Transport Malta’s MSIU issued an investigation report on the boiler furnace blowback on the container ship ‘New Hampshire Trader’ which caused injuries to two crew members, about 30 nautical miles from Qingdao Pilot Station, on 31 January 2018.
The incident
The vessel was on a passage from Dalian to Qingdao when the engineering OOW of the watch noticed that the auxiliary boiler was not operating normally and that several alarms had activated.
Although the electrician reset the boiler control system, the fault was not rectified, raising suspicions that the flame detector and the low water level sensor were both faulty. The boiler was restarted with these two sensors deactivated and it worked well for several hours.
In the meantime, advice was sought from the boiler manufacturers. Guidance was received from the manufacturer on what signals need to be checked. The electrician and the second engineer switched off the boiler to check the signals. During their inspection, a boiler furnace blowback occurred, injuring both of them.
The safety investigation concluded that the boiler furnace contained an explosive mixture of fuel and air which was ignited either by the residual heat inside or during a restart attempt by the two crew members.
Probable cause
Evidence available to the safety investigation did not indicate clearly the cause of the blowback. However, it was definite that the boiler furnace contained an explosive mixture of fuel and air, which had been ignited either by the residual heat inside or during a restart attempt by the two crew members.
Conclusions
- The boiler furnace contained an explosive mixture of fuel and air which had been ignited either by the residual heat inside or during a restart attempt by the two crew members;
- The safety investigation did not exclude the possibility that MDO leaked inside the furnace after the boiler was shut down;
- The boiler was operating on MDO and this would have led to an increased risk of an explosion inside the furnace;
- The safety investigation did not exclude the possibility that either a post-shut down purge had not been carried out or its duration was not long enough to expel unwanted exhaust gases and / or (flammable) gases;
- The autoignition temperature of MDO is about 260 oC, which is well within the range of a hot boiler furnace that had just been shut down;
- The two identified hazards in the risk assessment exercise were actually related and limited to the defective sensors on the boiler control system;
- Potential hazards generated by, for instance, the actual operation of the boiler in the emergency mode, had not been identified;
- Accidents similar to this one may have not been experienced before by the crew members involved;
- The crew members did not have the necessary foresight to address all the hazards in a systematic way.
Actions taken
–> During the course of the safety investigation, the Company issued a Safety Alert to all vessels within its fleet, in response to the boiler furnace explosion and injuries sustained by two crew members. The Safety Alert addressed the safe operation of boilers during the course of fault finding tasks, the preparation of a work plan and risk assessment prior to the commencement of any work.
–> The Company has also taken the following safety actions:
- managerial controls by the Technical Superintendent and Fleet Managers with respect to the preparation of work plans and risk assessments;
- service engineers from the manufactures have been requested on board in order to carry out a complete assessment of the boiler functions and carry out the necessary adjustments to the boiler operational parameters;
- the master of the vessel has discussed the accident during the onboard safety meeting; and
- the accident was also discussed during shore management meetings with all members of the engineering department.
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