6-on, 6-off Shift Schedule Blamed in Grounding and Subsequent Sinking

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Summary

On 13 October 2016, shortly after 01:00 Pacific Daylight Time, the articulated tug-barge composed of the tug Nathan E. Stewart and the tank barge DBL 55 went aground on Edge Reef near Athlone Island, at the entrance to Seaforth Channel, approximately 10 nautical miles west of Bella Bella, British Columbia. The tug’s hull was eventually breached and approximately 110 000 L of diesel oil were released into the environment. The tug subsequently sank and separated from the barge. The tug was removed from the environment 33 days after the occurrence. Seven 208 L drums of diesel oil–soiled absorbent pads were collected from the site.

Damage to the vessels

The DBL 55’s outer hull sustained damage below the waterline. In addition to numerous scrapes, keel fractures, deformations, and indentations to the outer hull, there were large puncture holes in the outer hull’s shell plating adjacent to the cargo tanks in the mid-section. The cargo tanks were not punctured. The tank barge was towed to Vancouver for repairs before it was put back into service.

Findings

  • The second mate, who was working alone on the bridge, was fatigued.
  • The second mate fell asleep and did not make the planned course alteration, and the articulated tug-barge struck and grounded on a reef.
  • The navigational alarms were not used and a bridge navigational watch alarm system was not available; the use of these could have prevented the second mate from falling asleep and provided a warning to other crew members.
  • The other crew member on watch was not on the bridge and did not reach the wheelhouse prior to the grounding.
  • Following the grounding, and after several hours of continuous interaction between the tug’s hull and the reef, the hull breached and released diesel oil into the environment.
  • The pollution boom around the tug did not contain the diesel oil; approximately 110 000 L of diesel oil were not recoverable and were left in the environment.
  • If a 1-person bridge watch is in use without mitigating measures, particularly during the hours of darkness, a single point of failure may occur, increasing the risk of an accident.
  • If a 6-on, 6-off shift schedule is used without fatigue-mitigating measures, there is a risk that crew members will be impaired by fatigue while on duty.
  • If there is no requirement for crews to receive fatigue-awareness or -management training, there is a continued risk that fatigue will not be identified, prevented, or mitigated.
  • If a coordinated and comprehensive evaluation of the response to an environmental spill is not conducted, there is a risk that shortfalls will go unidentified by the response groups as a whole, resulting in a missed opportunity to improve Canada’s spill response regime.
  • There was no delay in the agencies’ reaction to the incident and the oil spill response, and the recovery efforts of both the Western Canada Marine Response Corporation and the Canadian Coast Guard met the prescribed time standards.
  • Other responding agencies, and some Canadian Coast Guard personnel, were not familiar with the incident command system, which created confusion about the roles and responsibilities of all responding agencies and about who had final authority.

Actions required

On the aftermath of the accident, the TSBC noted that the use of the 6-on, 6-off shift schedule, which is a longstanding practice in the marine industry, was not designed according to principles of modern sleep science. Watchkeepers who work this schedule face challenges in achieving sufficient uninterrupted restorative sleep because of the needs presented by, for example, daily chores, meals, and shift-change briefings.

Furthermore, total daily sleep needs on this schedule can only be met by sleeping in 2 separate periods, which creates a situation that presents other challenges; for example, any sleep taken during the daytime period may be of poor quality given that it occurs at a time when human beings are physiologically prepared to be awake. Although the 6-on, 6-off shift schedule has been called into question by various studies and experts internationally, it continues to be used throughout the marine industry.

“For example, in this occurrence, the watchkeepers of the Nathan E. Stewart had been working this schedule for over 2 days prior to the grounding. Opportunities to sleep were provided, but the second mate’s inability to nap, combined with the sleep-inducing conditions on the bridge, led to increased fatigue and resulted in the second mate’s falling asleep while on watch. Consequently, a planned course alteration was not made and the tug ran aground.”

Although fatigue is widely accepted as an unavoidable condition within the marine industry and is recognized as a contributing factor in many marine accidents,there is a general lack of awareness of the factors that cause fatigue. If watchkeepers have an understanding of those factors and of the practical actions that can be taken to minimize their effects, there may be a significant reduction in the number of fatigue-related occurrences.

“The Board therefore recommends that the Department of Transport require that watchkeepers whose work and rest periods are regulated by the Marine Personnel Regulations receive practical fatigue education and awareness training in order to help identify and prevent the risks of fatigue.”

In addition to providing fatigue education and awareness training, all 24/7 transportation operations must effectively manage the risks associated with fatigue. Although training is one layer of defence, it is not enough to effectively and reliably prevent fatigue; a proactive, multifaceted approach is necessary.

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Source: Transportation Safety Board of Canada

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