Discounting an exit width when escape stairs have protected lobbies

[Guest Celine Hynes]

Hi could you clarify something please. BS9999 16.6.1 says you should discount a storey exit when calculating available exit width (if there is more than one storey exit). However, 17.3.2 says if your escape stairs have protected lobbies you don't need to discount a stair. If escape exits are at the bottom of the stairwells, and the stairwells have protected lobbies, can we avoid discounting one of the exit widths?

[AnthonyB]

No. Calculations for horizontal evacuation are separate from those for vertical.
Stage 1- assess escape from the room

Stage 2- assess escape from the floor

Stage 3- assess escape from the building

All seperate