I was involved in such things some years ago (probably around 15 years). At that time there did not appear to be a standard and different states did things in different ways, and not always consistently within a single state. We developed a standard for the country I was working in at the time and we focused on the design of the prohibited, restricted or danger area and ensured that there was a minimum buffer inside the area vertically of the appropriate IFR separation (which was always 1000ft) and a buffer horizontally of the greater of either the radar separation appropriate to other aircraft outside the D/P/R area, or the maximum horizontal visibility required for VFR flight at any time outside the D/P/R/ area. By doing this, any aircraft that remained outside the D/P/R area was at least the separation that an IFR flight would expect or a VFR flight would be able to see aircraft inside the D/P/R area. We added a bit to the buffer - I can't recall by how much - if the area would be used at any time for high-energy manoeuvers.
Originally Posted by LuCst
Vertical separation no less than 1/2 of the applicable vertical separation minima, i.e. 500ft to areas up to FL285 and 1000ft to areas above FL285.
Lateral separation is a bit less straight forward:
None required for IFR in Class G or VFR in any airspace class.
1NM to areas wherein there is no flying activity (or where any flying activity is limited to UAVs at or below 120m AGL).
2.5NM to areas wherein there is military flying activity controlled by fighter control or another ATSU.
3NM to areas with flying activity that is not controlled by anyone (soaring sectors, military flying without fighter control etc.).
That is interesting - is it an agreed standard?