Years ago when I approached my first reading of the full accounts of Slotin and Daghlian I did so as with any other info, since then I have forced myself to reread them several times as a reminder—as both the accounts and photos are grim. They ought to be part of compulsory safety training for anyone vaguely associated with the nuclear game.

Perhaps, as part of that training there should be more acting out roles with dummy materials similar to military exercises where adjudicators tag one as dead for making a 'lethal' mistake and can play no further role in the exercise. This may seem trite but it's not, being forced to play dead on the battlefield whilst the exercise continues because of one's incompetence is both formative and embarrassing (I speak from experience).

Moreover, like military training, the exercises should be practiced until one's actions are automatic.

That said, such training ought to be a second-line defense—as fastneutron rightly points out—as such work environments ought to be engineered to force compliance.