Agreed, there is some OCD here. It is the government, you see they will change the law here in QLD in the new year 2012, failure to comply with the duty of care will become a criminal offence in the first instance, whereas previously there was some latitude for Dept of Industrial Relations or the Dept of Health, OH&S etc to apply discretion, the way it is going now the Police will be forced to investigate and knowing them they will look for anything to use against you to support their case, if there was an incident. The fines are huge and you would definitely lose your business licence, no more tree climbing. So I have been researching this topic of hard hats because I was always unsure of the requirements (ANSI standards are the defacto Australian standard) and I figure 4 holes show more duty of care than leaving two holes empty. As for machine screws, a mate of mine got struck-by with this same setup on his head and he got the peltor wires, that is the solid steel bits that hold the muffs, he got one of those through his cheek and into his upper jaw, so I am looking to eliminate as much steel as possible there you see. I had to drill holes into the top to dissipate heat, it is very hot and humid here and the holes definitely help. I figure the holes can only compromise my safety, if at all, and they don't diminish my duty of care to others so my professional integrity is intact there. It is all a bit OCD for sure but good to know that I can defend my position if audited, now I can relax and carry on making money out of trees!
For the Queenslanders, here I've attached the QLD WHS-2011 guide, page 36 is the new stuff, comes into effect January 1st. Note this is not specific to arboriculture, it's general to all workplaces so hopefully they will leave us alone.