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Why spills happen

We find that nearly 80 percent of spills and close calls result from people and organizational problems.

When spills to water occur during vessel incidents, we investigate the immediate cause and contributing factors as part of our prevention and enforcement work.

We look at three things:

  • Immediate cause: What happened immediately prior to the incident; a triggering factor
  • Contributing factors: Underlying conditions that set the stage for the incident
  • Primary cause: The factor seen by the investigator as being most important in causing the incident

Causes of vessel incidents in Washington

These incidents can include a wide range of accidents, such as groundings, loss of propulsion, loss of steering, near collisions, allisions (when a moving ship collides with a stationery ship), and oil spills. We've investigated many types of commercial vessels like bulk carriers, car carriers, container ships, ferries, fishing vessels, tugs, tank barges, and tank ships.

Chart shows primary causes of investigated incidents closed between 1993-2016 in Washington. Organizational factors, 45%. Human factors, 40%. Equipment failure, 13%. Environmental factors, 2%.

Human and organizational factors cause 85 percent of vessel-related oil spills in Washington.

Most primary causes are related to human and organizational factors

We categorize incident causes broadly into “primary cause,” as determined by an investigator. For vessel incidents in Washington:

  • Organizational factors account for 45 percent of primary causes
  • Human factors account for 40 percent
  • Equipment failure accounts for 13 percent
  • Environmental factors account for 2 percent

Our detailed investigations show the continued dominance of human and organizational factors in incident cause. Our findings track closely with the U.S. National Transportation Safety Board data from 1996 through 2006 that indicates:

  • Organizational factors account for 48 percent of primary causes
  • Individual human error accounts for 37 percent of primary causes
  • Equipment accounts for 12 percent of primary causes
  • "Other" causes are 3 percent of the total

Ineffective vessel management increases spill incidents

Contributing factors — factors that create the underlying environment from which issues progress into incidents — are largely based on how a vessel is managed.

Top organizational factors that contribute to incidents are:

  • Equipment design or installation
  • Inadequate procedures and policies or the implementation
  • Poor management oversight
  • Inadequately planned maintenance programs
  • Insufficient personnel
Factor Percent of total  Cumulative percent
Most common contributing factors for vessel incidents in Washington, 1999-2016
Inattention 10% 10%
Equipment design 10% 20%
Judgment 10% 30%
Inadequate procedure/policy 8% 38%
Poor oversight 8% 46%
Inadequate planned maintenance program 6% 52%
Procedural error 5% 57%
Installation 5% 63%
Experience 4% 67%
Communication 4% 71%
Inadequate implementation of procedure/policy 4% 75%
Insufficient personnel 4% 79%
Sea state 3% 82%
Sabotage/intentional violation 3% 85%
Lack of supervision 3% 88%

Together, issues that relate to the design, installation, and maintenance of equipment represent the highest percentage of contributing factors. All of these factors can be controlled through robust management systems. However, the high incidence of procedural and 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.

Inattention and poor judgment contribute significantly to vessel oil spills

Individual human factors of inattention and judgment — particularly inattention — are significant to both immediate cause and contributing factors. Immediate causes tend to be related to human performance and failures of equipment.

Cause Percent of total incidents Cumulative percent
Most common immediate causes of vessel incidents in Washington, 1999-2016
Inattention 21% 21%
Mechanical 16% 37%
Procedural error 15% 52%
Judgment 13% 65%
Structural 5% 70%
Electrical 4% 74%
Wind 3% 77%
Inadequate implementation of procedure/policy 3% 80%
Inadequate procedure/policy 3% 83%