My query concerns a building used as a small/medium place of assembly with one exit to the public realm and a second exit to a rear walled garden (with no openings in any of the walls).  In principle, is it permissible to consider a walled garden a place of safety for the purposes of fire evacuation?  How deep must the walled garden be relative to the height of the building in order to qualify as a place of safety?  I can only find rules of thumb for the depth of the standoff distance, ranging from 1 x building height all the way to 2.5x the building height.  Is the governmental guidance silent on this aspect - leaving it to building operators to decide, or is there something I have missed when looking through the building and fire safety regulations?

Thanks in advance for any advice or references on where to look.

I would say that even if the walled garden offered sufficient space so that people could be far enough away, there would always be the temptation to re-enter the building to attempt to access the public realm so that they could go about their business. It certainly would be regarded as unacceptable in the hospitality sector where such circumstances often exist. FRS here wouldn’t permit and I absolutely concur.