Human error in instrumentation systems

Some common human errors in operations are misunderstanding instructions, writing down or entering the wrong value, missing a step in a procedure or task, misidentification, mis-estimation of quantity or extent, failure to communicate situations or conditions to other people (particularly across shifts), failure to properly lock out and tag out equipment, and lack of situational awareness.

Training is the most common solution. Training must include both normal and abnormal conditions. While well-designed systems and processes significantly contribute to error reduction, there is no substitute for motivated, good quality, experienced people.

Finally, mistakes happen in maintenance too. The wrong loop or equipment gets worked on, a transmitter gets calibrated to the wrong value, or a repair is botched. Some of these are due to slips, but others can be due to inexperience, lack of knowledge, poor maintainability, lack of motivation, poor supervision, or incompetence.

Downsizing is also reducing the experience level in maintenance departments. Meanwhile, technology changes rapidly, making it harder and harder to keep up with fewer and fewer people that have less and less experience.

Up-to-date drawings are a must. Out-of-date drawings can lead to errors when troubleshooting or repairing. Manually marked-up drawings can lead to errors. All drawings should go back to drafting and then be field-verified. Out-of-date or missing vendor documentation can also be a source.

Design for maintainability is a big issue in minimizing errors. If something is hard to work on, it may also be error-prone. Poor identification (tagging), poor access or work space, poor location, lack of or poor quality documentation, and poor lighting are contributors. A good working relationship with engineering that allows maintenance input into designs is a must. A maintainability checklist is another method to help assure the maintainability of instrument designs.

Maintenance procedures are also a means to help minimize errors. Standardization is another means to help minimize errors. The less variance there is in a system, the less potential for error.

Human error is inevitable. Failure to take this into account is courting disaster. The keys are to realize how and where errors can occur in your system, and then to adopt methods that lessen their occurrence, minimalize those that do occur, and mitigate their impact.

The Role of Human Factors
in Control System Errors, Part 2

MANAGEMENT systems, procedures, ergonomics, organization, and facility design are factors that can cause human error. Human error is blamed for many things. It is not uncommon to see in the paper that an airplane crash to be blamed on “pilot error,” or in the case of a recent explosion in a process plant, blamed on an operator error for failing to make the proper valve line up. But are these really human errors, or are they system errors in which the actual human error was just part of a larger problem that facilitated the human error?

Human factors is a term that is often seen when errors are analyzed. Human factors is actually a very broad subject of which human error is only a part. There is a variety of definitions for human factors. One of the definitions I like is:

“The human factors are the application of relevant information about human characteristics and behavior to the environment humans are operating in to maximize the benefit to the humans. “

Another definition could be:

“Human factors are the characteristics of human beings that are applicable to humans interacting with systems and devices.”

The terms human factors and ergonomics are often used interchangeably. Both can describe interactions between the worker and the job demands or work domain. Generally the difference between them is that ergonomics focuses on the physical interaction of humans with their work while human factors emphasizes broader scope of improving human performance in work tasks and reduce the potential for human error. One might say that ergonomics is really a subset of human factors.

Some human factors are based on human limitations or inherent behavior. Others can be based on psychological or sociological factors. Human limitations are based on the physical and mental capabilities of humans, while human-to-human interaction is based on human psychology. Sociological factors are group dynamics or culturally or ethnically based.

FIGURE 1: DESTROYED BY DESIGN

EPA and OSHA determined the 1997 explosion and fire that caused this damage to Shell's Deer Park, Texas, chemical plant was caused in part by a check valave that was not designed for the application. The process hazards analysis did not address the risk of valve shaft blowout. Lack of indication of a hydrocarbon leak in the control rool and inadequate communication during the accident contributed to its severity.

The culture-based human factors can be based on a local culture, for example, the culture of a plant, local area, or may be ethnic or society-based. While many people are not aware of their plant culture (can’t see the forest for the trees), each plant has a plant culture or essentially a way of doing things or how the plant responds to things.

Plant cultures result from the plant’s political and power structure, management and supervision style and attitude, procedures and practices, local area culture, plant experience, etc. Examples of plant culture extremes are the “not invented here syndrome,” isolation (no interest in how other people are doing things), and “it can’t happen here” syndrome.