Two fires occurred within five months on a coal and petroleum coke shiploader operating at the Los Angeles Port. The first fire occurred in September 2000; approximately eight hours after the shiploader had ceased operating for the day. The shiploader was reconstructed to its original design and after approximately 500 hours of operation, a second fire occurred in February 2001, one hour after the shiploader had ceased operating.
Exponent’s investigation of these fires included a design assessment of the shiploader that incorporated a unique shuttling and luffing conveyor system. We also determined the fire origin and spread mechanism by analyzing the burn patterns on the shiploader and conducting belt-stretch analysis, laboratory scale combustion tests on coke and coal mixtures, metallurgical examination of the conveyor idlers and bearings, and review of applicable standards.
Figure 1: Shiploader during first fire. Figure 2: Shiploader during second fire
Our investigation demonstrated that the outer race of a failed bearing from one of the conveyor return idlers reached temperatures over 1100ºF, sufficient to ignite coal and coke particles that had migrated into the bearing. The hot embers ignited a significant amount of coal and coke debris that had accumulated in a pocket near the bearing due to the geometry of the conveyor idler frame. This initial fire ignited the non fire-retardant conveyor belt that was part of the original design. The belt eventually snapped after it caught fire, spreading the fire to other parts of the shiploader and causing extensive damage.
Exponent determined that design considerations are available to prevent coke and coal accumulations around rotating machinery and conveyors and these design alternatives can minimize the likelihood of similar fires.
Figure 3. Cutaway view of roller showing bearing and seal.
Related Publication: Carnahan, R, Reza, A. Dracup, B., Ross, B., and Christiansen, E., “A Case Study of Two Shiploader Fires in a Coal and Pet Coke Facility,” 11th International Conference, Fire and Materials, San Francisco, CA, January 2007.