Not that I'm aware of, and I would think that a NEBOSH cert holder with experience of H&S management and knowledge of the industry area they are working in may well be better qualified to 'sign off' on various tasks that a NEBOSH Dip holder with less knowledge of the industry sector.
I'm a Dip holder and work in my industry with a number of cert holders who have a better understanding of the technical issues of their work. I acknowledge this and bow to them, they often turn to me for more legal and 'management system' based support

I really don’t see how there can be any sort of ‘recognised’ limit as the range of activities undertaken is potentially ‘limitless’. It would be effectively impossible for anyone to try and create a definitive list of what any one person, whatever their qualification could be reasonably expected to do. I think Tomkins makes a fair point.

The issue is really one of competence, and any limit needs, in the first instance, to be ‘recognised’ by you.

You should also note point 5 of the IOSH Code of Conduct

same as everyone - know your limitations

My understanding was the cert was deemed to be an entry level qualification and therefore you may be very astute to consider the limitations.

I am sure that most people will have a really in depth knowledge of their own particular field and what Cert and Dip give you is a greater breadth - I suggest that Dip just gives you far more breadth and therefore your limits become less