Timing-related: Some errors are caused by too little or too much time. The less time a person has to make a decision or take an action, the more likely he or she is to make a mistake. Ironically, the opposite can also be true, although too little time tends to create errors of commission, and too much time yields errors of omission. Some sources indicate that if a person has too little time, the likelihood of their making error is as much as 50 percent.
Chain errors: Many errors are really a chain of events stemming from one root error. Often these result from blind acceptance of information from other sources such as a computer.
Procedural errors: Sometimes procedures aren't appropriate for the given task. Procedures that go against current norms also might lead to confusion and errors. Procedures that are too complex, too simple or misleading also can lead to errors. Failure to follow all the steps of a procedure or adding steps would be a form of this error.
Violations: Violations are intentional errors, defined as non-compliance with accepted norms. These occur when people feel that a procedure or action is troublesome or unnecessary, or that a task is unpleasant. In the worst cases, such violations can be made with malicious intent.
Human error in system design
Human errors are reflected in the instrument design process by mistakes, specification errors, failure to communicate, lack of competency and functional errors. Often, simple steps like developing a checklist, systematic review processes and comprehensive training can help prevent these errors. However, the current downsizing trend has sometimes limited the opportunity to catch errors before they occur.
Mistakes: Probably the most common human errors in instrument designs are mistakes. Slips are the most typical type of mistake, but mistakes also can be due to incompetence or problems with the design systems, leading to data, drawing, informational and change errors.
With complex, detailed instrument system design, "the devil is in the details." Design-document-review processes and self-checking methods can help. People tend to make the same errors when dealing with details or small matters, particularly if there are no major consequences (e.g., misspelling the same word, or entering data incorrectly).
Becoming aware of your own pet errors can improve your ability to check your own work. Some of these errors result from short-term memory problems. Larger errors or errors with significant consequences should to be treated as learning experiences and analyzed to prevent them from recurring. Data errors result from improperly entering data or errors due to the propagation of data on design documents. Instrument designs contain a tremendous amount of data, much of it duplicated. The more frequently one enters the same data, the greater the opportunity for error.
Methods commonly used to reduce this error include time-delayed checking and multiple reviews. Designing the engineering process to minimize duplicate data entry also can reduce data errors. Data must flow from document to document in a design. If data paths are tortuous or complex, data might not get to where they should correctly. Data should be designed to flow in a way that minimizes error.
Drawing errors stem from errors on existing drawings that are used in a design. Examples include cases in which errors from previous designs are not caught, or changes by field forces are not relayed to engineering. Field verification is the primary method of minimizing these errors. Drawing errors also can come from using computerized cut-and-paste functions where the pasted function is not updated with the new drawing's data. Computer-aided design (CAD) has brought not only increased speed, but greater potential for errors as well.
Operating companies and engineering and construction firms might have a typical review process involving designers, a drafting checker, instrument engineer, instrument engineering supervisor, instrument maintenance and operations. Unfortunately, downsizing and competitive pressures have shortened review processes at many companies.
Specification errors often result when a project's initial scope was poorly defined. A well-known study of computerized systems by the United Kingdom's Health and Safety Executive  concluded that 44 percent of accidents were caused by a failure in specification.
In other cases, specification errors result from failing to communicate a specification from the conceptual stage to the detailed design stage. Communication lines can be strained, due to poor relationships between engineering, operations, and/or maintenance, cultural or even age differences.
Time also plays a part in the specification breakdown. Due to workload, priorities and reduced manpower in many plants, people might not allocate sufficient time to the initial scoping of the project, assuming details will be "filled in" later.
To prevent costly scoping problems and specification errors, some companies now require significant front-end engineering and design work for their projects. This front-end loading can add significant value, even to small projects.
Communication breakdown: Errors will result when the right information fails to reach the right people at the right time. Analyzing data flows to locate bottlenecks and error sources can minimize related errors.
Poorly managed changes in design also open the door to errors. Change management, although commonly applied by the process industries, seldom is used at the design level. Often, changes are not well thought-out because the appropriate people are not consulted.
Functional errors: Sometimes, errors in design lead to errors in function or operation. In these cases, equipment does not perform to its full potential or does not included the full range of operations or meet all specifications.