William A. Hyman: Human Factors for Manual Safety Systems

Safety systems may be primarily automatic, semiautomatic, or fully manual. Automatic systems operate independently of the user. Semiautomatic systems are substantially facilitated by the design, but also rely on the user to ultimately activate them, with the implication that the user can choose to not do so and still operate the device. Fully manual systems rely primarily on the user in various ways, from set-up to activation. Manually set alarm limits are one example of this, as is the consistent and safe use of a manually operated safety sharp. The design of manual safety systems has particular requirements because of their dependence on the user. These principles were the subject of a recent paper of mine in Patient Safety & Quality Healthcare, and I was asked by AAMI to summarize them here.

Important features of manually operated safety devices include their intuitiveness, obviousness of activation, and consistency with the general use of the device.

It is best when the means of achieving safety is intuitively clear. This minimizes training and facilitates effectiveness. Intuitive design should be based on a realistic assessment of general human expectations. It is also good design when only minimal effort is necessary to determine if a safety feature has been activated. Besides aiding the user, this facilitates a culture of safe use. Obviousness also helps protect against false reliance on a safety system that has not actually been activated. The design of a safety feature should also take into account how the device is actually used in practice, including the multi-tasking that is often the reality of clinical care.

The closer the use of a safety feature is to the underlying use of the device, the greater is the expectation that the safety feature will be consistently and properly used. This also minimizes training needs and the temptation to skip what might be extra steps.

These principles should be applied by the designers of medical devices, and should be addressed during the selection of devices and the evaluation of field experience. If relevant field issues are identified with the use of a safety feature of a device, it is appropriate to determine why the safety feature failed to provide the intended protection. If the conclusion is that it was the user’s fault, then we are back to blaming the user for the problem that was supposed to be prevented. What may be a better conclusion in many cases is that the design of the safety feature is such that it was unrealistic (if not disingenuous) to think that it could and would be used as intended.

Medical devices with manually operated safety features that can be skipped over present a specific human factors challenge with respect to real-world usability and effectiveness. This challenge is to make the use simple, intuitive, and actually safe. Merely creating a safety feature that could theoretically be used as intended is not adequate and moreover presents more of an appearance of safety rather than actual safety.

William Hyman, ScD, is professor emeritus of biomedical engineering at Texas A&M University. He now lives in New York where he is adjunct professor of biomedical engineering at The Cooper Union. Hyman may be contacted at w-hyman@tamu.edu

One thought on “William A. Hyman: Human Factors for Manual Safety Systems

  1. Where does the boundary lie between safety by design versus user responsibility and competent use ? As a pilot, I have to know enough about flying to know that if I point the nose of the aircraft at the ground I may cause my imminent demise. Is the current Stryker Neptune debacle an example of “safety by design” concept being taken too far? How far is too far? Where should the line be drawn?

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