Earlier quoted context omitted.
what is the acceptable number of people to die during bridge construction
If you set it at zero you will never build anything
That isn't to say you shouldn't make things safer but you have to take into account is your change a net positive over all. I have no idea what the trade off is for bridges. The bridge arguably increase commerce which means its completion created jobs. Poverty is a top killer of people so more jobs = less death.
That said, one thing I'm happy to see on construction sites, at least for buildings, they put up fences on every floor so it's harder to fall out. My guess is that really only became possible when they could create the fences out of plastic.