Highly sophisticated systems, such as chemical process units, airplanes, and nuclear power plants, require certain functions to be performed and actions taken in specific sequences for the system to operate properly. Checklists are often relied upon to help system operators ensure that all of the events take place in the proper sequence and to help delegate responsibilities and workload between the operating crew. There are many examples where problems existed with checklists, or where checklists were violated, and the result was a catastrophe. The improper use, or non use, of checklists is often cited as either the cause or a contributing factor in many chemical process plant accidents.
Problems also exist with checklists used in other industries. The airline industry recently had three accidents in a 25-month period that were at least partially due to problems with checklists. The airline industry is heavily dependent upon checklists, as air crews use checklists to ensure the plane is properly configured for each phase of flight. To address the checklist problem, NASA recently commissioned a study to investigate the use of checklists by flight crews (A. Degani, E. Wiener, "Cockpit Checklists: Concepts, Design, and Use", Human Factors, 1993, Vol. 35, No. 2, p.p. 345-359). The study discusses common problems found in checklists and makes recommendations on the features that should be designed into checklists.
One finding of the study was that, contrary to common belief, there is no standardization of checklist design in the airline industry. Checklists for the same type of airplane operated by different carriers often contained different items on the corresponding checklists. The lack of standardization apparently arises from the fact that each airline has its own philosophy on checklist design that reflects each company’s corporate culture.
When it comes to a strategy for selecting items to include on a checklist, there are two conflicting points of view, neither of which has a clear advantage. The first strategy argues that checklists should be detailed and lengthy. The problem with this is that at a certain point, excessive detail may cause some users to either skip over some contents (and create omission errors), or not use the checklist at all. The opposing strategy argues that because the checklist is redundant to the operator’s memory, only the most critical items should be included. This approach runs the risk of lacking sufficient detail to warn the operators of missed items, and the summation of small omissions could lead to a much more severe error.
The study listed recommendations for the design of checklists for the airline industry. The following is an interpretation of how the recommendations apply to designing checklists for the oil and chemical processing industry.
1) Checklists should provide the desired status or value of the item being checked. For example, all operating parameters referenced should be provided, such as pressures, temperatures, etc.
2) Where possible, the use of hands or fingers to point to or touch the appropriate control or display is recommended.
3) Long checklists should be divided into smaller checklists, or chunks, which can be associated with a particular system or function. For example, when shutting down a process, the checklist should call out the furnace shutdown procedures into a smaller checklist.
4) Sequencing of checklist items should follow the geographic organization of the items to be checked and should be done in a logical flow.
5) The most critical items should be listed as close as possible to the beginning to increase the likelihood of the item being completed before interruptions occur. This rule may conflict with the preceding rule. Where conflict occurs, this criticality rule should take precedence.
6) Critical items may need to be duplicated at some point in the checklist. Duplication should be used judiciously since it adds to the length of the list. Items duplicated in the air crew’s checklist are what is known as "killer items," because failure to complete them will usually result in a catastrophic failure.
7) Operators should be made aware, through training, that while checklists improve operator performance, they are still susceptible to errors, and that proper use of the checklists is critical.
Copyright © 1993 Beville Engineering, Inc. , All Rights Reserved
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