People in waiting areas are invariably not at work so I am confused as to why any such legislation would exist.

For England The Building Regulations and their supporting Approved Documents cover matters such as ventilation (Approved Document F volume 2: Buildings other than dwellings) but there are no defined "occupancy" rates in the manner you are considering.

The design of any waiting area is likely unique to the activity it is supporting (sales or service, number of chairs, specific designation by colour of seat and/or location) as consideration of the users (respect of privacy and personal space) the frequency with which the individuals are processed (so not the protracted wait at A&E) and any fire evacuation considerations (not putting chairs in front of fire doors or across access routes).

Approved Document B will help in setting out maxium occupancy figures for fire safety purposes

But as you have provided the waiting area space in m3, I am not sure that is what you are after?????????

Thank you all so much for your helpful comments, i have found what i was looking for. I  wanted guidance on occupancy level and this will relate to the number of exit doors, size etc  and is more fire safety as already pointed out.