Events are caused. Typically, they are triggered by human action. In most cases, the human action causing the event was in error. However, the action could have been directed by a procedure; or it could have been a shortcut to get the job done—a violation. In any case, an act initiates the undesired consequences. On a plant-by-plant basis, experience has shown that significant events tend to occur every few years, but no law of nature says they must. The cycle can be broken, but only by understanding how events come about through human error. The Anatomy of an Event provides a picture (see illustration) of the elements that exist before an event occurs. Breaking the links will prevent events.
Event
An event is an unwanted, undesirable change in the state of plant structures, systems, or components or in human/organizational conditions (health, behavior, administrative controls, environment, and so on) that exceeds established significance criteria. Usually, consequences are relative to a series of d-words:
- death,
- damage,
- dollars,
- dose,
- delays, and
- disgrace
Also, events may involve serious degradation or termination of the ability of equipment to perform its required function.
Initiating Action
An initiating action is an action by an individual, whether correct, in error, or in violation, that results in a plant event. Active errors are those errors that have immediate, observable, undesirable outcomes in the physical plant. They can be either acts of commission or omission. The majority of initiating actions are active errors. Therefore, a strategic approach to preventing events would be the anticipation and prevention of active errors where people touch risk-important equipment.
Flawed Defenses
Defects, under the right circumstances, may inhibit the ability of defensive measures to protect plant equipment or people against hazards or fail to prevent the occurrence of active errors. Defenses do the following:
- protect against various hazards (such as radiation, chemicals, heat, rotating machinery)
- promote consistent behavior—methods to consistently anticipate, prevent and catch errors at the job site
- mitigate the consequences of the hazard (for example, reduced reactor safety margin, personal injury, equipment damage, cost)
The terms, defense, control, barrier, and safeguard, are used interchangeably.
Error Precursors
Error precursors are unfavorable conditions that increase the probability of error at the moment of a specific action, that is, error-likely situations. An error-likely situation—an error about to happen—typically exists when the demands of the task and its environment exceed the capabilities of the individual(s) or the limitations of human nature. Error-likely situations are also known as error traps.
Latent Organizational Weaknesses
Hidden conditions in management control processes (for example, strategy, policies, work control, procedures, training, and resource allocation) or values (shared beliefs, attitudes, norms, and assumptions) that can provoke error (precursors) in the workplace and degrade the integrity of defenses (flawed defenses) are latent organizational weaknesses. Management’s decisions about expectations, resources, and rewards, as well as their personal style, determine what is done, where it is done, how well it is done, and when it is done, either contributing to the health of the organization or further weakening its resistance to error and events. The organization plays a greater role in the performance of a station than the workforce. When managers understand how their organizations work, they are better able to identify and eliminate latent conditions that either promote error or worsen the events triggered by error.
Source: Southern Nuclear Company Nuclear Management Guideline, (NMG)NMP-GM-005-GL03 Human Performance Tools, 2012