I think we can find terrible tragic stories in a range of places. As someone who had national responsibilities with employers, one of the challenges we had was making sure that our employees followed the health and safety procedures we put in place for them.
I oversaw the discipline of employees by our managers, where employees didn't follow the safety procedures that were there for them. I submit to you that not every unionized job site is as safe as you say just because it's unionized. It's going to be because of a combination of the attitude of the workers and the attitude of management.
There's some work out of Australia that suggests that our entire workers' health and safety system is fundamentally flawed and doesn't actually drive safe behaviour, because the accountability mechanisms are wrong. But that's a study for another day, I suggest.