External protection to protected stairways

[Guest Don1958]

Four storey block of flats with one protected stair and effective lobby protection and openable smoke window on top floor. Problem is the possibility of the protected stair being compromised by a fire in adjoining flats which are at right angles to the stair windows (Lower part PVC Fascia, upper non fire resting glazing) and is within about 0.5 m. Reference to the building regulations B1 para 5.24 states a minimum distance of 1.8 m or ensure that the windows to the stair have fire resistance. The evacuation policy is 'stay put'. Would it be reasonably practicable to make up the windows to achieve 30 mins as there must be 100's of buildings like this.

[Tom Sutton]

To prevent fires in one building igniting another adjoining building, have you considered Reg B4 requirements and does the buildings in question meet that requirement.

[Guest Don1958]

External fire spread is no problem, my query was a fire in a flat within the same building affecting the escape route due to the distance being less than 1.8m quoted in the Building Regs. See diagram Diagram 24   External protection to protected stairways.

[Tom Sutton]

I am assuming the building is less the 6 floors and protected lobbies are not required for the staircase.

The common corridors and the staircase should provide no risk, so the risk is the flats themselves and as each flat is fitted with an FD30s fire door c/w self closer, so any fire in a flat should be held in check for 30 minutes, allowing all occupants 30 minutes to escape immediately to ultimate safety, which is what is required for an immediate evacuation.    

If the fire strategy is a stay put, eventually the common corridor will be involved but the fire will have to breach the front door of each flat which will give the occupants another 30 minutes, 60minutes in total, which means the fire and rescue service will have 60mins to extinguish the fire.

My argument would be, no additional protection is required for the staircase because that protection is only required for 30 minutes and the staircase has served its purpose.