Fire risk of welding sparks : ignition of cardstock paper by a hot metal particle shower

Abstract

Ignition by welding sparks is responsible for many tragic industrial and building fires. In this work, welding sparks from a Type ZX7-400 welding machine, using a Type E4303 carbon steel welding rod and operated at varying welding currents and rod diameters, were dropped to ignite the representative papers with three distinct back-boundary conditions. Results first found that the average mass of sparks increased from 19 mg, 66 mg, to 125 mg, as the diameter of the welding rods increased from 2.5 mm, 3.2 mm, to 4.0 mm, respectively. Welding sparks can be regarded as porous spheres with a statistical porosity of 0.75 ± 0.05%. Various ignition phenomena, including flash-point, fire-point, and no ignition, were observed and described in detail. The paper was extremely easy to ignite by welding sparks, once the first sparks landed on a single sheet of paper under a fully open boundary. Ignition limits versus spark parameters were quantified, and larger particles (thicker rods) required fewer sparks (shorter exposure) for ignition. The calculated equivalent heat flux during the welding process remained constant at 12 kW/m2. Fire point ignition only occurred for open boundaries, indicating the greatest fire hazard. While semi-open and fully-sealed boundaries gradually restricted the oxygen supply, thereby increasing the hot-particle ignition limit of the fuel bed. This study deepens the understanding of weld-spark characteristics and the ignition process in industrial and building façade fires.