This report is based on the safety investigation conducted by the Marine Safety Investigation Unit (MSIU) regarding a boiler furnace blowback incident that occurred on 31 January 2018, approximately 30 nautical miles from Qingdao Pilot Station. The incident involved serious injuries to two crew members. The purpose of the investigation was to identify causes and contributing factors to prevent recurrence, not to assign blame or liability
What Happened
While the vessel was on passage from Dalian to Qingdao, the engineering officer of the watch observed that the auxiliary boiler was not operating normally, and several alarms had been triggered. The electrician attempted to reset the boiler’s control system several times, but the fault persisted. Believing that the flame detector and the low-water-level sensor were defective, these were bypassed, and the boiler was restarted in manual mode. It continued operating in this mode without abnormalities for several hours.
Following consultation with the boiler manufacturer, the second engineer and electrical engineer shut down the boiler to inspect the sensor signals as advised. During this inspection at 18:07, a furnace blowback occurred, forcing open the burner housing and releasing hot gases and flames, which injured both crew members. Later surveys identified damage to burner components, the motor, and the control panel. Further inspection revealed that a faulty water level switch and a defective combustion air flow timer had contributed to the malfunction. After the replacement of damaged electronic control units and adjustments by service engineers, the boiler was restored to normal function
Sustained Injuries
The second engineer and the electrical engineer sustained burns to their faces, chest, and hands. Both injured crew members were transferred ashore for treatment and were kept under observation at a hospital. Their health conditions improved steadily, and they were discharged several days later after receiving specialized medical care.
Analysis and Contributing Factors
The investigation concluded that the furnace contained an explosive mixture of fuel and air, which was ignited either by residual heat inside the furnace or during restart activities. There was also a possibility that marine diesel oil (MDO) leaked into the furnace after shutdown, which would have raised the risk of an explosion. Uncertainty remained about whether post-shutdown purging was carried out, or whether it lasted long enough to remove fuel vapors and gases. Since the boiler had been operating on MDO before shutdown, the likelihood of an explosive mixture forming was higher. Although a risk assessment was carried out before the event, it only considered hazards of flame failure and low water inside the boiler, focusing narrowly on defective sensors. The assessment overlooked hazards associated with manual operation, defective control systems, and fuel leakage. Furthermore, the injured electrician had not signed the risk assessment form, showing incomplete crew involvement in hazard identification and evaluation.
Safety Actions Taken
During the course of the safety investigation, the company issued a Safety Alert across its fleet, reminding all vessels about the safe operation of boilers during fault-finding and the importance of preparing work plans and risk assessments before starting any task. Additional safety measures included stronger managerial oversight by technical superintendents and fleet managers for work planning and assessments, engagement of manufacturer service engineers to inspect boilers and adjust operational parameters, and discussions of the accident in both onboard safety meetings and shore-based management meetings with the engineering department.
Safety Recommendations
No additional recommendations were issued by the MSIU, as corrective measures had already been implemented by the operator during the investigation.
Lessons Learned
- Safety-critical sensors must not be bypassed without comprehensive risk evaluation and manufacturer-approved procedures.
- Proper furnace purging is essential after shutdown to prevent accumulation of explosive mixtures.
- Risk assessments should be comprehensive, identifying not only immediate hazards but also risks from operating in emergency modes or with faulty systems.
- All personnel involved in technical interventions should participate in risk assessments to ensure awareness of hazards.
- Clear communication and adherence to manufacturer instructions are critical during troubleshooting.
- Regular inspections of control systems, sensors, and safety devices can prevent faults that compromise boiler safety.
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Source: MSIU
