What we usually call accidents are in fact factory negligence or user negligence for not maintaining the firearm or replacing worn parts.
Let's talk car accidents. Most are caused by one or both involved drivers. There may be other factors (weather, visibility, road conditions, etc.) but we can always say the operator "should" have taken these into account. Similarly, someone who falls on ice "should" have take more precautions--or the person who is responsible for that patch of ground "should" have done a better job of clearing it.
Yet, that word "accident" exists. In most contexts, it is meant to cover understandable, common, "human" lapses in attention or judgment.
I actually think there is a danger in labeling every accident a "negligent," as it implies that just be being vigilant and/or trained enough, all accidents can be prevented. I doubt that is true, given human frailties. And therefore, accepting the existence of accidents may cause us to use additional safeguards (like seatbealts and airbags), rather than just depend on attention alone.
It was a long time ago that first military pilots/aviators, and then commercial ones, decided to replace (or supplement) their "constant vigilance" with something much more dependable and less taxing.
A checklist.
We should perhaps all consider implementing one, and check it off everytime we handle a gun without intention of its discharging. Oh, BTW, it takes a minimum of 2 people to perform a checklist dependably. If you choose not to, well, you're just a negligent waiting to happen.
The Checlist Manifesto.