An explosion occurred in the firebox of an industrial boiler with a nominal fuel input rate of 100 MW (340 million Btu/hr), in a processing plant during final commissioning of the burner systems. This paper describes the investigation of the incident, root cause analysis, and lessons learned from the incident. The original burners in the boiler had recently been replaced with low NOx burners, and the facility was in the process of commissioning the new burner system. The boiler was running only on natural gas igniters at the time of the incident. While firing on igniters, an undetected stoppage of the control equipment occurred, which led to a restriction of airflow through the secondary air dampers. The boiler controls included programmable logic controllers (PLCs) for both the combustion control system (CCS) for regulation and the burner management system (BMS) for safety functions. The BMS was intended to detect a loss of control such as this and immediately stop fuel to the boiler; however, it did not. The BMS PLC was not configured to detect the dangerous states and allowed the igniters to continue to fire. An explosion subsequently occurred within the boiler firebox that caused extensive damages to the facility and equipment. This paper will describe the incident investigation and determination of multiple root causes for failure of the BMS to prevent the explosion. The inadequate configuration of the control systems was likely present for some time prior to the incident, and the explosion was eventually caused when the right conditions occurred during this commissioning. We found through the investigation that the BMS deficiencies could have been detected and prevented (and almost were) through standard hazard analysis techniques common in the chemical processing industries. This paper will also discuss how hazard analysis can be applied to detect and prevent similar system failures.

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