One of the work groups I co-chair has been addressing issues of usability lately. Another work group that same organization deals with issues of patient safety. We often closely collaborate, but the two areas simply not the same. It's a bit frustrating because I so often see the two combined, but they often have competing interests.
Here is a very simple example illustrating what I mean: Nearly a decade ago I worked on a product (no longer sold) that performed some analysis of transcribed text that would ease transitions to electronic medical records. From a patient safety perspective, the analyzed results would need to be clinically verified. From a usability perspective, many end users simply wanted to skip the clinical verification step because it took them a few extra clicks. The tension between "efficiency" and "patient safety" in this example is pretty clear.
Many issues of patient safety can very clearly be linked back to "usability design issues", but certainly not all of them. I've encountered (as a patient), other issues of patient safety that weren't at all related to product usability (in fact, it was product usability that made it possible for me to address the issue as the patient). Thus, usability != safety.
There are skills taught in the software industry that are generally applicable to usability, and which can be applied to electronic health records. There are also design and engineering skills that are generally applicable to product safety (and not just medical products) that are also generally taught which can also be applied. My brother-in-law works on Nuclear power plants, he has skills in risk identification, assessment, and mitigation that could just as easily be applied to aircraft manufacture or medical devices. These are separate, but often related skill sets.
Whenever you make a device that impacts lives, both skill-sets need to be applied, and the tensions between them need to be balanced appropriately. But to do that, you first have to realize that they are two separate things. Certainly they have overlapping areas of concern, and they highly influence each other.
Conflating the two is a mistake. It fails to recognize that they can sometimes be in tension, and it is often in those very cases where the most attention needs to paid.