Spills photo identifier

Spills Program

Investigated Vessel Incidents in Washington

Vessel incidents can include a wide range of accidents, including groundings, loss of propulsion, loss of steering, near collisions, allisions, and spills of oil or other hazardous materials. Ecology investigates vessel incidents to determine immediate contributing factors for enforcement (in the case of spills) and prevention. The types of commercial vessels investigated have included bulk carriers, car carriers, container ships, ferries, fishing vessels, tugs, tank barges and tank ships.

Immediate cause and contributing factors

Vessel incident investigations focus on two important areas: discovering the immediate cause of the incident and determining the factors that led to the immediate cause. For example, a vessel may have lost propulsion due to a failure in the electrical system, but the factors that lead to the electrical system failure may have included lack of maintenance, lack of crew training, or human error. Investigating beyond the immediate cause can help vessel operators understand why the problem occurred and what issues need to be addressed to prevent further problems.

It is often stated that 80% of problems result from 20% of key causes. This is known as the Pareto principle or Pareto effect. Vessel operators should consider collecting their own problems and key causes data in order to focus their prevention efforts. Developing management strategies that target key causes can substantially help reduce the risk of incidents.

The graphs below summarize immediate causes (Fig 1) and contributing factors (Fig 2) of vessel incidents from 1999 through 2014. A total of 133 investigations were conducted in which cause was determined for 130. This causal data was collected using guidelines set forth by the Pacific States/British Columbia Oil Spill Task Force. The prefixes used in the graph labels below are as follows:

  • EF = Equipment Failure
  • OF = Organizational Factor
  • HF = Human Factor
  • EXT= Environmental Factor

Fig 1. Immediate causes of vessel incidents. (Click to enlarge)
Immediate causes of vessel incidents


Fig 2. Contributing factors of vessel incidents. (Click to enlarge)
Contributing factors to vessel incidents

What do the graphs suggest?

The “key few” immediate causes are dominated by factors falling into the “human factor” and “equipment failure” categories, while the “key few” contributing factors more commonly fall into the “organizational factor” and “human factor” categories. This suggests that immediate causes tend to be related to human performance and failures of equipment, while contributing factors - factors that create the underlying environmentfrom which event chains progress into incidents - are largely based on how a vessel is managed.

Individual human factors of “inattention” and “judgment” - particularly inattention - are significant to both immediate cause and contributing factors. Ecology has developed a Safety Advisory Bulletin that discusses inattention in relation to oil transfer spills. Potential lessons for commercial vessel operators is that investment in technologies and company procedures that help maintain individual attention, alertness, information gathering, and operational structures that provide checks to trap and correct errors of individual judgment, are likely to bring significant safety benefits.

As the second graph shows, top organizational factors that contribute to incidents are:

  • Equipment design
  • Inadequate procedure/policies
  • Poor [management] oversight
  • Inadequately planned maintenance program
  • [Equipment] installation
  • Inadequate implementation of procedure/policy
  • Insufficient personnel

Three of these factors - together creating the highest percentage of key contributing factors - relate to the design, installation, and maintenance of equipment. All of these factors can be controlled through robust management systems. However, the high incidence of procedural/policy-related and management oversight factors indicates that the existence of a management system does not guarantee success - especially if it is incomplete, not implemented by personnel, and not monitored or enforced by vessel operators.

About 80% of incident primary causes are related to human and organizational factors.

Ecology categorizes incident causes more broadly into “primary cause,” as determined by an investigator. Primary cause is the over-arching, most contributory factor seen by the investigator, not the immediate cause. The distribution of primary causes found through Ecology’s detailed investigations are depicted in the graph below.

Primary causes of vessel incidents

Ecology’s findings track with the often-cited statistic that human and organizational factors are responsible for 80% of incidents. It also tracks very closely with the findings of a 2007 U.S. National Aeronautics and Space Agency (NASA) sponsored analysis of U.S. National Transportation Safety Board NTSB) maritime accident data for a 10-year period (1996-2006) which concluded, in part “The subsequent classifications showed that only 37% of causal factors in the NTSB study related to individual human error. In contrast, 48% of causes and contributory factors can be categorized as organizational. 12% related to equipment. ‘Other’ causes accounted for 3%.”

Ecology’s detailed investigations show the continued dominance of human and organizational factors in incident cause. A more detailed view of immediate cause and contributing factors indicates that vessel operators should continue to build and renew their management systems. Vessel operators are encouraged to build their own data set through detailed incident investigations and apply a Pareto analysis to causal factors to best target their own prevention efforts.