred. Two different modes were observed of downward fire spread. One was observed at a lower oxygen pressure. The molten iron oxide mass detached from the burning test piece end to become a droplet, so that the mode of fire spread in this case was much the same as that of upward fire spread. The other was observed at a higher oxygen pressure. The molten mass flowed down along the test piece. The fire spread in this case was accelerative and its rate was much larger than that in the aforementioned cases. An analysis for steady fire spead has been performed by considering heat transfer from the burning region to the unburned solid iron. It was shown that the ratio of the molten mass surface areas to the test piece cross section area is an important parameter for discussing the fire spread mechanisms. Based on the dependence of this ratio on the oxygen pressure or test piece diameter, it was inferred that the spread rate depends on the rate of oxygen adsorption at the molten mass surface and convective heat transfer at the molten-solid boundary.