Poor designs increase the likelihood that users or maintenance staff will make mistakes. No matter how good a design concept is, people still will make mistakes when operating and maintaining equipment based on that design. Designers often design for what they believe is normal operation with no expectation that the system will be operated in any other way. They also fail to anticipate errors with operation or maintenance. Consulting with operators and maintenance staff, and using checklists with desired criteria, can lead to systems that are user-friendly and reduce error. End-user input also will help prevent typical equipment design errors such as improper grounding, shielding or sizing; insufficient isolation; failure to consider ambient operating temperatures; use of the wrong materials of construction; failing to tailor equipment designs for hazardous area duty; lack of spare parts; and incorrect wiring or tagging. Checklists can minimize these design errors.
Errors in construction, operation and maintenance
Construction-phase errors typically are caught during commissioning or startup. However, other types of errors might not show up until much later. Examples include incorrectly identified or tagged equipment, equipment improperly installed in a hazardous area, improperly calibrated or ranged equipment, loose terminals or improper grounding or shielding. Upfront engineering that anticipates difficulties can minimize installation errors.
The common protections against errors are a competent installation crew and supervision, inspections, checklists, punchlists and planned commissioning tests.
Outside of simple slips, operating mistakes can be facilitated by poor system design or flawed training, procedures and practices. Often, training, procedures and practices are developed with normal conditions in mind, so trainees can fail under abnormal situations.
Complex procedures such as complicated or confusing tagging of equipment also are prone to errors. Stress resulting from pressures to keep the plant operating can also lead to errors. In one case, such stress prevented operators from shutting down the system, which led to an accident.
Common human operating errors include misunderstanding instructions, writing down or entering the wrong value, missing a step in a procedure or task, misidentifying equipment, incorrectly estimating a quantity, failing to communicate situations or conditions to others,"particularly across work shifts,"failing to lock out and tag out equipment and lack of situational awareness. Training will prevent many of these errors, but training must assume both normal and abnormal conditions.
Finally, mistakes happen in maintenance, too. The wrong loop or equipment is worked on, a transmitter is calibrated to the wrong value or a repair is botched. Some of these problems are due to slips, but others can be traced to inexperienced, under-motivated, ignorant, poorly supervised or incompetent staff. Downsizing has reduced the experience level in maintenance departments, while technology has advanced rapidly, making it more difficult for fewer, less-experienced people to keep up.
Up-to-date drawings are a must to avoid errors when troubleshooting or repairing. Manually marked-up drawings also can lead to errors. All drawings should go back to drafting and then be field-verified. Out-of-date or missing vendor documentation also can be a source.
Equipment should also be designed for easy maintenance to minimize errors. If something is difficult to work on, errors will likely result during maintenance. Fostering a good working relationship between engineering and maintenance departments is essential, since maintenance should offer suggestions on equipment designs. Use of maintenance-driven checklists will help optimize equipment designs.
Standardized maintenance procedures also can cut down on errors. After all, the less variance there is in any system, the less potential for error.
Bill Mostia, PE, of safety consultants Exida (www.exida.com) has more than 25 years experience applying safety, instrumentation and control systems in process facilities. He can be reached at firstname.lastname@example.org.