Hi,
Couple of observations from what you've posted;
If people are climbing over or standing on staging to do a job then to be honest the staging is in the wrong place. (or they don't have the right tools and/or training to use them)
Secondly, and I note your location, I have identified what I term "puppies" who exist in some form or other in most work places - intelligent, motivated but poorly educated, but not necessarily unskilled. They are usually very keen to demonstrate that they are hard working, "can do" people and the intelligence coupled with poor education leads them to go beyond what they have been told are the limits of the job, in other words they want to please the master and will take risks to garner recognition and reward. The only way to manage these "puppies" is to engage with them, many times a day, every day, encouraging, talking, showing etc. but with a work force of 4000 you have a massive task there.
Jim

I agree with the above comments. Poor management is your key issue.
Another is behavioral culture.

A few years back I was in a similar situation, although I was blessed with management support, my issue was the "mans world, bravado, just crack on culture, work hard play harder" attitudes of the labourers.

Sadly, when the attitude of the management is such as your managers, not only is your job to protect people but also to cover your own backside! (indirectly probably protecting the management who are not helping you!).

I would suspect that the management stubbornly believe they have done what is reasonably practicable and will not re-engineer the platform / staging any further due to cost (shortsighted) and no matter how loud you scream they will turn a deaf ear probably arguing "what is reasonably practicable!). As you have highlighted, if there is a real risk of a fall then the "clip on" with a fall restraint system really should be pushed hard as the minimum control.

Surely, the good practice by the installers is recognized by the management? This perhaps could support any argument to a fall restraint / arrest system?

Have you done any maths, the cost of fall restraint purchase and continuous monitoring versus a more suitable access system? Figures can win the bean counters over.

Lets go back to basics:

ERICPD

Eliminate - Cant happen, access needed
Reduce - Hand railed, staged platforms
Isolate - Limited to only necessary access personal?
Control - TBT / Training / Entry procedures / entry register?
PPE - Fall restraint (the gaping hole you have recognized)
Discipline - The last resort and one I try to avoid at all - but hey, if you have to discipline somebody then you do, better than letting them becoming a statistic.

One other thing, you say painting, welding, grinding etc. then assuming you manage to implement the fall from height equipment then you should have a robust, strict inspection regime for the inspection of the equipment. EN365 states twelve monthly, INDG367 recommends 3 monthly in arduous conditions or interim inspections as required - I spent a lot of time making sure our guys inspect and record the inspection record before each task - it was a year long battle but now they do it second nature.

A massive task, but to eat an elephant you start one chunk at a time! Good luck.