Common Areas of Flats Ventilation issue

[Stinky]

Hi guys,

I am currently undertaking a FRA on a small purpose built block of flats.  Aged 1990s.

Compartmentation is not thought to be an issue, as not that old and appears to be to a good standard where seen.

However the layout or design does not appear to conform to CP3, BS5588-1 or most version of AD B.

We have ground, 1st, 2nd, 3rd and 4th.  Single stair building.  Not small single stair building as one floor too many! However, the 4th floor must be at 11m or under, this is obviously helps.

3 flats per floor accessed from a lobby.  Travel distances are very small, easily within 4.5m.  AOV provided to head of stair.

No ventilation to lobby outside flats.

After considering guidance, it appears that the landlord may need to provide ventilation to the lobby.  However the lobby is not on an external facade, therefore no space for a shaft.

There is currently no fire alarm for the communal areas, I know it is not needed, I know evry argument there is against detection, as it can be more trouble in residential.
However, due to the lack of ventilation, would LD3 communal area detection compensate?
Or, does anyone think it should be ok as it is, considering travel is small and AOV at head of stair and the top floor is wihtin 11m from ground?

Stinky.

[kurnal]

If it were 4 floors it would be compliant. If as you say its a floor too high presumably logic says it must the people on the top floor who are at risk.
Is it reasonable to require the retro fit of ventilation? If I were a judge I would say not.  
And would the ventilation be required on all floors- impossible- on the top floor - possible but what would this achieve?

Now in the scheme of things I could take you to any number of 15 storey blocks built in the 60s to a similar design with a single staircase but with 4 flats per landing and little or no effective ventilation to the lobby.

I think in this case I would take a good look at the standards of the fire doors protecting the staircase and do what I could to make sure that these were as good as they can be.

Where there is ventilation in a lobby it is there to ensure that the lobby is at a negative pressure compared to the staircase. Its about protecting the staircase from smoke ingress- not about clearing smoke from the lobby. the occupants of the flats on the landng are expected to be able to make the short dash to the stair if they need to. In this case you cannot achieve the lobby ventialtion  so can you do anything to make the staircase ventilation more effective to actually clear any smoke that may enter? For example perhaps by ensuring that the AOV is controlled by smoke detectors at all levels. Perhaps even consider a bit of inlet air in the base to make it work better to keep the staircase clear?

[graz]

Hi, whilst ADB states no more than 3 floors, BS5588 Pt 1 para 12.3 states that a small building with a single stair is no more than 11m and no more than 4 floors above the ground floor. Therefore a vent may only be needed in the staircase as per diagram 14. hope this helps as it is getting late and it's been a long day and my ramblings may be... ramblings!

[Tom Sutton]

Hi, whilst ADB states no more than 3 floors, BS5588 Pt 1 para 12.3 states that a small building with a single stair is no more than 11m and no more than 4 floors above the ground floor. Therefore a vent may only be needed in the staircase as per diagram 14. hope this helps as it is getting late and it's been a long day and my ramblings may be... ramblings!

No ramblings I think you are spot on.

[Clevelandfire 3]

You may get smoke enter the staircase if the resident evacuates and it follows them out, most should be retained in the lobby. You will get quite a bit when firefighters go in to tackle the fire. On the lower floors this may mean fire gases will hang and linger as they cools and then start to drop. You may recommend the existing AOV is beefed up to ensure it can pull the gases out or introduce air in at the bottom of the staircase. I would have thought propping a few doors open at the bottom would be ok if the layout allows, enough to move the smoke toward the aov at least.

[Stinky]

Thank you very much for the feedback guys.  I was previously looking in BS5588 as well, don't know how I missed that. 

So it appears BS5588-1 is the most relaxed guidance for small single stair buildings.  Blocks of flats can still be designed to this guidance, so that is very interesting. 

Thanks again,

Stinky