Human error in instrumentation systems

Specification errors results many times from not communicating the design specifications from the conceptual design stage to the detail design stage. Communication lines are sometimes strained in plants due to poor relationships between engineering, operations, and/or maintenance leading to communication breakdowns and errors. Internal cultural differences or even age differences can also contribute to the failure to properly communicate a project scope.

Time also plays a part in the specification breakdown. Due to workload, priorities, and reduced manpower in many plants, people may not allocate sufficient time to the initial scoping of the project. They assume the details will be filled in later, thus leading to a poorly defined and communicated scope and downstream changes leading to potential errors in the design.

Getting the specification right can significantly reduce the amount of potential human error in the design process. Some companies have gone so far as to have significant "front-end loading" on large projects to minimize the potential for specification error. Front-end loading can be a significant value-added process, even on small projects.

Communication Breakdown--The failure to communicate information or changes can lead to errors. If the correct information does not flow smoothly, to the right spots, and at the right time, errors may result. Both individuals and the design system affect the flow of information. Analysis of data flows to locate bottlenecks, kinks in the data flow, and error sources is a method of minimizing this kind of error source.

Changes in design open the door to errors. Changes are common in engineering designs but are typically poorly managed. Changes typically can come from many sources and must propagate to many places. Many times, changes are not well thought-out because the appropriate people are not consulted. Change management is a common practice in the process industry, but it is seldom applied at the design level.

Lack of Competency--These errors result from inexperience to outright incompetence. This type of error can come from the lack of the ability, skills, knowledge, and/or experience in the instrument design. Morale also effects this. In a low morale environment, even competent people's skill levels can waver. This is becoming more of an issue with the "brain drain" that is resulting from downsizing. Motivated and competent people are the mainstay against this error source.

Functional Errors--Sometimes, errors in design lead to errors in function or operation. The most obvious error is that the instrument design does not work. Some less obvious ones are an instrument design works but is of mediocre design (does not perform to its potential) or one that does not have the full expected range of operation or meets all the specifications.

Another type of functional error is a design that facilitates people making mistakes in the operation or maintenance of the design. If your design does not meet the operational expectations of the customer, your design may facilitate human errors. Operation from right to left rather than left to right, colors that don't agree with standard colors in the facility, backwards order of operation, things of different function but similar in appearance or arrangement, not following existing plant practices or standards, etc., are examples. This is one of the reasons behind standardization.

It is important to understand that no matter how good a design is, people will still make mistakes in operating and maintaining the equipment. Designers many times design for what they believe is normal operation with no expectation that the system will be operated in any other manner or that errors will made in its operation or maintenance. Failure to consult with the operators and maintenance personnel can lead to systems that are difficult to operate and maintain. If we anticipate other reasonable operational modes or possible errors, we can adjust our designs in regard to human factors, error recoverability, error tolerance, etc. Checklists are a good practice to minimize these kinds of errors.

Common Errors in Instrument Design--Some of these are improper grounding, improper shielding, failure to provide isolation, improperly sized equipment, wrong range or trip point for an instrument, failure to consider ambient temperature range (particularly the low end), wrong materials of constructions, equipment not properly rated for hazardous area, failure to consider power quality issues, no spare parts, incorrect wiring, incorrect tagging, failure to tag wires properly, poorly located, hard to maintain, etc. Again, checklists are a common method of minimizing errors in designs.

Errors in Construction, Operation, Maintenance
Error can occur in the construction phase of a project. Errors that affect the operation of the equipment are typically caught during commissioning or startup. However, other types of errors may not be. Some examples are wrongly identified or tagged equipment, equipment not properly installed in a hazardous area, improperly calibrated or ranged instruments, loose terminals, improper grounding, improper shielding, etc. Upfront constructability consideration can minimize difficult installations helping minimize installation errors.
 
The common protections against installation errors are a competent installation crew and supervision, installation inspections, checklists, punchlists, and planned commissioning tests.

Humans also make mistakes in operating equipment and processes. Some of these are simple slips but others may be facilitated by the design of the system or by the training, procedures, and practices. Some times the training, procedures, and practices functionality are considered only under normal conditions, while under abnormal conditions they may facilitate errors. Complex procedures are also prone to errors. Complicated or confusing tagging of equipment can lead to operational errors. Stress of the operating environment can contribute significantly. In one plant, the stress of keeping the plant operating led operators to delay a decision to shut down, which led to an accident.